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In the nebulaes of galaxies are stars born, but the gasses and dust they are made of comes from exploded stars (fe supernovas). So it looks like these processes can go on continuesly. But is that really the case, or does according to entropy(?) galaxies extinguish because fe the galaxie went too big so gravity has no opportunity to form other stars any more. And before colliding with other galaxies it is passed away. So is there any sign that galaxies are getting smaller or less active?

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Galaxies are gradually being extinguished. Most star formation activity occurs near the start of a galaxy's life, or in response to merger activity with other galaxies.

The star formation rate of the universe peaked at redshifts of around 3, corresponding to a look-back time of around 9 billion years. Since then the star formation rate has declined as the universe expands; mergers are less frequent, gas is driven out of galaxies by supernovae and active galactic nuclei.

However, most of the stars that have been formed are of lower mass (K- and M-dwarfs) than the Sun and will live on for tens or hundreds of billions of years. They are however much fainter than the Sun. So although high-mass, luminous O- and B stars live their short lives and are not replaced at the same rate, the low-mass stars continue to shine. This means that galaxies will get fainter on average as the remaining stellar populations increase in average age and decrease in average mass.

It is a slow process though. High mass stars are still being formed in our galaxy after 12 billion years, and most spiral galaxies have ongoing star formation. However, star formation has more-or-less ceased in gas-poor elliptical galaxies.

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  • $\begingroup$ -Can you put names to the stars in your statement, Just so the OP don't get confused and think that there is still a unknown classification of stars still out in our Universe.It would make your statement more easier to picture and compute. $\endgroup$ Feb 5 '16 at 21:56
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Far more stars die than stars are born, The number isn't exact but I would say 90 to 10.Then what occurs next is a large percentage of those dead stars form black holes from supernovas and the occasional neutron star collision will form black holes, Giving the new stars less of a chance to reach maturity.The Universe is being consumed from the point it was created.The reason why the Universe can not repair itself is because it was almost entirely created all at once so everything will decay at once leaving no chance for restructure.

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