I Dark matter and black hole interaction

[infinitebubble]

Reading some of the recent info on black holes and how they ingest gas matter including stellar material... why doesn't dark matter be absorbed into the black hole and according to the article dark matter is part of black hole formation?

https://www.nasa.gov/feature/goddar...etween-primordial-black-holes-and-dark-matter

 

[phinds]

Reading some of the recent info on black holes and how they ingest gas matter including stellar material... why doesn't dark matter be absorbed into the black hole and according to the article dark matter is part of black hole formation?

https://www.nasa.gov/feature/goddar...etween-primordial-black-holes-and-dark-matter

Dark matter contributes to BH formation exactly as does regular matter BUT dark matter passes right through an accretion disk so is less LIKELY to go into a black hole. That is, unless a dark matter particle is either traveling fairly slowly so as to be attracted by gravity before it passes by, or is headed straight for a BH, it won't fall in.

 

[Janus]

I'm not quite sure what your question is. The article you linked to contains the suggestion that Black holes left over from the formation of the universe are what what account for what we now call dark matter, it doesn't deal with any interaction between black holes and dark matter.

If Black holes and dark matter are different in composition, then black holes would ingest any dark matter that crossed their event horizon. The difference between regular matter and dark matter in this respect is due to the fact that normal matter interacts with itself electromagnetically and DM doesn't. This interaction of normal matter causes it radiate away energy as it gets near the black hole, which slows it down and increases the likelihood of it falling into the event horizon . DM, on the other hand, has no such means to radiate away energy, so unless the initial trajectory takes it across the event horizon, it will not be injested by the black hole. In a way, Black holes makes a "larger target" for normal matter than it does for dark matter.

 

[infinitebubble]

OK... so my understanding is the DM at the event horizon is not being 'sucked' into the BH but instead is either oozing on by? The article about BH and DM interaction was the only relevant one I found, I am sure there are other articles on the subject but didn't have time to look for them.

Going back to my original question if gas and stellar materials are being swallowed by the BH, why wouldn't DM be continually fueling the BH? What equivalent energy is released from this DM?

Accretion onto a black hole is the most efficient process for emitting energy from matter in the Universe, releasing up to 40% of the rest mass energy of the material falling in.

 

[Janus]

OK... so my understanding is the DM at the event horizon is not being 'sucked' into the BH but instead is either oozing on by?

No. Anything that crosses the event horizon falls into the black hole. It is just that normal matter, due to its interaction with other matter near the black hole is more likely to cross the event horizon

Going back to my original question if gas and stellar materials are being swallowed by the BH, why wouldn't DM be continually fueling the BH? What equivalent energy is released from this DM?

Accretion onto a black hole is the most efficient process for emitting energy from matter in the Universe, releasing up to 40% of the rest mass energy of the material falling in.

Th emitted energy is the energy lost that I was talking about above, caused by interaction between matter falling into the black hole. Since DM does not have this mechanism for emitting/losing energy, no equivalent energy will be emitted by the consumption of the Black hole by dark matter. Such consumption will have the effect of increasing the mass of the black hole, which in turn would have an effect on the energy emission by normal matter falling into the black hole.

 

[Drakkith]

OK... so my understanding is the DM at the event horizon is not being 'sucked' into the BH but instead is either oozing on by?

The answer is directly linked to orbits. Take the ISS for example. Why doesn't the ISS fall to Earth? The easy answer is of course that it is in orbit. It is moving fast enough that the path it is falling in (yes, it is literally falling. It is constantly in free fall) does not intersect with the Earth's surface. Instead, if we take a rough approximation, the path makes a ellipse and is called a closed orbit. Since the path of objects in closed orbits does not intersect the larger body, the object does not "fall in". We'll talk more about that in a moment.

But what about other objects that aren't in closed orbits? What about a random space rock that comes speeding in from beyond the solar system? Obviously its path must intersect with the Earth's surface for it to impact. But if it doesn't, then it's likely going fast enough that its path forms a hyperbola (or a parabola, but that's not a realistic orbit), not an ellipse. This is known as an open orbit. Few people other than pedantic astronomers would call this an orbit in regular conversation, though it is still technically an orbit.

