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by privong·7y ago·view on hn ↗
It's worth nothing that the authors of the original NGC1052-DF4 article claiming little to no dark matter have disputed the conclusions of the Trujillo+2019 (i.e., the paper the phys.org article is based on): https://ui.adsabs.harvard.edu/abs/2019RNAAS...3b..29V/abstra...

I think it's safe to say that the jury is still out on this one.

Edit: One reason this is difficult is that you can think of galaxies as having two major contributions to the line-of sight velocity we observe from earth: expansion of the Universe ("Hubble flow") and "peculiar" velocity (motion due to the local gravitational field in which the galaxy lives). The latter velocities are typically a few hundred km/s (or later if the galaxy is in a cluster). NGC 1052 has an observed recession velocity of 1510 km/s (https://ned.ipac.caltech.edu/byname?objname=NGC%201052&hcons...). Assuming a peculiar velocity of 300 km/s, that means the peculiar velocity is on the order of 20% of the total velocity. But we don't know what component of the peculiar velocity is along the line of sight or whether it's positive or negative. So with these numbers it's "hubble flow" velocity could be from 1200 km/s to 1800 km/s. If you naive plug those two recession velocities into a cosmology model (e.g., the latest model derived from Planck observations) the distance range you get is 17.3-26.1 Mpc, or a ~40% uncertainty. So we cannot rely just on the Universe's measured expansion to get a sufficiently reliable distance estimate.

So one must use other techniques to measure distances. They each have their own advantages and disadvantages. In general most distance estimates are build on the "Cosmic distance ladder" and accumulate uncertainty as you move up the ladder: https://en.wikipedia.org/wiki/Cosmic_distance_ladder

1 comments
What I don't understand here is: You have a galaxy where mass doesn't add up. There are rivaling explanations, one being that you estimated the distance wrong, the other that there is no Dark Matter. Isn't the first one the more likely one you should investigate?
> There are rivaling explanations, one being that you estimated the distance wrong, the other that there is no Dark Matter. Isn't the first one the more likely one you should investigate?

If you look back at the original paper claiming the discovery of the dark matter free galaxy, they do explore several different ways of estimating the distance and argue that they're consistent and imply the more distant value. So that's something they had considered and attempted to cross-check between different distance indicators. Later came the Trujillo paper saying essentially, hey you didn't consider "X" which argues that the galaxy is closer. The authors of the original paper then published a Research Note (that I'd liked in my original post) saying that "X" doesn't agree with the other data.

So people did consider distance errors before claiming the absence of dark matter. But getting accurate galaxy distances Is Hard and there are multiple ways to do it. The original paper considered the distance estimates they could think of and they were essentially consistent. So they did investigate that first.