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News Briefs

Monday, November 14, 2016--Carnegie Mellon Hosts Large Synoptic Survey Telescope Hack Week

While the Large Synoptic Survey Telescope (LSST) is being built in Chile, researchers from around the world are working hard to develop the research infrastructure that they will need to interpret the vast amounts of data that the telescope will create as it surveys the sky over the course of 10 years.

To expedite research progress toward using LSST data to measure dark energy, 65 faculty, post-docs and graduate students from around the world came to Carnegie Mellon’s Pittsburgh campus for the LSST Dark Energy Science Collaboration (DESC) Hack Week on Nov. 7-11. Hack Week was organized by McWilliams Center for Cosmology researcher and Associate Professor of Physics Rachel Mandelbaum. Mandelbaum is a member of the leadership team of the DESC and also chairs its collaboration meeting committee.

LSST Hack Story 

The researchers and students, who included physicists, computer scientists and statisticians, worked on projects that included building a pipeline for weak lensing analysis with the LSST and testing it using existing data, and writing and testing software for identifying and classifying different types of supernovae, which can be used to measure the expansion rate of the universe.

The LSST’s decade-long survey will map tens of billions of stars and galaxies. The unprecedented data set created by the telescope will allow scientists to determine the properties of dark energy and dark matter and the composition and history of our galaxy and solar system. 

By: Jocelyn Duffy,, 412-268-9982

Tuesday, January 26, 2016--Assembly Bias In Galaxy Clustering

Rachel Mandelbaum, has shown that the relationship between galaxy clusters and their surrounding dark matter halo is more complex than previously thought. The researchers’ findings, published in Physical Review Letters, are the first to use observational data to show that, in addition to mass, a galaxy cluster’s formation history plays a role in how it interacts with its environment.

There is a connection between galaxy clusters and their dark matter halos that holds a great deal of information about the universe’s content of dark matter and accelerating expansion due to dark energy. Galaxy clusters are groupings of hundreds to thousands of galaxies bound together by gravity, and are the most massive structures found in the universe. These clusters are embedded in a halo of invisible dark matter. Traditionally, cosmologists have predicted and interpreted clustering by calculating just the masses of the clusters and their halos. However, theoretical studies and cosmological simulations suggested that mass is not the only element at play — something called assembly bias, which takes into account when and how a galaxy cluster formed, also could impact clustering.

“Simulations have shown us that assembly bias should be part of our picture,” said Mandelbaum, a member of Carnegie Mellon’s McWilliams Center for Cosmology. “Confirming this observationally is an important piece of understanding galaxy and galaxy cluster formation and evolution.”

In the current study, the research team, led by Hironao Miyatake, Surhud More and Masahiro Takada of the Kavli Institute for the Physics and Mathematics of the Universe, analyzed observational data from the Sloan Digital Sky Survey’s DR8 galaxy catalog. Using this data, they demonstrated that when and where galaxies group together within a cluster impacts the cluster’s relationship with its dark matter environment.

The researchers divided close to 9,000 galaxy clusters into two groups based on the spatial distribution of the galaxies in each cluster. One group consisted of clusters with galaxies aggregated at the center and the other consisted of clusters in which the galaxies were more diffuse. They then used a technique called gravitational lensing to show that, while the two groups of clusters had the same mass, they interacted with their environment much differently. The group of clusters with diffuse galaxies were much more clumpy than the group of clusters that had their galaxies close to the center.

“Measuring the way galaxy clusters clump together on large scales is a linchpin of modern cosmology. We can go forward knowing that mass might not be the only factor in clustering,” Mandelbaum said.

Additional authors include: David N. Spergel, Princeton University; Eli S. Rykoff, Kavli Institute for Particle Astrophysics & Cosmology; and Eduardo Rozo, University of Arizona.

This research was supported by the Japan Society for the Promotion of Science, the World Premier International Research Center Initiativethe FIRST program, the National Science Foundation (NSF) (AST-1311756), NASA and the U.S. Department of Energy (DoE). The Sloan Digital Sky Survey (SDSS-III) is funded by the Alfred P. Sloan Foundation, the SDSS-III participating institutions, NSF and the DoE Office of Science.

By: Jocelyn Duffy,, 412-268-9982

Monday, September 21, 2015--Dark Energy Spectroscopic Instrument Receives Next Step of Approval from DOE

Carnegie Mellon’s Shirley Ho Co-Chairs Working Group for Upcoming Major Sky Survey, Which Will Improve Understanding of the Universe

PITTSBURGH— The Dark Energy Spectroscopic Instrument (DESI) has reached its next major milestone. The project has received Critical Decision-2 approval from the U.S. Department of Energy (DOE). This approval authorizes the project’s scientific scope, schedule and funding profile, ensuring that the project will be supported into the next decade.

Shirley Ho, a member of Carnegie Mellon University’s McWilliams Center for Cosmology, is the co-chair of DESI’s Galaxy and Quasar Clustering Working Group. The working group will produce the flagship science results for DESI’s probes of dark energy and gravity.

When complete, DESI will provide valuable information about how dark energy and gravity have created structure in the universe, and about the universe’s expansion history. Ever since scientists discovered that the universe was expanding at an accelerated rate, they have been looking to understand the reasons for this acceleration, which aren’t explained by Einstein’s theory of gravity.

“DESI will push science further than we have ever gone before,” said Ho, the Cooper-Siegel Assistant Professor of Physics in Carnegie Mellon’s Mellon College of Science. “DESI will push science further than we have ever gone before. We will get a map of the universe from when the universe was very young, about one-seventh of its current age. This will help us to better understand dark matter, dark energy and other mysterious things in our universe.”

DESI is a state-of-the-art spectrometer that will be mounted on top of the National Optical Astronomy Observatory-operated Mayall Telescope located near Tucson, Arizona. To accommodate DESI, the telescope has been retrofitted with new glass lenses that will focus light onto DESI’s focal plane.  The focal plane will have 5,000 small robotic arms, each of which holds an optical fiber. Once the telescope and spectrometer are operational, the robotic arms will position the fibers to capture light from a single galaxy or quasar at a time.  In all, the spectrometer will capture the spectra of a more than 30 million galaxies and quasars. At the end of the project, researchers will be able to measure the spectra of 10 times as many galaxies as DESI’s predecessor, the Baryon Oscillation Spectroscopic Survey of the Sloan Digital Sky Survey.

From these data, they will be able to create the largest three-dimensional map of the universe yet -- one that reaches earlier in the universe’s history than ever before. The map will show how galaxies and other matter cluster together. The map also can be used to visualize fluctuations of density in the early universe called baryon acoustic oscillations (BAOs), which act as a standard ruler to measure the effect dark energy has on the universe’s expansion.

Beyond BAOs, DESI will be used to weigh the total mass of neutrinos in the universe, providing insight into the standard model of particle physics. It also will provide data that can be used to test the theory of General Relativity, Einstein’s theory of gravity, and models for the expansion of the universe.

Two hundred physicists and astronomers from institutions around the world will participate in DESI.

The DESI Project is funded by the U.S. Department of Energy, Office of Science; additional support has been provided by the U.S. National Science Foundation, the Gordon and Betty Moore Foundation, the Heising-Simons Foundation, the Science and Technologies Facilities Council of the United Kingdom, the Consejo Nacional de Ciencia y Tecnología, Mexico, the Chinese Academy of Sciences, and the DESI Membership from: Aix-Marseille University; Argonne National Laboratory; Barcelona-Madrid Regional Participation Group; Brookhaven National Laboratory; Boston University; Carnegie Mellon University; CEA-IRFU, Saclay; China Participation Group; Cornell University; Durham University;  École Polytechnique Fédérale de Lausanne; Eidgenössische Technische Hochschule, Zürich; Fermi National Accelerator Laboratory;  Granada-Madrid-Tenerife Regional Participation Group; Harvard University; Korea Astronomy and Space Science Institute; Korea Institute for Advanced Study; Institute of Cosmological  Sciences, University of Barcelona; Lawrence Berkeley National Laboratory; Laboratoire de Physique Nucléaire et de Hautes Energies; Mexico Regional Participation Group; National Optical Astronomy Observatory; Siena College; SLAC National Accelerator Laboratory;  Southern Methodist University; Swinburne University; The Ohio State University; Universidad de los Andes; University of Arizona; University of California, Berkeley; University of California, Irvine; University of California, Santa Cruz; University College London; University of Michigan at Ann Arbor; University of Pennsylvania; University of Pittsburgh; University of Portsmouth; University of Queensland; University of Toronto; University of Utah; UK Regional Participation Group; Yale University. For more information, visit


Image caption and credit: The Dark Energy Spectroscopic Instrument (DESI) will be mounted on the 4-Meter Mayall telescope at Kitt Peak National Observatory. It will collect spectra from 30 million galaxies and quasars to make the biggest 3D map of the universe ever. (R. Lafever and J. Moustakas for the DESI Collaboration, background image by Dark Energy Camera Legacy Survey.)

