Why do galaxies not get overpopulated with stars?

Post Reply New Topic

Why do galaxies never produce so many stars that they start colliding with each other or get knocked into intergalactic space?

there's plenty of space in space.



i think that's why they call it that actually. space is so vast, empty and generally beyond our comprehension we could not come up with a word for it and instead used the word that already refers emptiness and the absence of things.

That's mainly it. The space between stars is so vast.

A mediocre sized star (like our sun) is about a million miles wide. Or about five light seconds wide.

Earth is eight "light minutes" from the Sun. Neptune (at what usually thought of as the outer edge of the Solar System) is about three and half light hours from the sun. But the nearest star is Alpha Centauri -- at a distance of four light years from the Sun. Stars are five light seconds wide, but in our galaxy average about five or six light years distance from each other. Crowding isn't much of an issue with that vast a ratio between size and distance.

Two galaxies could collide (and they often do), but they would just pass through each other like a pair of ghosts with out a star in either galaxy colliding with a star in the other. A book I read said that "a pair of flies in in the Grand Canyon would be more likely randomly collide than stars in a pair of colliding galaxies".

Also stars are not like the corona virus, nor like bed bugs in your apartment, nor like mice, nor like humans, nor even like elephants (longest gestation period, and slowest reproductive rate of any mammal). They don't multiply exponentially. Even a pair of elephants could have a millions of descendants if elephant reproduction were left unchecked for even a few generations because even the slow reproducing elephant is a living thing that reproduces exponentially.

New stars form out of a finite amount of gas and dust in the galaxy. Star formation happens fast when the galaxy is young, and then slows as the raw material for stars gets used up. Sometimes a star explodes and turns supernova, and sends out new raw material. But still over time the population growth of stars in a galaxy slows down, and there is no "compound interest" in their population growth the way there is with bed bugs and humans.

Actually, they do.  Even some dense globular clusters will eject stars.  The halo of stars around our own galaxy are more likely to have originated within our galaxy than in the cold vacuum of intergalactic space.

Someone was saying recently that when the Milky Way and Andromeda collide there won't be any collisions - that's a bit of a mind-bender considering how many stars would be involved.

Also for galaxies 'producing' too many stars - I believe they have the equivalent of China-style family planning and plenty of free porn. If I understand it right all of the stars that our universe was going to have were birthed in the early universe, some new ones form through enough dispersed fuel from nebulae and supernovae, but ultimately it's all headed to a place where it'll be nothing but red dwarves and black holes, eventually just black holes, and possibly... when all of those black holes pop out from Hawking radiation there isn't enough left over to tack down spacetime, the hourglass flips, and you have another big bang.

That's the general idea. Not all stars were born the moment the Universe was born. But all of the raw material for the stars was born at that moment.

The sun is about a third the age of the Universe (so its a third generation star). Some dwarf stars will last a trillion years, and some giant stars live fast and die young in only a few million years. But yes -the same matter gets cooked in the stars, gets exploded in novas, and then gets recycled into new stars. The later generation stars get to have heavier elements (like iron and carbon). So they can have nice things in their solar systems like planets...and maybe even living things. But yes- basically its a zero sum game. Star stuff gets rearranged, and repackaged, and turned into different stuff. But the amount of stuff stays the same.