# What Powers Quasars?

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According to Wiki quasars are too energetic for mere nuclear fusion:

"...The emission of large amounts of power from a small region requires a power source far more efficient than the nuclear fusion which powers stars. The release of gravitational energy by matter falling towards a massive black hole is the only process known that can produce such high power continuously."

I also heard the energy of a quasar is simply gas and dust getting heated to extreme temperatures. What do they mean by "gravitational energy". Is that just fancy talk for heating gas and dust to extreme temperatures?

Or can the awesome energy output be explained by matter and antimatter being created and annihilated?

http://en.wikipedia.org/wiki/Quasar

Edited by Airbrush
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According to Wiki quasars are too energetic for mere nuclear fusion:

"...The emission of large amounts of power from a small region requires a power source far more efficient than the nuclear fusion which powers stars. The release of gravitational energy by matter falling towards a massive black hole is the only process known that can produce such high power continuously."

I also heard the energy of a quasar is simply gas and dust getting heated to extreme temperatures. What do they mean by "gravitational energy". Is that just fancy talk for heating gas and dust to extreme temperatures?...

http://en.wikipedia.org/wiki/Quasar

You know an asteroid falling towards some other body when it hits can release enough heat to melt rock. It can melt part of the asteroid and part of the crater---even vaporize. That is just a small conversion of gravitational energy. How much energy depends (among other things) on the square of the escape velocity at the surface of the target body.

The grav. energy in this context is what does the heating. It isn't just a "fancy talk" equivalence---it is a meaningful straight-talk equivalence.

Nuclear fusion only gets you on the order of 1% of the mass converted to energy (gamma radiation, kinetic or heat energy)

Gravity lets you make a much more efficient conversion. As long as the grav. field that the thing is falling thru is strong enough.

The creation and annihilation of matter/antimatter would not play an essential role or have a net effect.

The essential thing must be the conversion of gravitational potential energy into kinetic/heat energy (by compression and "friction" in the accelerating/inspiraling disk of matter).

Edited by Martin
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Nuclear fusion only gets you on the order of 1% of the mass converted to energy (gamma radiation, kinetic or heat energy)

Gravity lets you make a much more efficient conversion. As long as the grav. field that the thing is falling thru is strong enough.

The creation and annihilation of matter/antimatter would not play an essential role or have a net effect.

The essential thing must be the conversion of gravitational potential energy into kinetic/heat energy (by compression and "friction" in the accelerating/inspiraling disk of matter).

Thanks for the explanation. Do you mean that the gravitational field is SO strong that it crushes a volume of gas and dust at such a high pressure and high rate that the "sparks" that fly out (EM radiation all across the spectrum) makes the fusion reaction look tame in comparison? This would be a dramatic increase in temperature from relatively low temperature to Trillions of degrees (or much higher?) in such a small amount of time, and getting accelerated to near light speed, that it bypasses nuclear fusion?

Edited by Airbrush
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Thanks for the explanation. Do you mean that the gravitational field is SO strong that it crushes a volume of gas and dust at such a high pressure and high rate that the "sparks" that fly out (EM radiation all across the spectrum) makes the fusion reaction look tame in comparison? This would be a dramatic increase in temperature from relatively low temperature to Trillions of degrees (or much higher?) in such a small amount of time, and getting accelerated to near light speed, that it bypasses nuclear fusion?

In part your questions show me my understanding is inadequate. So I looked around and didn't find much. I did find this:

http://www.scholarpedia.org/article/Accretion_discs

I may find more later. You sound like you have it pictured in mind at least as well as I do, or did until reading the Scholarpedia on Accretion discs.

My intuitive picture is based on the ideas of conservation of energy and of angular momentum.

I know that around a BH there is a minimum circular orbit size, where stuff is circling at near the speed of light.

I haven't done a back-of-envelope calculation to estimate the amount of gravitational potential energy something has when it is, say, 5 million miles out from solar mass hole, compared with what it has when it is 5 miles out.

It seems to me that if you could lower something on a pulley from 5 million miles down to 5 miles you could extract a lot of work. If something is spiraling in, then much of that energy has to be dissipated. A lot of energy (and angular momentum) has to be somehow blown off.

I think you were hinting at that in what you just said, and offering images of how the energy might be ejected. so as to let the thing spiral down in closer.

I have to go do something. Can't satisfactorily get this clear right now. Maybe someone else will help.

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bear in mind that the material falling in has too much angular momentum to fall directly in.

