Their conclusions, reported Jan. 8 at the American Astronomical Society meeting in Kissimmee, Florida, clarify why quasar SDSS J1011+5442 changed so dramatically in the handful of years between observations.

“We are used to thinking of the sky as unchanging,” said 91̽»¨ astronomy professor , who is principal investigator of the SDSS’s Time-Domain Spectroscopic Survey. “The SDSS gives us a great opportunity to see that change as it happens.”

Quasars are the compact area at the center of large galaxies, usually surrounding a massive black hole. The black hole at the center of J1011+5442, for example, is some 50 million times more massive than our sun. As the black hole gobbles up superheated gas, it emits vast amounts of light and radio waves. When SDSS astronomers made their first observations of J1011+5442 in 2003, they measured the spectrum of the quasar, which let them understand the properties of the gas being swallowed by the black hole. In particular, the prominent “hydrogen-alpha” line in the spectrum revealed how much gas was falling into the central black hole.

The SDSS measured another spectrum for this quasar in early 2015, and noticed a huge decrease between 2003 and 2015. The team made use of additional observations by other telescopes over those 12 years to narrow down the period of change.

“The difference was stunning and unprecedented,” said 91̽»¨astronomy graduate student , a member of the research team. “The hydrogen-alpha emission dropped by a factor of 50 in less than 12 years, and the quasar now looks like a normal galaxy.”

The change was so great that throughout the SDSS collaboration and astronomy community, the quasar became known as a “changing-look quasar.” The black hole is still there, of course, but over the past 10 years, it appears to have swallowed all the gas in its vicinity. With the gas fallen into the black hole, the SDSS team were unable to detect the spectroscopic signature of the quasar.

“This is the first time we’ve seen a quasar shut off this dramatically, this quickly,” said , a postdoctoral researcher at Pennsylvania State University.

Before Runnoe, Ruan and their colleagues could come to this conclusion, they had to rule out two other possibilities. A thick layer of dust could have passed through the host galaxy, obscuring their view of the black hole at its center. But, they concluded that there is no way that any dust cloud could have moved fast enough to cause a 50-fold drop in brightness in just two years. Another possibility is that the bright quasar in 2003 was just a temporary flare caused by the black hole ripping apart a nearby star. While this possibility has been invoked in similar cases, it cannot to explain the fact that the changing-look quasar had been shining for many years before it turned off.

The team’s conclusion is that the quasar has used up all the glowing-hot gas in its immediate vicinity, leading to a rapid drop in brightness.

“Essentially, it has run out of food, at least for the moment,” says Runnoe. “We were fortunate to catch it before and after.”

The changing-look quasar is the first major discovery reported for the Time-Domain Spectroscopic Survey, one component of SDSS’s fourth phase, which will continue for the next several years.

“We found this quasar because we went back to study thousands of quasars seen before,” said Anderson. “This discovery was only possible because the SDSS is so deep and has continued so long.”

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For more information, contact Runnoe at jcr26@psu.edu or 814-863-9343, Ruan at jruan@astro.washington.edu or 206-543-5185 and Anderson at anderson@astro.washington.edu or 206-685-2392.

Download animation:  (credit: Dana Berry/SkyWorks Digital, Inc.). This animation shows an artist’s conception of the changing-look quasar as it evolved from 2003 to 2015. The beginning of the animation shows gas falling into the central black hole, along with the first SDSS spectrum. The black hole then uses up all the surrounding gas, and it is shown with the spectrum recently obtained by the Time-Domain Spectroscopic Survey. The camera then pulls back to reveal the entire galaxy as the quasar shuts off, after which is looks like just another normal galaxy. The animation then fades into an artist’s conception of Hanny’s Voorwerp, a prior SDSS discovery that shows the record of a similar quasar shutting off.

Adapted from “The Case of the Missing Quasar,”  prepared by Jordan Raddick for the American Astronomical Society and the Sloan Digital Sky Survey.

is a professor in the 91̽»¨ Department of Astronomy. He is one of working on the , or LSST, which will begin scanning the sky in 2022 from its location atop Cerro Pachón, a mountain in northern Chile.

He has called it “one of the most exciting experiments in astrophysics today,” adding, “it could completely transform our knowledge of the universe, from understanding how dark energy drives the expansion of the universe, to identifying asteroids that may one day impact the Earth.”

Over the years, Connolly has worked on a number of areas in the design and construction of the LSST, from running the 91̽»¨data management group that develops software to study information that will come from the telescope, to leading a team developing simulations of what this powerful new telescope might see. On his web page he says, “My science focuses on analyzing large astronomical data sets to study the formation and evolution of galaxies and cosmology.”

Throughout his career he has been involved with big data projects. As a postdoctoral researcher he was involved in the , or SDSS, a collaboration of about 200 astronomers at more than 40 institutions on four continents that has been scanning the sky and collecting data since 2000. During a sabbatical in 2006 at Google, Connolly was the project leader for , which incorporated images from the and the SDSS into Google Earth.

Connolly answered a few questions about his work and the promise of big data and tools such as the LSST to astronomy.

Q: Where are you spending the year, and what are you working on?