So here we have two classes of orbits, open and closed. But what does this have to do with black holes and dark matter? Well, if we look at a black hole with an appreciable amount of dust, gas, and other matter surrounding it, most of this matter is in a closed orbit about the black hole and is located well away from the event horizon. But we just talked about a closed orbit above and came to the conclusion that objects in closed orbits don't fall in, right?

The truth is that our conclusion above ignores a very important feature and isn't entirely correct. If it were, then the ISS, satellites, and other objects in orbit wouldn't have to make occasional burns to correct their orbits. The reason they do is that space isn't a perfect vacuum and there is an appreciable amount of gas and dust around large objects like planets and stars. Objects in orbit run into this gas and dust and, due to air friction, gradually lose energy and fall into a lower orbit. Without making orbital corrections, their paths would eventually decay so much that they intersect with the Earth's surface and the objects fall to Earth.

For black holes with accretion disks, the gas and dust particles are all in slightly varying orbits and constantly bang up against each other, heating up and losing energy as EM radiation. Since it is losing energy, some portion of this gas and dust ends up spiraling further and further down towards the event horizon until it eventually crosses it. Over time, black holes can grow to huge sizes through this mechanism.

However, Dark Matter doesn't interact through electromagnetism. Instead of colliding with itself or other matter, it passes right through. This means that it cannot lose energy like regular matter can. So dark matter cannot form accretion disks and spiral down into the event horizon. It has a hard time even getting into a closed orbit around the black hole. The vast majority of it simply passes by the black hole on an open orbit and continues on its way. It's only if its path happens to intersect the event horizon that dark matter gets sucked into the black hole. And since black holes are extremely compact, only a few dozen kilometers in diameter, it is extremely unlikely that significant amounts of dark matter get pulled in. You'd have a better chance of landing a hole-in-one during a hurricane while blindfolded.

 

[russ_watters]

If Black holes and dark matter are different in composition, then black holes would ingest any dark matter that crossed their event horizon. The difference between regular matter and dark matter in this respect is due to the fact that normal matter interacts with itself electromagnetically and DM doesn't. This interaction of normal matter causes it radiate away energy as it gets near the black hole, which slows it down and increases the likelihood of it falling into the event horizon . DM, on the other hand, has no such means to radiate away energy...

If dark matter doesn't radiate energy, does it keep that feature once inside a black hole and if so does that mean such a black hole can't produce Hawking radiation and evaporate?

 

[phinds]

If dark matter doesn't radiate energy, does it keep that feature once inside a black hole and if so does that mean such a black hole can't produce Hawking radiation and evaporate?

If I understand Hawking Radiation correctly, it does not originate inside the EH and so it doesn't matter what's in the BH, just how strong the tidal force is at the EH.

 

[stefan r]

...

Th emitted energy is the energy lost that I was talking about above, caused by interaction between matter falling into the black hole. Since DM does not have this mechanism for emitting/losing energy, no equivalent energy will be emitted by the consumption of the Black hole by dark matter. Such consumption will have the effect of increasing the mass of the black hole, which in turn would have an effect on the energy emission by normal matter falling into the black hole.

I thought dark matter could effect the black hole's spin. The angular momentum then effects normal matter and can be radiated.

 

[newjerseyrunner]

Going back to my original question if gas and stellar materials are being swallowed by the BH, why wouldn't DM be continually fueling the BH? What equivalent energy is released from this DM?.

Let's use something more familiar as an example: an asteroid and a star. If you have an asteroid moving in the direction of a star, what will happen? Sometimes sometimes it'll get sucked into the star, but the most likely case is that it'll make a near miss of the star and get shot away. Depending on it's original trajectory, it may be thrown out of orbit, or it may be captured. Once captured, it's not going to fall into the star, it has too much momentum to carry it past the star each time. In order for it to fall into the star, it has to slow down.

