How hungry are black holes

[Johanluus]

I have some questions on black holes.

 

1. Is there any information regarding the ratio of how much matter/energy supermassive black holes swollow in relation to how much they eject in the form of plasma jets (blasars) or any other radiation.

 

my reason for this question is is related to my next question.

 

2. Will black holes ever reach a "maximum" filled state where it cannot

consume anymore due to space energy density limits , and then only

spew out these jets we now observe in blasars.

There may be an effective upper boundary ( radius) as to where black holes cannot grow larger.

 

Then they would only serve as catalysts for converting matter to energy and redistrubuting them into the universe for other galaxies and stars to form.

[vordhosbn]

I don't want to blur the topic, but aren't properties of black holes purely theorethical? To the best of my knowledge, we only speculate about the quantitive and qualitive characteristics of large mass bodies, no matter how probable or percise these speculations might be.

[toastywombel]

I don't want to blur the topic, but aren't properties of black holes purely theorethical? To the best of my knowledge, we only speculate about the quantitive and qualitive characteristics of large mass bodies, no matter how probable or percise these speculations might be.

 

No the properties of black holes are not purely theoretical, there is some we know. This is from wikipedia,

 

"Despite its invisible interior, a black hole can be observed through its interaction with other matter. A black hole can be inferred by tracking the movement of a group of stars that orbit a region in space. Alternatively, when gas falls into a stellar black hole from a companion star, the gas spirals inward, heating to very high temperatures and emitting large amounts of radiation that can be detected from earthbound and Earth-orbiting telescopes."

 

Many of the properties of black holes are calculated through equations, but many of these equations have been validated by observations. The properties of a black hole can usually be categorized as mass, spin, and charge.

 

"It is now widely accepted that the center of every or at least nearly every galaxy contains a supermassive black hole.[76][77] The close observational correlation between the mass of this hole and the velocity dispersion of the host galaxy's bulge, known as the M-sigma relation, strongly suggests a connection between the formation of the black hole and the galaxy itself."[76]

 

and,

"In 1967, astronomers discovered pulsars,[10][11] and within a few years could show that the known pulsars were rapidly rotating neutron stars. Until that time, neutron stars were also regarded as just theoretical curiosities. So the discovery of pulsars awakened interest in all types of ultra-dense objects that might be formed by gravitational collapse"

 

So as you see the properties of black holes are not neccesarily just based of speculation. Maybe some, but not all. As far as the question posed by the op. .. .

 

 

1. Is there any information regarding the ratio of how much matter/energy supermassive black holes swollow in relation to how much they eject in the form of plasma jets (blasars) or any other radiation.

 

Not that I know of, but the second question is really the key here,

 

2. Will black holes ever reach a "maximum" filled state where it cannot

consume anymore due to space energy density limits , and then only

spew out these jets we now observe in blasars.

There may be an effective upper boundary ( radius) as to where black holes cannot grow larger.

 

No, generally the more massive a black hole, the less dense it is. This is from wikipedia as well,

 

"Since the average density of a black hole inside its Schwarzschild radius is inversely proportional to the square of its mass, supermassive black holes are much less dense than stellar black holes (the average density of a large supermassive black hole is comparable to that of water).[65] Consequently, the physics of matter forming a supermassive black hole is much better understood and the possible alternative explanations for supermassive black hole observations are much more mundane. For example, a supermassive black hole could be modelled by a large cluster of very dark objects. However, typically such alternatives are not stable enough to explain the supermassive black hole candidates."

 

Hope this helps.

[Johanluus]

yes they are "purely theoretical " ?? thats why we speculate?

[toastywombel]

yes they are "purely theoretical " ?? thats why we speculate?

 

No they aren't completely, of course somethings are speculated, but we can observe black holes and how they interact with the matter around them. Here are a couple lists of potential black holes that are being observed.

 

http://www.johnstonsarchive.net/relativity/bhctable.html

http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html

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

 

From observing these black hole candidates as they move through clouds of matter, we can determine certain properties.

[vordhosbn]

About the "density" of black holes...

I thought that black holes are essentaly infinately small singularities with huge mass, thus the Schwarzschild radius of a black hole is just the property of space-time, created by that singularity.

[Johanluus]

thanks for your response. it does shed light.

