APOD: Dark Matter in a Simulated Universe (2024 Oct 20)

[johnnydeep]

"Temperature" is a thermodynamic property that only makes sense across a statistically meaningful population of particles. A single atom doesn't have a "temperature". It reflects the average kinetic energy of a collection of particles.

But a collection of a million atoms could have the same temperature as a collection of 100 atoms due simply to the average velocity of the atoms being the same (however impeded by collisions those atoms may be). So, it makes sense to me to say that a single atom with that same average velocity could be said to have that same temperature.

Except in actual usage, "temperature" simply isn't used that way. Absent a large enough population of particles for statistics to be meaningful, you would just consider the energy of a particle (which could be all over the place as it absorbs or emits photons and changes its energy state).

Because our ordinary usage of "temperature" involves collisions between particles and the transfer of energy, and because particles of dark matter essentially don't interact, they don't really possess a temperature as such (although they may have very high velocities, so in some settings are treated as having a sort of temperature. But it's not something we measure; rather, it's a theoretical concept).

Why couldn't dark matter interact with itself via collisions? We already know dark matter can affect other dark matter via gravity.

Particle collisions are extremely rare. At the particle scale, baryonic matter interacts with itself through the electromagnetic force. Not the very weak gravitational force. Very, very early in the Universe the particle density of dark matter may have been high enough that actual collisions occurred. No more.

Ok, thanks. That said, I understand there could very well still be as yet undetected (or undetectable) dark matter black holes, around which any dark matter particles could be interacting quite frequently.

[Chris Peterson]

But a collection of a million atoms could have the same temperature as a collection of 100 atoms due simply to the average velocity of the atoms being the same (however impeded by collisions those atoms may be). So, it makes sense to me to say that a single atom with that same average velocity could be said to have that same temperature.

Except in actual usage, "temperature" simply isn't used that way. Absent a large enough population of particles for statistics to be meaningful, you would just consider the energy of a particle (which could be all over the place as it absorbs or emits photons and changes its energy state).

Why couldn't dark matter interact with itself via collisions? We already know dark matter can affect other dark matter via gravity.

Particle collisions are extremely rare. At the particle scale, baryonic matter interacts with itself through the electromagnetic force. Not the very weak gravitational force. Very, very early in the Universe the particle density of dark matter may have been high enough that actual collisions occurred. No more.

Ok, thanks. That said, I understand there could very well still be as yet undetected (or undetectable) dark matter black holes, around which any dark matter particles could be interacting quite frequently.

I don't think the concept of a dark matter black hole makes any sense. The nature of the matter is completely lost in a black hole. It's a singularity with mass. Why would one formed from baryonic matter be any different from one formed from dark matter?

[johnnydeep]

Except in actual usage, "temperature" simply isn't used that way. Absent a large enough population of particles for statistics to be meaningful, you would just consider the energy of a particle (which could be all over the place as it absorbs or emits photons and changes its energy state).


Particle collisions are extremely rare. At the particle scale, baryonic matter interacts with itself through the electromagnetic force. Not the very weak gravitational force. Very, very early in the Universe the particle density of dark matter may have been high enough that actual collisions occurred. No more.

Ok, thanks. That said, I understand there could very well still be as yet undetected (or undetectable) dark matter black holes, around which any dark matter particles could be interacting quite frequently.

I don't think the concept of a dark matter black hole makes any sense. The nature of the matter is completely lost in a black hole. It's a singularity with mass. Why would one formed from baryonic matter be any different from one formed from dark matter?

Yes, that's true. But the black hole still might have been formed predominantly from dark matter initially, though perhaps we'd never be able to confirm that. And clearly, since dark matter perfuses all of space, black holes must be swallowing some up all the time!

[VictorBorun]

Except in actual usage, "temperature" simply isn't used that way. Absent a large enough population of particles for statistics to be meaningful, you would just consider the energy of a particle (which could be all over the place as it absorbs or emits photons and changes its energy state).


Particle collisions are extremely rare. At the particle scale, baryonic matter interacts with itself through the electromagnetic force. Not the very weak gravitational force. Very, very early in the Universe the particle density of dark matter may have been high enough that actual collisions occurred. No more.

