I Rotation curve with neutral hydrogen and dark matter

[Ranku]

Flat rotation curve in galaxies is determined by observing neutral hydrogen which is co-distributed with dark matter. What is the rotation curve profile of neutral hydrogen in galaxies where there is less dark matter?

 

[mathman]

How is neutral hydrogen observed?

 

[Ranku]

How is neutral hydrogen observed?

Through 21-centimetre radio emission arising out of collision between neutral hydrogen atoms.

 

[stefan r]

Keplerian.

 

[Ranku]

Keplerian.

So is the flat rotation curve only due to the presence of more matter in the form of dark matter, or is it also due to some unexplained property of dark matter.

 

[sophiecentaur]

So is the flat rotation curve only due to the presence of more matter in the form of dark matter, or is it also due to some unexplained property of dark matter.

The disc structure is very common at all scales of rotating groups of objects in space. From what I understand, dark matter is not needed to explain small scale phenomena (Solar System). Is it needed for galactic rotation explanation?

 

[Ranku]

The disc structure is very common at all scales of rotating groups of objects in space. From what I understand, dark matter is not needed to explain small scale phenomena (Solar System). Is it needed for galactic rotation explanation?

Velocity dispersion in outer regions of galaxies are higher than expected, indicating presence of more matter than the visible matter, which are mostly concentrated toward the centre.

 

[Janus]

The disc structure is very common at all scales of rotating groups of objects in space. From what I understand, dark matter is not needed to explain small scale phenomena (Solar System). Is it needed for galactic rotation explanation?

The solar system as a whole has a much higher density than the galactic disk in terms of baryonic matter. So even though the density of
DM is roughly the same, the ratio of baryonic to dark matter in the solar system is extremely high compared to the disk as whole. Thus in the solar system, baryonic matter dominates the orbital dynamics, while in the disk as a whole, DM contributes to a larger percentage of the gravitational interaction.