By: Jocelyn Duffy,, 412-268-9982

Wednesday, August 5, 2015--Milky Way-Like Galaxies May Have Existed in the Early Universe
Large-Scale Simulation Provides Theoretical Evidence of Early Disk Galaxies

large scale simulation

PITTSBURGH—A new, large-scale computer simulation has shown for the first time that large disk galaxies, much like our own Milky Way, may have existed in the early days of the universe.

The simulation, created by physicists at Carnegie Mellon University’s McWilliams Center for Cosmology and the University of California Berkeley, shows that the early universe —a mere 500 million years after the Big Bang — might have had more order and structure than previously thought.

Their findings, which will be published in The Astrophysical Journal Letters, will help guide researchers using next-generation telescopes like the Wide Field Infrared Survey Telescope (WFIRST) and the James Webb Space Telescope (JWST) as they search the sky for evidence of the first galaxies.

“It’s awe inspiring to think that galaxies much like our own existed when the universe was so young,” said Tiziana Di Matteo, professor of physics at Carnegie Mellon. “The deepest Hubble Space Telescope observations have thus only covered small volumes of space and have found very irregular, clumpy galaxies at these early epochs. It is not surprising that in these small volumes some of the small galaxies do not have regular morphologies like large disk galaxies. Similarly, numerical simulations have been limited in size so they have only made predictions for the smaller, clumpier galaxies at these early times.”

Di Matteo and fellow CMU Physics Professor Rupert Croft have long been at the forefront of simulation cosmology, completing some of the largest simulations ever created. Their current simulation, called BlueTides, is 100 times larger than previous simulations. It was so large that it monopolized all of the National Science Foundation (NSF) supercomputer BlueWater’s memory and almost 1 million CPUs in order to complete the simulation.

Di Matteo, Croft and their former graduate student Yu Feng, now a post-doctoral researcher at UC Berkeley, began by seeding their simulation with constraints provided by the cold dark matter theory, the prevailing theory that explains what may have happened in the universe after the Big Bang.

After the simulation was completed, the researchers looked at their data to see what they could find, much like observational cosmologists would do with data gathered using a telescope. They were surprised to find a number of disk galaxies in the universe at 500 million years post-Big Bang. Since disk galaxies are so large and complex, most researchers assumed that they would take a very long time to form and would be rare, if they existed at all, in the early universe.

“Theoretically we thought that when the universe was only 5 percent of its present age, it would be a place full of chaos and disorder,” Croft said. “Our simulation showed that the early universe might be far from being just this. It might contain beautiful symmetrical galaxies, like the Milky Way.”

From their simulation, the researchers were able to make predictions about the galaxies’ luminosities, angular sizes, morphologies, colors and expected number. When telescopes like WFIRST and JWST come online, they will be able to search for galaxies that fit the descriptions developed by the BlueTides simulation. If simulation and observational results match, it could be a strong proof of the cold dark matter theory.

 “Right now, we’re converging on an exciting time in cosmology. Previously, we couldn’t study disk galaxies in the early universe using telescopes because the galaxies were so faint and rare. We couldn’t study them in a computer because no computers were large enough to cope,” Di Matteo said. “The technology has caught up, and we can complete the simulations using today’s large supercomputers, and we will be able to use telescopes like WFIRST to make the observations.”

This research was funded by the NSF (OCI-0749212, AST-1009781). BlueWaters is located at the National Center for Supercomputing Applications at the University of Illinois.

A larger version of the image above can be found here.

Related Link: "Forming Disk Galaxies Early in the Universe,"


About Carnegie Mellon University: Carnegie Mellon ( is a private, internationally ranked research university with programs in areas ranging from science, technology and business, to public policy, the humanities and the arts. More than 13,000 students in the university’s seven schools and colleges benefit from a small student-to-faculty ratio and an education characterized by its focus on creating and implementing solutions for real problems, interdisciplinary collaboration and innovation.

By: Jocelyn Duffy,, 412-268-9982

Tuesday, March 10, 2015--Unexpected Gamma-Ray Emission From Dwarf Galaxy May Point to New Understanding of Dark Matter


PITTSBURGH—A newly discovered dwarf galaxy orbiting our own Milky Way has offered up a surprise — it appears to be radiating gamma rays, according to an analysis by physicists at Carnegie Mellon, Brown and Cambridge universities. The exact source of this high-energy light is uncertain at this point, but it just might be a signal of dark matter lurking at the galaxy’s center.

“Something in the direction of this dwarf galaxy is emitting gamma rays. There’s no conventional reason this galaxy should be giving off gamma rays, so it’s potentially a signal for dark matter,” said Alex Geringer-Sameth, a postdoctoral research associate in CMU’s Department of Physics and the paper’s lead author.

The galaxy, named Reticulum 2, was discovered within the past few weeks in the data of the Dark Energy Survey, an experiment that maps the southern sky in the hope of understanding the accelerated expansion of the universe. At approximately 98,000 light-years from Earth, Reticulum 2 is one of the nearest dwarf galaxies yet detected. Using publicly available data from NASA’s Fermi Gamma-ray Space Telescope, Carnegie Mellon’s Geringer-Sameth and Matthew Walker, and Brown’s Savvas Koushiappas have shown gamma rays coming from the direction of the galaxy in excess of what would be expected from normal background.

“In the search for dark matter, gamma rays from a dwarf galaxy have long been considered a very strong signature,” said Koushiappas, an assistant professor of physics at Brown. “It seems like we may now be detecting such a thing for the first time.”

The researchers have submitted their analysis to the journal Physical Review Letters, and posted it on arXiv [arXiv:1503.02320]. They caution that while these preliminary results are exciting, there’s more work to be done to confirm a dark matter origin.

No one knows exactly what dark matter is, but it is thought to account for around 80 percent of the matter in the universe. Scientists know that dark matter exists because it exerts gravitational effects on visible matter, which explains the observed rotation of galaxies and galaxy clusters as well as the fluctuations in the cosmic microwave background.

“The gravitational detection of dark matter tells you very little about the particle behavior of the dark matter,” said Walker, assistant professor of physics and a member of CMU’s McWilliams Center for Cosmology. “But now we may have a non-gravitational detection that shows dark matter behaving like a particle, which is a holy grail of sorts.”

A leading theory suggests that dark matter particles are WIMPs, or Weakly Interacting Massive Particles. When pairs of WIMPs meet, they annihilate one another, giving off high-energy gamma rays. If that’s true, then there should be a lot of gamma rays emanating from places where WIMPs are thought to be plentiful, like the dense centers of galaxies. The trouble is, the high-energy rays also originate from many other sources, including black holes and pulsars, which makes it difficult to untangle a dark matter signal from the background noise.

That’s why dwarf galaxies are important in the hunt for the dark matter particle. Dwarfs are thought to lack other gamma-ray-producing sources, so a gamma ray flux from a dwarf galaxy would make a very strong case for dark matter.

“They’re basically very clean and quiet systems,” Koushiappas said.

Scientists have been looking at them for signs of gamma rays for the last several years using NASA’s Fermi Gamma-ray Space Telescope. There’s never been a convincing signal, until now.

Over the past few years Geringer-Sameth, Koushiappas and Walker have been developing an analysis technique that searches for weak signals in the gamma ray data that could be due to dark matter annihilation. With the discovery of Reticulum 2, Geringer-Sameth turned his attention to that part of the sky. He looked at all of the gamma rays coming from the direction of the dwarf galaxy as well as gamma rays coming from adjacent areas of the sky to provide a background level.

“There did seem to be an excess of gamma rays, above what you would expect from normal background processes, coming from the direction of this galaxy,” Geringer-Sameth said. “Given the way that we think we understand how gamma rays are generated in this region of the sky, it doesn’t seem that those processes can explain this signal.”

Further study of this dwarf galaxy’s attributes could reveal hidden sources that may be emitting gamma rays, but the researchers are cautiously optimistic.

“The fact that there are gamma rays and also a clump of dark matter in the same direction makes it quite interesting,” Walker said.


Media Contacts:
CMU: Jocelyn Duffy,, 412-268-9982
Brown: Kevin Stacey,, 401-863-3766

Monday, November 17, 2014--Eye on the Sky

Rendering of the LSST dome with a cut away to show the telescope within
Rendering of the LSST dome
with a cut away to show
the telescope within.

