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The Light Splitter

Chris Clemens built SOAR's Goodman Spectrograph, the instrument that will separate incoming light into different wavelengths. This isn't something you can put together with a Home Depot kit and a hot glue gun: there are only around ten spectrographs in the world like SOAR's. Clemens was hired specifically to build it. It took him the better part of two years' thinking and four years' work.

Without a spectrograph, a telescope is just taking pictures, which are useful to an extent. But a telescope's image of a star is really just a brighter version of what you can see with your eye. To really know something about a star — how it's spinning, what it's made of, what its surface gravity is like, and whether it has a magnetic field — you need to split up the light. For much of the history of astronomy, that's been a wildly inefficient process. Before the 1970s, spectrographs were operating at only 3 percent efficiency. "You went through all that trouble and expense to collect the light, and you threw away ninety-seven percent of it," Clemens says. Efficiency jumped up to 70 or 80 percent in the 1970s, but the dispersers — the part that actually splits the light — didn't improve at all. Now, by making something called a volume holographic grating, Clemens has just pushed his spectrograph's visible-light efficiency up to around 60 percent.

SOAR's spectrograph also holds another trump card: at around 50 percent, it's currently the most ultraviolet-efficient spectrograph in the world (the competition is as low as 3 percent efficient in the UV). Ultraviolet spectroscopy is a narrow research window, but one that holds interesting things for many astronomers.

Clemens will use SOAR to study stellar seismology. Certain stars, called variable stars, regularly change in brightness. This may be due to seismic disruption: basically, starquakes. By using time-resolved spectroscopy, which involves getting a lot of spectral "snapshots" over a certain period of time, Clemens can learn something about what's inside these variable stars.

But astronomers like Clemens really want to know about fundamental stellar physics: what's holding stars together? In some stars, it's air pressure or gas pressure, just like in a balloon. But the physics get trickier in denser stars. "We can't study any of that stuff in a lab; we can only study it in space," Clemens says.

Even so, what goes on way out there and what happens on the lab bench are more closely related than you might think. Physicists first began to study nuclear reactions because astronomers knew the reactions must be going on in stars. "There's a definite connection between what we do and what physicists do in the lab," Clemens says. "Our lab is just bigger."

The SOAR telescope ready for action. Photo by Thomas A. Sebring, SOAR project manager. Click to enlarge.

A Universal Architect

James Rose wants to know how our universe got the structure it now has. Most astronomers believe the universe was originally gas — mostly hydrogen and helium — and that it somehow became filled with galaxies, galaxy clusters, and even clusters of clusters of galaxies (called superclusters). There's a hierarchy here: smaller objects such as galaxies tend to form first. Those may later interact to form larger objects, such as clusters. Or as Rose puts it, "it's all smaller lumps forming bigger lumps."

Individual galaxies move around within galaxy clusters like bees inside a swarm. These clusters are often saturated by one-hundred-million-degree goop — a gas, actually — called intergalactic medium. When a galaxy plows into this intergalactic medium at two and a half million miles an hour, the heat and resulting shock wave can push the galaxy's own gas right out. Any gas that doesn't get pushed out can get compressed to form new stars. So when astronomers see a lot of star formation along one edge of a galaxy, they suspect intergalactic medium might be wreaking its havoc.

Rose studies Pegasus I, a cluster of galaxies 150 million light-years from Earth (right in our back yard, as clusters go). Pegasus I isn't behaving. "It's kind of a ratty little cluster," Rose says. "The galaxies are not moving around very fast, and there's not much intergalactic medium there." Yet some galaxies in Pegasus I act like they're moving through intergalactic medium — they appear to be losing gas and forming new stars along one edge.

Rose would like to find out why. He uses all sorts of data sources, including X-ray observations, but it really helps to have good images and good data from the spectrograph. SOAR should be able to give him both, and he won't have to wait for telescope time to get them.

