Black Holes, Quasars and Galaxies

[Ganymede12]

What is the connection between Black Holes, Quasars and Galaxies? I know that Black Holes are at the centre of Quasars and that they form them. Doesn't that mean that every black hole should be in a quasar? How do Quasars turn into Galaxies like the Milkyway? Was the Milkyway ever a Quasar? and what is a "dormant" Black Hole?

[JulianO]

What is the connection between Black Holes, Quasars and Galaxies? I know that Black Holes are at the centre of Quasars and that they form them. Doesn't that mean that every black hole should be in a quasar? How do Quasars turn into Galaxies like the Milkyway? Was the Milkyway ever a Quasar? and what is a "dormant" Black Hole?

Pretty much all galaxies have a black hole at the centre, at least all the ones that have been checked so far have.

A quasar is basically an active black hole, a so called active galaxy. This is a black hole that is feeding, taking in dust and gas and this stuff infalling generally makes for very strong jets that if we aligned in the right direction can look very strong (Blazars). Most galaxies settle down after a while, having consumed all the local gas and dust, and so the black hole shuts down as an energy source.

In the current epoch there aren't so many quasars or active galaxies around, as they've used up the locally available fuel. Looking further back there are more quasars visible, as they were in their prime then. Locally we see lots of galaxies with very big central black holes but without the brilliance of a quasars - these are probably essentially dead quasars.

Occasionally the BH's light up again when galaxies collide or merge, and the dust and gas is all messed up and funneled back into the BH.

Our own BH in the milky way shows occasional flares, assumed to be it feeding on a passing cloud of dust, but nothing on the scale of quasars.

[Ronnie67]

most astronomers believe that quasars, radio galaxies and the centres of so-called active galaxies just are different views of more or less the same phenomenon: a black hole with energetic jets beaming out from two sides. When the beam is directed towards us we see the bright lighthouse of a quasar. When the orientation of the system is different we observe it as an active galaxy or a radio galaxy

[Ganymede12]

Thank you! It makes a lot of sense now.

So the super massive black hole at the centre of our galaxy (Sagittarius A*) is meant to be "dormant" but what does "dormant" mean? Is it just that there is no material for it to consume and if you were to get close enough it would behave as active or can you get closer to a dormant black hole without being pulled in?

[JulianO]

Yes - just means there is nothing much around it for it to consume. After its eaten up stuff in its local area, it will go dormant, unless its disturbed and gets more stuff. There are lots of stars in orbit around it, and these are pretty stable, so they just go round and round it, like the planets around our sun. There isn't a lot of difference - black holes don't have any magical powers - they're just big masses, and stuff orbits them.

Gas and dust can fall in, because it is subject to friction and slows down to fall in. Planets and suns don't do this so much.

[Ganymede12]

So how are the jets of radio waves formed by quasars and why don't they get sucked in to the black hole?

[JulianO]

The jets are formed by the infalling gas and dust, they heat up hugely as they release the gravitational potential energy. Its a very efficient process, even more efficient than fusion. So it radiates out all this energy as jets of energy in x-ray, radio and all between.

This is perpendicular to the accretion disk, aided by magnetic fields, so coming out as beams.

[Ganymede12]

So why doesn't gravity draw the radio waves into the black hole?

[JulianO]

Gravitation force diminishes with distance, in fact with the square of the distance. So after a certain distance from the black holes centre, the force of gravity is not strong enough to suck light in. This is the event horizon of the black hole. The jets and beams are produced by material well outside this event horizon, so has lots of chance to escape.

So like this

Only the bit right in the middle is black.

[Ronnie67]

Some neutron stars emit radio waves that pulse on and off. These stars are called pulsars. Pulsars don't really turn radio waves on and off--it just appears that way to observers on Earth because the star is spinning. What happens in that the radio waves only escape from the North and South magnetic poles of the neutron star. If the spin axis is tilted with respect to the magnetic poles, the escaping radio waves sweep around like the light beam from a lighthouse. Far away on Earth, radio astronomers pick up the radio waves only when the beam sweeps across the Earth.

[Ganymede12]

How do Quasars become galaxies?

[JulianO]

How do Quasars become galaxies?

They are galaxies already, its just the effects of the very bright active black hole we see, which means its difficult to see the dimmer rest of the galaxy in contrast. The quasar/black hole shuts off eventually after its consumed stuff, and you end up with a more regular galaxy.

[J_M_Franklin]

I have read lots of theories and published research on this topic (not published by me I must add) and it makes me wonder why people seem to just accept the given idea that all Galaxies has supermassive black holes in them, that all radio galaxies are the result of this black hole, and that all quasars are also the action of this black hole...

