APOD: M72: A Globular Cluster of Stars (2012 Aug 19)

[Beyond]

This is how I understand it (but I may very well be wrong, mind you).

Even though the star runs out of hydrogen in its core, and helium in its core, it still contains hydrogen and helium in shells around the core. So the stars fuse hydrogen or helium (not both at the same time, I think) in those shells. The fusion process takes place closer to the surface of the star, making it swell. It could be, too, although I'm not sure, that more of the mass of the star is being used for fusion when the fusion process "has moved outwards" in the star than when it was confined to the core.

Stars also swell and get very bright just when their cores "go dead", or stop fusing. Then the cores shrink, a lot of energy is released, and the stars swell and get brighter.

Ann

Sort of like being on it's 'last' gasps, then?

[bystander]

Sort of like being on it's 'last' gasps, then?

See Stellar evolution: Maturity of a star

[ThePiper]

Missing / Wanted: Supernovae and Remnants in Star Clusters.
There are a lot of old Red Giants. Will they never die?

Supernova remnants are not missing in globular clusters...

Thank you Ann, for the good description. My question was influenced by the sharp HST-pictures of various star clusters.
Like balls of glittering diamonds in a black environment, clean, clear, no dust, no colorfull Gas clouds, no chaotic nebulas - clean and transparent.

It seems that the swinging through the galacitc center or disk works like a carwash...

[Ann]

Missing / Wanted: Supernovae and Remnants in Star Clusters.
There are a lot of old Red Giants. Will they never die?

Supernova remnants are not missing in globular clusters...

Thank you Ann, for the good description. My question was influenced by the sharp HST-pictures of various star clusters.
Like balls of glittering diamonds in a black environment, clean, clear, no dust, no colorfull Gas clouds, no chaotic nebulas - clean and transparent.

It seems that the swinging through the galacitc center or disk works like a carwash...

Indeed, a passage through the galacitc disk - not to mention several passages through the galacitc disk - certainly works like a carwash!

As a matter of fact, nebulae are brief phenomena. Many young clusters contain no nebulae at all - they have completely lost their "natal clouds". An example of such a "naked young cluster" is NGC 2362. Gaseous supernova remnants, too, can be expected to evaporate quickly in cosmic terms - in less than a million years.

Ann

[Starswarm Magellan]

Since globular clusters contain the oldest stars, wouldn't they be the most apt to nurture life on any orbiting bodies? I suppose they are too distant to investigate for "planet wobble" and such. One imagines inhabitants by now having very large, pulsing veined heads and wearing identical clothing as advanced races do. Then again, the current Mars mission could prove that any rocky planet's ability to support life is naturally finite. BTW, congrats, NASA. America is proud of you. I'd personally get elected just to award you all medals except I can't stand kissing babies.

[rstevenson]

Since globular clusters contain the oldest stars, wouldn't they be the most apt to nurture life on any orbiting bodies? I suppose they are too distant to investigate for "planet wobble" and such. ...

Stars that are that old (and any planets that may have formed with them) are primarily composed of hydrogen and helium, and have few of the heavier elements in them that we have in our star and its system of planets. Since many of those heavier elements are necessary for life (as we know it) -- elements such as carbon, iron and oxygen, to pick just a few obvious examples -- we assume there could be no life (as we know it) in such systems. Whether any other kind of life could evolve, we don't know, but it seems unlikely.

Rob

[Chris Peterson]

Since globular clusters contain the oldest stars, wouldn't they be the most apt to nurture life on any orbiting bodies? I suppose they are too distant to investigate for "planet wobble" and such. One imagines inhabitants by now having very large, pulsing veined heads and wearing identical clothing as advanced races do. Then again, the current Mars mission could prove that any rocky planet's ability to support life is naturally finite. BTW, congrats, NASA. America is proud of you. I'd personally get elected just to award you all medals except I can't stand kissing babies.

Besides what Rob pointed out, there is also the fact that the dense nature of globular clusters, along with the rather chaotic orbits experienced by member stars, makes it unlikely that any planetary systems will survive more than a few hundred million years- or at the least, the positions of planets around their stars will be jostled every few tens of millions of years. That's probably not a situation very conducive to supporting life- at least, not advanced life.

[eltodesukane]

some galaxies (bottom left corner):