A.C.: I am in Cambridge (the UK version) for a year. I’m working on a few different areas ranging from the detection of objects whose light has been bent (or gravitationally lensed) by distant galaxies, to studying how we can survey the sky to maximize how quickly we can get science from the LSST.

These may seem like very different questions and problems but they are in fact related. They both involve searching for subtle signals from large complex data sets. Signals that are hard to extract but if we can, we might be able to understand how the universe evolves (driven by dark energy and dark matter).

We have a lot of different ways to look at the sky (different telescopes and instruments) and many tools that can be used when working with data, but it is only when you start applying these techniques to real observations that you can understand how well they will perform in practice. I’m trying to use some of the techniques that we will use on the LSST but on today’s data sets.

So you could say that I am getting my hands dirty with data, which has been a lot of fun, especially with the LSST a few years away.

Q: In your TED talk you say that a single image from the LSST will be equivalent to 3,000 images from the Hubble Space Telescope. How is this achieved?

A.C.: The LSST isn’t the biggest telescope in the world (unlike the new generation of telescopes that will have mirrors 30 meters across), nor does it have the highest-quality images (such as those from space base telescopes like the Hubble).

What it does have is a very large field of view (one image covers an area seven times the width of the full moon) and the largest digital camera in the world (with 3.2 billion pixels). This means it can survey half of the sky every three nights to discover if anything has changed or moved (something Hubble would take about 120 years to do just once).

One of the great aspects of all of the telescopes and instruments we are building today is that they have different and complementary capabilities (e.g. the Hubble can look at great detail at very faint sources but can’t cover large areas of the sky). Combined, we get to reveal both the big picture and the details of how the universe has evolved up to the present day.

Q: What are the challenges that you face in order to answer these “big questions”?

A.C.: Within the next decade new telescopes (on Earth and in space), and new cameras and spectrographs will realize a 1,000-fold increase in the amount of data accessible to astronomers. The size of the data will enable us to answer some of the most fundamental questions in astrophysics today — questions we have been asking since we started looking up at the stars and wondering how they came into being.

Discoveries that might come from the data include:

• Measurements of the shapes of distant galaxies could reveal the properties of dark energy with an accuracy 10 times better than today. This could change our understanding of general relativity if it shows that gravity works differently on large scales.
• Surveys of the faint radio sky may detect the epoch at which stars and galaxies first began to form within the universe.
• Tracking the orbits of asteroids and comets could reveal if the environment in which the Sun formed was responsible for the distribution of the planets in our solar system or identify asteroids that might one day impact the Earth (at distances where we can do something about it).

Some of the most exciting discoveries will be answers to questions that today we don’t even know how to ask.

But this data-rich era comes with a big challenge: Scientific discovery is beginning to be limited not by how we collect or store data, but how we extract the knowledge it contains.

We are reaching a stage where our data are much richer than many of the analyses we apply to them, and where software and algorithms have the potential to become the next instrument for exploring the universe.

Fixing this gap between the science and the amount of data is something that we need to address. The increasing complexity and size of data coming from these instruments means astrophysics is becoming ever more dependent on developments in computing. It also means that there is a great opportunity for discovery if we can prepare the next generation of students and postdocs with the skills that are needed for an era rich in data.

Q: You also mention that “the smart use of data” and new tools will transform astronomy in coming years, “opening up a window in the universe — the window of time.” What new understanding of the cosmos might this bring?

A.C.: There are so many things we know about the universe but don’t understand. We know it is expanding and this expansion is getting faster, but we don’t understand what causes the acceleration.

We know that the dynamics of the universe suggest that most of the matter is not visible, but we don’t understand what particles might make up that matter. We can see the diversity of stars and galaxies that have formed in the universe, but we don’t understand, in detail, the physical processes that drive the formation and evolution of galaxies or the formation of the first stars.

It is a great time to be an astronomer because a new generation of telescopes and surveys might help us unlock these answers by providing a view of the universe that has unprecedented detail. Data will answer these questions (hopefully) and this revolution in data will occur over the next decade.

• Visit for more information about the 91̽»¨and the LSST.
• Watch a video of Connolly’s 2014 TED talk (and learn more ):

The , of which the 91̽»¨ is part, will soon see the entire sky, and even peer into the Milky Way’s galactic center.

The sky survey, called SDSS for short, is a multi-institution group of astronomers who since 2000 have searched the skies with the 100-inch, wide-angle optical telescope at the Apache Point Observatory in New Mexico.

“We have mapped the large-scale structure of the universe, traced out previously unknown structures in the Milky Way, and made unanticipated discoveries from asteroids in our own solar system to the most distant quasars,” said Michael Blanton, an astrophysicist with New York University and director of the new phase of the survey.

Now, the group is adding a second participating telescope high in the Chilean Andes, and a program using an innovative technology — aided by 91̽»¨engineers — to observe and make detailed maps of thousands of previously unstudied nearby galaxies.

“The SDSS has observed more than half a million Milky Way stars over the past 14 years, which I call a good start,” said Jennifer Johnson, astronomer at The Ohio State University and the scientific spokesperson for the project. “However, from the Northern Hemisphere, the Earth blocks our view of a quarter of the Milky Way, and mostly obscures our view of the galactic center.”

