What a Brilliant Flash in a Distant Galaxy Can Tell Us
Every once in a while I see a posting by an astronomer who has discovered something unique. The latest one is from Dr. Melissa Graham (@mlg3k) at the University of California-Berkeley. She was working with some colleagues on a project called the Hubble Frontier supernova survey and spotted the telltale “light-up” of a Type Ia supernova in a view of a galaxy cluster some 6 billion light-years away.
For her work, not only does Melissa get a great discovery, but she gets to name the supernova. The usual practice for the Hubble Frontier Field survey is to use Star Trek names. So, she called her object SN Crusher, which is pretty darned cool. (Its official title is HFF15Cru.) And, lots of folks are taking notice, including actor Wil Wheaton (@WilW), who played Wesley Crusher. He caught the news, and congratulated Dr. Graham on her finding! He also let his “Trek” mom (Gates McFadden, who played Dr. Beverly Crusher) know, as well. It all played out on Twitter, where I happened to catch Dr. Graham’s first announcement.
What’s a Type Ia Supernova?
There are two types of supernovae: Type I and Type II. The second kind, a Type II supernova, is a catastrophic explosion of massive supergiant star. They’re cool, but that’s not what Dr. Graham saw. She spotted a Type Ia supernova. These events have interesting implications, particularly for understanding distances in the universe.
Usually Type Ia supernovae occur where two stars orbit as a close binary pair. One of them is likely a white dwarf. As they dance around each other, material from one star escapes and “accretes” (gathers) onto the surface of the other. Eventually, the second star reaches a limit to how much material it can accept, and it explodes, providing an extremely bright flash of light and other radiation. The exact mechanism for this explosion is still being modeled by astronomers.
These explosions eject material out to space, and are so bright they can outshine their home galaxy for a short period of time. Type Ia supernovae emit a pretty standard brightness level and astronomers have used them as so-called “standard candles” to measure distances in space. In 1998, astronomers observing Type Ia supernovae found an interesting result as part of their observations: the expansion of the universe appears to be accelerating.
The Frontier Fields Survey
To see how the expansion of the universe is changing over time, astronomers want to look at Type Ia supernovae throughout the cosmos. To do this, they gather light from objects that exist across great distances in space. That’s where the Hubble Frontier Fields Survey comes in.
Frontier Fields observers study massive clusters of galaxies using the the Hubble Space Telescope. The gravity of these clusters warps and magnifies the faint light of the distant galaxies behind them. As a result, astronomers can see some of the most distant galaxies as they looked back in the infancy of the universe. And, they’re also finding — as Dr. Graham did — the signals from ancient Type Ia explosions. Those events give them even more information about the expansion rate of the universe at the time those events occurred.
Want to see more info about this supernova? Check out Dr. Graham’s discovery telegram here.