Imagine a color movie of the sky, where you could see near-Earth asteroids hurtling through space or stars exploding in distant galaxies.

It might sound like something that can only be produced in a Hollywood studio, but scientists from across the U.S., including Carnegie Mellon University, will make it a reality with the Large Synoptic Survey Telescope (LSST).

At the end of August, the National Science Foundation (NSF) signed a cooperative agreement with the Association of Universities for Research in Astronomy (AURA) that allows construction of the telescope to begin. In addition, the Department of Energy has agreed to fund the construction of the telescope's 3.2-billion pixel camera. A consortium made up of U.S. universities and national laboratories hopes to break ground on the telescope's Chilean facility in 2015.

"Carnegie Mellon is proud to participate in the LSST and its science program, which will be at the forefront of cosmology research for the coming decades," said Fred Gilman, dean of the Mellon College of Science and chair of the AURA Council overseeing the LSST's construction.

With what will amount to be the world's largest digital camera, the LSST will — in a single exposure — be able to take an image that covers 49 times the area of the moon. Each night as it takes images of patches of the sky, it will collect 30 terabytes of data. Over the course of 10 years, it will visit each patch of sky an estimated 1,000 times, creating the world's largest astronomical data set.

Hidden within this data will be information about the history of the galaxy and the nature of dark matter and dark energy. The data also will be used to create movies that show activity happening billions of years ago in distant galaxies as well as recent activity in our solar system.

Working with big data such as this is an area where the physicists, statisticians and computer scientists working in Carnegie Mellon's McWilliams Center for Cosmology excel. CMU joined the project in 2008.

Members of Carnegie Mellon's faculty have leadership roles within the project. During his tenure as director of the NSF, CMU President Subra Suresh gave the go-ahead for the LSST's final design phase.

Other participants include:
•    Fred Gilman, dean of the Mellon College of Science, is a member of the LSST Corporation's executive board in addition to being the chair of the AURA Council overseeing the LSST's construction.
•    Associate Professor of Physics Rachel Mandelbaum is on the project's Science Advisory Committee, and she and Assistant Professor of Physics Shirley Ho are co-leaders of working groups in the LSST Dark Energy Science Collaboration.
•    Physics Professors Rupert Croft and Tiziana Di Matteo, and Assistant Professor of Physics Hy Trac will lend their expertise to developing cosmological simulations that will be used to interpret the LSST data.
•    Additional faculty from the Physics, Statistics and Computer Science departments, including Computer Science Professor Jeff Schneider and Assistant Professor Barnabas Poczos; and Statistics Professors Christopher Genovese and Larry Wasserman, Associate Professors Ann Lee and Chad Schafer and Project Scientist Peter Freeman, will work together to develop simulation and analysis tools that will extract valuable scientific information from the LSST data.

"The McWilliams Center's multidisciplinary team is ready for the challenge that the LSST data will present," said Gilman. "We will seek answers to many fundamental questions in cosmology, including the nature of dark energy, by using our expertise in physics, computer science and statistics."

Monday, November 3, 2014--Tabitha Voytek wins award from the Society of Women Engineers

Tabitha Voytek showing the radio telescope she built.
Tabitha Voytek showing the radio
telescope she built.

Tabitha Voytek, a PhD student in the Department of Physics and a member of the McWilliams Center for Cosmology, has won the outstanding collegiate member award from the Society of Women Engineers (SWE). She was specifically honored "for being a role model for women in science and engineering and inspiring graduate student involvement in SWE through creative new initiatives." The prize was awarded at the annual SWE conference, which took place in Los Angeles this year.

The Society for Women Engineers is a not-for-profit educational and service organization that aims to empower women to succeed and advance in the field of engineering. It also strives to help women getting recognition for their life-changing contributions as engineers and leaders. SWE currently has almost 30,000 members from all over the world, who range in age from undergraduates to retirees. It is also active in advocacy for Title IX and STEM initiatives at the National level.

“I got involved with SWE as an undergraduate student,” says Voytek, who received a B.S. in engineering physics from the University of the Pacific. “There really wasn’t an obvious professional society for me to join at the time, and I connected well with the SWE group because most of my female engineering friends were also in SWE as well as my engineering faculty advisor.”

Voytek joined the Physics Department at Carnegie Mellon University in 2009, where she now works with her Ph.D. advisor Prof. Jeffrey Peterson on observational 21-cm cosmology, aiming to unveil the early history of the universe by looking at its large-scale structure. “Tabitha’s research work is really very exciting,” commented Peterson. “She is searching for a weak sky glow that will tell us when the Universe first began to produce stars, just a hundred million years after the Big Bang started.” Besides cutting edge science, there are also other perks involved: “Her work takes her to some of the most remote Islands on the planet,” Peterson adds.

One might think that the transition from engineering physics to cosmology is a huge step, but Voytek does not think so. “The questions are more scientific than what I did as an undergraduate, but much of my day-to-day work isn’t actually that different from what I did as an engineer,” she explains. “My Ph.D. work involves building a radio telescope for picking up the signal of neutral hydrogen in the cosmos, and that also takes some engineering skills. Besides, a lot of the challenges that I face as a female grad student in Physics really aren't that different from the challenges of the female engineering PhDs.”

But there’s also another aspect: “It’s somewhat curious, but there isn’t an equivalent organization for women in science,” adds Voytek. “As a consequence, SWE has emerged as the pre-eminent organization advocating for women in STEM, with nearly 30,000 members and an active presence in Washington. SWE really makes an effort to reach across the STEM disciplines into all areas of technology, which is why it’s so large and active. One example of this is that this year’s SWE conference (WE14) was done in combination with the ‘International Conference of Women in Engineering and Science’ (INWES) that only happens once every four years. In comparison, I’ve connected with the American Astronomical Society’s ‘Committee on the Status of Women in Astronomy’, which only has a few hundred participants.”

Voytek’s involvement in SWE and her commitment to a friendly workplace has also made her a much valued colleague. “I would go to Tabitha for most of the questions I had about the department when I came here as a new faculty, and she was not only helpful, but also always upbeat and welcoming. It made my life as a new faculty a lot better,” explains Shirley Ho, an assistant professor at the McWilliams Center for Cosmology.

“One of my favorite things about SWE, and what I always tell people when they ask, is that I have a huge network of women in STEM across the world thanks to SWE,” explains Voytek, who is also very active in SWE’s regional group, which covers Kentucky, Ohio, Pennsylvania and West Virginia. “I always love to go to the annual conference for SWE, where I get to hang out with my friends. Even though I am in regular electronic communication with them throughout the year, I really only see them face-to-face at this event. I know if I'm struggling with something, there are people I can go to and get help from because of my SWE connections.”


Story by Markus Deserno and Shirley Ho

Thursday, August 28, 2014--NSF Authorizes Agreement for the Construction of the Large Synoptic Survey Telescope

PITTSBURGH -- The National Science Foundation (NSF) has authorized a cooperative agreement with the Association of Universities for Research in Astronomy (AURA) for construction of the Large Synoptic Survey Telescope (LSST), which will digitally image the sky for a decade.  The LSST will be built through an NSF and Department of Energy (DOE) partnership. NSF will provide $473M for the telescope, site, data management, education and outreach, and the DOE will provide about $165M for the 3.1 billion pixel camera and related instrumentation.

Early development of the LSST was carried out by the LSST Corporation, a consortium of universities, laboratories, and research institutes.  Carnegie Mellon and its McWilliams Center for Cosmology has been deeply involved since joining the consortium in 2008, with Fred Gilman, Dean of the Mellon College of Science, serving as both a member of the LSST Corporation Executive Board and as chair of the AURA Council that oversees the LSST's construction.  Major milestones that led to the start of construction included the National Research Council's 2010 Astronomy and Astrophysics Decadal Survey committee naming the LSST as the top-ranked ground-based facility, and the NSF, then under the direction of current Carnegie Mellon President Subra Suresh, giving the go-ahead to final design in 2012.

The Telescope's major mirrors have already been largely constructed using gifts from the Charles and Lisa Simonyi Foundation, Bill Gates, and others.  The official start of federal funding allows the project to begin to construct the summit facility in Chile, the telescope mount assembly, and the camera lenses.  When the LSST project is completed, which is projected to be in 2022, the telescope will create a new paradigm for ground-based astronomy by scanning the sky over and over again, collecting many petabytes of data each year. This data promises to yield exciting new discoveries across the face of astronomy, from the motions of present-day asteroids to establishing the history of our galaxy and understanding the nature of dark matter and dark energy.

