Betelgeuse Star undergoing rapid shrinking

[Lord Relvenous]

Yeah, I found myself stunned a little when I counted the digits of the last one. The fact that Jupiter's orbit would easily fit inside the Cephei stars was a nice reminder of why I love stellar astronomy so much. I mean, intellectually I know how big these stars are, but it's always fun to put it into different terms.

[Edi]

The Cephei stars aren't the biggest ones around. VY Canis Majoris is nearly half again as big.


Picture to scale

[starslayer]

This issue here is not that it is a rapid collapse, but rather it is this slow. Everyone expected that the final collapse would be rather fast and furious, with material falling back towards the iron core and get expelled out. And this process actually generates a huge bulk of the heavy elements which otherwise normal fusion in the star would never produce (because the huge amount of energy and compaction that occurs in the rebound).

This rather slow contraction contradicts generally accepted models. I am not too familiar with the data from known supernovae and whether they have shown this slow contraction or not, but most of what I have read seems to imply that nothing has contradicted the existing model too much beyond tweaking the parameters. Of course, having a supernova blow up this close will probably generate more data than the average supernova just by the sheer quantity of light that will arrive here.

The final collapse must be rapid, although the outer layers never see it; they just see the rebounding shockwave coming up to meet them at a significant fraction of c. Once the iron in the degenerate core starts being photodisintegrated (this occurs when the iron core reaches a mass of about 1.5 M_sun), it collapses from something around the size of the Earth to the size of Manhattan in less than a second. This releases about 1E46 J of GPE in that time. While most of this energy leaves as neutrinos, the rest of it (about 1E43 J, IIRC) goes into destroying the star.

Because supernovae are so damned bright (brighter than the combined light of the galaxy they are in, in fact), being far away is not really much of an obstacle for data-gathering purposes. What can be learned about them is mostly in the form of spectra, and those can be taken of even very distant events. What Betelgeuse gives us is a marvelous opportunity to study a very massive star late in its life from now until it blows itself the fuck up, and beyond. Supernovae are also not short-lived objects; they don't even reach maximum brightness for about a month after the initial explosion, and then steadily fade for over a year, usually. This gives us plenty of time to take images of spectra of them, whether they are near or far.

[Lord Relvenous]

The Cephei stars aren't the biggest ones around. VY Canis Majoris is nearly half again as big.


Picture to scale

Yeah, they were just the ones in the video, so I addressed them.

@Starslayer: I did not get the indication that the astronomers who observed this collapse believe that it is the final one. In fact I got just the opposite. What they seemed to be pointing out as weird was the size of the shrinkage. It's interesting that they point to instabilities within the star maybe causing this, as supergiants are already pretty unstable (of course there is quite a range, depending on the type of supergiant). If a stability issue is what is causing this, it's gotta be pretty major. It'll be interesting to see what we're able to decipher from spectra readings in the future.