Ok, thanks. That said, I understand there could very well still be as yet undetected (or undetectable) dark matter black holes, around which any dark matter particles could be interacting quite frequently.

I don't think the concept of a dark matter black hole makes any sense. The nature of the matter is completely lost in a black hole. It's a singularity with mass. Why would one formed from baryonic matter be any different from one formed from dark matter?

They say an electric charge is conserved after a collapse to a black hole*. What if the dark matter possesses some kinds of dark charge and those are conserved in black holes too?

For all we know the dark charges may interact in some strange way like neither mutually repel nor attract but chase one another or go around one another. It may help to sustain a puffy galactic dark halo even if the dark matter is not quite as non-colliding as they think. It may make darkly charged black holes interact and merge. But to study dark charges is a challenge for a baryonic creature like us.

___
* like there's a chance for electrically charged interstellar media to get together and feed a black hole

[Chris Peterson]

Ok, thanks. That said, I understand there could very well still be as yet undetected (or undetectable) dark matter black holes, around which any dark matter particles could be interacting quite frequently.

I don't think the concept of a dark matter black hole makes any sense. The nature of the matter is completely lost in a black hole. It's a singularity with mass. Why would one formed from baryonic matter be any different from one formed from dark matter?

They say an electric charge is conserved after a collapse to a black hole*. What if the dark matter possesses some kinds of dark charge and those are conserved in black holes too?

For all we know the dark charges may interact in some strange way like neither mutually repel nor attract but chase one another or go around one another. It may help to sustain a puffy galactic dark halo even if the dark matter is not quite as non-colliding as they think. It may make darkly charged black holes interact and merge. But to study dark charges is a challenge for a baryonic creature like us.

___
* like there's a chance for electrically charged interstellar media to get together and feed a black hole

Well, pretty much by definition dark matter can't have an electric charge. To the extent black holes have any charge, it is by taking in charged material after formation. But any actual charge will be extremely tiny. Suffice to say, there's no reason to think that a black hole would vary in properties in some way based on the nature of the matter that formed it or feeds it.

[VictorBorun]

I don't think the concept of a dark matter black hole makes any sense. The nature of the matter is completely lost in a black hole. It's a singularity with mass. Why would one formed from baryonic matter be any different from one formed from dark matter?

They say an electric charge is conserved after a collapse to a black hole*. What if the dark matter possesses some kinds of dark charge and those are conserved in black holes too?

For all we know the dark charges may interact in some strange way like neither mutually repel nor attract but chase one another or go around one another. It may help to sustain a puffy galactic dark halo even if the dark matter is not quite as non-colliding as they think. It may make darkly charged black holes interact and merge. But to study dark charges is a challenge for a baryonic creature like us.

___
* like there's a chance for electrically charged interstellar media to get together and feed a black hole

Well, pretty much by definition dark matter can't have an electric charge. To the extent black holes have any charge, it is by taking in charged material after formation. But any actual charge will be extremely tiny. Suffice to say, there's no reason to think that a black hole would vary in properties in some way based on the nature of the matter that formed it or feeds it.

Yes but I am talking about darkly charged BHs (if there are any kinds of dark charge, puffing up dark galactic halos maybe)

[Chris Peterson]

They say an electric charge is conserved after a collapse to a black hole*. What if the dark matter possesses some kinds of dark charge and those are conserved in black holes too?

For all we know the dark charges may interact in some strange way like neither mutually repel nor attract but chase one another or go around one another. It may help to sustain a puffy galactic dark halo even if the dark matter is not quite as non-colliding as they think. It may make darkly charged black holes interact and merge. But to study dark charges is a challenge for a baryonic creature like us.

___
* like there's a chance for electrically charged interstellar media to get together and feed a black hole

Well, pretty much by definition dark matter can't have an electric charge. To the extent black holes have any charge, it is by taking in charged material after formation. But any actual charge will be extremely tiny. Suffice to say, there's no reason to think that a black hole would vary in properties in some way based on the nature of the matter that formed it or feeds it.

Yes but I am talking about darkly charged BHs (if there are any kinds of dark charge, puffing up dark galactic halos maybe)

"Dark charge"?

[johnnydeep]

Well, pretty much by definition dark matter can't have an electric charge. To the extent black holes have any charge, it is by taking in charged material after formation. But any actual charge will be extremely tiny. Suffice to say, there's no reason to think that a black hole would vary in properties in some way based on the nature of the matter that formed it or feeds it.