What I find astounding is that in all the universe with all the numbers of active galaxies and quasars out there, the nearest active quasar is 3C273 @ 1.7 Billion Light years and the nearest (IC2497) we assume to have been one is some 760-790 million light years away.

Why are then none closer? Even if we were not in their beam for direct detection, plenty have been found by their interaction with cold hydrogen between galaxies or at least i the galactic halo...yet there are none within 1 billion light years???

I do wonder if we have this theory all wrong...although I have no idea what a decent or credible alternative would be!!

EDIT: to clarify I had not published research!!

[Knight of Clear Skies]

Why are then none closer? Even if we were not in their beam for direct detection, plenty have been found by their interaction with cold hydrogen between galaxies or at least i the galactic halo...yet there are none within 1 billion light years???

Because conditions in the early universe were much more favourable towards Quasar formation. A quasar is simply an active galaxy which is accreting materiel at a rapid rate. M87 - approximately 50 million light years away - is emitting a 5,000 light year long jet of plasma from its core. IIRC, M87 is accreting matter at about 100/th the rate of a typical Quasar.

There is also a selection effect at work here: the further away you look and the further back in time, the more galaxies you see because you are looking at a (vastly) larger volume of space.

[J_M_Franklin]

Because conditions in the early universe were much more favourable towards Quasar formation. A quasar is simply an active galaxy which is accreting materiel at a rapid rate. M87 - approximately 50 million light years away - is emitting a 5,000 light year long jet of plasma from its core. IIRC, M87 is accreting matter at about 100/th the rate of a typical Quasar.

There is also a selection effect at work here: the further away you look and the further back in time, the more galaxies you see because you are looking at a (vastly) larger volume of space.

I'm aware of that, but the bulk of Quasars are nowhere near what is supposed to be the limit of the visible universe, in fact the bulk are between 2.5 and 8 billion light years, so whilst I agree there is a selection bias here due to field depth, i can't help but wonder if we are missing something...

One of the current theories for Quasar formation is galactic collisions, but there are numerous such events in the (relatively) nearby universe and yet none show Quasar like outputs. I think it could be a red herring to assume that an active galaxy must once have been a Quasar as some thing because nature has this real nasty habit of proving us wrong when we make assumtptions about things just because it appears to fit what we believe.

ULAS J1120+0641 is the farthest known Quasar with a redshift reported at z=7.085, this relates to a speed of 0.969864c and a distance of 28.75 billion light years. This object is supposed to have an output of 6.3×10¹³ stars the power of the Sun, and yet be contained in a space no larger than the solar system, powered by a black hole of 2

+1.5

−0.7

×10⁹ times the mass of the Sun. So we have to accept that this object has more energy output than both M31 and The Milky Way combined, and that the black hole has the mass on par with a decent sized Galaxy, in fact it is almost the mass of M33!!

Now I understand the physics of all this, but I remain to be convinced 100% that Singularities not only reside in the centre of galaxies but grow to such enormous sizes. I have not seen any mechanism that has explained this fully as of yet. I am not saying it is wrong, but I remain to be convinced.

[Knight of Clear Skies]

One of the current theories for Quasar formation is galactic collisions, but there are numerous such events in the (relatively) nearby universe and yet none show Quasar like outputs.

Early galaxies had a far greater abundance of gas - because much of it had not yet accreted to form stars. Galactic mergers are thought to increase quasar activity, but they are not thought to be necessary for quasars to form. Consider this please: there is a huge concentration of mass at the centre of the Milky Way; how did it form, and how violent was that process?

I think it could be a red herring to assume that an active galaxy must once have been a Quasar as some thing because nature has this real nasty habit of proving us wrong when we make assumtptions about things just because it appears to fit what we believe.

The current theory is based on a lot of clever detective work and underpinned by observation and calculation. Certainly, there is some uncertainty and some of the physics is poorly understood, but the numbers do fundamentally add up. The gravitational potential energy of millions of solar masses of material is enormous - this is what powers the Quasar. If we didn't observe any quasars, that would be far more puzzling. In order for massive, compact objects to form, angular momentum needs to be shed.

So we have to accept that this object has more energy output than both M31 and The Milky Way combined, and that the black hole has the mass on par with a decent sized Galaxy, in fact it is almost the mass of M33!!

Nature abounds with stupendous numbers; the above is no more - or less - amazing than countless others. The universe is astonishing.

If you are interested in unsolved problems in Physics, there is a long list here.