It first goes into a small orbit around the black hole

angular momentum = mvr

since the mass isnt changing we get v = 1/r

so if the material falls from a distance of 1000 LY to a distance of 0.001 LY (63 au) then

the transverse velocity must increase by 1,000,000

the earth moves at 30 km/sec

If the suns mass increased 100,000,000 fold then for the earth to stay in its present orbit its velocity would have to increase 10,000 fold

which would be 300,000 km/sec which is the speed of light.

if earths orbit were 100 times bigger then the speed would be 30,000 km/sec

Edited by granpa
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According to Wiki quasars are too energetic for mere nuclear fusion:

"...The emission of large amounts of power from a small region requires a power source far more efficient than the nuclear fusion which powers stars. The release of gravitational energy by matter falling towards a massive black hole is the only process known that can produce such high power continuously."

I also heard the energy of a quasar is simply gas and dust getting heated to extreme temperatures. What do they mean by "gravitational energy". Is that just fancy talk for heating gas and dust to extreme temperatures?

Or can the awesome energy output be explained by matter and antimatter being created and annihilated?

http://en.wikipedia.org/wiki/Quasar

What happens with a black hole, is it can sometimes get into very gas rich regions. A star like our sun wouldn't be much for a black hole, so quasars tend to be at the cores of galaxies, or in the presence of a super-massive star. When the gas spirals into a black hole, if its a large amount of the gas, gravity from the black hole will cause friction between the gas. Just before the gas enters the event horizon of the black hole, some of it is SO compacted as such a high velocity that it is forced upward at tremendous speeds. Other energetic particles also arise from this. When they say gravitational energy, I think most likely they are talking about the friction from the gravity compacting and heating up the gas.

Edited by steevey
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I really appreciate the above contributions. I'm trying to visualize something that is beyond experience. Take for instance the most massive quasar known, OJ287, 18 Billion solar masses. Let's forget about its' binary partner. It has an accretion disk about 10 light weeks in diameter. I recall seeing the number one Trillion miles as the diameter of the OJ 287 accretion disk, correct me if I am wrong. Also the quasar is about the size of our solar system, with an event horizon out to about the orbit of Mercury.

Nowhere could I find estimates of how bright it is, but quasars are supposed to be as bright as Trillions of Suns. So is it unreasonable to assume that OJ287 is at least as bright as 10 Trillion solar? All that energy radiating from how large a region? I would think that most of the "sparks" are flying out of a region bounded by about the orbit of Mercury (at the event horizon) out only a few million miles, with most of the gravitational energy reaction taking place very close to the event horizon. Don't forget that accretion disks may be very flat like the rings around Saturn.

It is feeding on an accretion disk of matter composed of mostly gas, then dust, and even some solid fragments the size of planets, moons, and asteroids (whatever supernova remnants). What generates Trillions of solar brightness, is happening inside a small region. But how small is that region? Again think flat disk. The reaction probably happens very, very fast, and it makes nuclear fusion look feeble in comparison. And all from feeding upon only about one solar mass per few weeks. Large Quasars eat about one solar mass per month. Maybe if matter is compressed in such an extreme way, it produces an unknown energetic reaction Billions of times as great as nuclear fusion. How else can so much energy be generated by such a small amount of matter falling into it from a relatively small region?

Edited by Airbrush
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the Schwarzschild radius is 2Gm/c² = m * 1.48 × 10^−27 meters/kg

18 billion solar masses = 3.580056 × 10^40 kilograms

3.580056 × 10^40 kg * 1.48 × 10^−27 meters/kg = 5.29848288 * 10^13 meters = 354.181398 Astronomical Units= 2.04558293 light days

considerably bigger than the orbit of mercury

you are also considerably underestimating the energy in the gravitational field of 18 billion solar masses

Edited by granpa
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Thanks Granpa, my estimate was way off. You are correct. OJ287 would have an event horizon that extends out 354 AU as you calculated. Neptune is only 30 AU from the Sun. That is an event horizon over 100 times the distance from the Sun to Neptune, all the way out to the Oort cloud. I wonder where I got the orbit of Mercury?

So the region of extreme gravitational energy would be a blazing flat ring (how flat?) with a diameter of 708 AU. How deep could the region of energetic reaction be? Would it be relatively narrow band millions of miles deep, compared to how broad the ring's diameter is? I'm trying to get an idea of the dimensions and proportions of the giant ring that generates Trillions in solar brightness.

Also how can you explain how it feeds on only 10 to 20 solar masses per year? That incredible large ring, OJ287's event horizon, really spreads that amount of matter very thin.

Edited by Airbrush
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Nowhere could I find estimates of how bright it is, but quasars are supposed to be as bright as Trillions of Suns.

