Starship Asterisk*

VictorBorun wrote: ↑Wed Oct 23, 2024 9:09 pm

Chris Peterson wrote: ↑Wed Oct 23, 2024 1:46 pm

johnnydeep wrote: ↑Wed Oct 23, 2024 1:42 pm

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 wrote: ↑Wed Oct 23, 2024 1:46 pm

johnnydeep wrote: ↑Wed Oct 23, 2024 1:42 pm

Chris Peterson wrote: ↑Wed Oct 23, 2024 1:32 pm

"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.

Chris Peterson wrote: ↑Wed Oct 23, 2024 1:46 pm

johnnydeep wrote: ↑Wed Oct 23, 2024 1:42 pm

Chris Peterson wrote: ↑Wed Oct 23, 2024 1:32 pm

"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 wrote: ↑Wed Oct 23, 2024 1:42 pm

Chris Peterson wrote: ↑Wed Oct 23, 2024 1:32 pm

VictorBorun wrote: ↑Wed Oct 23, 2024 6:28 am

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 wrote: ↑Wed Oct 23, 2024 1:32 pm

VictorBorun wrote: ↑Wed Oct 23, 2024 6:28 am

Chris Peterson wrote: ↑Wed Oct 23, 2024 3:14 am

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"?

VictorBorun wrote: ↑Wed Oct 23, 2024 6:28 am

Chris Peterson wrote: ↑Wed Oct 23, 2024 3:14 am

VictorBorun wrote: ↑Wed Oct 23, 2024 2:59 am

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 wrote: ↑Wed Oct 23, 2024 3:14 am

VictorBorun wrote: ↑Wed Oct 23, 2024 2:59 am

Chris Peterson wrote: ↑Mon Oct 21, 2024 10:18 pm
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 wrote: ↑Wed Oct 23, 2024 2:59 am

Chris Peterson wrote: ↑Mon Oct 21, 2024 10:18 pm

johnnydeep wrote: ↑Mon Oct 21, 2024 7:19 pm

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 wrote: ↑Mon Oct 21, 2024 10:18 pm

johnnydeep wrote: ↑Mon Oct 21, 2024 7:19 pm

Chris Peterson wrote: ↑Mon Oct 21, 2024 1:37 pm

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?

Chris Peterson wrote: ↑Mon Oct 21, 2024 10:18 pm

johnnydeep wrote: ↑Mon Oct 21, 2024 7:19 pm

Chris Peterson wrote: ↑Mon Oct 21, 2024 1:37 pm

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?

johnnydeep wrote: ↑Mon Oct 21, 2024 7:19 pm

Chris Peterson wrote: ↑Mon Oct 21, 2024 1:37 pm

johnnydeep wrote: ↑Mon Oct 21, 2024 1:21 pm

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.

Chris Peterson wrote: ↑Mon Oct 21, 2024 1:37 pm

johnnydeep wrote: ↑Mon Oct 21, 2024 1:21 pm

Chris Peterson wrote: ↑Sun Oct 20, 2024 11:38 pm
"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.

Christian G. wrote: ↑Mon Oct 21, 2024 1:40 pm

johnnydeep wrote: ↑Mon Oct 21, 2024 1:28 pm

Christian G. wrote: ↑Mon Oct 21, 2024 1:11 pm Thank you for your answers, Chris and Victor.



Coud the smaller and denser early universe be one such condition? I'm thinking specifically of the recent discovery of black holes just a few million years after the Big Bang that were more massive than expected; could one factor be that they have captured large amounts of dark matter, or would that be a negligeable part of their precocious mass?

How heavy is dark matter compared to baryonic matter, for that matter (no pun intended)? Galaxies have more dark matter mass than ordinary matter but that's because of the huge amount of dark matter, but say we compare a cubic meter of ordinary matter vs a cubic meter of dark matter, would the latter be heavier?

It would only make sense to compare the density (g/m³) of baryonic matter to that of dark matter. Unless you mean to compare, say, a proton, to a "comparable" particle of dark matter whatever that might be?