[JulianO]

I have read lots of theories and published research on this topic (not published by me I must add) and it makes me wonder why people seem to just accept the given idea that all Galaxies has supermassive black holes in them, that all radio galaxies are the result of this black hole, and that all quasars are also the action of this black hole...

I'm not sure everyone accepts it, but the evidence seems to all point that way.

The evidence is

• There is something VERY massive at the center of all galaxies that have had their rotational velocities measured (and its a pretty huge number now). Things that have a mass of 10⁶ to 10¹⁰ solar masses. So millions to billions the masss of our sun.
  
• By looking at changes in intensity from some of these sources, and in the case of our own galaxies the motion of stars in the center, the thing that has this huge mass is less than the size of our solar system.
  

So - looking for something millions or billions of times the mass of the sun all squashed into a few AU, you have to conclude there are very few things that will fit the bill. Black holes are certainly one of them, its difficult to think of anything else of comparable density.

Also the stupendous output of energy from quasars can't be generated by nuclear fusion, the efficiency of these reactions is ~1%. Accreting black holes can convert matter to energy with efficiencies of up to 40%. The biggest stars we see today are ~100 solar masses, perhaps the biggest there ever were in the early universe might have tipped ~1000 solar masses, which still doesn't give enough luminosity.

So I don't think its just acceptance, but more a very plausible theory supported by quite a lot of applicable evidence.

[Ganymede12]

All makes sense so far.

If all massive stars become black holes and all black holes become quasars and all quasars are galaxies then that means that galaxies form within galaxies. A bit of a Chicken and Egg* situation. How were the first stars created? Also, why aren't there any quasars in the milky way?

*I know this statement isn't really valid now, since we all know the egg came first, but you get the point.

[JulianO]

If all massive stars become black holes ...

OK - but they become small black holes - like 5-10 solar masses.

and all black holes become quasars

No - not all black holes become quasars. Only super massive black holes can become quasars if the conditions are right.

So they have to be about 1,000,000 solar masses or so to become quasars. They do not form from massive stars, but by some other mechanism of collapse - probably related to early universe conditions.

and all quasars are galaxies then that means that galaxies form within galaxies. A bit of a Chicken and Egg* situation. How were the first stars created? Also, why aren't there any quasars in the milky way?

All galaxies have SMBHs - but not all are active, so wouldn't be counted as quasars. Some like our own just sit there not doing very much.

[Ronnie67]

Yeh just like my wife, ooopss! did I just say that, , only kidding

[J_M_Franklin]

Early galaxies had a far greater abundance of gas - because much of it had not yet accreted to form stars. Galactic mergers are thought to increase quasar activity, but they are not thought to be necessary for quasars to form. Consider this please: there is a huge concentration of mass at the centre of the Milky Way; how did it form, and how violent was that process?

That is not accurate, whilst young Galaxies may certainly have had more free material than more evolved Galaxies, one of the paradoxes is that all Quasars seem to be in highly evolved galaxies, and this has always been an explanation at finding them at middle range red shifts, however now they are being found at higher red shifts this view is starting to be questioned. What nature is showing us is that preconceived ideas need to be flexible or they die. The views of the early Universe are changing, supposedly ULAS J1120+0641 was as we see it only 700 million years after the universe was born, which clearly introduces a massive conflict. The problem is that it is so far away it is impossible to resolve details of individual stars that would then allow for the aging of the star and thus improving our view of the early Universe...perhaps our concept of the age of the Universe is totally wrong.

The current theory is based on a lot of clever detective work and underpinned by observation and calculation. Certainly, there is some uncertainty and some of the physics is poorly understood, but the numbers do fundamentally add up. The gravitational potential energy of millions of solar masses of material is enormous - this is what powers the Quasar. If we didn't observe any quasars, that would be far more puzzling. In order for massive, compact objects to form, angular momentum needs to be shed.

That is not strictly accurate, but not wrong either. The angular momentum of matter falling onto a large gravitational well (whether that be a neutron star or black hole) is lost as material collides, but the largest proportion actually comes from the acceleration of material to relativistic speeds inside the huge magnetic fields believed to surround these objects, and considering the way magnetic fields increase in flux density as their source is compacted, the magnetic fields of supermassive black holes, assuming they rearlly are there, must be truly staggering in their power.

Nature abounds with stupendous numbers; the above is no more - or less - amazing than countless others. The universe is astonishing.

Really, who would have guessed

If you are interested in unsolved problems in Physics, there is a long list here.

