Friday, November 1, 2013

Milky Way supernova should be visible from Earth in next 50 years

Barred Spiral Milky Way. Illustration Credit: R. Hurt (SSC), JPL-Caltech, NASA

Astronomers at Ohio State University have calculated the odds that, sometime during the next 50 years, a supernova occurring in our home galaxy will be visible from Earth.

The good news: they've calculated the odds to be nearly 100 percent that such a supernova would be visible to telescopes in the form of infrared radiation.

The bad news: the odds are much lower—dipping to 20 percent or less—that the shining stellar spectacle would be visible to the naked eye in the nighttime sky.

Yet, all this is great news to astronomers, who, unlike the rest of us, have high-powered infrared cameras to point at the sky at a moment's notice.

For them, this study suggests that they have a solid chance of doing something that's never been done before: detect a supernova fast enough to witness what happens at the very beginning of a star's demise.

A massive star "goes supernova" at the moment when it's used up all its nuclear fuel and its core collapses, just before it explodes violently and throws off most of its mass into space.

Chris Kochanek
"We see all these stars go supernova in other galaxies, and we don't fully understand how it happens. We think we know, we say we know, but that's not actually 100 percent true," said Christopher Kochanek, professor of astronomy at Ohio State and the Ohio Eminent Scholar in Observational Cosmology.

"Today, technologies have advanced to the point that we can learn enormously more about supernovae if we can catch the next one in our galaxy and study it with all our available tools."

The results will appear in an upcoming issue of The Astrophysical Journal.

First through calculations and then through computer models, generations of astronomers have worked out the physics of supernovae based on all available data, and today's best models appear to match what they see in the skies.

But actually witnessing a supernova—that is, for instance, actually measuring the changes in infrared radiation from start to finish while one was happening—could prove or disprove those ideas.

Kochanek explained how technology is making the study of Milky Way supernovae possible.

Astronomers now have sensitive detectors for neutrinos (particles emitted from the core of a collapsing star) and gravitational waves (created by the vibrations of the star's core) which can find any supernova occurring in our galaxy.

The question is whether we can actually see light from the supernova because we live in a galaxy filled with dust—soot particles that Kochanek likened to those seen in diesel truck exhaust—that absorb the light and might hide a supernova from our view.

"Every few days, we have the chance to observe supernovae happening outside of our galaxy," said doctoral student Scott Adams.

"But there's only so much you can learn from those, whereas a galactic supernova would show us so much more. Our neutrino detectors and gravitational wave detectors are only sensitive enough to take measurements inside our galaxy, where we believe that a supernova happens only once or twice a century."

Adams continued: "Despite the ease with which astronomers find supernovae occurring outside our galaxy, it wasn't obvious before that it would be possible to get complete observations of a supernova occurring within our galaxy."

"Soot dims the optical light from stars near the center of the galaxy by a factor of nearly a trillion by the time it gets to us. Fortunately, infrared light is not affected by this soot as much and is only dimmed by a factor of 20."

By balancing all these factors, the astronomers determined that they have nearly a 100 percent chance of catching a prized Milky Way supernova during the next 50 years. Adams summarized the findings in a video:

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