Rare Supernova Caught In Before-and-After Photos

The scoop: Before supernova SN 2005gl hit the cosmic scene, only one other star had been spied before going ka-boom.

With a new before-and-after snapshot of the explosive and final moments of a star's life, what can scientists learn?

Discovery Space chats with Doug Leonard, an astrophysicist at San Diego State University.

Dave on Earth (12:00 PM): Hi Doug, Dave Mosher from Discovery Space here.
Or is Dr. Leonard more suiting?

Supernovae Hunter (12:00 PM): Doug is fine!

Dave on Earth (12:01 PM): Excellent. So we're online today to chat about things that go KA-BOOM in the night (sky).
Can you fill me in on what it is, exactly, that you do?

Supernovae Hunter (12:03 PM): Well, I study things that explode.
And supernovae represent the explosive demise of stars.
One of my main areas is finding out exactly which types of stars end their lives by blowing up.

Dave on Earth (12:04 PM): Got it. So what's the consensus so far?
Is the sun bound for, um, explosive greatness?

Supernovae Hunter (12:05 PM): Nope. For better or worse, we're pretty confident that the sun will not end its life in a blaze of glory.
It will probably end with a rather gentle "puff", where it pushes its outer atmosphere away, and then settles down into a very compact state known as a white dwarf.
No explosion, alas.

Dave on Earth (12:06 PM): Now if I understand it correctly, there's really been only one case of astronomers seeing a star before it explodes.
...but you and your colleague Avishay Gal-Yam possibly just found the second?

Supernovae Hunter (12:10 PM): Yes, that's technically correct.
In only one other case, that of supernova SN 1987A -- a very nearby explosion "only" about 160,000 light-years away -- do astronomers have essentially conclusive proof of the so-called "progenitor star's" identity:
A "before explosion" picture, a "during explosion" picture, and a "long after explosion" picture -- showing that the original star had disappeared.
What Avishay and I did was do the same for a different supernova:
Supernova SN 2005gl, which was much further away (~215 million light years).

Dave on Earth (12:11 PM): Only two? Sounds a bit low considering there's billions of stars out there!

Supernovae Hunter (12:11 PM): Right; there are several other very likely progenitor detections that just lack that final image for confirmation.
They will likely be confirmed in the near future!
But right now, yes, there are only two.

Dave on Earth (12:12 PM): Big question -- quite literally -- how can we make out a star 215 million light-years away?

Supernovae Hunter (12:15 PM): Well, this is why it's so tough!
Being so far away, only the very brightest stars are easily visible on images; and at that distance, one really needs the Hubble Space Telescope to "see" individual stars.
Fortunately, in the case of this supernova, the galaxy it occurred in was photographed by Hubble about 8 years prior to the explosion, and the star that blew up was over 1 million times the luminosity of the sun.
I.e., among the most luminous stars known to exist in nature.

Dave on Earth (12:16 PM): Wow.
Another thing I find weird -- you mentioned a "before explosion"
What do you mean by that? Isn't a supernova a supernova?

Supernovae Hunter (12:19 PM): Well, "supernova" refers to the actual event of a star blowing up -- a point when it becomes millions to billions of times brighter than it was during its "life."
Now, when this happens, everyone notices!
Prior to the star exploding, though, no one had taken any particular notice of the star... so we just have to get lucky and hope that someone took an image of the star for some other reason.
E.g. someone likes to study the galaxy that it's in.
So, the "before explosion" image is just a serendipitous image of the star that eventually went on to explode.
Of course, all of this "before" stuff refers technically to "before the light reached us, here on Earth."
In reality, this star that we're studying here exploded 215 million years ago!
So our "before" picture is really 215 million years + 8 years ago...

Dave on Earth (12:22 PM): Hmm... are there telescopes tracking down stars for this very purpose -- to see which ones are ticking time bombs?
Or is it mostly just the work of astronomers going through the painstaking work of "contrast and compare" after __ years have passed?

Supernovae Hunter (12:24 PM): Yup, there are programs in place now with HST (Hubble Space Telescope) that image nearby galaxies for the express purpose of hoping they host future supernovae, so that we have the "before" picture.
But still, there are lots of galaxies out there, and Hubble has taken lots of pictures for other purposes.
So many times the "before" images are just found in the general archive of images taken for other reasons.

Dave on Earth (12:26 PM): Was it a pain in the butt to find this new one?