The Galaxy-Black Hole Cnnection

[BlackHoleAndromeda]

I have some queries. First, does anyone know exactly how hot an area in space has to be in order for a star to be born? Second, isn't it true that even stars that wonder too close can throw each other out of their own orbits? Third, if a young super massive black hole is sucking up enough material to equal the mass of the galaxy around it, doesn't that mean that the black hole must have spewed enough matter back into space to do so?


All these questions point to the galaxy-black hole connection. These are the explanatory ideas that put all the pieces in place in my opinion.

 

[MeteorWayne]

I have some queries. First, does anyone know exactly how hot an area in space has to be in order for a star to be born?

Well there'so real easy anwer. The better question is how much mass. The ability to fuse atoms is a combination of both temperature and pressure...with more pressure, the required temperature is lower since the nuclei are more confined. And in star formation, the temperature comes from compression by gravity, so that's why the mass is the more important parameter. It's about 80 times the mass of Jupiter for pure Hydrogen. If some of the Hydrogen is Deuterium (a neutron and a proton in the nucleus) the required mass is lower.

Second, isn't it true that even stars that wonder too close can throw each other out of their own orbits?

Any two or more gravitationally interacting bodies can eject one or more of the members, be they asteroids, moons, planets, stars, black holes, or galaxies.

Third, if a young super massive black hole is sucking up enough material to equal the mass of the galaxy around it, doesn't that mean that the black hole must have spewed enough matter back into space to do so?

A common misperception is that black holes have some magical sucking power. It ain't true. A 1000 solar mass black hole has exactly the same gravity as 1000 suns, whether it's a black hole, or 5, or 50, or 1000, or 10,000 stars. Unless you are very close to the event horizon of a black hole, it makes no difference at all. It's just a certain amount of mass.

Black holes do not spew matter into space. They do redistribute matter from it's accretion disk into jets that exist at the poles, but that matter was never in the black hole itself.

The matter that forms black holes comes from the stars or galaxies that they are created from.

 

[SpaceTas]

First, does anyone know exactly how hot an area in space has to be in order for a star to be born?

Adding to MeteorWayne.
To star off the star formation process the initial cloud of dust/gas must be dense enough so that it's gravity is stronger than internal forces (heat/pressure magnetic fields ...). The cloud at this point is very cold (easier for gravity to start collapse).
Fast forward to last stages of star formation:
For the protostar to start nuclear reactions it's core must be hot and dense enough for the reactions to start, this requires that the star must be above a certain mass. Where this boundary is a bit fuzzy because it depends a bit on composition and the theory of the low energy reactions is not nailed down yet. This is borders between low mass stars and brown dwarfs and brown dwarfs and planets.

? Third, if a young super massive black hole is sucking up enough material to equal the mass of the galaxy around it, doesn't that mean that the black hole must have spewed enough matter back into space to do so?

Adding to Meteor Wayne's reply:

The black holes found at the center of galaxies may have masses measuring in millions of suns, but the galaxies have trillions of suns worth of matter. No black hole found has a large fraction of the total mass of its host galaxy.

Extend:
There is an observational relationship between the mass of the central black hole and the mass of the stars in the central bulge of the galaxy. This relationship holds from larges globular clusters, through spirals to giant elliptical galaxies.
ie the mass of the black hole is a constant fraction (roughly) of the mass of the central part of galaxies. This strongly suggests that the formation of central black holes and galaxies is linked. At the moment there are several ideas. One idea is that as galaxies grow by merging with generally smaller galaxies the central black holes also merge. The seed black holes being formed by the first generation of massive stars. These merged as they settled toward the center of their galaxies. The settling being caused by mutual gravitational interaction between the holes as well as with rest of galaxy. But there are lots of argument about the steps; it is uncertain whether or not the individual seed black holes can actually merge quickly enough to explain the million mass holes that we observe now.