Cosmology Views

Analyzing a Galaxy Halo

This story describes an attempt to analyze one galaxy's halo.

A fast radio burst from a distant galaxy passed through the halo of an intervening galaxy.

When checking the polarization of that radio burst,  conclusions can be drawn about the halo contents.

This is the first galaxy providing this combination of two galaxies in line, for this analysis.

Among these conclusions:

galactic halo reveals a surprisingly quiescent halo with very low density and weak magnetic field

 The researchers calculated that the density of the halo gas must be less than a tenth of an atom per cubic centimeter (equivalent to several hundred atoms in a volume the size of a child’s balloon).

The density constraints also limit the possibility of turbulence or clouds of cool gas within the halo (“cool” being a relative term, referring here to temperatures around 10,000 Kelvin, versus the hot halo gas at around 1 million Kelvin). “One favored model is that halos are pervaded by clouds of clumpy gas. We find no evidence for these clouds whatsoever,” Prochaska said.

The final conclusion is quite sparse:
“This galaxy may be special,” Prochaska said. “We will need to use FRBs to study tens or hundreds of galaxies over a range of masses and ages to assess the full population.”

my conclusion:

The results do not match the 'favored model.'

This was the initial assumption:
Although this hot, diffuse gas makes up more of a galaxy's mass than stars do, it is nearly impossible to see.
A galactic halo contains both dark matter and ordinary (“baryonic”) matter, which is expected to be mostly hot ionized gas.

Perhaps these assumptions are wrong.
The assumed 'hot ionized gas' is plasma but almost none was found.

The halo is also assumed to have dark matter because gravity is always assumed to be the single critical factor in a galaxy.
However it is interesting what can be learned from analyzing electromagnetic radiation.

I added this comment:

After posting I realized I needed this additional conclusion:

If they found what amounts to a diffused number of atoms what is the difference between finding that and concluding they found the  intervening intergalactic medium with no extended halo?