A gas atom is the same way, if it misses the star, it'll be slingshotted around and has to slow down before it can get sucked in. With gas, thes is largely due to friction with other gas that's also trapped in orbit. That's the accretion disk.

Evidence from the Bullet Cluster shows us that dark matter doesn't experience friction, so it can't really slow down, so the most likely case is that it'll miss the black hole and be slingshotted away. Dark matter is certainly attracted to the black hole, but now without any way to gently fall into it, it will most likely miss it. Let's remember that the EH of most black holes are tiny compared to stars.

 

[Janus]

I thought dark matter could effect the black hole's spin. The angular momentum then effects normal matter and can be radiated.

Yes, but that is a indirect effect and does not necessarily lead to an increase of radiation from the black hole. The in-falling DM can just as easily decrease the black hole's spin, decreasing its angular momentum. The point is, that while the DM can have effects on the nature of the Black hole, which in turn effects how the Black Hole interacts with normal matter and how that matter radiates, there is no direct radiation of energy by the in fall of the DM.

 

[phinds]

Yes, but that is a indirect effect and does not necessarily lead to an increase of radiation from the black hole. The in-falling DM can just as easily decrease the black hole's spin, decreasing its angular momentum. The point is, that while the DM can have effects on the nature of the Black hole, which in turn effects how the Black Hole interacts with normal matter and how that matter radiates, there is no direct radiation of energy by the in fall of the DM.

Unless I'm mistaken, this is slightly misleading because it implies that there IS direct radiation of energy by the in-fall of regular matter. My understanding is that neither DM nor regular matter causes any immediate radiation on in-fall but rather they contribute to the mass of the BH which in the long run contributes to the total amount Hawking Radiation.

 

[Janus]

Unless I'm mistaken, this is slightly misleading because it implies that there IS direct radiation of energy by the in-fall of regular matter. My understanding is that neither DM nor regular matter causes any immediate radiation on in-fall but rather they contribute to the mass of the BH which in the long run contributes to the total amount Hawking Radiation.

During the in-fall, regular matter interacts with other matter falling in prior to crossing the event horizon to radiate away energy. Thus the process of feeding regular matter into a black hole can produce energy. Dark matter being fed into a black hole does not have this mechanism of energy release, so its only effect will be that caused by the increase of the mass of the black hole.

 

[phinds]

During the in-fall, regular matter interacts with other matter falling in prior to crossing the event horizon to radiate away energy. Thus the process of feeding regular matter into a black hole can produce energy. Dark matter being fed into a black hole does not have this mechanism of energy release, so its only effect will be that caused by the increase of the mass of the black hole.

Ah. I thought you were saying that it radiates at the EH. I understand about the accretion disk as I explained in an earlier post.

 

[stefan r]

During the in-fall, regular matter interacts with other matter falling in prior to crossing the event horizon to radiate away energy. Thus the process of feeding regular matter into a black hole can produce energy. Dark matter being fed into a black hole does not have this mechanism of energy release, so its only effect will be that caused by the increase of the mass of the black hole.

...
Accretion onto a black hole is the most efficient process for emitting energy from matter in the Universe, releasing up to 40% of the rest mass energy of the material falling in.

My understanding was that you can extract energy from a rotating black hole. That energy is taken from the black hole's angular momentum. Penrose process. The wikipedia article says a particle goes in and a particle comes back out with energy added.

I expect a black hole accretion disk will radiate energy same as any accretion disk. But is this jet from an accretion disk?

messier 87

 

[phinds]

The wikipedia article says a particle goes in and a particle comes back out with energy added.

Into the accretion disk and back out, NOT into the BH itself and back out

 

[Janus]

My understanding was that you can extract energy from a rotating black hole. That energy is taken from the black hole's angular momentum. Penrose process. The wikipedia article says a particle goes in and a particle comes back out with energy added.

