Attention all astronomers! There is a new Type Ia supernova that has been seen in the nearby spiral galaxy M101, and it's very young -- currently only about a day old! This is very exciting news; getting as much data on this event as possible is critical. Most likely professional astronomers are already aware of the supernova, since observations have already been taken by Swift (no X-rays have yet been seen, but it's early yet) and Hubble observations have been scheduled. Still, I would urge amateur astronomers to take careful observations of the galaxy. [As an aside, I'll note that this supernova won't get bright enough to see naked eye and poses no threat at all to us here on Earth. It may be visible in decent-sized telescopes, though, and as you'll see this may be a very important event in the annals of astronomy.]
First of all, a supernova is an exploding star -- one of the most violent events in the Universe. There are different kinds of supernovae, but a Type Ia occurs, it's thought, when a superdense white dwarf -- the remnant core of a dead star -- siphons material off a companion star. If enough material piles on top of the white dwarf, it can suddenly start to fuse hydrogen into helium. This starts a runaway effect, and the entire star explodes. This supernova can release so much energy it can actually outshine its host galaxy! If you want more details, I've written about Type Ia supernovae before: Astronomers spot ticking supernova time bomb and Dwarf merging makes for an explosive combo. So this kind of supernova is incredibly bright, making them easy to spot over vast distances. These events are very important, because we think that each Type Ia supernova is very similar in the way it explodes, making them useful as benchmarks in gauging distances to very distant galaxies. In fact, it is the study of these explosions that has helped us nail down how fast the Universe is expanding, and also led to the discovery of dark energy. Clearly, the more we know about them, the better. M101 is a spiral galaxy only about 25 million light years away, making it one of the closest big spirals in the sky. It's also huge, boasting a trillions stars, ten times the mass of our Milky Way. You can read all about it in an earlier post featuring the image at the top of this article. Given M101's close distance, this new supernova will be relatively easy to study. And the best part is that the exploding star was caught young: most of the ones we see are far away, and too faint to be seen until they start to reach their maximum brightness after a few days. Getting data on them early is absolutely critical for understanding them, and it's the hardest part of all this. I am not exaggerating to say this new supernova could be a linchpin in our understanding of these events.
Interestingly, Hubble took images of this galaxy in 2002, and astronomers dug up the archived images and looked at the spot of the supernova to see if anything was there back then. Nothing shows up in the blue filter, but in the red (shown here) there are two stars very close to the position of the future supernova (the circle is centered on the best measurement of the supernova's position). From their brightness and color, both of these stars are red giants, stars like the Sun but near the ends of their lives. That would fit with the Type Ia supernova: red giants are so big that if there's a white dwarf nearby, it could suck up their matter and start the chain of events that led to its doom. Further observations may pin this down. If one of these stars is what fed the supernova, that's seriously cool; there are only a handful of supernova progenitor stars that have ever been seen*. All in all, this is pretty much a big deal. The galaxy is close, pretty, a bit odd, and is hosting the nearest Type Ia supernova seen in decades which was caught when it was less than a day old. I'm excited! I know a lot of telescopes will be aimed at the northern skies over the next few days, and I'll be very interested to find out what they see.
Image credits: Hubble M101 image: NASA, ESA, K. Kuntz (JHU), F. Bresolin (University of Hawaii), J. Trauger (Jet Propulsion Lab), J. Mould (NOAO), Y.-H. Chu (University of Illinois, Urbana), and STScI; Type Ia art: NASA/CXC/M.Weiss; Hubble image: NASA/ESA/Hubble. Tip o' the dew shield to paulwarren73.
^* Technically, if one of the red giants was behind this event, it wasn't the star that actually exploded -- the white dwarf which actually blew up was far, far too faint to be seen here. Still, very cool.