"Titanic galaxy cluster collision in the early universe challenges standard cosmology"

[RedshiftDrift]

https://phys.org/news/2023-09-titanic-galaxy-cluster-collision-early.html
by Elena Asencio, Indranil Banik, and Pavel Kroupa, of course.

The open access paper.

[RedshiftDrift]

"Three critical tests alone in this year 2024 find dark matter and the LCDM model to be incorrect"
by Pavel Kroupa and Eda Gjergo

[LifeIsStrange]

Gaia measurements are only robust at mid distance. Moreover even if we were to assume they were robust enough, this data alone is useless if you don't model properly the shape and radial velocities of the Milky Way halo (Cf H3 study I sent you before)
We should get a clearer picture with ongoing spectroscopic surveys.
While Gaia data is hard to use to assess the galactic rotation of the Milky Way and its mass, it can still derive robust conclusions via other tests, e.g. Wide binaries accelerations, on that topic the discrepancy between banik result and Chae are completely dissonant and the research is a mess, I don't know what to conclude from it but it's likely GAIA DR4 will give us a definite answer.

[mikehelland]

Mid distance?

What's the motion of stars in other galaxies based on?

.

[LifeIsStrange]

I serendipitously stumbled upon this paragraph

Gaia DR3 data, after accounting for statistical corrections, indicates a distance of 4.1+0.3 −0.2 kpc.

If, however, the remnant’s distance was somehow actually ∼ 4 kpc like that of CI Cam, then its angular diameter of 2.5◦ ×3.0◦ would imply unlikely dimensions of 180 pc × 215 pc ranking it as perhaps the largest and oldest Galactic SNR known despite its bright [O III] filaments indicating relatively high shock velocities.

https://www.prophy.science/article/178403947/
Which is an example that GAIA has high uncertainty past (and even below IIRC) 1 kiloparsec.

The motion of stars in distant (not local group) galaxies are in most cases, if I understand correctly, not resolved (unless exceptional gravitational lens maybe of star cluster)
The mass, metallicity and rotation curve of the galaxy are inferred from the total galactic emission which supposedly work despite many stars being effectively dust obscured.

[mikehelland]

Just to clarify.... Are you saying we know the movement of stars in other galaxies better than we know them in the Milky Way?

[LifeIsStrange]

I believe we have no idea of the motion of individual stars in distant galaxies beyond the local group.
I mean except maybe for some giant stars like supernovaes, of which maybe e.g. via asteroseismology and spectroscopy some inferences, about their rotation, radial velocities and maybe astrometry might be possible, with low accuracy.