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: 2, Funny) by Runaway1956 on Wednesday January 31, @10:30PM
Some of us know where the dark matter is. https://www.nethack.org/ [nethack.org]
Do political debates really matter? Ask Joe!
(Score: 5, Funny) by VLM on Wednesday January 31, @11:33PM (1 child)
Why this overall topic is relevant, is per Occam's razor the simplest explanation for weird radial velocity distributions is simply creationism.
If you run the simulation in reverse and it breaks "awhile ago" then there's something wrong with your simulation code (unlikely, or so we think) or your input data (unlikely, we double checked the hell out of it all) or there's some discontinuity in the past (maybe?).
I'm just stating without belief or prejudice that the state of astrophysics since the 70s is that the theory that best explains galactic rotation is "Young Earth Creationism". I'm not throwing down the authoritarianism that certain groups are right or wrong or will always be right or always be wrong, and perhaps theory will go beyond that someday in the future, but I'm just saying galactic astrophysics for the last 50 years has only one successful predictive model and its not as atheistic as some other branches of science.
Also I'm not saying "Young Earth Creationism" works better as a predictive theory for geology, or oil prospecting, or genetic research, or a crap-ton of other scientific fields. I am, however, seriously claiming "Young Earth Creationism" is currently the best predictive theory galactic astrophysicists have been able to come up with for half a century.
My impression of astrophysics, especially galactic scale stuff like this dark matter controversy, is like imagining the ancient Greeks trying to debate emacs vs vi, or theorize about what would Julius Caesar think of AMD vs Intel processor strategies circa late 2010s. Human civilization at this stage can't get beyond numerology and generally tossing stuff at the wall to see what sticks WRT astrophysics, sorry, better off ignoring the situation and come back later in a couple centuries when we MIGHT have a better chance at figuring it out.
We did a great job at the industrial revolution because civilization was at the right stage at the right time WRT math and engineering and finance to figure out stuff like, for example, steam tables and advanced steel metallurgy. But 2000s era civilization isn't ready to do galactic scale astrophysics research. We CAN fund people to F around and do numerology and make shit up, kind of like the soft-sciences of psych and sociology, but "we" can't make progress in astrophysics at this time. Maybe in a couple centuries. But for now, for better or worse, WRT galactic scale astrophysics, "Young Earth Creationism" is the theory that best matches our observations and we may as well save time and money and stick with that until we have a realistic chance at real progress in the field. Basically we've been flushing money down the toilet for the last half century. If we had just piled up the money and burned it, at least we could have roasted some marshmallows.
(Score: 1, Insightful) by Anonymous Coward on Thursday February 01, @06:49AM
oh wacky VLM is at it again
(Score: 4, Funny) by Gaaark on Wednesday January 31, @11:35PM (7 children)
It's got no dark matter, which proves dark matter exists!
What? It HAS dark matter? PROOF that dark matter exists!
It has LESS dark matter than we thought! Proof dark matter exists!
Dark matter MUST exist because GR begs for it, which means DM MUST exist...because GR NEEDS it which means it MUST exist......
Just wish we could find it. :P
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 1) by khallow on Thursday February 01, @03:00AM
(Score: 4, Interesting) by Thexalon on Thursday February 01, @04:29AM (2 children)
Any cosmologist worth their degree will tell you that dark matter is very much a placeholder, and they have little clue what it might be, they just know it makes all the equations work properly again.
My own completely speculative and damn-near-impossible-to-prove conjecture on this: Stuff that falls into a black hole gets accelerated so fast it ends up as tachyons, that wonderful hypothetical FTL matter. That stuff is theorized to behave very much like matter, except moving the other way through time, and since matter creates gravity that moves at C, it stands to reason that tachyons would be both unobservable with current equipment (because they're moving too fast), and also create gravity that moves at C. Oh, and since the way FTL makes any sense at all is that time is reversed, all that stuff gets to slide backwards in time to the Big Bang, where it creates what we would observe as a white hole, and that's where all the normal matter we can observe came from.
The only thing that stops a bad guy with a compiler is a good guy with a compiler.
(Score: 1, Interesting) by Anonymous Coward on Thursday February 01, @07:24AM (1 child)
That theory would actually work better to explain dark energy. Time-reversed gravity would push things apart.
(Score: 2) by Thexalon on Thursday February 01, @12:14PM
I used the word "conjecture" for a reason: The idea definitely doesn't rise to the level of "theory" yet, not even close.
The only thing that stops a bad guy with a compiler is a good guy with a compiler.
(Score: 2) by tangomargarine on Thursday February 01, @06:47AM (2 children)
I wonder if dark matter will be proved to not exist in my lifetime, like Einstein and that extra variable to make the universe static, or the search for Planet X because Neptune's density was different than expected so the orbital discrepancy worked itself out.
That 80+% of the universe is somehow "invisible" is just such a wild idea.
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: 2) by crafoo on Thursday February 01, @02:52PM
I don't know, I don't think it's all that wild at all. It's more likely that dark matter is real than not. We've only experienced the universe from a single physical point and in a timespan that is so short it is irrelevant in terms of astrophysics. We are instinctually wired to believe that the E&M spectrum is fundamentally prime as it is our primary sensory input into our brain.
Maybe there is something else in the universe going on and it only just barely interacts with any of the physics we know through gravitational changes.
What ever dark matter is or isn't, it is not worth arguing about, discouraging other theories, or trying to tell someone they are wrong about it. No one knows or has the authority at this point to say one way or another. The best course is, as always, to pick an avenue and provide positive work in that direction to help prove or eliminate that particular branch. All of these discussion about it at of now are absolutely worthless. It's very much similar to Catholics and Protestants arguing.
(Score: 2) by Freeman on Thursday February 01, @07:34PM
In the event that as someone posted already that including dark matter makes everything else work in general relativity. Then, it's quite plausible that the "whatever is missing" which they're calling dark matter is something. I'm also of the opinion that there's more Nobel Prizes in Physics to win.
Joshua 1:9 "Be strong and of a good courage; be not afraid, neither be thou dismayed: for the Lord thy God is with thee"
(Score: 3, Interesting) by weirsbaski on Thursday February 01, @07:12AM
IANAAP (Astro-Physicist), but there's something I've been wondering. Maybe someone can offer some insight why I'm wrong.
While a figure skater is twirling, she brings her arms in. To conserve angular momentum, this causes her rotational speed to increase. Likewise, as matter spirals in to a black hole to meet its fate, its angular speed increases. But matter can't accelerate to C (speed of light), so regardless of how close the matter gets to the black hole, there's only so much angular momentum it can provide (because it'd have to move faster than C to keep the momentum constant as it draws extremely near).
What if the galaxy's faster-than-expected rotation is frame-dragging caused by the falling matter? Ie- the matter can't accelerate far enough to keep the equations balanced, so spacetime itself absorbs some of the momentum by circling itself faster around the black hole?
Again, I'm curious but IANAAP.
(Score: 4, Interesting) by PiMuNu on Thursday February 01, @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, @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, @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, @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, @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.
(Score: 1) by lush7 on Friday February 02, @02:58AM
In a whirl pool, to the best of my understanding, things speed up as they near the center.
I haven't quite understood why it's a cosmological problem that the edge of galaxies move slower than the inside.