How quasars are related to black holes in galaxies?

[blumfeld0]

Can anyone point me to some good links about the our current understanding of quasars-in particular why they are so far away? and also how they are related to black holes in galaxies?

thanks

 

[MindRafter]

Can anyone point me to some good links about the our current understanding of quasars-in particular why they are so far away? and also how they are related to black holes in galaxies?

thanks

I have another question to add to blumfeld's question - What exactly are quasars? I'm very confused because I've read somewhat different explanations in different books...

 

[SpaceTiger]

Quasars are what we observe when a supermassive black hole (SMBH) at the center of a galaxy is accreting a lot of matter and, as a result, emitting a lot of light. We think all quasars are powered by SMBHs, but not all SMBHs power quasars. For example, the SMBH at our galaxy center does not power a quasar.

Quasars almost certainly accrete from a disk, which is made up of matter that somehow managed to dissipate enough energy and angular momentum to approach the supermassive black hole. The exact structure of these disks is still a mystery, but it likely varies from quasar to quasar.

Quasars are generally found at large distances (and therefore earlier times) because SMBHs were accreting more matter at earlier times in the universe. Quasar activity peaked when the universe was about a fifth of its current age. The reason is not known exactly, but it probably is explained by some combination of the growth of structure in the standard cosmological model (objects collapse more easily prior to dark energy domination), the growth of SMBHs (which can shine more brightly as they grow), and the general evolution of galaxies and galaxy clusters.

 

[MindRafter]

So what I understand is that - Quasars are flashes of light around the galactic centre. Am I right?

Quasars almost certainly accrete from a disk, which is made up of matter that somehow managed to dissipate enough energy and angular momentum to approach the supermassive black hole. The exact structure of these disks is still a mystery, but it likely varies from quasar to quasar.

could you explain what do you mean by "disk"??
This is very interesting I must say :)

 

[end3r7]

A disk of matter looks like this
http://www.urania.be/sterrenkunde/images/quasar.jpg

And it's basically what it sounds, a disk-shapped area full of matter, including atoms, planets, stars, etc.
As the SMBH consumes this matter, it will give off light.
Eventually the feeding stops, and that is thought to have something to do with the speed of the stars in the end of the disk and the size of the black hole itself.

And in case you are wondering, every galaxy, including ours, has its very own SMBH billions of times the mass of our sun. ;)

 

[SpaceTiger]

Eventually the feeding stops, and that is thought to have something to do with the speed of the stars in the end of the disk and the size of the black hole itself.

I'm not sure what this is supposed to mean. The mechanism by which matter is brought to the quasar is not yet understood.

And in case you are wondering, every galaxy, including ours, has its very own SMBH billions of times the mass of our sun. ;)

Not quite every galaxy. SMBHs are generally found in bulges, so spirals without bulges (like M33) tend not to host an SMBH. The mass you quote is only seen in the largest of SMBHs, which are likely the ones that power quasars. By contrast, the Milky Way's black hole is only a few million solar masses.

 

[end3r7]

I'm not sure what this is supposed to mean. The mechanism by which matter is brought to the quasar is not yet understood.

Well, I'm not sure how up-to-date this is, but supposedly all spiral galaxies are supposed to have a black hole in their center which would start sucking up matter, giving off energy (creating a quasar), and growing larger in size.
Eventually, this "feeding" would stop once the black hole has pushed the disk of matter far enough from itself, and the black hole would just lie there somewhat dormant, like in our galaxy, so no more quasar then.
That's what I meant when I said the constant feeding stopped.
Feeding = Quasar.
Not feeding = our galaxy = no quasar.

Like I said, not sure how up to date this is, but I thought it was pretty recent. =)

Not quite every galaxy. SMBHs are generally found in bulges, so spirals without bulges (like M33) tend not to host an SMBH. The mass you quote is only seen in the largest of SMBHs, which are likely the ones that power quasars. By contrast, the Milky Way's black hole is only a few million solar masses.

You are right about every galaxy not having a SMBH, and I didn't know about our black being so "small" (this is somewhat disappointing). I stand corrected. :)

 

[SpaceTiger]

I don't disagree with your description of where quasar light comes from, I'm just saying that the mechanism by which this feeding starts (and subsequently stops) is still a mystery. Most likely, a quasar stops shining when it has already "consumed" the matter around it, but it's not clear how this matter got there in the first place.

 

[MindRafter]

So that means (from what you'll have been discussing) the whole process of feeding is gives rise to something we call Quasar, and its' basically just light produced from the process of feeding.
So have Black Holes been discovered finally? I'm not at all up-to-date on this knowledge about Black holes/SMBHs because...because.
Hehe - HELP friends!

 

[ek]

I just read in a textbook of mine last night something I thought was very interesting. They postulated that certain AGN evolved into each galaxy type. That quasars/blazars became radio galaxies which became run of the mill ellipticals, and that QSOs became Seyfert Galaxies which evolved into ordinary spirals. This is of course an evolutionary path based on the categorization of the AGN as radio loud/quiet.

It was just a theory, but has there been any more work on this in recent times? Science always loves to unify, and this would be quite the unification.