Some of those will be answered in the coming years, some are not truly mysteries, but misunderstandings of difficult concepts...or so some theoreticians would have us believe

[Knight of Clear Skies]

@J_M-Franklin - Your last post comes across to me as somewhat confused and nitpicky I'm sorry to say.

My point was that a sense of personal incredulity is not a reliable guide to assessing science. Theories such as the Big Bang, Cosmic Inflation and Black Holes remain somewhat hypothetical, but they are the best we have right now, and each represents many lifetimes of aggregated thought and effort. It is somewhat dismissive to label them as 'assumptions'. Certainly, they should be - and are - continually challenged, but casting doubt on the accepted models without providing any viable alternative is not really helpful.

My understanding of these theories is limited - I am neither a physicist or a mathematician, but I find the subject fascinating nonetheless. Anything I say on these subjects should be treated with caution. At best, I am somewhat qualified to explain aspects of them to other amateurs, as I take a great deal of care with my posts. I'm happy to make the attempt as I often learn something new in the process of doing so.

[J_M_Franklin]

@J_M-Franklin - Your last post comes across to me as somewhat confused and nitpicky I'm sorry to say.

My point was that a sense of personal incredulity is not a reliable guide to assessing science. Theories such as the Big Bang, Cosmic Inflation and Black Holes remain somewhat hypothetical, but they are the best we have right now, and each represents many lifetimes of aggregated thought and effort. It is somewhat dismissive to label them as 'assumptions'. Certainly, they should be - and are - continually challenged, but casting doubt on the accepted models without providing any viable alternative is not really helpful.

My understanding of these theories is limited - I am neither a physicist or a mathematician, but I find the subject fascinating nonetheless. Anything I say on these subjects should be treated with caution. At best, I am somewhat qualified to explain aspects of them to other amateurs, as I take a great deal of care with my posts. I'm happy to make the attempt as I often learn something new in the process of doing so.

It's nitpicky for two reasons, one your post required that response and secondly, so is science.

I did not mean my post as anything more than a simple response, I understand the maths around the physic of Black Holes and other aspects of Astrophysics and science in general, i am only an amateur such as yourself and do not have enough time to devote to the subject these days as I did some 25 years ago when I completed a BSc on the subject (Open university) and I am an Electrical Engineer. I am not saying the theory is wholly wrong, I am simply saying that I, at this time, remain to be convinced of the matter to the totality that many others are. I accept that I could be totally wrong, and I am happy with that, I just think it rather convenient that we are finding anomalies all over where Black Holes, and super massive ones, conveniently fit the bill, I am simply concerned that this could be steering us down a blind ally and we may be missing something even more spectacular.

Nature has a habit of recycling in one form or another, Black Holes seem to fly in the face of this, but as our understanding advances I am sure this will be clarified to everyone's satisfaction, including mine.

Edited for Spelling mistake..Doh!!

[Mr Q]

Ant - The chicken or the egg didn't come first - they both evolved from a more earlier form of the species

All makes sense so far.

If all massive stars become black holes and all black holes become quasars and all quasars are galaxies then that means that galaxies form within galaxies. A bit of a Chicken and Egg* situation. How were the first stars created? Also, why aren't there any quasars in the milky way?

*I know this statement isn't really valid now, since we all know the egg came first, but you get the point.

All makes sense so far.

If all massive stars become black holes and all black holes become quasars and all quasars are galaxies then that means that galaxies form within galaxies. A bit of a Chicken and Egg* situation. How were the first stars created? Also, why aren't there any quasars in the milky way?

*I know this statement isn't really valid now, since we all know the egg came first, but you get the point.

So where did the egg come from? If the egg came first, what laid it? The answer is neither - they BOTH evolved from a more ancient form of animal. Sorry, couldn't resist By the way, can you now see what you're saying with those glasses? Just kidding...or am I

[Knight of Clear Skies]

It's nitpicky for two reasons, one your post required that response and secondly, so is science.

An example of what I consider to be confusion and nitpicking is your digression into the physics of accretion discs. I simply said that angular momentum needs to be shed, but said nothing about the mechanism of how it is lost. Your post didn't address the thrust of mine, that there is a plausible energy source for Quasars. If you like, I'm talking about the battery, and you start talking about the transmitter. You've added some useful information to the thread, but in a rather messy manner, making it difficult - I imagine - for other readers to follow. I think this thread has gone past the point of serving any useful purpose.

Incidentally, I read physics as an undergraduate, but I work in a different field and my knowledge and experience is far short of an actual physicist. In particular, my maths skills have atrophied, and they were never great to begin with.