That's not a fair comparison for at least three of reasons. First off, stars radiate more or less uniformly over all space (i.e., over 4*pi steradians). Quasars are highly directional. Second, stars burn for millions of years, billions of years, or more. Active galactic nuclei burn fiercely, and quickly. Third, quasars are from a long, long time ago. The universe was denser and much less metallic.

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how much is expelled in the jets?

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how much is expelled in the jets?

As I recall, black holes are very sloppy eaters. Most of the matter that gets sucked in gets thrown off into space. In the case of Quasars, which are powered by supermassive black holes, most of the matter gets expelled, but how much goes into the jets and how much illuminates the superbright ring around the event horizon? How can a ring over 700 AU in diameter be so bright that it looks like a point source of light from a distance of 3.5 Billion light years? Because when the energy is scattered it fills in the central dark region.

The brightness of quasars is still uncomprehensible to me.

...stars radiate more or less uniformly over all space (i.e., over 4*pi steradians). Quasars are highly directional.

This is a good point. Also maybe the high gravity bends the light rays inward to conceal the SBH at the center. Jets may also be seen but I think jets are not always seen, just the high luminosity coming from an indeterminable sized ring around its' vast event horizon. It must be a disk, but how flattened, and how deep is the region that generates most of the Trillions of solar brightness?

wikipedia: "...To create a luminosity of 1040 W, or Joules per second, (the typical brightness of a quasar), a super-massive black hole would have to consume the material equivalent of 10 stars per year. The brightest known quasars devour 1000 solar masses of material every year. The largest known is estimated to consume matter equivalent to 600 Earths per minute...."

http://en.wikipedia.org/wiki/Quasar

OJ287 is consuming far more than I estimated, 1,000 solar masses per year. That is less than 3 solar masses per 24-hour day. Over 95% of that matter is converted totally into energy, only a little falls into the black hole. But don't you think 3 solar masses per day is still spread thin around a ring 700 AU in diameter?

Edited by Airbrush
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Nowhere could I find estimates of how bright it is, but quasars are supposed to be as bright as Trillions of Suns. So is it unreasonable to assume that OJ287 is at least as bright as 10 Trillion solar? All that energy radiating from how large a region? I would think that most of the "sparks" are flying out of a region bounded by about the orbit of Mercury (at the event horizon) out only a few million miles, with most of the gravitational energy reaction taking place very close to the event horizon. Don't forget that accretion disks may be very flat like the rings around Saturn.

You can sort of base its mass based on how bright it is, but a very important key factor that you wanted to leave out is its binary partner. If scientists can figure out the time it takes for those two things to orbit each-other at what distance, you scientists can figure out its mass that way too. But, from brightness, your mostly making an assumption about its mass because it could just be that the bright object is a dimmer object but just a lot closer. The reason you didn't find it on the internet is probably because the energy output of the friction in gas from the quaser isn't in a direct relationship to the mass, but rather the speed and temperature of the gas.

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the energy output of the friction in gas from the quaser isn't in a direct relationship to the mass, but rather the speed and temperature of the gas.

Yes, speed and temperature of the gas is the key. OJ287 has an accretion disk 10 light weeks in diameter and an event horizon 4 light days in diameter. Each day about 3 solar masses of gas is devoured. This amount of gas is probably accelerated to near light speed as it spirals inward, but this amount of gas is spread over a circumference of about 12 light days.

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Yes, speed and temperature of the gas is the key. OJ287 has an accretion disk 10 light weeks in diameter and an event horizon 4 light days in diameter. Each day about 3 solar masses of gas is devoured. This amount of gas is probably accelerated to near light speed as it spirals inward, but this amount of gas is spread over a circumference of about 12 light days.

Well there has to be A LOT of matter then to be spread out over 12 light days and still have enough friction to heat up all the way into the gamma-spectrum. Because although it isn't a direct relationship, the friction comes from the fact that there's a large amount of matter being forced into a small space.

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...there's a large amount of matter being forced into a small space.

Exactly, but 3 solar masses seems tiny when you spread it out over a circumference of 12 light days. Maybe this indicates that the accretion disk is very, VERY thin. All that gas and dust has to get in line, single file like for a ride at Disneyland. The supermassive black hole forces the matter into impossibly small dimensions. As the matter gets accelerated up to near light speed, and crushed into a tiny space, converted almost totally into energy escaping in a great ring following a coherent path, like laser light. Near the poles are the jets. The combined effect is as bright as Trillions of Suns.

