An otherwise nondescript binary star system in the Whirlpool Galaxy has
brought astronomers tantalizingly close to their goal of observing a star just
before it goes supernova.
The study, submitted in a paper to the Astrophysical Journal,
provides the latest result from an Ohio
galaxy survey underway with the Large Binocular Telescope, located in Arizona.
In the first survey of its kind, the researchers have been scanning 25
nearby galaxies for stars that brighten and dim in unusual ways, in order to
catch a few that are about to meet their end. In the three years since the
study began, this particular unnamed binary system in the Whirlpool Galaxy was
the first among the stars they’ve cataloged to produce a supernova.
The astronomers were trying to find out if there are patterns of brightening
or dimming that herald the end of a star’s life. Instead, they saw one star in
this binary system dim noticeably before the other one exploded in a supernova
during the summer of 2011.
Though they’re still sorting through the data, it’s likely that they didn’t
get any direct observations of the star that exploded—only its much brighter
Yet, principal investigator Christopher Kochanek, professor of astronomy at Ohio State
and the Ohio Eminent Scholar in Observational Cosmology, does not regard this
first result as a disappointment. Rather, it’s a proof of concept.
“Our underlying goal is to look for any kind of signature behavior that will
enable us to identify stars before they explode,” he says. “It’s a speculative
goal at this point, but at least now we know that it’s possible.”
“Maybe stars give off a clear signal of impending doom, maybe they don’t,”
says study co-author Krzystof Stanek, professor of astronomy at Ohio State,
“But we’ll learn something new about dying stars no matter the outcome.”
Postdoctoral researcher Dorota Szczygiel, who led the study of this
supernova, explains why the galaxy survey is important.
“The odds are extremely low that we would just happen to be observing a star
for several years before it went supernova. We would have to be extremely
lucky,” she says.
“With this galaxy survey, we’re making our own luck. We’re studying all the
variable stars in 25 galaxies, so that when one of them happens go supernova,
we’ve already compiled data on it.”
The supernova, labeled 2011dh, was first detected on May 31, 2011, and is
still visible in telescopes. It originated from a binary star system in the
Whirlpool Galaxy—also known as M51, one of the galaxies that the Ohio State
astronomers have been observing for three years.
The system is believed to have contained one very bright blue star and one
even brighter red star. From what the astronomers can tell, it’s likely that
the red star is the one that dimmed over the three years, before the blue star
initiated the supernova.
When the Ohio State researchers reviewed the Large
Binocular Telescope data as well as Hubble Space Telescope images of M51, they
saw that the red star had dimmed by about 10 percent over three years, at a
pace of three percent per year.
Szczygiel believes that the red star likely survived its partner’s
“After the light from the explosion fades away, we should be able to see the
companion that did not explode,” she says.
As astronomers gather data from more supernovae—Kochanek speculates that as
many as one per year could emerge from their data set—they could assemble a
kind of litmus test to predict whether a particular star is near death. Whether
it’s going to spawn a supernova or shrink into a black hole, there may be
particular signals visible on the surface, and this study has shown that those
signals are detectable.
The team won’t be watching our sun for any changes, however. At less than
10% of the mass of the star in supernova 2011dh, our star will most likely meet
a very boring end.
“There’ll be no supernova for our sun—it’ll just fizzle out,” Kochanek says.
“But that’s okay—you don’t want to live around an exciting star.”