Thanks, indeed I should have been more precise, I meant comparing them at similar densities as well, not just volume.

Christian G. wrote: ↑Mon Oct 21, 2024 2:30 pm

Chris Peterson wrote: ↑Mon Oct 21, 2024 2:27 pm

Christian G. wrote: ↑Mon Oct 21, 2024 2:19 pm And speaking of density, another enigma for me is why doesn't dark matter contract on and on, collapse, how does it put the brakes on gravity, in the same way for example that electron degeneracy pressure puts the brakes in white dwarfs (unless there might exist super compact dark matter bodies but that's getting a little speculative)

Gravity does not cause collapse unless there is some mechanism for removing energy from the material. Gravity causes all the particles or bodies in a system to be in orbit around each other. Solar systems don't collapse. Globular clusters don't collapse. The only time we see material collapse (as in star formation) is where the densities are high enough that friction and fluid dynamics become significant, causing orbital decay. But those things are mediated by the electromagnetic force, which does not affect dark matter.

Enigma solved, thank you!

Chris Peterson wrote: ↑Mon Oct 21, 2024 2:27 pm

Christian G. wrote: ↑Mon Oct 21, 2024 2:19 pm And speaking of density, another enigma for me is why doesn't dark matter contract on and on, collapse, how does it put the brakes on gravity, in the same way for example that electron degeneracy pressure puts the brakes in white dwarfs (unless there might exist super compact dark matter bodies but that's getting a little speculative)

Gravity does not cause collapse unless there is some mechanism for removing energy from the material. Gravity causes all the particles or bodies in a system to be in orbit around each other. Solar systems don't collapse. Globular clusters don't collapse. The only time we see material collapse (as in star formation) is where the densities are high enough that friction and fluid dynamics become significant, causing orbital decay. But those things are mediated by the electromagnetic force, which does not affect dark matter.

Christian G. wrote: ↑Mon Oct 21, 2024 2:19 pm And speaking of density, another enigma for me is why doesn't dark matter contract on and on, collapse, how does it put the brakes on gravity, in the same way for example that electron degeneracy pressure puts the brakes in white dwarfs (unless there might exist super compact dark matter bodies but that's getting a little speculative)

johnnydeep wrote: ↑Mon Oct 21, 2024 1:28 pm

Christian G. wrote: ↑Mon Oct 21, 2024 1:11 pm Thank you for your answers, Chris and Victor.

Chris Peterson wrote: ↑Sun Oct 20, 2024 1:29 pm I'm sure they can capture dark matter under the right conditions

Coud the smaller and denser early universe be one such condition? I'm thinking specifically of the recent discovery of black holes just a few million years after the Big Bang that were more massive than expected; could one factor be that they have captured large amounts of dark matter, or would that be a negligeable part of their precocious mass?

How heavy is dark matter compared to baryonic matter, for that matter (no pun intended)? Galaxies have more dark matter mass than ordinary matter but that's because of the huge amount of dark matter, but say we compare a cubic meter of ordinary matter vs a cubic meter of dark matter, would the latter be heavier?

It would only make sense to compare the density (g/m³) of baryonic matter to that of dark matter. Unless you mean to compare, say, a proton, to a "comparable" particle of dark matter whatever that might be?

johnnydeep wrote: ↑Mon Oct 21, 2024 1:21 pm

Chris Peterson wrote: ↑Sun Oct 20, 2024 11:38 pm

johnnydeep wrote: ↑Sun Oct 20, 2024 9:50 pm

Thanks. A few more...

Can we then measure the temperature of dark matter? I'd guess not since the temperature of other stuff in the universe is measurable by the frequency of light they emit, and dark matter emits no light, and we also don't know how fast dark matter "particles" are moving?

Does a single hydrogen atom or a single proton have a temperature that's directly proportional to its velocity?

"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.

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.

Christian G. wrote: ↑Mon Oct 21, 2024 1:11 pm Thank you for your answers, Chris and Victor.