"the average density of a large supermassive black hole is comparable to that of water"

This is astounding!

This is the "average" within the Schwarzschild radius as you noted , but what about the density of the volume of the actual "matter" within the Radius (if one could still call it matter/energy). This matter/energy must occupy SOME volume. An that volume must have an upper limit, to which no more matter/energy can be added. down to plank quantum energy levels. "A kind space with no more space to fit anything".

 

Is there no maximum energy density of space? I guess this is my question. comparable to the other extremes

 

Absolute zero for temprature ( 0 k).

c for velocity.

[toastywombel]

thanks for your response. it does shed light.

"the average density of a large supermassive black hole is comparable to that of water"

This is astounding!

This is the "average" within the Schwarzschild radius as you noted , but what about the density of the volume of the actual "matter" within the Radius (if one could still call it matter/energy). This matter/energy must occupy SOME volume. An that volume must have an upper limit, to which no more matter/energy can be added. down to plank quantum energy levels. "A kind space with no more space to fit anything".

 

Is there no maximum energy density of space? I guess this is my question. comparable to the other extremes

 

Absolute zero for temprature ( 0 k).

c for velocity.

 

I don't know if there is a maximum energy density in space, but energy is really present in any given point in space. But it would seem that even if there were, a black hole would never reach that because it simply becomes less dense as it grows. Now this is only average density, so there could be a singularity, but I don't think there is an upper limit, simply because it is widely accepted that black holes may give off energy through pulsars, jets, and hawking radiation.

[Johanluus]

" don't know if there is a maximum energy density in space"

honest answer!

My view on the matter is this.

If the singularity did exist within the black hole (which im inclined not to support).

Then we cannot put an upper limit for Energy density in space.

A singularity IMPLIES , the mass within the supermassive black hole can approach infinity, which in turn implies that there can exist a black hole with a Schwarzschild radius that can also be infinately large).As time tends to infinity everything will become one black hole.

Then why have all the galaxies not yet been swollowed up by these singularities. This is not what we observe today.

There are galaxies , there are black holes at there centres, all of different sizes, and different stages of their evolution. Some are active and some are dormant.

There is a upper limit , which keeps the balance.

Just like an electron in the box , if we reduce the size of the potential walls , at some limit the electron cannot exits within its boundaries , due to its wavelength , so it will be ejected.

That is my analagy of the upper limit of energy density of space.

[Arch2008]

A black hole singularity has zero volume and therefore infinite density (density is mass divided by volume). This is because stars spin and when they collapse their mass spins down into the singularity like water going down a drain. The spin property, called angular momentum cannot be lost. So a spinning singularity is actually an infinitesimal ring (called a Kerr Ring Singularity after the fellow who figured this out) with length and width but no height. It is squashed absolutely flat (height of zero, hence the volume of zero) by its mass.

 

P.S.-I believe that someone at wikipedia has taken the volume of the space inside the event horizon and confused this with the volume of a black hole. This of course is very obtuse, as the mass of the singularity is not evenly spread throughout this volume.

Edited March 12, 2010 by Arch2008

[Johanluus]

i understand the "concept" of singularity , i just question why they have to exist, even in theory?

[vordhosbn]

Can we make an actual empirical verification of the internal structure behind the event horizon (EH)?

Like for example - go with a spaceprobe near the EH and measure the coherency of the gravitational pull (does it comes from a single point or a spherical object).

[Arch2008]

NASA has imaged an accretion disk around a suspected black hole and confirmed that the disk was spinning in such a way that the singularity must also be spinning. Single points do not exhibit spin.

[Mr Skeptic]

2. Will black holes ever reach a "maximum" filled state where it cannot

consume anymore due to space energy density limits , and then only

spew out these jets we now observe in blasars.

There may be an effective upper boundary ( radius) as to where black holes cannot grow larger.

 

No, black holes cannot spew out matter. Think of a baby eating (without vomiting). What goes in, stays in, but that doesn't mean that it all goes in. Black holes are messy eaters.

 

Some scientists have tried to calculate a maximum size to black holes, based on the energy density of the universe. This is not an intrinsic limit, but rather that our models of the universe require that black holes could not have had that much matter available to the to consume in the time available since the start of the universe.

