3 ms·

>A local dark matter density of the order of 0.01M⊙/pc3 corresponds to approximately one Planck-scale white-hole per each 10.000Km3. These objects are presumabl

by floxy 2y ago

>A local dark matter density of the order of 0.01M⊙/pc3 corresponds to approximately one Planck-scale white-hole per each 10.000Km3. These objects are presumably moving fast with respect to our local frame, since we are rotating with the galaxy at hundreds of Km per second, while dark matter probably isn’t. Anyone know why dark matter wouldn't be rotating along with the rest of the galaxy?

gitaarik 2y ago
Dark matter is what should explain the anomalies we see in gravitational behavior of galaxies. So it's influencing gravity but it's not acting like regular matter and can't be detected apart from the gravitational influence it has on regular matter. So if dark matter would be rotating along with the galaxy then it would behave like regular matter so it wouldn't be dark matter.
mjan22640 2y ago
It does not interact electromagnetically and does not have friction because of that.
- floxy 2y ago
  Chandrasekhar dynamical friction https://en.wikipedia.org/wiki/Dynamical_friction https://en.wikipedia.org/wiki/Dynamical_friction
mikhailfranco 2y ago
Dark matter probably is. Dark matter is matter. It gravitates. It obeys conservation of angular momentum. Unless the dark matter clump happened to form in a spherically symmetric contraction, it will be rotating, almost certainly coupled to the rotation of the galaxy.
- Sharlin 2y ago
  The difference is that while the dark matter halo almost certainly has has net angular momentum, individual DM particles would not be coupled to the galaxy’s rotation to any meaningful degree, and would have essentially random velocities relative to a local corotating frame. The entire reason that spiral galaxies exist is that baryonic matter interacts electromagnetically and can dissipate kinetic energy via heat (photons). That causes matter to eventually flatten into a disc rotating more-or-less uniformly. In this sense a DM halo is similar to elliptical galaxies which certainly have net angular momentum, but their stars have essentially random orbital planes.
  - codethief 2y ago
    > The difference is that while the dark matter halo almost certainly has has net angular momentum, individual DM particles would not be coupled to the galaxy’s rotation to any meaningful degree Does this take into account frame-dragging induced rotation?
    - Sharlin 2y ago
      Spacetime is essentially flat on a galactic level for any general-relativity purposes. I'm pretty sure you can safely ignore frame-dragging here.
fguerraz 2y ago
> Anyone know why dark matter wouldn't be rotating along with the rest of the galaxy? No one knows if dark matter exists and what it's made of, so you can make as many assumptions as you want to help your fancy research as long as it doesn't contradict other observations.

by floxy 2y ago

gitaarik 2y ago

Dark matter is what should explain the anomalies we see in gravitational behavior of galaxies. So it's influencing gravity but it's not acting like regular matter and can't be detected apart from the gravitational influence it has on regular matter. So if dark matter would be rotating along with the galaxy then it would behave like regular matter so it wouldn't be dark matter.

mjan22640 2y ago

It does not interact electromagnetically and does not have friction because of that.

floxy 2y ago
Chandrasekhar dynamical friction https://en.wikipedia.org/wiki/Dynamical_friction https://en.wikipedia.org/wiki/Dynamical_friction

mikhailfranco 2y ago

Dark matter probably is. Dark matter is matter. It gravitates. It obeys conservation of angular momentum. Unless the dark matter clump happened to form in a spherically symmetric contraction, it will be rotating, almost certainly coupled to the rotation of the galaxy.

Sharlin 2y ago
The difference is that while the dark matter halo almost certainly has has net angular momentum, individual DM particles would not be coupled to the galaxy’s rotation to any meaningful degree, and would have essentially random velocities relative to a local corotating frame. The entire reason that spiral galaxies exist is that baryonic matter interacts electromagnetically and can dissipate kinetic energy via heat (photons). That causes matter to eventually flatten into a disc rotating more-or-less uniformly. In this sense a DM halo is similar to elliptical galaxies which certainly have net angular momentum, but their stars have essentially random orbital planes.
- codethief 2y ago
  > The difference is that while the dark matter halo almost certainly has has net angular momentum, individual DM particles would not be coupled to the galaxy’s rotation to any meaningful degree Does this take into account frame-dragging induced rotation?
  - Sharlin 2y ago
    Spacetime is essentially flat on a galactic level for any general-relativity purposes. I'm pretty sure you can safely ignore frame-dragging here.

fguerraz 2y ago

> Anyone know why dark matter wouldn't be rotating along with the rest of the galaxy? No one knows if dark matter exists and what it's made of, so you can make as many assumptions as you want to help your fancy research as long as it doesn't contradict other observations.