Post
by Ann » Sat Jun 11, 2011 5:40 am
That's a fantastic APOD!
The two images of M51 gives a great insight into the kind of stellar environment that produced the two supernovae, both of type II (that is, they were produced by very massive stars that ran out of fuel in their cores). If you look at the image on the left, the one with the SN2005cs supernova, you can see the part of the galaxy that would produce the SN2011dh supernova six years later. This "pre-supernova" area looks like roundish patch which is bluer in color than its surroundings.
To the right of this patch, in the "inter-arm" region of the galaxy, the color of the stellar population is brownish, characterized by low-mass stars that can't produce Type II supernovae.
To the left of the patch, the color of the stars is generally blue, but a more muted blue than the blue patch, characterized by an intermediate population of stars, whose high-mass stars have already died, possibly by exploding as supernovae.
Above and, in particular, below this patch, there are pink star formation regions. Here there are very massive stars, but they are so young that they haven't had time to run out of fuel and explode as supernovae.
But in the blue patch, star formation has ceased, and the massive stars are just about to run out of fuel. Only six years after the image on the left was taken, one of the blue stars in that patch blew its top! (Note, by the way, that the supernova appears to sit smack in the middle of this blue patch, perhaps where the concentration of "supernova-ripe" massive stars is the highest.
What about the part of the galaxy where the 2005 supernova exploded? We can look at that part of the galaxy in the 2011 image of M51. The part of the galaxy that produced SN2005cs is not as blue as the blue patch that produced SN2011dh. My guess is that there are fewer "supernova-ripe" stars in the general area of SN2005cs than in the general area of SN2011dh. But that doesn't mean that there can't be a few massive oddball stars there that are just the right mass and age to explode.
Ann
Color Commentator
Supernovae in the Whirlpool