[Arch2008]

The least massive and the most massive black hole singularities all have infinite density. The Wiki statement about black holes having the density of water is an invalid abstraction. When more matter is forced into the event horizon than can enter the black hole the run off is twisted by magnetic fields into opposing jets. This is not material from inside the black hole. SMBHs do not recycle matter. This is a misconception that proponents of the steady state theory use (misuse).

[ajb]

We can calculate the density of a black hole very easily.

 

Let us assume we have a non-rotating uncharged black hole. The Schwarzschild metric describes such a black hole. We know it is a static solution and is asymptotically flat. So, I will define the size of the black hole in terms of the horizon which we know to have spherical topology.

 

Recall the Schwarzschild radius is given by

 

[math]r_{s} = \frac{2 G M }{c^{2}}[/math]

 

where [math]M[/math] is the mass parameter of the black hole.

 

So, then taking the horizon to describe a spherical shell gives

 

[math]Vol = \frac{4}{3} \pi (r_{s})^{3} = \frac{4}{3}\pi \left( \frac{2 G }{c^{2}}\right)^{3} M^{3}[/math].

 

Then we define the mass density as the mass per unit volume and we have

 

[math]density = (\frac{4}{3}\pi \left( \frac{2 G }{c^{2}}\right)^{3} M^{2})^{-1}= \left( \frac{3}{4 \pi}\right) \left(\frac{2 G}{c^{2}}\right)^{-3} \frac{1}{M^{2}}[/math].

 

Lets convert to solar masses so, [math]M = m M_{0}[/math] and we arrive at

 

[math]density = \left( \frac{3}{4 \pi}\right) \left(\frac{2 G}{c^{2}}\right)^{-3} \frac{1}{M_{0}^{2}} \left( \frac{1}{m} \right)^{2}[/math].

 

In SI units we have [math]\frac{2G}{c^{2}} = 1.5 \times10^{-27} \: m \:\:kg^{-1}[/math] and one solar mass is [math]2 \times 10^{30}\: kg[/math].

 

So,

 

[math]density = 2 \times 10^{19} \frac{1}{m^{2}} [/math] kg per meter cubed .

 

So if [math]m = 1.5 \times 10^{8}[/math] would give a black hole with density near that of liquid water. This is within the measured masses of supermassive black holes.

 

 

By my calculations a black hole with [math]m = 3 \times 10^{7}[/math] would have the density of about that of uranium or osmium (or other heavy metals).

 

Interestingly to get the density of air (~ 1 kg per meter cubed) be need [math]m = 5 \times 10^{9}[/math]. Which may be on the large side. The biggest black hole to my knowledge is [math]m = 3 \times 10^{9}[/math]. So we are in the right neighbourhood here.

Edited March 12, 2010 by ajb
added comments heavy metals

[Johanluus]

"When more matter is forced into the event horizon than can enter the black hole the run off is twisted by magnetic fields into opposing jets. This is not material from inside the black hole. SMBHs do not recycle matter. This is a misconception that proponents of the steady state theory use (misuse)."

 

This is how i interpret it as well.

 

ajb

you have elegantly demonstrated to my inferior brain how to calculate the density of a black hole , using first principals. and i actually understand it.

thank you.

 

 

But in my previous post i mentioned.

 

This is the "average" within the Schwarzschild radius as you noted , but what about the density of the volume of the actual "matter" within the Radius (if one could still call it matter/energy). This matter/energy must occupy SOME volume. An that volume must have an upper limit( with respect to density), to which no more matter/energy can be added. down to plank quantum energy levels. "A kind space with no more space to fit anything". All that happens is that vulume increases , increasing the (SR).

 

Is there no maximum energy density of space? I guess this is my question. comparable to the other extremes

absolute temp = 0k;

velocity c;

 

remember a black hole by definition , evolves because the volume of the "actual matter" is less than the volume of the Schwarzschild radius(SR) . which would suggest that there is a "layer" within the SR that does not contain matter.

 

Does this sound plausable?

[toastywombel]

A black hole singularity has zero volume and therefore infinite density (density is mass divided by volume). This is because stars spin and when they collapse their mass spins down into the singularity like water going down a drain. The spin property, called angular momentum cannot be lost. So a spinning singularity is actually an infinitesimal ring (called a Kerr Ring Singularity after the fellow who figured this out) with length and width but no height. It is squashed absolutely flat (height of zero, hence the volume of zero) by its mass.

