This is very exciting: the star that blew up to form Supernova 2012aw may have been seen in an older Hubble image!
First, here's a lovely shot of the galaxy and supernova:
[Click to galactinate.]
This is not from Hubble! It's from Adam Block, a frequent contributor of stunning pictures to this blog, who took it using the 0.8 meter (32") Schulman Telescope at Mt. Lemmon on March 20. The supernova is the bright bluish star sitting on a spiral arm to the right and just below the core of the galaxy.
M95 is a relatively nearby barred spiral galaxy just about 37 million light years away, so we can see a lot of detail in it. In fact, it's close enough that with big telescopes, individual stars can be seen in it. Once the supernova was spotted and its location determined, astronomers found a picture of M95 taken with Hubble a few years ago, long before the supernova event, and combed through it. Sure enough, they found a star sitting right where the supernova went off! It's almost certainly the progenitor of SN2012aw.
Interestingly, given the color and brightness of the the star in the Hubble image, it was not terribly massive, maybe 8 times the mass of the Sun. That's at the lower limit for how much mass an exploding star of this type can have. It's probable the star had more mass when it was younger, and shed a lot of it during its short, furious life. I poked around online and found another example like this; SN2003gd was a supernova in the nearby galaxy M74, which is also close enough that a progenitor star was found in older images. Interestingly, it too had about 8 times the Sun's mass, and had other characteristics similar to this new supernova.
Being able to find the star that blew up in older images is terribly exciting! It's not that common to find them -- they have to be in nearby galaxies, or else they're too faint to see. And they really help constrain the physics of the explosion. We have a pretty good grasp of the basics on how high-mass stars explode, but the devil's in the details. The mass of the star right before it blows up, how bright it is, what color it is, what kind of environment it's sitting in -- all these things help astronomers understand better how and why stars like this explode. In fact, Supernova 1987A sparked a revolution of sorts in supernova astrophysics because it was found to be a blue supergiant when it went off -- before that, it was thought only red supergiants could explode.
So SN2012aw joins the short -- but growing -- list of supernovae that have a star identified as the culprit. The more we find, the merrier astronomers will be.
Image credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona. Tip o' the Chandrasekhar limit to DeepSkyVideos on Twitter.
- Supernova 2012aw: the pictures!
- Breaking: possible supernova in nearby spiral M95
- Supernova update: it’s peaking now! (about a supernova in galaxy M101 in 2011)
- Supernovae popping off like firecrackers in Carina