Kaius wrote: Ann wrote:
It is interesting to compare the near side of the disk of NGC 4526 with the near side of the disk of M104
, which isn't bluish at all. I'd say that more of the disk is young in NGC 4526 than in M104.
I can understand that blue stars are young since they are massive and approach the end of their lives quickly. But is it possible that the stars in the disk of M104 are also young, but just with a smaller mass? Not sure if this is a stupid question, but I'm new to astronomy.
Ann wrote:I believe that supernovas, even Type Ia supernovas, are more likely to appear in galaxies with a young population than in galaxies that all but lack young stars. Ann
Is there a physical explanation for this? Are all types of supernovae more likely to appear in galaxies with a younger star population?
Good questions, Kaius.
Yes, it is definitely possible to have low-mass star formation. So like you said, there might be low-mass young stars in the disk of M104. Such stars, however, will not go core-collapse, Type II supernova. Can they go Type Ia supernova? I think it is harder for them to do it, and it takes a longer time. It is in fact possible that it takes such a long time to do it that the universe is not old enough for stars like the Sun to have gone pop yet!
Consider. There are main sequence stars rather similar to the Sun in globular clusters, which are typically about 12 billion years old. The universe is about 14 billion years old, and it didn't start producing stars right away. To have a supernova Type Ia you first need a main sequence star, and then that star must evolve until it is ready to go supernova Ia. Astronomers are fairly certain that it takes either a white dwarf and a red giant to produce a Type Ia supernova, or else two white dwarfs. Main sequence stars don't produce supernovas. In order to get a white dwarf, a main sequence star first has to evolve into a red giant and then into a white dwarf. For low-mass stars, that takes a long time. For higher mass stars it happens a lot quicker. There are no stars similar to A0-type star Vega, about tree times more massive than the Sun, in globular clusters. Yes, there just might be blue stragglers, which are likely products of merging low-mass stars. But even the blue stragglers are unlikely to be as blue and bright as Vega. And in any case, there are no blue stragglers similar to B7-type 3.4 solar mass star Regulus in globular clusters. Regulus and Vega are destined to become white dwarfs, and that will happen to them while the Sun, which is much older than either of them, is still a main sequence star.
Interestingly, while Vega is a single star, Regulus does indeed seem to have a companion:
Jim Kaler wrote
Much more intriguing is a tight fourth companion detected only spectroscopically that orbits Regulus proper with a period of a mere 40.11 days. Analysis suggests that it is white dwarf with an anomolously low mass of just 0.3 solar, far below the minimum of 0.55 allowed by current stellar evolution. Kepler's laws then give a separation of about 0.35 Astronomical Units. Astronomers speculate that when the white dwarf was a luminous giant (far larger and brighter than Regulus is now) that it transferred much of its mass (through tidal interaction) to the star that is now Regulus, and in doing so, sped it up to its current fast rotation rate (which fits with the white dwarf scenario.
It is unclear (at least to me) if a 0.3 solar mass white dwarf can go supernova. But if it can, it is possible that the Regulus star system may produce a supernova in the future, when Regulus evolves into a red giant and starts spilling material on its white dwarf companion.