Carnegie Mellon faculty members are actively engaged in preparing to do science with the LSST data, and have taken a number of leadership roles.  For example, Associate Professor Rachel Mandelbaum is on the Science Advisory Committee for the LSST project. She and Assistant Professor Shirley Ho are each co-leaders of working groups in the LSST Dark Energy Science Collaboration.  Professors Rupert Croft and Tiziana DiMatteo and Assistant Professor Hy Trac are lending their expertise to the task of developing the enormous volume of cosmological simulations that will be needed to interpret the LSST data.  Faculty from Physics, Statistics and School of Computer Science (SCS) are working together to develop simulation and analysis tools that will permit enormous improvements in extracting science from LSST data, exemplified by the research supported by a recent Department of Energy grant to Professors Ho, Mandelbaum, and Trac in Physics, Jeff Schneider and Barnabas Poczos in SCS, and Christopher Genovese in Statistics.

Read more:

By: Jocelyn Duffy,, 412-268-9982

Friday, August, 29, 2014--Weighing the Milky Way

PITTSBURGH—Does the Milky Way look fat in this picture?  Has Andromeda been taking skinny selfies? It turns out the way some astrophysicists have been studying our galaxy made it appear that the Milky Way might be more massive than its neighbor down the street, Andromeda.

Not true, says a study published in the journal Monthly Notices of the Royal Astronomical Society by an international group of researchers, including Matthew Walker of Carnegie Mellon University's McWilliams Center for Cosmology. In the paper, they demonstrate a new, more accurate method for measuring the mass of galaxies. Using this method, the researchers have shown that the Milky Way has only about half the mass of its neighbor, the Andromeda Galaxy.

In previous studies, researchers were only able to estimate the mass of the Milky Way and Andromeda based on observations made using their smaller satellite dwarf galaxies. In the new study, researchers culled previously published data that contained information about the distances between the Milky Way, Andromeda and other close-by galaxies — including those that weren't satellites — that reside in and right outside an area referred to as the Local Group.

Galaxies in the Local Group are bound together by their collective gravity. As a result, while most galaxies, including those on the outskirts of the Local Group, are moving farther apart due to expansion, the galaxies in the Local Group are moving closer together because of gravity. For the first time, researchers were able to combine the available information about gravity and expansion to complete precise calculations of the masses of both the Milky Way and Andromeda.

"Historically, estimations of the Milky Way's mass have been all over the map," said Walker, an assistant professor of physics at Carnegie Mellon. "By studying two massive galaxies that are close to each other and the galaxies that surround them, we can take what we know about gravity and pair that with what we know about expansion to get an accurate account of the mass contained in each galaxy. This is the first time we've been able to measure these two things simultaneously."

By studying both the galaxies in and immediately outside the Local Group, Walker was able to pinpoint the group's center. The researchers then calculated the mass of both the ordinary, visible matter and the invisible dark matter throughout both galaxies based on each galaxy's present location within the Local Group. Andromeda had twice as much mass as the Milky Way, and in both galaxies 90 percent of the mass was made up of dark matter.

The study was supported by the UK's Science and Technology Facilities Council and led by Jorge Peñarrubia of the University of Edinburgh's School of Physics and Astronomy. Co-authors include Yin-Zhe Ma of the University of British Columbia and Alan McConnachie of the NRC Herzberg Institute of Astrophysics. 

By: Jocelyn Duffy,, 412-268-9982

Friday, July, 25, 2014--Shirley Ho Wins Outstanding Young Researcher Award From International Organization of Chinese Physicists and Astronomers

PITTSBURGH—Shirley Ho, assistant professor of physics and a member of the McWilliams Center for Cosmology at Carnegie Mellon University, has been named a co-winner of the 2014 Outstanding Young Researcher Award from the International Organization of Chinese Physicists and Astronomers. The Macronix Prize, which is given to young, ethnic Chinese physicists or astronomers working outside of Asia, recognizes Ho for her leadership in large, international collaborations that have resulted in the most precise measurement of cosmic distances and contributed to the understanding of the nature of the expansion history of the universe.

"I am very honored to have been recognized with the Macronix Prize," Ho said. "This is a wonderful recognition of all of the collaborations I have been part of, especially the Sloan Digital Sky Survey, that have pushed forward the science of the universe's large-scale structure."

Ho conducts research that seeks to provide a greater understanding of our universe, including dark matter and dark energy. She is best known for leading the Sloan Digital Sky Survey III teams that completed the most precise measurement of a standard ruler of the universe — baryon acoustic oscillations — both perpendicular to and along the line of sight of observers, and completed the most accurate calculation of the distribution of matter in the universe to date. Well known for her work in developing techniques that correct for systematic errors in data collected by telescopes, Ho and other researchers have been able to precisely measure initial conditions, cosmic distance scales and the growth of structure in the universe, thereby providing a picture of the universe's expansion history.

"Early in her career, Shirley has a list of major accomplishments," said Fred Gilman, dean of Carnegie Mellon's Mellon College of Science and director of the McWilliams Center. "I have no doubt that she will be at the forefront of cosmology for decades."

Ho is an instrumental member of Carnegie Mellon's McWilliams Center, driving the center's participation in a number of large-scale international cosmology collaborations. She is one of 55 members selected to the U.S. team working on the EUCLID project, is co-chair of the intergalactic medium working group for the Sloan Digital Sky Survey IV, and is co-chair of working groups planning the next generation of research at the Large Synoptic Survey Telescope and the Dark Energy Spectroscopic Instrument projects.

A native of Hong Kong, Ho earned bachelor's degrees in physics and computer science from the University of California, Berkeley and her doctoral degree in astrophysical sciences from Princeton University. She completed her postdoctoral work at the Lawrence Berkeley National Laboratory under a Chamberlain Fellowship and a Seaborg Fellowship. She joined the Carnegie Mellon faculty in 2011.

Ho shares the 2014 Macronix Prize with Kang-Kuen Ni, assistant professor of chemistry and chemical biology at Harvard University.

"Newsmaker: Shirley Ho" TribLive story

By: Jocelyn Duffy,, 412-268-9982

Monday, May 26, 2014--Raphael Flauger publishes paper that questions BICEP2’s gravitational wave discovery

Two months ago, a team of cosmologists reported that it had spotted the first direct evidence that the newborn universe underwent an exponential growth spurt known as inflation (Science, 21 March, p. 1296).   Raphael Flauger, who will join the McWilliams Center and CMU Physics faculty this fall, has published a paper that questions the BICEP2’s gravitational wave discovery.  His analysis suggests the signal, a subtle pattern in the afterglow of the big bang, or cosmic microwave background (CMB), could be an artifact produced by dust within our own galaxy.

For further details and other articles, see

Time Magazine article
Science Magazine article
Washington Post article
Science Magazine (Latest News)
Nature article
Science News

Wednesday, January 8, 2014--International Group of Researchers Measure Universe to 1 Percent Accuracy

Carnegie Mellon’s Shirley Ho and Mariana Vargas-Magaña Co-Lead Measurement of the Scale of the Universe for the Sloan Digital Sky Survey III’s BOSS Collaboration

PITTSBURGH—An international group of researchers, including physicists from Carnegie Mellon University’s McWilliams Center for Cosmology, have made the most precise calibration of the standard ruler that is used to measure the universe. The researchers, who are part of the Sloan Digital Sky Survey III’s (SDSS III) Baryon Oscillation Spectroscopic Study (BOSS), announced today at the 223rd Meeting of the American Astronomical Society (AAS) that they have used this standard ruler to measure the scale of the universe to an accuracy of 1 percent using galaxies more than six billion light years away.

“Before, our picture of the universe looked fuzzy. It was like we were nearsighted, but didn’t have glasses,” said Shirley Ho, assistant professor of physics at Carnegie Mellon. “Now we’re seeing 20/20 and we’re able to measure the scale of the universe’s structure to an accuracy of 1 percent. This can help us to better understand the expansion history of the universe and tell us vital information about the nature of the dark energy that drives the expansion.”

The distance and distribution of galaxies can be measured using what cosmologists call a standard ruler. Standard rulers can be thought of like a car’s headlights. The distance between the two headlights of most cars is more or less the same. The farther away a car is from the observer, the closer together the headlights appear to be. If we measure the angular separation between the headlights, we’re able to calculate how far away the car is. If we have multiple measurements, we can tell how fast the car is moving.

