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extragalactic stellar evolution [Q&A]


Vibha of Poornaprajna College asks, do all galaxies have the same type of stellar evolution?

This is a current hot topic of research, so the correct answer is, it is still being worked out. However, we can say that the broad picture of stellar evolution is the same: stars form on to the so-called Main Sequence in the Hertzsprung-Russell Diagram burning Hydrogen at the cores, and then evolve off the Main Sequence as they exhaust the Hydrogen fuel and start burning increasingly heavier elements. This causes the luminosity to increase, but the stars also become larger in size, with a resulting drop in temperature, so they appear redder. More massive stars evolve faster than less massive ones. The really massive stars eventually explode in Supernovae and form neutron stars or black holes, and the less massive ones, like the Sun, slowly slough off their envelopes and settle into white dwarfs.

That said, there are many wrinkles in the details. The earliest stars in the galaxies would have a low metallicity, which affects their evolutionary track. Heavy elements are synthesized during supernova explosions, which feed into the later forming stars and subtly change their evolutionary behavior. In the early epochs, there is a propensity for more massive stars to form because the dust clouds which are condensing into stars is larger. So in almost every case, the history of star formation is different.

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