Chris Peterson wrote: ↑Sun Oct 20, 2024 1:29 pm I'm sure they can capture dark matter under the right conditions

Coud the smaller and denser early universe be one such condition? I'm thinking specifically of the recent discovery of black holes just a few million years after the Big Bang that were more massive than expected; could one factor be that they have captured large amounts of dark matter, or would that be a negligeable part of their precocious mass?

How heavy is dark matter compared to baryonic matter, for that matter (no pun intended)? Galaxies have more dark matter mass than ordinary matter but that's because of the huge amount of dark matter, but say we compare a cubic meter of ordinary matter vs a cubic meter of dark matter, would the latter be heavier?

Chris Peterson wrote: ↑Sun Oct 20, 2024 11:38 pm

johnnydeep wrote: ↑Sun Oct 20, 2024 9:50 pm

Chris Peterson wrote: ↑Sun Oct 20, 2024 7:21 pm

Not stupid at all!

Dark matter does form "clumps". We see that in the halos it forms around galaxies.

Temperature isn't about photons, it's about the energy of a particle, generally given by its speed. Dark matter particles (assuming the particle theory is correct) certainly move, so they have kinetic energy and they can transfer that energy to other particles, which means they have a temperature. They don't have to emit blackbody photons for that to be true.

I agree that "repulsive gravity" is a very poor term for dark energy... which as far as we know is unrelated to gravity.

Thanks. A few more...

Can we then measure the temperature of dark matter? I'd guess not since the temperature of other stuff in the universe is measurable by the frequency of light they emit, and dark matter emits no light, and we also don't know how fast dark matter "particles" are moving?

Does a single hydrogen atom or a single proton have a temperature that's directly proportional to its velocity?

"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.

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).

Christian G. wrote: ↑Mon Oct 21, 2024 1:11 pm Thank you for your answers, Chris and Victor.

Chris Peterson wrote: ↑Sun Oct 20, 2024 1:29 pm I'm sure they can capture dark matter under the right conditions

Coud the smaller and denser early universe be one such condition? I'm thinking specifically of the recent discovery of black holes just a few million years after the Big Bang that were more massive than expected; could one factor be that they have captured large amounts of dark matter, or would that be a negligeable part of their precocious mass?

How heavy is dark matter compared to baryonic matter, for that matter (no pun intended)? Galaxies have more dark matter mass than ordinary matter but that's because of the huge amount of dark matter, but say we compare a cubic meter of ordinary matter vs a cubic meter of dark matter, would the latter be heavier?

Chris Peterson wrote: ↑Sun Oct 20, 2024 1:29 pm I'm sure they can capture dark matter under the right conditions

Chris Peterson wrote: ↑Sun Oct 20, 2024 7:21 pm

johnnydeep wrote: ↑Sun Oct 20, 2024 7:10 pm So many stupid questions:

- Dark matter is affected by gravity and has gravity of its own, so presumably it could create clumps of greater density due to random concentration fluctuations, correct?

- Dark matter is unaffected by the electromagnetic field and so doesn't generate any photons. Does that imply that dark matter has a temperature of absolute zero? That is, don't all things that vibrate (i.e., have a non-zero temperature) emit photons a la "black body radiation"? If so, dark matter must have a zero temperature.

- Dark energy has "repulsive gravity"? That seems like a poor metaphor. Gravity is gravity. Dark energy works in opposition to gravity, but is not a type of gravity that is repulsive, right?

Not stupid at all!

Dark matter does form "clumps". We see that in the halos it forms around galaxies.

Temperature isn't about photons, it's about the energy of a particle, generally given by its speed. Dark matter particles (assuming the particle theory is correct) certainly move, so they have kinetic energy and they can transfer that energy to other particles, which means they have a temperature. They don't have to emit blackbody photons for that to be true.

I agree that "repulsive gravity" is a very poor term for dark energy... which as far as we know is unrelated to gravity.