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http://www.wolframalpha.com/input/?i=3+solar+masses+%2F+%2812+light+days*+1+light+day+*+1+light+day%29

using some basic assumptions about the dimensions of the disk (equivalent to a cuboid 1*1*12 light days in dimension) the density isn't shockingly low for the conditions. 28.6 nanograms per cubic meter is pretty decent.

its some 8.5*10^15 hydrogen atoms per cubic meter. this some 10^9 times denser than molecular coulds.

yes you will get frictional heating but you will also get magnetic heating as well as the atoms will exist as completely ionized nuclei. due to its self interaction you'll likely get spots far denser than the average.

EDIT: forgot about fusion heating. you're going to get a fair amount of that too.

Edited by insane_alien
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3 solar masses is just the amount being sucked in.

we dont know how long it was in the disk before that

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no, but it seems likely the retention time will be somewhat longer than a day. so if the black hole is consuming three solar masses per day then the lower bound is likely to be greater than 3 solar masses. if its plausible to have lots of friction with 3 solar masses then with a greater density it is even more plausible.

Edited by insane_alien
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something else to consider is that by the time the speed of the infalling material becomes relativistic then the orbit becomes a spiral

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How long, or short, will it take a volume of matter approaching the event horizon to be heated from very low temperatures to such extreme temperatures? At the critical instant when it takes a dive into the black hole, does matter by-pass nuclear fusion converted mostly to energy before nuclear fusion can occur? Also can the relativistic speeds of the matter just before getting converted into energy interfere with nuclear fusion?

granpa: "...by the time the speed of the infalling material becomes relativistic then the orbit becomes a spiral"

The material always had a spiral orbit. What do you mean by "becomes a spiral"?

Maybe as the material reaches near light speed, that prolongs its existence, magnifying the energy output to Trillions of solar brightnesses. Sorry if this sounds like nonsense. I'm taking shots in the dark. I'm just trying to understand Trillions of solar brightnesses from 3 solar masses per day.

Does anyone think the accretion disk of a quasar is very thin, comparable to the rings of Saturn?

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http://www.wolframalpha.com/input/?i=%28%283+solar+masses+*+c^2%29%2Fday%29%2Fsolar+luminosity

most of the mass is converted to energy via various processes, a lot of the rest is consumed by the black hole and the rest of the rest is ejected.

converting 3 solar masses to energy per day gives a luminosity 16.13 trillion times that of our sun. from the imperfect conversion, consumed and ejected matter a value of a trillion isn't so hard to believe.

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http://www.wolframalpha.com/input/?i=%28%283+solar+masses+*+c^2%29%2Fday%29%2Fsolar+luminosity

most of the mass is converted to energy via various processes, a lot of the rest is consumed by the black hole and the rest of the rest is ejected.

converting 3 solar masses to energy per day gives a luminosity 16.13 trillion times that of our sun. from the imperfect conversion, consumed and ejected matter a value of a trillion isn't so hard to believe.

Thanks for your help Mr. Alien, granpa, & Steevey. Nice to know that.

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http://www.wolframalpha.com/input/?i=%28%283+solar+masses+*+c^2%29%2Fday%29%2Fsolar+luminosity

most of the mass is converted to energy via various processes, a lot of the rest is consumed by the black hole and the rest of the rest is ejected.

That means there are 3 possibilities for matter falling into the black hole. Most is converted totally into energy, some becomes black hole mass, and some matter is blasted out into space. Are the polar jets matter or energy or both?

Do you agree that the luminosity of a quasar is not from the jets. Jets may or may not be detected, I think depending on how rapidly it is rotating? I am visualizing an extremely bright ring of luminosity that gets distorted by the black hole's extreme gravity to makes itself look like a point source of light. Then there may also be jets, and when a jet is pointed directly at us, it is known as a "blasar".

Edited by Airbrush
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That means there are 3 possibilities for matter falling into the black hole. Most is converted totally into energy, some becomes black hole mass, and some matter is blasted out into space. Are the polar jets matter or energy or both?

its matter with energy. energy isn't a substance of its own. it needs to be carried by something.

Do you agree that the luminosity of a quasar is not from the jets. Jets may or may not be detected, I think depending on how rapidly it is rotating? I am visualizing an extremely bright ring of luminosity that gets distorted by the black hole's extreme gravity to makes itself look like a point source of light. Then there may also be jets, and when a jet is pointed directly at us, it is known as a "blasar".

the jets will play a role. they will be incredibly bright near the disk and radiating a huge amount of light. this will also be coming from the disk. i don't think you can consider one without another when considering the luminosity.

even when you have a 'dormant' quasar with no visible jets there will still be a large amount of material thrown off simply due to the size of the damn thing but they won't be anywhere near as intense when it is in an active state.

jet formation is still a bit of a hot topic in astrophysics with much debate on the particulars.

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