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Comment by zionic | Hacker News Reader

Does this have implications for dark matter? The whole angle there is explaining “missing mass” right?

It doesn’t. Galaxies studied were very far from Milky Way and hence much older. This discovery shows that era of massive stars ended later in evolution of universe than we’ve assumed, not that we got mass of stars wrong.

We still see younger galaxies with less massive stars not rotating as expected.

> Galaxies studied were very far from Milky Way and hence much older

You mean younger, right?

Weird English quirk when you have relativistic distances: They are older in a sense that they aren't recent. They aren't older in a sense that they've existed for a longer time. (At least in the radiation we're seeing.)

Like looking at an old photograph of a child. Both older and younger at the same time.

The research is about the distribution of stars in a galaxy, not mass that is missing or extra. Distant galaxies apparently have more massive stars than whatever widely used model says. From the article:

Stars in distant galaxies are typically more massive than those in our "local neighborhood"

I don't think so because many of the observations of the galaxys that make folks think that dark matter must be present (because the visible matter is not sufficient to make the galaxy stick together) are in the local group.

My first thought too

Funny thing about the missing mass. Papers will say "this could be explained by a dark matter Halo with this distibution". They assume it gravitationally affects regular matter the same way regular matter does. What is usually missing is 1) how dark matter interacts with dark matter 2) why it should have this particular distribution - dynamic model. Without those things, the explanation is IMHO worse than MOND because it doesnt make sense that some matter would end up with a completely different distribution. Oh and we cant actually detect it directly either, but trust us it must be there.

This is not actually missing from the models. See for instance https://www.nature.com/articles/s41550-021-01598-4

There is no reason for matter with very different interaction properties from the familiar stuff to have the same distribution.

In particular, familiar stuff has ways to dispose of kinetic energy, allowing it to clump into our stars and planets, that might be unavailable to putative dark matter, making any dark matter more diffuse.

Generally, you can start with the assumption that people working on dark matter hypotheses are not idiots. They might still be wrong, but if they are, they will be wrong in interesting and subtle ways, not obvious ones.

>> There is no reason for matter with very different interaction properties from the familiar stuff to have the same distribution.

Sure there is. It has similar interaction with regular matter. Any other properties need to be defined and shown to produce this claimed distribution as a result of a dynamic process. Anything less and we can just say dark matter is fairy dust.

"different interaction" != "similar interaction".

Apparent effort to understand what you criticize may make your criticism seem worth more.

>> Generally, you can start with the assumption that people working on dark matter hypotheses are not idiots.

Actually no I cant. When someone looks at galaxy rotation curves and is surprised they dont follow keplers laws, it activates the bozo bit in my mind.

Are there others?

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