Yes but I am talking about darkly charged BHs (if there are any kinds of dark charge, puffing up dark galactic halos maybe)

"Dark charge"?

Victor conjectured that dark matter might possess a "dark charge" in his prior post (which for some reason isn't appearing in my reply to your reply that does show it).

[Chris Peterson]

Yes but I am talking about darkly charged BHs (if there are any kinds of dark charge, puffing up dark galactic halos maybe)

"Dark charge"?

Victor conjectured that dark matter might possess a "dark charge" in his prior post (which for some reason isn't appearing in my reply to your reply that does show it).

Yeah, well maybe it possesses dark magnetism or dark unicorns. Making up a word without any underlying basis isn't science. Dark matter is understandable to the extent its observed behavior makes rational sense, and that is a particle of some kind that doesn't interact with the electromagnetic force (or only extremely weakly). If dark matter did interact with EM, that would be apparent in behavior that we explicitly do not observe, and would expect to.

[johnnydeep]

"Dark charge"?

Victor conjectured that dark matter might possess a "dark charge" in his prior post (which for some reason isn't appearing in my reply to your reply that does show it).

Yeah, well maybe it possesses dark magnetism or dark unicorns. Making up a word without any underlying basis isn't science. Dark matter is understandable to the extent its observed behavior makes rational sense, and that is a particle of some kind that doesn't interact with the electromagnetic force (or only extremely weakly). If dark matter did interact with EM, that would be apparent in behavior that we explicitly do not observe, and would expect to.

(And it seems that the quoting support only allows going three levels deep!)

[VictorBorun]

"Dark charge"?

Victor conjectured that dark matter might possess a "dark charge" in his prior post (which for some reason isn't appearing in my reply to your reply that does show it).

Yeah, well maybe it possesses dark magnetism or dark unicorns. Making up a word without any underlying basis isn't science. Dark matter is understandable to the extent its observed behavior makes rational sense, and that is a particle of some kind that doesn't interact with the electromagnetic force (or only extremely weakly). If dark matter did interact with EM, that would be apparent in behavior that we explicitly do not observe, and would expect to.

the hole topic of any dark feed to black holes is poorly based

one (rather weak) argument I thought of for a dark charge is "non-colliding" puffy dark halos around galaxies and clusters of galaxies.
Either dark particles only interact via gravitation or the dark charge acts puffing the heap up, with not mutual attraction but making dark particles chase one another or go around one another

the other (rather weak) argument I thought of for a dark charge is that the astrophysics currently struggles to model enough BHs' merges to explain why SMBHs are so many, and so massive, and so early. It would help if BHs could approach one another not only via their interaction with the stellar population but by stopping their orbiting because of some dark charge interaction. Say, their dark charges tell them to go around each other in one direction and their initial orbital spin after the first approach was in the opposite direction; those BHs would merge real fast.

[Chris Peterson]

Victor conjectured that dark matter might possess a "dark charge" in his prior post (which for some reason isn't appearing in my reply to your reply that does show it).

Yeah, well maybe it possesses dark magnetism or dark unicorns. Making up a word without any underlying basis isn't science. Dark matter is understandable to the extent its observed behavior makes rational sense, and that is a particle of some kind that doesn't interact with the electromagnetic force (or only extremely weakly). If dark matter did interact with EM, that would be apparent in behavior that we explicitly do not observe, and would expect to.

the hole topic of any dark feed to black holes is poorly based

one (rather weak) argument I thought of for a dark charge is "non-colliding" puffy dark halos around galaxies and clusters of galaxies.
Either dark particles only interact via gravitation or the dark charge acts puffing the heap up, with not mutual attraction but making dark particles chase one another or go around one another

the other (rather weak) argument I thought of for a dark charge is that the astrophysics currently struggles to model enough BHs' merges to explain why SMBHs are so many, and so massive, and so early. It would help if BHs could approach one another not only via their interaction with the stellar population but by stopping their orbiting because of some dark charge interaction. Say, their dark charges tell them to go around each other in one direction and their initial orbital spin after the first approach was in the opposite direction; those BHs would merge real fast.

It all sounds like pseudoscience to me.