I expect a black hole accretion disk will radiate energy same as any accretion disk. But is this jet from an accretion disk?
View attachment 205180
messier 87

With such a process the particle passes into the ergosphere (an oblate spheroid region extending outside of the event horizon). Inside of this region, matter is required to travel in the same direction as the black hole rotates. Such matter can rob the black hole of angular momentum and leave the ergosphere with more KE than it entered with. Now if it is your purpose to "use" this energy, then you would have to extract that KE from the exiting matter. I see no reason why dark matter can't rob a black hole of angular momentum through the same process, However, since DM doesn't interact other than through gravitation, there would be no easy way to usefully extract the KE it gained. The Black hole would lose energy without us being able to "harvest" it.

 

[Simon Peach]

What if dark matter is the product of black holes? That is, another form of matter that exists in our universe but is undetectable by the normal forms of observation.

 

[Drakkith]

What if dark matter is the product of black holes?

If you can find a peer-reviewed source that discusses this, then we can talk about it. Otherwise we cannot, as per PF rules.

 

[stefan r]

What if dark matter is the product of black holes? That is, another form of matter that exists in our universe but is undetectable by the normal forms of observation.

If you can find a peer-reviewed source that discusses this, then we can talk about it. Otherwise we cannot, as per PF rules.

It is in the original post:

In his new paper, published May 24 in The Astrophysical Journal Letters, Kashlinsky analyzes what might have happened if dark matter consisted of a population of black holes similar to those detected by LIGO.

"The Astrophysical Journal Letters" is peer reviewed.

What if dark matter is the product of black holes? That is, another form of matter that exists in our universe but is undetectable by the normal forms of observation.

When people say 80% dark matter and 20% observable matter they have rounded. So if future astronomers discover that dark matter is only 76% of milky way's mass we cannot claim the figure was wrong.

My impression was that black holes are almost certainly some of the dark matter. Black holes without accretion disks are a subset of MACHOs (massive compact halo objects). Free comets and rogue planets are also MACHOs. Some papers on MACHOs say they do not have enough mass to explain all of dark matter. For example:

The total implied mass in MACHOs within 50 kpc is

9 × 10¹⁰ M

, quite independent of the dark halo model. This is substantially larger than all known stellar components of the Galaxy. However, one of our most important conclusions is that a 100% all-MACHO Milky Way halo is ruled out at the 95% confidence level for a wide range of reasonable models. One explanation of our results is a Milky Way halo consisting of about 20% MACHOs. Another possibility is an LMC halo that dominates the microlensing, and no MACHOs in the Milky Way halo.

That is fairly strong evidence for believing that part of dark matter is MACHOs.

For the original post question:

... why doesn't dark matter be absorbed into the black hole...

Black holes do merge. LIGO detected several.

 

[Drakkith]

It is in the original post:

The article talks about primordial black holes being dark matter, it doesn't talk about dark matter being the product of black holes.

 

[stefan r]

The article talks about primordial black holes being dark matter, it doesn't talk about dark matter being the product of black holes.

You might be right. I assumed the sentence meant something like "the observations that lead cosmologists to believe dark matter exist are actually produced by black holes".
I would always phrase a sentence like "earth has gravity" not "earth produces gravity". Also "the sun has a chromosphere" and maybe "the sun produces particles of solar wind".

 

[Janus]

You might be right. I assumed the sentence meant something like "the observations that lead cosmologists to believe dark matter exist are actually produced by black holes".
I would always phrase a sentence like "earth has gravity" not "earth produces gravity". Also "the sun has a chromosphere" and maybe "the sun produces particles of solar wind".

I would read the sentence you quoted as meaning that is the observations that are being produced by black holes. In other words, we have a set of observations that indicate the existence of dark matter, and that these observations may actually be caused by black holes instead.

 

[infinitebubble]

Thanks all for these informed insights on the subject... still remains uneasy on the subject how these DM particles interact along the EH of the DH's and will need much further reading perhaps some new ground going forward.

 

[phinds]

You might be right.