BOSS uses similar methods to measure baryon acoustic oscillations (BAO), relics of sound waves from the early universe that present themselves as ripples visible in the distribution of galaxies, as a standard ruler. Using the Sloan Foundation Telescope at the Apache Point Observatory in New Mexico, the BOSS researchers mapped more than 1.2 million light-emitting galaxies, and then used fundamental physics calculations to measure BAO. They then combined this data with measurements of temperature variation within the cosmic microwave background (CMB) radiation to reveal information about the acceleration of the expansion of the universe, and as a result, dark energy.

Ho, and Mariana Vargas-Magaña, a post-doctoral researcher at Carnegie Mellon’s McWilliams Center, led the portion of the project that focused on measuring the BAO standard ruler in two directions, parallel and perpendicular to the line of sight from the telescope ( Ho also collaborated with researchers from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory to pair the two-dimensional sky coordinates with their redshifts to create a three-dimensional map of the density of galaxies in space, which allowed researchers to visualize the spacing of the galaxies and calculate the BAO.

“The observed spacing of galaxies is not the same in all directions, so we can’t assume that measuring a standard ruler in one direction would be sufficient. By measuring it in two directions we can create more stringent constraints,” Ho said. “And combining this measurement with what we know about the cosmic microwave background radiation, we can get the best understanding of our universe, and the dark energy that accelerates its expansion.”

Vargas-Magaña also led an in-depth analysis of the subtle effects that could distort or alter the BOSS measurements ( This troubleshooting allowed the BOSS team to be confident in their measurements to the unprecedented 1 percent.

“When you’re dealing with something as large as the universe, there are many things that could interfere with you measurements,” Vargas-Magaña said. “To get to 1 percent, we needed to be meticulous about our measurements.”

For more information, please see the SDSS-III press release:

November, 2013--GREAT3 Challenge to Find New Methods
for Measuring Weak Gravitational Lensing Launches

Challenge is Co-led by Carnegie Mellon’s Rachel Mandelbaum and UCL’s Barnaby Rowe

PITTSBURGH— Think you can figure out a way to unlock one of the biggest secrets of the universe? The recently launched third Gravitational Lensing Accuracy Testing challenge (GREAT3) is giving researchers the opportunity to do just that.

GREAT3, which is led by Carnegie Mellon University’s Rachel Mandelbaum and UCL’s (University College London’s) Barnaby Rowe, invites researchers from many fields, including astrophysics, statistics and machine learning, to test new and existing methods for measuring weak gravitational lensing. Weak gravitational lensing is one of the most direct – but also most difficult – ways scientists have to learn about the mysterious invisible dark matter and dark energy that dominates our universe.

“In previous challenges, people have come up with entirely new methods for measuring weak gravitational lensing that we are using in practice today. We’re excited to think about what people will come up with in this challenge, and to think about what new information we’ll learn about existing methods for measuring weak lensing,” said Mandelbaum, who is an assistant professor of physics and member of the McWilliams Center for Cosmology at Carnegie Mellon.

When light from distant galaxies travels through the universe, its path is deflected as it passes by other galaxies or large clumps of matter, including dark matter. This effect, called weak gravitational lensing, results in small distortions in how distant galaxies are viewed from earth and space-based telescopes. Scientists can use lensing measurements to map dark matter and study how it has changed over time. As a result, they can better understand dark energy.

Measuring weak lensing, however, is extremely difficult. The distortions are so tiny that researchers must collect and sift through data from millions of galaxies. They must also be able to correct for things like blurring caused by telescopes or the atmosphere.

"Analyzing weak lensing is tricky, there are a number of things in the atmosphere and in our instruments that can meddle with our data" said Rowe, a postdoctoral research associate at UCL.  "GREAT3 is a fair test to see how new and current methods handle these types of problems and provide accurate results."

In the challenge, participants download simulated data created by GalSim, an open-source image simulation software package developed by a team including Mandelbaum and Rowe for GREAT3. The images, which are similar in format to what is gathered by today’s high-powered telescopes, contain galaxies that have some weak lensing distortion that is known only to the developers of the challenge. The participants are given a series of experiments, each of which test for a different problem or set of problems specific to weak lensing measurements. The participants then use their own algorithm for measuring weak lensing to figure out what weak lensing distortion was used in the simulation. They send their results to the organizers, and the team that comes the closest to measuring the weak lensing distortion that was actually in the simulations wins. 

The competition is not just open to scientists studying weak lensing. In fact, the organizers hope that researchers from other areas of science, like machine learning and statistics, will join the challenge.  “Computer scientists and particle physicists excelled in previous challenges,” said Rowe “And this brings new skills and ideas to the problem.”

“For those outside of the astrophysics community, there can be a great barrier to studying weak lensing,” said Mandelbaum. “But fields like machine learning could prove to be invaluable for helping us pull information out of our huge data sets, which can contain tens of millions of galaxies.  The controlled nature of the simulations, along with the simple and well-described data formats used for the challenge, lowers the barrier to entry for people outside of astronomy.”

Information about GREAT3 is available at the challenge website, and data for GREAT3 is available from Participants have until April 30, 2014 to complete the challenge, and the winner will receive a prize such as a laptop, in addition to worldwide recognition of their efforts.

GREAT3 is funded by NASA through the Strategic University Research Partnership Program of the Jet Propulsion Laboratory, California Institute of Technology and the IST Programme of the European Community under the PASCAL2 Network of Excellence.

Tuesday, February 12, 2013 -- Carnegie Mellon Astrophysicists To Participate in European Space Agency's Dark Energy Mission: McWilliams Center Researchers Shirley Ho and Rachel Mandelbaum Named to US Science Team Working With Space-based Telescope

PITTSBURGH—NASA has named Carnegie Mellon University astrophysicists Shirley Ho and Rachel Mandelbaum to a 40-member U.S. science team that will participate in the European Space Agency’s (ESA’s) Euclid mission. A space-based telescope, Euclid will be used to investigate the greatest mysteries of the universe — dark matter and dark energy.
NASA will support the researchers from 2013 to 2028 as they prepare for and carry out collaborative scientific research using the data gathered by Euclid, which is planned for launch in 2020.
Ordinary visible matter, like stars and galaxies, make up about 4 percent of the universe; the remaining 96 percent is made of dark matter and dark energy that can’t be seen directly. Even though scientists can’t see it, they can learn more about dark matter and dark energy by studying how it impacts what can be seen. Euclid’s telescope and instruments will gather information from approximately two billion galaxies contained in one-third of the sky. Researchers will use the data to measure weak gravitational lensing, baryon acoustic oscillations and redshift space distortions, which will allow them to analyze the effects of dark matter and dark energy.
Mandelbaum, an assistant professor of physics and member of CMU’s Bruce and Astrid McWilliams Center for Cosmology, studies weak gravitational lensing. As light from distant galaxies travels toward earth, it passes by other galaxies. The ordinary and dark matter contained in the galaxies create a gravitational field that causes the light rays to bend, distorting the images seen by telescopes, like Euclid. Mandelbaum and other researchers who study weak lensing measure and average the slight distortions seen over many galaxies. From these averages, they can derive how much dark matter lies in and between galaxies and how it is distributed throughout space. They also can study how these distortions change over time, which can reveal valuable information about dark energy.
“With lensing we can learn about the large scale distribution of all of the matter of the universe — even the dark matter we can’t see. If we truly want to understand the structure and evolution of the universe, we need a tool like lensing that reveals the presence of all of the matter,” Mandelbaum said.

Ho, an assistant professor of physics and member of CMU’s McWilliams Center, specializes in studying baryon acoustic oscillations (BAOs) and redshift space distortions. BAOs are relics of sound waves from the early universe. These remnants can be measured and used as a standard cosmological ruler to calculate how the universe has expanded over time. With an understanding of this expansion, researchers can learn about the mysterious dark energy that dominates 70 percent of the universe and drives the accelerating rate of expansion and the dark matter that makes up nearly 25 percent of the universe. Ho, in collaboration with her European colleagues, also will use Euclid to measure the velocity of galaxies and study redshift space distortions, which can be used to measure dark matter, the growth of the universe and test Einstein’s theory of relativity.

“By using spectra for approximately 70 million galaxies that will be provided by Euclid, we can explore the universe using a variety of dark energy probes, such as BAOs, weak lensing and redshift space distortions,” Ho said. “Euclid scientists can combine what is learned from these probes to test our understanding of what the universe is made of and how the universe works.”

Euclid is a European Space Agency mission with science instruments and data analysis provided by the Euclid Consortium ( with important participation from NASA. NASA's Euclid Project Office is based at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. The JPL will contribute the infrared flight detectors for one of Euclid's two science instruments. NASA’s Goddard Space Flight Center in Greenbelt, Md., will assist with infrared detector characterization and will perform detailed testing on flight detectors prior to delivery. Three U.S. science teams, led by JPL, Goddard and the Infrared Processing and Analysis Center at Caltech, will contribute to science planning and data analysis. Ho and Mandelbaum are members of the JPL team. Caltech manages JPL for NASA.


