Academics and Research / Current Issue

Astronomy professor publishes star system discovery in science journal

University of Denver astronomy Professor Robert Stencel helped capture an image of the mysterious binary star system Epsilon Aurigae. Photo: Wayne Armstrong

For more than a century, there has been a mystery. For decades, there have been hypotheses. For years, University of Denver astronomy Professor Robert Stencel has sought answers.

But there hasn’t been an image. Until now.

Stencel and DU PhD student Brian Kloppenborg are co-authors of a paper that appeared in April in the international science journal Nature. The paper details how the two worked with teams from Georgia State University and the University of Michigan to capture an image of the mysterious binary star system Epsilon Aurigae.

The system, with one bright star that appears to “blink” every 27 years, was discovered in 1821. The blink, which is actually an eclipse, lasts for two years. The cause of the eclipse was unknown. Some astronomers suggested an orbiting twin star or a black hole, but there was no way to capture an image and be sure.

Stencel has studied the system since the 1980s and was joined by teams of scientists and even amateur astronomers—all funded by four separate National Science Foundation grants. Stencel and the teams from Michigan and Georgia tested Stencel’s proposal to combine the University of Michigan’s newly developed imager and software with Georgia State’s giant array of conjoined telescopes in the California mountains near Los Angeles to produce a snapshot of what exactly is going on during the eclipse.

“What we’re seeing has been the subject of hypotheses for decades. What we’ve never had was a ‘picture’ of what is actually happening,” Stencel says. “We’ve produced a reconstruction of an image based on sampling done with multiple telescopes. A reasonable analogy is what you ‘see’ with MRI (magnetic resonance imaging). You don’t have a shutter going off, but you’ve scanned the object repeatedly, and after a while the computer has enough information to put together a picture.”

For the first time, scientists are seeing what’s happening some 2,000 light-years away: A huge star 150 times the mass of our sun is being eclipsed by a whirling dust cloud 930 million miles across. “What we’re seeing, that we’ve never seen before, is this giant cloud,” Stencel says. “It’s just that, a giant, dense cloud of dust.”

Because astronomers had not been able to see much light from the system, they had described it as a smaller star orbited by a disk of dust that had to be precisely aligned with the star’s orbit and then again aligned along the same plane as the Earth’s orbit to catch the eclipse. It was all very unlikely.

The new images show that as nearly impossible as that seems, it is the case. “This really shows that the basic paradigm was right, despite the slim probability,” says University of Michigan Professor John Monnier. “It kind of blows my mind that we could capture this.”

Stencel says getting everything to work—from the funding to a “Citizen Sky” initiative that encouraged amateur astronomers to help assemble data to getting the critical telescope time from the California array—took an immense amount of time and work, and a bit of luck. This plus the work of graduate students such as Kloppenborg, who processed the volumes of raw data, made the discovery possible.

“This has been a very good project for all of us,” Stencel says. “We have a picture of something that until now we’ve only had hypotheses about. We are certainly not done, but this is a big step forward.”


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