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https://phys.org/news/2024-01-stars-slowly-milky-edge-galaxy.html
By clocking the speed of stars throughout the Milky Way galaxy, MIT physicists have found that stars further out in the galactic disk are traveling more slowly than expected compared to stars that are closer to the galaxy's center. The findings raise a surprising possibility: The Milky Way's gravitational core may be lighter in mass, and contain less dark matter, than previously thought.
The new results are based on the team's analysis of data taken by the Gaia and APOGEE instruments. Gaia is an orbiting space telescope that tracks the precise location, distance, and motion of more than 1 billion stars throughout the Milky Way galaxy, while APOGEE is a ground-based survey.
The physicists analyzed Gaia's measurements of more than 33,000 stars, including some of the farthest stars in the galaxy, and determined each star's "circular velocity," or how fast a star is circling in the galactic disk, given the star's distance from the galaxy's center.
[...] The team translated the new rotation curve into a distribution of dark matter that could explain the outer stars' slow-down, and found the resulting map produced a lighter galactic core than expected. That is, the center of the Milky Way may be less dense, with less dark matter, than scientists have thought.
(Score: 4, Interesting) by PiMuNu on Thursday February 01 2024, @11:48AM (4 children)
The fundamental premise of the fine article is completely wrong and not consistent with the originating journal article. Namely,
> found the resulting map produced a lighter galactic core than expected.
If we view the preprint:
https://arxiv.org/abs/2303.12838 [arxiv.org]
Figure 8 shows that the data is entirely consistent with all previous studies except for one early study where errors were large (Huang et al 2016); all other measurements deviate statistically significantly from the Huang et al paper. Indeed the conclusions explicitly state:
"Our circular velocity curve shows good agreement with other recent studies that utilize Gaia DR3 astrometry measurements"
Further the model fits with theoretical possibility. See for example figure 7 (left) where the data is fit with a so-called "Einasto" profile.
https://en.wikipedia.org/wiki/Einasto_profile [wikipedia.org]
The authors point out further in the conclusions:
"We point out that a DM density core for a Milky Way-like galaxy can form principally in simulations (Lazar et al. 2020). The previous dynamic study of the galactic bulge by Portail et al. (2017) also shows evidence for a shallow cusp or core DM profile."
DM deniers will no doubt point out that the Einasto profile is "just" a fit and they are correct. And they will complain, no doubt, that we have no model to predict the mass density profile of the universe from first principles, which is also correct. It does not follow that Dark Matter is a wrong theory.
(Score: 2) by loonycyborg on Thursday February 01 2024, @06:06PM (3 children)
What does follow is that the idea of dark matter is non-falsifiable. It's possible to fit any possible observation with appropriately constructed dark matter distribution. So what is the theoretical benefit of even considering dark matter at this point?
(Score: 2) by hendrikboom on Thursday February 01 2024, @06:43PM (1 child)
What is the theoretical bebefit? We might see patterns that lead to a more constrained theory.
Just as epicycles (which can model any periodic motion) were replace by ellipses, later explained by Newton's Principis.
(Score: 3, Insightful) by loonycyborg on Thursday February 01 2024, @08:24PM
You don't need to assume dark matter to look for patterns. Actually observed motion is enough. If relativistic effects in Mercury's motion were discovered before relativity theory itself was would explaining it with dark matter be of any help for purpose of actually discovering said theory? I don't think so.
(Score: 2) by PiMuNu on Monday February 05 2024, @12:23PM
> the idea of dark matter is non-falsifiable
Also note the idea of matter is non-falsifiable. It's possible to fit any possible observation with appropriately constructed matter distribution.