You should not be hesitant about his correctness. He is ALWAYS right. He has told me so several times.

 

[mfb]

still remains uneasy on the subject how these DM particles interact along the EH of the DH's

They are simply in free fall. If they hit the black hole directly, they get absorbed - but black holes are tiny, it is much more likely that they fly past and escape again.

 

[Drakkith]

You might be right. I assumed the sentence meant something like "the observations that lead cosmologists to believe dark matter exist are actually produced by black holes".
I would always phrase a sentence like "earth has gravity" not "earth produces gravity". Also "the sun has a chromosphere" and maybe "the sun produces particles of solar wind".

Ah, I see where you were coming from now.

You should not be hesitant about his correctness. He is ALWAYS right. He has told me so several times.

Lies! Lies and slander! No dinner for you!

 

[ProfChuck]

Recent observations suggest that the black hole population in galaxies is much greater than initially believed. In addition to a massive object at the center of most galaxies there may be a number of black holes scattered throughout the galaxy including in globular clusters. Considering that "naked" black holes, those without an accretion disk, are difficult to observe how will this impact the dark matter model?

 

[MichaelMo]

Recent observations suggest that the black hole population in galaxies is much greater than initially believed. In addition to a massive object at the center of most galaxies there may be a number of black holes scattered throughout the galaxy including in globular clusters. Considering that "naked" black holes, those without an accretion disk, are difficult to observe how will this impact the dark matter model?

Hmmmm. That's an intriguing philosophical question. Nucleosynthesis predictions and CMB predictions of LCDM theory tend to require a highly specific percentage of non-baryonic matter to be present in the early universe to work correctly. In theory, an increased population of stellar sized black holes would decrease the need for, and the likelihood of finding any other type of stable forms of exotic matter. I suppose in theory that the increased population of black holes could mostly be made of exotic types of matter to start with, so there's some wiggle room in there somewhere. :)

I suspect that when you consider the mass sizes involved, and the projected population of stellar sized black holes in a galaxy, that the total mass won't be very significant in the first place. It's still a very interesting philosophical question and dilemma. :)

 

[Drakkith]

Considering that "naked" black holes, those without an accretion disk, are difficult to observe how will this impact the dark matter model?

As far as I know, it shouldn't impact it that much. The amount of mass in the form of dark matter is several times the amount of mass in normal, visible matter. The number of black holes required to explain a significant portion of dark matter is enormous. Far above what we'd expect.

 

[mfb]

Primordial black holes lighter than a solar mass have been ruled out as large contribution by microlensing searches, black holes significantly more massive have been ruled out by searches for binary systems and other measurements. In the range where the LIGO mergers are, we have an indirect excusion from CMB observations - a bit model-dependent, but a lot of primordial black holes sound unlikely. They could have formed later, however.
Here is a good summary.

 

[DarkMattrHole]

Thanks all for these informed insights on the subject... still remains uneasy on the subject how these DM particles interact along the EH of the DH's and will need much further reading perhaps some new ground going forward.

From the sounds of it, DM particles simply, and silently, follow the laws of gravity, curving through space-time but without the 'friction' of either radiating any energy or by being encumbered by other normal matter particles swept into the outer disk. As i recall, please correct if wrong, DM particles don't interact with other DM particles either, and if so, then being pinned to a BH singularity may be the first and only experience in a DM particles' long life.

 

[Chronos]

PBH's as a significant fraction of the matter budget in the early universe has been virtually ruled out by CMB data. Planck pretty much put the nail in the coffin. This constraint could be avoided if black holes largely originated at later epochs, but, observational evidence suggests this is an increasingly unlikely scenario as new data becomes available.

 

[mfb]

As i recall, please correct if wrong, DM particles don't interact with other DM particles either

They cannot interact too often, but all we can do is set upper bounds. They could interact with each other via the weak interaction. Annihilation is also a possible process.

 

[Buzz Bloom]

My impression was that black holes are almost certainly some of the dark matter.

