Light cannot escape a black holes gravity?

[MTDEW]

Originally posted by: GodlessAstronomer
To answer a couple of questions:
Black holes don't fill up, although recent research suggests that there is a maximum mass for black holes (a mere 10,000,000,000 solar masses). The most widely accepted hypothesis for this upper limit is that radiation from the black hole evaporation pushes back against matter that is falling towards the black hole.

I think black holes are more of a consequence of galactic formation than they are a key role. Galactic neuclii tend to be very dense by their very nature. The super massive black holes that make up galactic centers don't look much like what most people expect a black hole to look like. The density of super massive black holes can be very low - the average density of the milky way's central black hole is probably less than that of the air you're breathing. If you fell past a super massive black hole's event horizon it's likely that you wouldn't notice for quite some time - the tidal forces are very low, so you wouldn't be "spagettified" like most people expect from a black hole.

Interesting, i woulda thought a Super Massive Black Hole would have more gravitational pull than normal black holes due to size.
But being less dense makes sense, since its larger.

But didnt we discover the Super Massive Black Hole in our galazy because nearby stars were effected by its gravitational pull?

 

[GodlessAstronomer]

Originally posted by: MTDEW

Originally posted by: GodlessAstronomer
To answer a couple of questions:
Black holes don't fill up, although recent research suggests that there is a maximum mass for black holes (a mere 10,000,000,000 solar masses). The most widely accepted hypothesis for this upper limit is that radiation from the black hole evaporation pushes back against matter that is falling towards the black hole.

I think black holes are more of a consequence of galactic formation than they are a key role. Galactic neuclii tend to be very dense by their very nature. The super massive black holes that make up galactic centers don't look much like what most people expect a black hole to look like. The density of super massive black holes can be very low - the average density of the milky way's central black hole is probably less than that of the air you're breathing. If you fell past a super massive black hole's event horizon it's likely that you wouldn't notice for quite some time - the tidal forces are very low, so you wouldn't be "spagettified" like most people expect from a black hole.

Interesting, i woulda thought a Super Massive Black Hole would have more gravitational pull than normal black holes due to size.
But being less dense makes sense, since its larger.

But didnt we discover the Super Massive Black Hole in our galazy because nearby stars were effected by its gravitational pull?

We have observed it's gravity, but if I remember correctly it was theorised before it was discovered. You may be thinking of the Great Attractor, a big-ass blob of intergalactic who-knows-what that has the mass of something like 30,000 times our entire galaxy. We've never observed anything in the area but it's gravitational pull is enormous.

Keep in mind that density doesn't affect the gravity of an object. If you have a sphere of evenly distributed matter, the gravity imparted by it does not change regardless of how dense the sphere is (assuming you are measuring it's gravity from outside of the sphere). In fact it turns out that any sphere of matter is mathematically equivalent to a point of the same mass in the center of the sphere, and similar (but more complicated) rules apply for generalising disk-shaped objects like a galaxy. If you think about it, this means that, gravitationally, a star will behave identically to a black hole from a distance, and similarly for galaxies.

The gravity of a mass is not changed just because that mass happens to be a black hole. This makes sense when you realise that the only criteria for any piece of matter to be a black hole is that it's Schwazschild radius be larger than the mass's physical radius (although it's more complicated if the mass is spinning).

 

[EGGO]

Originally posted by: MTDEW

Originally posted by: GodlessAstronomer
To answer a couple of questions:
Black holes don't fill up, although recent research suggests that there is a maximum mass for black holes (a mere 10,000,000,000 solar masses). The most widely accepted hypothesis for this upper limit is that radiation from the black hole evaporation pushes back against matter that is falling towards the black hole.

I think black holes are more of a consequence of galactic formation than they are a key role. Galactic neuclii tend to be very dense by their very nature. The super massive black holes that make up galactic centers don't look much like what most people expect a black hole to look like. The density of super massive black holes can be very low - the average density of the milky way's central black hole is probably less than that of the air you're breathing. If you fell past a super massive black hole's event horizon it's likely that you wouldn't notice for quite some time - the tidal forces are very low, so you wouldn't be "spagettified" like most people expect from a black hole.

Interesting, i woulda thought a Super Massive Black Hole would have more gravitational pull than normal black holes due to size.
But being less dense makes sense, since its larger.

But didnt we discover the Super Massive Black Hole in our galazy because nearby stars were effected by its gravitational pull?

I haven't looked at Wikipedia for this, but isn't the super massive black hole the center of the galaxy?

 

[MTDEW]

I just recall a lady scientist on the Science Channel getting so excited when she discovered we had a Super Massive Black Hole in the center of our galaxy by tracking the movement of stars in the center of the galaxy. (she's apparently the one who proved the theory)

What she saw was the stars had strange orbits and they sped up at certain points. (presumably when their orbit was nearest the black hole)
She pin pointed the black holes location by tracking all the stars in the galaxys center.

She also pointed out that the the Super Massive Black Hole was no longer feeding, and they didnt know why black holes stop feeding or how to predict if if it would start feeding again.

EDIT: Found a link
http://edition.cnn.com/2008/TE....black.hole/index.html

 

[The Boston Dangler]

Originally posted by: Born2bwire

Originally posted by: The Boston Dangler
black holes are among my most hated things, ever.

Even more than Jefferson Starship?

jefferson starship, as airplane, had a couple good years. black holes, no good years. after woodstock, the suckage approaches 1:1.