Completing that picture will be the Irénée du Pont Telescope at Las Campanas Observatory in Chile, home to the clearest skies on the planet. The second telescope will also study stars in the nearby , giving astronomers a better understanding of the Milky Way’s immediate neighborhood.

The sky survey’s new program, dubbed , is a set of three surveys involving a collaboration of 200 astronomers across 40 institutions and four continents. The work is made possible in part by a new technique of bundling sets of fiber-optic cables into tightly-packed arrays. These collect light from across an entire galaxy, enabling detailed measurements of more than 10,000 nearby galaxies at 20 times the rate of previous surveys.

Staff and students in the , led by research scientist Nick MacDonald, are active in the design, engineering and testing of the innovative fiber-optic arrays.

The new surveys will enable astronomers to:

• Explore the compositions and motions of stars across the entire Milky Way in unprecedented detail.

• Measure the expansion of the universe during a poorly understood five-billion-year period of the universe’s history.

• Make detailed maps of the internal structure of thousands of nearby galaxies to learn how they have grown and changed over billions of years.

Another program in this new phase will follow up on objects whose light output varies with time.

“Such investigations discover and characterize a menagerie of astrophysical extremes,” said Scott Anderson, 91̽»¨Astronomy Department chair and co-lead on that survey, joined by researchers from other participating institutions and assisted by 91̽»¨graduate student John Ruan.

“These range from flaring or pulsating single stars and binary star systems in our own Milky Way to luminous quasars powered by material spiraling into supermassive black holes at the centers of distant galaxies.”

The 91̽»¨was among the first eight members of the sky survey group. The telescope, optics and buildings at the Apache Point Observatory were designed at the UW. Former 91̽»¨astronomer Bruce Margon, now with the University of California, Santa Cruz, was the survey’s first scientific director.

Margon’s words when the sky survey began are no less true today. Calling it “an encyclopedia of the sky,” he added, “the possible projects resulting from the information are never-ending.”

Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation and the participating institutions.

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This was adapted from a by the Sloan Digital Sky Survey. For more information on the UW’s contributions, contact Anderson at sfander@u.washington.edu.

• Watch “The SDSS at Night,” a video by John Parejko of Yale University and the Sloan Digital Sky Survey collaboration. Workers are seen working on and studying the heavens with the Sloan Foundation Telescope at Apache Point Observatory, Sunspot, New Mexico.

91̽»¨ astronomers and colleagues have measured the distance to galaxies six billion light-years away — about halfway back to the Big Bang — to an accuracy of just 1 percent.

The Sloan Digital Telescope measurement also may aid in understanding the mysterious force, often called “dark energy,” thought to be accelerating the expansion of the universe.

The findings come from the , the largest of four projects that together comprise the III, conducted by a consortium of about four dozen universities at the Sloan Foundation’s telescope at Apache Point Observatory in New Mexico.

“We know the universe started much smaller and is currently expanding, but we don’t know much about the history of that expansion,” said Lauren Anderson, a 91̽»¨astronomy doctoral student and first author of a presented at the annual meeting of the American Astronomical Society in Washington, D.C.

“The light we measure from a galaxy carries the information of how much the space between us and the galaxy grew. Then, pinning down the physical distance to that galaxy tells us the average expansion history of that chunk of space,” Anderson said. Measuring that rate of expansion, she added, is astronomers’ best way to learn about the dark energy apparently causing the expansion of the universe to speed up.

Such precise measurements from billions of light-years away require a different technique than those used to measure planets in the solar system or the Milky Way. This survey measures “baryon acoustic oscillations,” or occasional ripples in the distribution of galaxies in the universe. The ripples are imprints of pressure waves that moved through the early universe, and can be measured today by mapping galaxies. The size of these imprints can be used as a standard ruler to measure distances.

The new analysis covers an area twice as large and with greater accuracy than earlier mapping in 2013. The work also includes the first measurements from a sample of nearby galaxies.

“Making these measurements at two different distances allows us to see how the expansion of the universe has changed over time, which will help us understand why it is accelerating,” said co-author Rita Tojeiro of the University of Portsmouth in the U.K.

91̽»¨work on the project included assistance with data management by Anderson and graduate student and co-author Vaishali Bhardwaj, and the drilling of aluminum plates used to hold in place the fiber optic cables that collect the light from each targeted galaxy.

Funding for the Sloan Digital Sky Survey III was provided by the Alfred P. Sloan Foundation, the National Science Foundation, the U.S. Department of Energy Office of Science and participating institutions.

“There are not many things in our daily life that we know to 1-percent accuracy,” said David Schlegel, a physicist at Lawrence Berkeley National Laboratory and the Baryon Oscillation Spectroscopic Survey’s principal investigator.

“I now know the size of the universe better than I know the size of my house.”

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This article was based in part on a by the consortium of institutions participating in the Sloan Digital Sky Survey III. For more information on 91̽»¨participation in this work, contact Anderson at 206-543-9584 or lmanders@astro.washington.edu.