Hi stephen:

There is a constraint on how much of the matter comprising a BH is DM. To explain this constraint, it is probably useful to designate the fraction of BHs created prior to the primordial nuclear synthesis (PNS) of helium and deuterium occurred as Primoridial BHs (PBHs), and use "BH" for later formed BHs. Note that PNS started within the first few seconds following the big-bang.

The constraint is that the density of deuterium observed to exist in the universe depends on the density of baryonic matter (BM) during PNS, which in turn constrains the ratio of BM to DM that exists today. As explained in this thread, most (almost all?) of the content of a BH is BM. Therefore it is not reasonable to consider BHs to comprise any significant amount of DM. On the other hand, it is not known how much of the pre-PNS matter consisted of PBHs, and it is not known how much of PBHs consisted of DM, since the mechanism for forming PBHs is not known. This means it is possible that much of the matter in PBHs may have been and still may be DM, but this is entirely speculative.

Regards,
Buzz

 

[maria_phys]

Assuming that our central black hole is sucking dark matter, can we explain the reason why it's mass is 10^9 solar masses? Dark matter interacts with the ordinary matter (or with any stellar object) via gravity, thus the mass of a black hole is increasing without having any paradox (at first sight).

 

[mfb]

Black holes do not "suck". They attract things based on their mass like everything else does. The amount of dark matter falling into the central black hole (or any other black hole) is tiny.

 

[maria_phys]

Black holes do not "suck". They attract things based on their mass like everything else does. The amount of dark matter falling into the central black hole (or any other black hole) is tiny.

Why? I imagine exactly the opposite. Dark matter interacts with the ordinary matter only via gravity. Assuming an object with very strong gravity, the dark matter would fall immediately into the black hole because of this strong interaction. So, all the dark matter of the universe would fall into the primordial black holes. Hmm, that seems not correct..

Something I'm missing...

Thank you for your answer, anyway :)

 

[phinds]

Why? I imagine exactly the opposite. Dark matter interacts with the ordinary matter only via gravity. Assuming an object with very strong gravity, the dark matter would fall immediately into the black hole because of this strong interaction. So, all the dark matter of the universe would fall into the primordial black holes. Hmm, that seems not correct..

Something I'm missing...

Thank you for your answer, anyway :)

See post #2 --- it explains what you are "missing"

 

[Drakkith]

Why? I imagine exactly the opposite. Dark matter interacts with the ordinary matter only via gravity. Assuming an object with very strong gravity, the dark matter would fall immediately into the black hole because of this strong interaction. So, all the dark matter of the universe would fall into the primordial black holes. Hmm, that seems not correct..

In order to fall into a black hole your path would need to take you directly into the event horizon. But black holes are usually very tine. A black hole of perhaps a few solar masses is only about a dozen miles in diameter or something. The chances of any dark matter crossing that tiny section of space is minuscule.

Note that gravity isn't like a vacuum cleaner. Objects don't spiral into a black hole unless they have some way to slow down so that they "fall" towards the black hole. For regular matter, collisions in the accretion disk slow the dust and gas and, over time, lead to a slow in-spiral until it passes the event horizon. Since dark matter doesn't interact with itself or with normal matter though anything but gravity, it cannot collide with anything and thus cannot lose speed and fall into the event horizon.

 

[phinds]

In order to fall into a black hole your path would need to take you directly into the event horizon. But black holes are usually very tine. A black hole of perhaps a few solar masses is only about a dozen miles in diameter or something. The chances of any dark matter crossing that tiny section of space is minuscule.

Note that gravity isn't like a vacuum cleaner. Objects don't spiral into a black hole unless they have some way to slow down so that they "fall" towards the black hole. For regular matter, collisions in the accretion disk slow the dust and gas and, over time, lead to a slow in-spiral until it passes the event horizon. Since dark matter doesn't interact with itself or with normal matter though anything but gravity, it cannot collide with anything and thus cannot lose speed and fall into the event horizon.

As I said; see post #2