About Carnegie Mellon University: Carnegie Mellon ( is a private, internationally ranked research university with programs in areas ranging from science, technology and business, to public policy, the humanities and the arts. More than 12,000 students in the university’s seven schools and colleges benefit from a small student-to-faculty ratio and an education characterized by its focus on creating and implementing solutions for real problems, interdisciplinary collaboration and innovation. A global university, Carnegie Mellon’s main campus in the United States is in Pittsburgh, Pa. It has campuses in California’s Silicon Valley and Qatar, and programs in Africa, Asia, Australia, Europe and Mexico. The university is in the midst of “Inspire Innovation: The Campaign for Carnegie Mellon University,” which aims to build its endowment, support faculty, students and innovative research, and enhance the physical campus with equipment and facility improvements.

By: Jocelyn Duffy,, 412-268-9982

November 13, 2012--Astronomers measure the Universe's deceleration before dark energy took over

For the past five billion years, the expansion of the Universe has been speeding up, powered by the mysterious repulsive force known as "dark energy." But thanks to a new technique for measuring the three-dimensional structure of the distant Universe, astronomers from the Sloan Digital Sky Survey (SDSS-III) including  have made the first measurement of the cosmic expansion rate just three billion years after the Big Bang. The new measurement does not look at galaxies . Instead, it makes use of the clustering of intergalactic hydrogen gas in the distant Universe. We can see this gas because it absorbs some light from quasars lying behind. When we measure the spectrum of a quasar, we see not only the light emitted by the quasar, but also what happened to that light in its long journey to Earth. McWilliams Center cosmologists Rupert Croft and Shirley Ho participated in the measurement which is explained in more detail here:

Friday, August 3, 2012-- NSF Advances Large Synoptic Survey Telescope to Final Design Stage

The National Science Board (NSB) of the National Science Foundation (NSF) has given the Large Synoptic Survey Telescope (LSST) project ddapproval to advance to the final design phase.  The NSB approval permits the NSF Director to include funds for construction of the 8-meter wide-field survey telescope in a future budget request.  The NSF will construct the LSST in partnership with the Department of Energy’s Office of Science, which is funding the LSST camera.

“The decision by the National Science Board is great news for U.S. science and especially for all of those who have been working on the LSST,” said Fred Gilman, dean of Carnegie Mellon University’s Mellon College of Science and chair of the AURA Management Council for the LSST (AMCL) that oversees the project. “The LSST, along with other large scale surveys like the current Sloan Digital Sky Survey, will place U.S.-based researchers at the forefront of cosmological research for the coming decades, providing data to probe the nature of dark energy.” 

Construction on the LSST is hoped to begin in 2014 atop Cerro Pachón, a mountain in Northern Chile. When fully operational, the 8.4-meter telescope will use its 3 billion-pixel camera to survey the entire visible sky in multiple colors.  The telescope will take snapshots every 15 seconds, creating a movie that will allow researchers to study objects that change or move on rapid timescales, like exploding supernovae, potentially hazardous near-Earth asteroids, and distant Kuiper Belt Objects. The images will also be used to trace millions of remote galaxies and to help answer questions about dark matter and dark energy. 

Since joining the LSST collaboration in 2008, CMU and its Bruce and Astrid McWilliams Center for Cosmology have taken an increasing leadership role in the project. A member of the LSST Executive Board, Gilman was named chair of the AMCL in 2012.   Assistant Professors of Physics Shirley Ho and Rachel Mandelbaum are co-leaders of research tasks within the recently formed LSST Dark Energy Science Collaboration, which also involves research by CMU theoretical astrophysicists Rupert Croft, Tiziana Di Matteo and Hy Trac

By: Jocelyn Duffy,, 412-268-9982

May 12, 2012-- Mandelbaum Receives Department of Energy Early Career Award for Dark Matter and Dark Energy Research

PITTSBURGH—Carnegie Mellon University physicist Rachel Mandelbaum was awarded a five-year, $750,000 grant from the U.S. Department of Energy (DOE) to study the elusive dark matter and dark energy that make up the majority of the universe.

Mandelbaum is one of 68 researchers nationwide to receive funding from the DOE's Early Career Research Program this year. The program, which has been in place for three years, provides funding for outstanding scientists within 10 years of completing their doctoral degree.

"The funding from the DOE will support my research into some of the key mysteries in the field of cosmology," said Mandelbaum, who is an assistant professor of physics and a member of the Bruce and Astrid McWilliams Center for Cosmology. "This generous support will allow me to work with some of the major ongoing and upcoming astronomical surveys in order to study the nature of dark matter and dark energy."

Mandelbaum's ongoing research focuses on weak gravitational lensing. When light from distant galaxies travels through the universe, its path becomes deflected as it passes by massive objects like large galaxies. This effect, called weak gravitational lensing, results in small distortions in how we observe distant galaxies from Earth. When carefully measured, weak gravitational lensing is the most direct way to study the distribution of dark and ordinary matter in the universe.

Mandelbaum will use data collected from several large astronomical spectroscopic and imaging surveys including the Sloan Digital Sky Survey III's Baryon Oscillation Spectroscopic Survey and the Hyper Supreme-Cam at the Subaru Telescope to measure weak gravitational lensing. She will then combine her results with other cosmological observations to provide a better understanding of the nature of dark energy. The findings will help to inform future research by next-generation astronomical imaging surveys, like the one set to be completed by the Large Synoptic Survey Telescope.

By: Jocelyn Duffy,, 412-268-9982

Thursday, February 16, 2012--Physicist Rachel Mandelbaum Receives the Annie Jump Cannon AwardRachel Mandelbaum

Assistant Professor of Physics Rachel Mandelbaum was presented with the 2011 Annie Jump Cannon Award at the semi-annual meeting of the American Astronomical Society held in January 2012.

Mandelbaum was cited “for her groundbreaking contributions to the field of weak gravitational lensing of galaxies. Her work on understanding and eliminating numerous systematic effects inherent in weak lensing data have advanced this technique to the point where it can now be used with confidence for precision cosmology.”

As light from distant galaxies travels through the universe, it’s path is deflected as it passes by massive objects, causing the images of the galaxies to be distorted. The distortions are usually small, and therefore the effect is called weak gravitational lensing. When carefully measured and analyzed, weak lensing can be used to determine the large-scale distribution of both ordinary and dark matter throughout the universe.

The award is given to women within five years of receiving their doctoral degree who have made distinguished contributions to astronomy or for similar contributions in related sciences that have immediate application to astronomy.

By: Jocelyn Duffy,, 412-268-9982

Wednesday, January 11, 2012--Group Led by Carnegie Mellon’s Shirley Ho Uses SDSS-III Data To Calculate Power Spectrum of the Universe

Researchers Begin To Read Largest Map of the Universe

imgAUSTIN, Texas—Researchers led by Shirley Ho, an astrophysicist at Carnegie Mellon University’s Bruce and Astrid McWilliams Center for Cosmology and the U.S. Department of Energy’s Lawrence Berkeley National Laboratory, have analyzed a trillion pixel map of the universe to create the most accurate calculation of the power spectrum of the universe over the past six billion years.

The group’s findings were presented Jan. 11 at the annual meeting of the American Astronomical Society (AAS) in Austin, Texas, and will appear in a future issue of the Astrophysical Journal. The results are currently available at

Last year at the AAS meeting, researchers working on the Sloan Digital Sky Survey III (SDSS-III) unveiled the largest three-dimensional color map of the universe to date. The trillion-plus pixel image taken from the SDSS-III’s telescope at the Apache Point Observatory in New Mexico covers more than a quarter of the sky and contains more than a half billion objects, a quarter billion stars and a quarter billion galaxies.

This image shows the positions of the 900,000 luminous galaxies used in these studies. Each green dot represents one galaxy. The image covers a redshift range from 0.25 to 0.75, a time when the universe was between 7 billion and 11 billion years old. (Image Courtesy David Kirkby, UC-Irvine and SDSS-III Collaboration)
“We have this huge map of the universe, the next step was to begin to read the map to find out what we could learn,” Ho said.

Ho and colleagues selected 900,000 luminous red galaxies from among more than 1.5 million galaxies observed through the SDSS-III’s Baryon Oscillation Spectrographic Survey (BOSS). They measured the galaxies’ brightness in five different colors; from this information the researchers were able to determine the age of the galaxies. Using the imaging data, the group then gleaned the most accurate measurement of the power spectrum of the universe — a statistical representation of how the density of matter varies throughout the universe.

