Local professor helps discover our galaxy's most distant stars

Rider University professor John Bochanski stands next to a simulated image demonstrating how small the Milky Way would look from one of the cool red giants he helped discover while at Haverford College.
Rider University professor John Bochanski stands next to a simulated image demonstrating how small the Milky Way would look from one of the cool red giants he helped discover while at Haverford College. (TOM GRALISH / Staff Photographer)
Posted: September 04, 2014

When John Bochanski was 7, he would sit on the porch at night in Washington Township and watch as his grandfather pointed out the constellations.

By 12, he was reading everything he could find about astronomy. The following year, he saved up more than $400 from his Gloucester County paper route to buy an 8-inch telescope.

Lately he has been setting his sights quite a bit farther: more than 5 quintillion (five followed by 18 zeroes) miles away.

That is the distance between Earth and the most distant known star in the Milky Way - a "cool red giant" that Bochanski helped discover while a visiting assistant professor at Haverford College. He and colleagues also found a second such star that they calculated was a mere 4.5 quintillion miles hence.

If you could travel at the speed of light, it would take 775,000 years to reach the closer one and 900,000 for the other.

"They're way out there," said Bochanski, 34.

The team reported its findings in July, in a publication called Astrophysical Journal Letters. There are plenty of more distant stars in other galaxies, but these two are about as far as you can go in the Milky Way, and will be useful to astronomers in piecing together the story of how our corner of the universe came to be.

Bochanski, who started a new job this month as assistant professor of physics at Rider University, north of Trenton, started his search for the most distant stars in the galaxy in the fall of 2012, when he arrived at Haverford as a postdoctoral fellow. Working with Haverford associate professor Beth Willman and colleagues from the Harvard-Smithsonian Center for Astrophysics and other institutions, Bochanski cast a wide net.

The team started by using software to sift through 6 million star candidates contained in public databases - troves of unidentified celestial objects that had been captured by ground-based telescopes in New Mexico and Hawaii.

The scientists whittled the list down to 400 stars whose color, position, and faintness were indicative of faraway cool red giants. But they knew that many of them would turn out to be closer stars called cool red dwarfs. These common stars have a similar reddish hue yet are much dimmer and smaller, so they can give the illusion of being distant giants.

The team members' next step was to make their own detailed observations at the MMT Observatory on Mount Hopkins in Arizona, a joint venture of the Smithsonian and the University of Arizona.

Using sophisticated instruments to analyze the light spectrum emitted by each candidate object, they finally came up with the two most distant stars, which they identified only by long strings of letters and numbers. Each is about 100 times the size of the sun, though quite a bit cooler.

Their temperatures are about 3,000 to 3,500 degrees Kelvin, Bochanski said. The surface of the sun measures about 6,000 degrees Kelvin (more than 10,000 degrees Fahrenheit).

Maureen Teyssier, a postdoctoral fellow in the Rutgers University department of physics and astronomy, said that finding the stars may help confirm models of how our galaxy formed.

"Discoveries like these very distant stars could've been predicted by the simulations," said Teyssier, who was not involved with the research. "On the other hand, they're just predictions. So having the discovery of really distant stars like this is pretty awesome."

Still unclear is how these stars came to be in such a distant, isolated part of the Milky Way. Bochanski said one possible explanation is that they are remnants of a smaller "dwarf" galaxy. Another is that they were formed in the inner Milky Way and then ejected to its outer reaches.

The astronomer said it was hard to say for sure. He does not know whether stars in these far-flung locations are rare, and the team just happened to find them, or if there are others like them, which would allow further analysis of their origins.

"With only two, I'm not really ready to make a strong statement either way," Bochanski said. "With two, it's a little tricky because you don't know for sure if you're dealing with two unique examples or if we're starting to discover another class of distant stars."

Teyssier, the Rutgers researcher, is intrigued enough that she plans to collaborate with Bochanski on a related project this year.

"We study these remnants like a CSI would study bits of broken car on the side of the highway," Teyssier said. "We take a lot of clues and put them together."

Bochanski, meanwhile, will spend a good deal of his time this fall teaching. His new job at Rider calls for him to teach general physics classes to undergrads.

But his students should not be surprised if he throws in a few starry-eyed observations along the way.


tavril@phillynews.com215-854-2430

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