The Whiz Kid

If you were an undergraduate and Dan Reichart moved into your dorm, you wouldn't think anything of it. He wouldn't even need to put up the Star Wars poster that hangs in his office. He might pass for a student — Christiansen and Carney have been working on SOAR since Reichart was twelve — but Dan Reichart is actually a rising star among astronomers. And he studies a sexy topic, as astronomy goes.

Gamma ray bursts are cosmic explosions. They're so bright that we can detect them from far away — in fact, astronomers figure gamma ray bursts are the most distant detectable things in the universe — and they illuminate whatever's between us and them. Reichart wants to use gamma ray bursts to backlight the universe and get new clues about how it formed.

But until recently, gamma ray bursts were leaving us in the dark. We didn't know where they came from or what they were. In 1997, scientists discovered that gamma ray bursts were coming from deep space. Then in 1999, Reichart was one of three scientists to discover that these cosmic explosions happen when stars at least thirty times larger than our sun die off.

There's only one catch: to see a gamma ray burst, you have to be quick. They peak within minutes, sometimes seconds. With existing technology, Reichart might not be alerted to a gamma ray burst for hours, and by then, most of the interesting data are already gone. But Reichart is building six small telescopes to chase these intergalactic ghosts. If his scopes pick up a burst, and it turns out to be something interesting, Reichart will be able to interrupt SOAR.

Here's where SOAR's versatility can really pay off. If a gamma ray burst happens while SOAR is getting optical data, the telescope operator can redirect the light to SOAR's infrared instruments — which are used to see gamma ray bursts — in under a minute. SOAR moves pretty quickly, too. "Within two minutes I can get anywhere in the sky," Reichart says. "Let's say we find the most distant thing in the universe. If Keck — the largest telescope in the world — doesn't have the infrared on, they're out of luck."

The Space-Time Trailblazer

If you can't find Charles Evans, look in the woods. He just might be off leading a Boy Scout camping trip with one of his sons. And though he might not be the first to bring it up, Evans has quietly blazed his own trails in theoretical astrophysics, Bruce Carney says.

Evans likes to think in relative terms: when two black holes encounter each other, they distort space-time and send ripples of gravity through the universe. At that point, Isaac Newton's gravity isn't a good enough compass to get astronomers out of the woods. So they turn to Einstein's general relativity. "The equations are nasty to the point of almost always being intractable, incapable of solution in any traditional sense," Carney says. But Evans has helped pioneer ways of calculating numerical solutions.

Gravitational waves — those space-time ripples caused by black holes and other objects — are hard to detect from earth. So hard that the Laser Interferometer Gravitational Wave Observatory (LIGO) built two detectors, each with a pair of "arms" that are four kilometers long. Any gravitational waves headed our direction minutely change the lengths of those arms. LIGO uses lasers to measure these giant arms as their lengths change — to a precision of less than one one-thousandth of an atomic nucleus. But even when LIGO does detect gravity waves, we have trouble telling what caused them. Evans' theoretical work is meant to help sort that out.

When it's time to SOAR, Evans' knowledge of black holes will dovetail nicely with Dan Reichart's study of gamma ray bursts (they're occasionally associated with black holes). Since these bursts fade so fast, the two will work together to learn as much as SOAR can tell them about a given burst.

Evans hopes some of those bursts will be from collisions involving two neutron stars, or a neutron star and a black hole. A neutron star might have a mass one and a half times that of our sun, but squeezed into a space only ten or so kilometers across. A black hole is even denser than that. Both are remnants of dead stars. There are places in the universe where these "stellar corpses" are doing weird things. Say a black hole and a neutron star are orbiting each other. Over millions of years, they spiral closer and closer together because of the gravity waves they give off. Once their orbit shrinks to one hundred kilometers or so, these massive objects whiz by each other hundreds of times per second.

"It only takes a few minutes for the end to come once they get that close," Evans says, "and it's a spectacularly violent event."

These collisions give off enough energy that we could expect to detect them via satellite, with LIGO, and with optical observation from SOAR — getting three kinds of data on one event. "That would be the Rosetta Stone," Evans says. "That's when you really learn something."