“The power spectrum tells you how fast the universe is expanding, and how much dark energy, dark matter and neutrinos exist in the universe,” Ho said. “The power spectrum contains a wealth of information that could help to explain what happened at the beginning of the universe and during the expansion of the universe.”

For example, the researchers used the power spectrum to gather information about baryon acoustic oscillations (BAOs), relics of sound waves that can be used to measure dark energy in the universe. By using the new measurements, Ho and colleagues were able to precisely measure BAOs farther back in time than ever before using the colors of galaxies. They also were able to use the data to estimate that dark energy accounts for 73 percent of the density of the universe — a finding that matches estimations from other datasets.

The researchers will continue to mine the data to find more information about the universe, its expansion and contents.

This video shows the positions of the 900,000 luminous galaxies used in these studies. Each green dot represents one galaxy. The image covers a redshift range from 0.25 to 0.75, reaching to six billion years ago. The rotation of the image provides a view that shows what the distribution would look like from all sides.

For more information visit:

Related papers from the research group include:

Ross et al. (2011): "Ameliorating Systematic Uncertainties in the Angular Clustering of Galaxies: A Study using SDSS-III" 2011, MNRAS, Vol 417, pp. 1350-1373.

Ho et al. (2012): "Clustering of Sloan Digital Sky Survey III Photometric Luminous Galaxies: The Measurement, Systematics and Cosmological Implications"

Seo et al. (2012): "Acoustic scale from the angular power spectra of SDSS-III DR8 photometric LRGs" To appear on arXiv Thursday, January 12, 2012; preprint available at

de Putter et al. (2012): "New Neutrino Mass Bounds from Sloan Digital Sky Survey III Data Release 8 Photometric Luminous Galaxies"


About Carnegie Mellon University: Carnegie Mellon ( is a private, internationally ranked research university with programs in areas ranging from science, technology and business, to public policy, the humanities and the arts. More than 11,000 students in the university’s seven schools and colleges benefit from a small student-to-faculty ratio and an education characterized by its focus on creating and implementing solutions for real problems, interdisciplinary collaboration and innovation. A global university, Carnegie Mellon’s main campus in the United States is in Pittsburgh, Pa. It has campuses in California’s Silicon Valley and Qatar, and programs in Asia, Australia, Europe and Mexico. The university is in the midst of a $1 billion fundraising campaign, titled “Inspire Innovation: The Campaign for Carnegie Mellon University,” which aims to build its endowment, support faculty, students and innovative research, and enhance the physical campus with equipment and facility improvements.     

About the Sloan Digital Sky Survey III: Funding for the SDSS-III has been provided by the Alfred P. Sloan Foundation, institutional members of the SDSS-III, the National Science Foundation and the U.S. Department of Energy Office of Science.  The SDSS-III website is SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, University of Cambridge, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University.

By: Jocelyn Duffy,, 412-268-9982

Friday, December 9, 2011 -- Early Black Holes Grew Big Eating Cold, Fast Food

Largest Cosmological Simulation To-Date Explains How Supermassive Black Holes Came Into Existence Shortly After the Big Bang


The large scale cosmological mass distribution in the simulation volume of the MassiveBlack. The projected gas density over the whole volume ('unwrapped' into 2D) is shown in the large scale (background) image. The two images on top show two zoom-in of increasing factor of 10, of the regions where the most massive black hole - the first quasars - is formed. The black hole is at the center of the image and isbeing fed by cold gas streams. Image Courtesy of Yu Feng.

PITTSBURGH -- Researchers at Carnegie Mellon University’s Bruce and Astrid McWilliams Center for Cosmology have discovered what caused the rapid growth of early supermassive black holes – a steady diet of cold, fast food. 

Computer simulations, completed using supercomputers at the National Institute for Computational Sciences and the Pittsburgh Supercomputing Center and viewed using GigaPan Time Machine technology, show that thin streams of cold gas flow uncontrolled into the center of the first black holes, causing them to grow faster than anything else in the universe.  The findings will be published in the Astrophysical Journal Letters.

In the early days of the universe, a mere 700 to 800 million years after the Big Bang, most things were small. The first stars and galaxies were just beginning to form and grow in isolated parts of the universe.  According to astrophysical theory, black holes found during this era also should be small in proportion with the galaxies in which they reside. Recent observations from the Sloan Digital Sky Survey (SDSS) have shown that this isn’t the case -- enormous supermassive black holes existed as early as 700 million years after the Big Bang.

“The Sloan Digital Sky Survey found supermassive black holes at less than 1 billion years.  They were the same size as today’s most massive black holes, which are 13.6 billion years old,” said Tiziana Di Matteo, associate professor of physics at Carnegie Mellon.  “It was a puzzle.  Why do some black holes form so early when it takes the whole age of the universe for others to reach the same mass?”
Supermassive black holes are the largest black holes, with masses billions of times larger than that of the sun.  Typical black holes have masses only up to 30 times larger than the sun's. Astrophysicists have determined that supermassive black holes can form when two galaxies collide and their two black holes merge into one.  These galaxy collisions happened in the later years of the universe, but not in the early days.  In the first few millions of years after the Big Bang, galaxies were too few and too far apart to merge.

“If you write the equations for how galaxies and black holes form, it doesn’t seem possible that these huge masses could form that early,” said Rupert Croft, an associate professor of physics at Carnegie Mellon.   “But we look to the sky and there they are.”

 To find out exactly how these supermassive black holes came to be, Di Matteo, Croft and Carnegie Mellon post-doctoral researcher Nishikanta Khandai created the largest cosmological simulation to-date.  Called MassiveBlack, the simulation focused on recreating the first billion years after the Big Bang.

“This simulation is truly gigantic.  It’s the largest in terms of the level of physics and the actual volume.  We did that because we were interested in looking at rare things in the universe, like the first black holes.  Because they are so rare, you need to search over a large volume of space,” said Di Matteo.

They began by running the simulation under conditions laid out under the standard model of cosmology – the accepted theories and laws of modern day physics governing the formation and growth of the universe. 

“We didn’t put anything crazy in.  There’s no magic physics, no extra stuff. It’s the same physics that forms galaxies in simulations of the later universe,” said Croft. “But magically, these early quasars, just as had been observed, appear.  We didn’t know they were going to show up.  It was amazing to measure their masses and go ‘Wow! These are the exact right size and show up exactly at the right point in time.'  It’s a success story for the modern theory of cosmology.”

Their simulation data was incorporated into a new technology developed by Carnegie Mellon computer scientists called GigaPan Time Machine. The technology allowed the researchers to view their simulation as if it was a movie.  They could easily pan across the simulated universe as it formed, and zoom in to events that looked interesting, allowing them to see greater detail than what could be seen using a telescope.

As they zoomed in to the creation of the first supermassive black holes, they saw something unexpected.  Normally, when cold gas flows toward a black hole it collides with other gas in the surrounding galaxy. This causes the cold gas to heat up and then cool back down before it enters the black hole. This process, called shock heating, would stop black holes in the early universe from growing fast enough to reach the masses we see. Instead, Di Matteo and Croft saw in their simulation thin streams of cold dense gas flowing along the filaments that give structure to the universe and straight into the center of the black holes at breakneck speed, making for cold, fast food for the black holes.  This uncontrolled consumption caused the black holes to grow exponentially faster than the galaxies in which they reside. 

And since when a galaxy forms when a black hole forms, the results could also shed light on how the first galaxies formed, giving more clues to how the universe came to be.  Di Matteo and Croft hope to push the limits of their simulation a bit more, creating even bigger simulations that cover more space and time.


For more information, visit:

Terapixel Imaging of Cosmological Simulations
Feng, Y., Croft,  R.A.C., Di Matteo, T., et al. 2011, ApJS, 197, 18

The Formation of Galaxies Hosting z~6 Quasars
Khandai, N., Feng, Y., DeGraf, C., Di Matteo, T., & Croft, R.A.C.
2011, arXiv:1111.0692

Early Black Holes in Cosmological Simulations: Luminosity Functions and Clustering Behaviour
DeGraf, C., Di Matteo, T., Khandai, N., et al.\ 2011, arXiv:1107.1254

Cold Flows and the First Quasars
Di Matteo, T., Khandai, N., DeGraf, C., et al.\ 2011, arXiv:1107.1253

Gigapan link:

Supermassive Growth Spurt

MCS Press Release

April 25, 2011 -- Giga Pan Time Machine Allows Visual Exploration of Space and Time

time machine Researchers at Carnegie Mellon University’s Robotics Institute have leveraged the latest browser technology to create GigaPan Time Machine, a system that enables viewers to explore gigapixel-scale, high-resolution videos and image sequences by panning or zooming in and out of the images while simultaneously moving back and forth through time. Viewers, for instance, can use the system to focus in on the details of a booth within a panorama of a carnival midway, but also reverse time to see how the booth was constructed. Or they can watch a group of plants sprout, grow and flower, shifting perspective to watch some plants move wildly as they grow while others get eaten by caterpillars. Or, they can view a computer simulation of the early universe, watching as gravity works across 600 million light-years to condense matter into filaments and finally into stars that can be seen by zooming in for a close up.