 

P.S.-I believe that someone at wikipedia has taken the volume of the space inside the event horizon and confused this with the volume of a black hole. This of course is very obtuse, as the mass of the singularity is not evenly spread throughout this volume.

 

No, no one at wikipedia is obtuse. We are talking about the density of a black hole, from observation. We use the part that is black as the boundary of the black hole, and measure the density inside of that. That is why its called the average density. Of course the density most likely isn't evenly spread out, but it is really an unknown.

 

There is no way to prove or disprove that there is a singularity inside of a black hole, this is one of the mysteries of science. Many scientists doubt that there is a singularity of infinite density. You cannot prove that there is a singularity inside of a black hole because you cannot observe anything in a black hole without being in the black hole.

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The least massive and the most massive black hole singularities all have infinite density. The Wiki statement about black holes having the density of water is an invalid abstraction. When more matter is forced into the event horizon than can enter the black hole the run off is twisted by magnetic fields into opposing jets. This is not material from inside the black hole. SMBHs do not recycle matter. This is a misconception that proponents of the steady state theory use (misuse).

 

I would also like to note, that it is currently an unknown whether black holes recycle matter. Hawking Radiation seems very possible. And again, you cannot prove that black hole singularities have a density of infinity or that they don't, but I think many scientist don't neccesarily believe there is an actual singularity. A singularity is what is implied by relativity, but a singularity may be a part where relativity breaks down, and quantum mechanics is needed to understand it.

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Merged post follows:

Consecutive posts merged

remember a black hole by definition , evolves because the volume of the "actual matter" is less than the volume of the Schwarzschild radius(SR) . which would suggest that there is a "layer" within the SR that does not contain matter.

 

Does this sound plausable?

 

Well I would think that it is more shades of gray, as a hypothetical observer moves from the boundary, the density would be increasing as it approaches the center of the schwarzschild radius. Whether the increasing density is gradual or not is really an unknown.

Edited March 13, 2010 by toastywombel
Consecutive posts merged.

[Johanluus]

Yes that sounds like a reasonable conclusion

thank you for your input

[ajb]

 

remember a black hole by definition , evolves because the volume of the "actual matter" is less than the volume of the Schwarzschild radius(SR) . which would suggest that there is a "layer" within the SR that does not contain matter.

 

Does this sound plausable?

 

I don't know. The Schwarzchild metric describes a point mass, more particularly removing this point you have a vacuum solution. You would need to think about matching the non-vacuum solution that describes matter and the Schwarzchild metric.

 

When thinking about "feeding" a black hole it makes sense to think about test particles. That is particles that interact gravitationally, but do not produce their own gravitational field.

[Airbrush]

"...spew out these jets we now observe in blasars..."

 

Blazars are quasars are supermassive black holes. The difference between a blazar and a quasar is the blazar jet is pointed directly at us. Quasar jets are not. However, a quasar's jet must be pointed in our general direction in order for us to even detect it.

[Arch2008]

No one will ever “know” what goes on inside the event horizon. We have mathematical models of the universe that are proven that point to singularities and we have research models that are really interesting that point elsewhere but lack that proof thing. Roy Kerr used the proven mathematical model of General Relativity to show how the mass of the collapsing, spinning star becomes a ring with no height and hence a volume of zero with infinite density. When a massive star collapses to a volume denser than a neutron star then space time itself gets ripped and you get an event horizon around “something”. So what is the density of this black hole minus its former collapsar? Zero. The stellar “remnant” had all of the mass and the rest of the “volume” of the black hole had none of it. Space time within the black hole itself gets twisted. To say that the volume of the black hole is X is thus also a misnomer.

The last time I checked, really great research gets trumped by proven theory.

[vordhosbn]

And how exactly does mass "fall" trough the "empty" space of a black hole towards it's center? With the speed of light?

[Arch2008]

Yep.

Due to time dilation, the mass accelerated to c takes forever to reach the center to an observer outside the event horizon. So it is “plastered” to the surface region of the black hole (so that its information is not lost to the universe) and again does not really add to an ad hoc “density of the black hole”.