500pesos wrote:That galaxy in front must be really enormous, and it doesn't seem to have any dust and looks quite reddish. It looks as if there is no new star formation going on and all the stars are super old.
What do you say is to happen to such a big galaxy populated by Betelgeuse-like stars? How is it going to be when all these millions of old stars swell up and start going supernovas (supernovae?)? will they trigger some new star formation from the debris and shock waves and breathe some new life into the old galaxy or it all's just going to go mega-boom in the sky?
There are probably no Betelgeuse-like stars in this galaxy at all, assuming there has been no recent star formation there. Stars like Betelgeuse, massive stars that have turned into enormous supergiants, are all young, and they are not found in elliptical galaxies like the one in today's APOD. Therefore, the supernovae that are likely to explode in this galaxy will not come from supergiant stars like Betelgeuse, but from compact white dwarfs smaller than the Earth.
So if there are no Betelgeuse-like stars in this galaxy, then why is it red? Well, frankly, it isn't red, but yellow. There are undoubtedly trillions of small "red" stars in that galaxy, stars much smaller and cooler than the Sun, and yet they are no redder than the light from an ordinary light bulb. So these "red" stars are really yellow. (What about the color of our own Sun, then? Isn't it yellow, too? No, our Sun is much whiter than the light from an ordinary light bulb, so it should be described as white.)
(Admittedly, the red galaxy in today's APOD may contain trillions of "brown" (but really red) dwarfs, but the "brown" dwarfs are so faint that they basically don't contribute to the light of this galaxy at all.)
But while the "red" galaxy contains no "Betelgeuses" it does contain a respectable number of relatively modest "red" (but really yellow) giants like Arcturus and Aldebaran. All these yellow stars give the galaxy a yellow color.
However, the galaxy is sufficiently far away that the expansion of the universe "stretches" the light that is emitted from this galaxy, so that it actually looks orange or red. But the intrinsic color of this galaxy is yellow.
The "red" galaxy is indeed huge and massive, because otherwise its mass wouldn't have made such an impressive "indentation" in the "fabric" of spacetime. And if that hadn't happened, the light from background galaxy wouldn't have been forced to change its path due to the altered "topography" of spacetime. And if that hadn't happened, the galaxy wouldn't have looked like a ring to us, and it would have looked very much fainter to us than it does now.