August 13, 2010 -- Large Synoptic Survey Telescope (LSST) Project Receives Top Priority From the Decadal Survey of Astronomy and Astrophysics

Large Synoptic Survey Telescope (LSST)A committee convened by the National Academy of Sciences to conduct a decadal survey of astronomy and astrophysics has ranked the Large Synoptic Survey Telescope (LSST), a collaborative research project in which Carnegie Mellon University is a partner, as its top priority among ground-based projects.

The committee's report titled "New World and New Horizons in Astronomy in Astrophysics" evaluates astrophysics and astronomy programs in terms of their risks, readiness, schedule and costs. Findings from this survey serve as a recommendation to the National Science Foundation (NSF), NASA and the Department of Energy (DoE) about which projects should receive funding over the next 10 years. 

In the report the committee recommended that the NSF and DoE consider the LSST for immediate funding, citing that the telescope was poised to accomplish the research goals set forth by the survey and was the "most ready-to-go" among ground-based projects. The telescope should achieve "first light" by the end of the decade.

LSST Press Release

CMU Press Release

For further details, see the MCS press release.

July 21, 2010 -- Radio Astronomers Develop New Technique for Studying Dark Energy

The Robert C. Byrd Green Bank Telescope (GBT) at Sunset.Pioneering observations made by researchers from Academia Sinica in Taiwan, Carnegie Mellon University and the University of Toronto with the National Science Foundation's giant Robert C. Byrd Green Bank Telescope (GBT) have validated a new tool for mapping large cosmic structures. Observations made using the method, called intensity mapping, promise to provide valuable clues about the nature of the mysterious "dark energy" believed to constitute nearly three-fourths of the mass and energy of the universe. The findings will be published in the July 22 issue of Nature.
"Since the early part of the 20th century, astronomers have traced the expansion of the universe by observing galaxies. Our new technique allows us to skip the galaxy-detection step and gather radio emissions from a thousand galaxies at a time, as well as all the dimly-glowing material between them," said Jeffrey Peterson, of Carnegie Mellon's Bruce and Astrid McWilliams Center for Cosmology.

October 26, 2009 -- DOE Grant launches CMU initiative to automate discovery of Astrophysical Phenomena

August 31, 2009 -- Tiziana Di Matteo's work highlighted in Pittsburgh Post Gazette

Prof. Di Matteo's recent work on black holes has been highlighted in the Pittsburgh Post Gazette in an article entitled: "The Thinkers: Black holes, black energy and the history of the universe".

Pittsburgh Post Gazette article:

July 1, 2009 -- Bruce McWilliams featured in Physics World

"Once a Physicist: Bruce McWilliams" is the feature article in the Careers section of

Physics World article:

March 20, 2009 -- Tiziana Di Matteo takes part in panel on Computational Physics at APS March Meeting

During Friday's session of the meeting of the American Physical Society at the David L. Lawrence Convention Center in Pittsburgh, CMU cosmologist Tiziana Di Matteo was part of a panel on computational physics.

Pittsburgh Post Gazette article:

Pittsburgh Tribune-Review article:

February 18, 2009 -- Tiziana Di Matteo Presents Detailed Cosmological Simulations at AAAS Meeting

Tiziana Di Matteo, Associate Professor of Physics at Carnegie Mellon University, is harnessing the power of supercomputing to recreate how galaxies are born, how they develop over time, and ultimately how they collapse.  Di Matteo presented an overview of her cosmological simulations as part of the "Big, Small, and Everything in Between: Simulating Our World Using Scientific Computing" session at the 2009 American Association for the Advancement of Science (AAAS) Annual Meeting, Feb. 15 in Chicago.

Carnegie Mellon Press Release:

Medill Reports, Chicago, Northwestern University article:
"Supercomputing means better models of earthquakes, cells and the universe"

September 10, 2008 -- First Beam Sent Around Large Hadron Collider

The first beam in the Large Hadron Collider at CERN Laboratory in Geneva was
successfully steered around the full 27 kilometers of the world\uffffs most
powerful particle accelerator. This historic event marks a key moment in the
transition from over two decades of preparation to a new era of scientific
discovery. Carnegie Mellon physicists constructed the state-of-the-art
electronics, consisting of 150,000 channels, for the endcap muon system of
the LHC's compact muon solenoid detector.

LHC, near Lake Geneva.

September 2, 2008 Giant Furnace Opens to Reveal 'Perfect' LSST Mirror Blank

The mirror blank for the Large Synoptic Survey Telescope (LSST) has been successfully cast at the University of Arizona's Steward Observatory Mirror Lab. The telescope requires three large mirrors to give crisp images over a record large field of view. The two largest of these mirrors are concentric and fit neatly onto the 51,900 pound and 27.5 foot in diameter mirror blank. Carnegie Mellon is one of 23 universities, national laboratories and corporations involved in constructing the telescope.

Image Credit: Howard Lester/LSST Corporation.

LSST press release, video and images:

April 22, 2008

Carnegie Mellon Celebrates the Establishment of the Bruce and Astrid McWilliams Center for Cosmology
Carnegie Mellon Press Release:

“CMU, Pitt Seek to Solve Space Mysteries,” Pittsburgh Tribune Review:

“Gift Helps CMU Probe Cosmic Mystery,” Pittsburgh Post-Gazette:

April 22, 2008

Joel Primack to Give “Brief History of Dark Matter” at Buhl Lecture
Carnegie Mellon Press Release:

March 28, 2008 LSST Mirror Casting Event

Using 51,900 pounds of glass, The University of Arizona's Steward Observatory Mirror Laboratory has began castting of the mirrors to be used in the Large Synoptic Survey Telescope (LSST). Representatives from LSST's 23 member organizations, including Carnegie Mellon's Fred Gilman, gathered in Tucson March 28 to celebrate "High Fire," the point where the furnaces heating the glass reached their peak temperature of 2150 degrees Fahrenheit.

LSST's High Fire Event Page:

University of Arizona Press Release:

Pittsburgh Tribune Review Article:

March 28, 2008 Carnegie Mellon Receives $4.15 Million in Grants From the Gordon and Betty Moore Foundation

Part of the grant will fund a computer super-cluster. Shared with researchers in Computer Science, Carnegie Mellon cosmologists will use this cluster to carry out complex simulations of the early universe.

Carnegie Mellon Press Release:

February 1, 2008dimatteo

Tiziana DiMatteo Wins Emerging Female Scientist Award at Carnegie Science Center Awards for Excellence
DiMatteo received the award for her contributions in the field of cosmology. Having developed the most detailed computer simulations of galaxy formation to date, she has provided vital information needed to gain deeper understanding into how galaxies evolve over time.

January 22, 2008

Compact Muon Solenoid Celebrates the Lowering of Final Detector Element
Carnegie Mellon is one of 155 institutions involved in constructing the Compact Muon Solenoid (CMS), one of the detectors in the Large Hadron Collider. Carnegie Mellon physicists constructed the state-of-the-art electronics, consisting of 150,000 channels, for the endcap muon system of the CMS detector.

compact muon

CERN Press Release

CMU Press Release

January 8, 2008lsst

Carnegie Mellon Joins Large Synoptic Survey Telescope Project
Carnegie Mellon is now among 23 universities, national laboratories and corporations involved in constructing the world's most powerful survey telescope

December 18, 2007

detectorCompact Muon Solenoid Tracking Detector Successfully Installed

CERN Press Release

Fall 2007

Profile of Bruce McWilliams
Packaging the Goods: Bruce McWilliams Delivers Tomorrow’s Technology and Talent,” MCS News

June 27, 2007

Carnegie Mellon Leads International Team in Conducting Most Detailed Cosmological Simulation To Date
By incorporating the physics of black holes into a highly sophisticated model running on a powerful supercomputing system, an international team of scientists has produced an unprecedented simulation of cosmic evolution that verifies and deepens our understanding of relationships between black holes and the galaxies in which they reside.

Carnegie Mellon Press Release

February 28, 2007

Giant Compact Muon Solenoid Magnet Goes Underground