An Observer, In Theory

Laura Mersini is a theoretical physicist, but SOAR helped draw her to Carolina. She says that when it comes to what we know about the universe, current physics theory is lagging a little behind. For example, the Big Bang theory might not be enough to explain the origin of all the matter in the universe (everything from the universe's large-scale structure — galaxies and the like — to cosmic microwave background radiation, dark matter, and the rest). But theory can't catch up without observation. "We need new physics, and that's exactly why we need SOAR," she says.

Laura Mersini. Photo by Valery Tenyotkin. Click to enlarge.

The Governor's Man

When Robert McMahan is wearing his astronomer's hat, he talks about what SOAR can do for science and what he might like to do with SOAR. When he's wearing his Raleigh hat as N.C. Governor Mike Easley's senior advisor for science and technology, he talks about SOAR as a long-range, strategic investment for the university and the state. Building new instruments for the telescope means pushing new technologies, he says. "And SOAR can become a catalyst for the university to do much more," he adds — to inspire students and expose them to cutting-edge technology, to create a scientific infrastructure that brings the brightest people and best ideas together, and to increase Carolina's visibility internationally.

Take Chris Clemens and his volume holographic grating. They're now in high demand for other telescope projects. Clemens has designed gratings for the world's largest telescope, called TMT (Thirty-Meter Telescope). "Our technology is at the core of every project from now on," Clemens says. "We've more or less conquered a technology that people need. We're building not only science, but a technological expertise. And that expertise is going to take us wherever we want to go."

Back under his astronomer's hat, McMahan has spent a good bit of time studying the large-scale structure of the universe. Galaxies, as it turns out, aren't evenly spread through our universe, but instead occur in the "interstitial regions of large voids," McMahan says. Think of soap bubbles in your kitchen sink. Galaxies tend to be distributed through the universe as if they were lying on the surfaces of those bubbles, without much stuff in between the galaxies (inside the bubbles).

But SOAR's got McMahan thinking again about something he worked on early in his career: white dwarfs. They're the small cores of dying, low-mass stars that cool off slowly, over billions of years. Once they do cool, they're very faint: when the Hubble Space Telescope found seventy-five white dwarfs in the Scorpius constellation, the brightest of them was about as dim as a one-hundred-watt light bulb on the moon as seen from Earth. "The hotter stars are well-observed," McMahan says. But white dwarfs are a little neglected. SOAR can help McMahan begin to change that.

SOAR has been near and dear to McMahan since he got to Carolina in 1989. Did McMahan ever think SOAR wasn't going to happen? "Oh, gosh, lots of times," he says. "Sometimes it was just sheer pig-headedness that got the project through, and a desire not to let it go."

Pig-headedness or not, it has paid off. Carney feels SOAR is a quantum leap for Carolina. He and Christiansen can remember when supplies were going up to Cerro Pachon by horse and mule, and how the bulldozer driver they hired to cut the road to SOAR had worn out one of his blades only halfway up the mountain. Fast-forward fifteen years to April 2004, just before SOAR's dedication ceremony, when Carolina's astronomers held a V.I.P. videoconference from SOAR's control room in Chile back to Chapel Hill. "Wayne Christiansen had a smile on his face a mile wide," Dan Reichart remembers. "You could have mugged him and not wiped that smile off his face."

The National Optical Astronomy Observatory will fund SOAR's yearly operation. SOAR would not have been possible without help from former Senator Lauch Faircloth, Representative David Price, Len and Morris Goodman, Richard and Kit Barkhouser, Henry Cox, Edgar and Samantha Cato, Billy and Janie Armfield, and the U.S. Department of Defense. Carney is professor of astrophysics and senior associate dean in the College of Arts and Sciences. Cecil, Christiansen, Rose, and Evans are professors of astrophysics. Clemens is associate professor and McMahan is research professor of astrophysics. Reichart and Mersini are assistant professors of astrophysics.

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