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John Timmer authored an Ars Technica story reporting on research published on 15 March 2017, which appears to show that as we look farther back in time, galaxies had less dark matter.
From the Ars Technica article:
One of the earliest indications of the existence of dark matter came from an examination of the rotation of nearby galaxies. The study showed that stars orbit the galaxy at speeds that indicate there's more mass there than the visible matter would indicate. Now, researchers have taken this analysis back in time, to a period when the Universe was only a couple billion years old, and the ancestors of today's large galaxies were forming stars at a rapid clip.
Oddly, the researchers find no need for dark matter to explain the rotation of these early galaxies. While there are a number of plausible explanations for dark matter's absence at this early stage of galaxy formation, it does suggest our models of the early Universe could use some refining.
[...]
In fact, it's thought that dark matter catalyzed the formation of most galaxies. Simulations suggest that gravity draws dark matter into a web of filaments, and galaxy formation occurs primarily at the sites where these filaments meet. This explains why most galaxies we see today exist in clusters. Given this model, it's simple to assume that the condensation of dark matter into galactic disks preceded or ran in parallel with the production of the visible portion of the galaxies.
The new data would suggest otherwise. The authors took advantage of existing survey data to identify six large early galaxies that don't appear to have recently undergone a merger and have an abundance of stars. They are thought to be the precursors of galaxies such as our own and are already big enough to show a clean rotation curve. Their rotation was then measured using the red and blue shifts of light emitted by hydrogen, based on observations with the Very Large Telescope.
[...]
The authors of the new paper see a number of possible explanations. One is that the early galaxies are very gas-rich, and these clouds of gas can experience local instabilities or collisions. This could cause the regular matter in the inner galaxy to compact, resulting in a normal-matter-dominated portion of the galaxy. The other possibility is that rather than forming the seeds of galaxies, dark matter starts off rather diffuse and takes time to form a disk-like structure that mirrors that of the visible galaxy. Either of these would explain the apparent matter dominance.
This doesn't turn current theories of dark matter on their heads, but it may provide avenues for research in better understanding both dark matter and large-scale cosmic structures.
Referenced Paper: Strongly baryon-dominated disk galaxies at the peak of galaxyformation ten billion years ago (Nature, 2017. DOI: 10.1038/nature21685).
(Score: 1) by DeKO on Saturday March 18 2017, @01:33PM (3 children)
First tell me your credentials, Mr Armchair Astrophysicist. Since you're so sure of it, show us your modified General Relativity that explains the observations. You have to be literally smarter than Einstein to be claiming that, so please show us how you're reaching that conclusion.
(Score: 2) by Gaaark on Saturday March 18 2017, @09:38PM (2 children)
My credentials are: i believe the data, not the fantasy.
From an actual physicist:
"In 1915 Einstein finished general relativity and this theory has been successful in regimes where the acceleration is high (such is in the inner Solar system and close-orbiting binary stars. Then in 1933 (by Fritz Zwicky) and in 1980 (by Vera Rubin) it was found that galaxies were orbiting so fast at their low-acceleration edges that, if they had any decency at all, they should explode centrifugally. Yet they don't: they generally persist in sensible bound/round shapes.
This means that most of the observed cosmos, the bit with a low acceleration, does not agree with general relativity. The theory has been hugely falsified, but tell that to a mainstream physicist at a conference (I have done) and you'll be pigeon-holed in a category somewhere below holocaust denier and they'll walk away in disgust. Speaking objectively, given GR's failure with 90% of the data, you can either claim that general relativity is wrong, and invent a new theory (for example I have suggested MiHsC, which reduces the outward centrifugal force in galaxies) or you can claim that there is a huge amount of invisible matter holding the galaxy together by gravity: dark matter."
https://physicsfromtheedge.blogspot.ca/search?q=Dark+matter [blogspot.ca]
The amount of dark matter you have to add to each galaxy you observe is random and non-predictive and non-predictable: you need to add 100 dark matters to this galaxy to make the data work, but for THIS galaxy, you need to add 246.89754 dark matters to make the data work.
If you have to add imaginary stuff in a non-predictable way JUST in order to make the data work, SOMETHING IS WRONG!!!!
Einstein solved part of the problem, but even HE realised something was wrong and tried unsuccessfully to make things right in his later years.
Just because Einstein is almost a God, doesn't mean he couldn't make mistakes: you need to keep questioning, just as Einstein himself did.
The important thing is not to stop questioning. Curiosity has its own reason for existing.
---Albert Einstein
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 3, Disagree) by maxwell demon on Sunday March 19 2017, @08:19AM (1 child)
You mean, like the introduction of the neutrino JUST to make the conservation laws work in the beta decay? Well, that in the end turned out to be RIGHT, didn't it?
Oh, and to quote Terry Pratchett: Multiple exclamation marks are a sure sign of an insane mind.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by Gaaark on Sunday March 19 2017, @01:32PM
You mean, like the introduction of quantised inertia just might be what that 'dark matter's really is?
'Dark matter' solves nothing, but hopefully it will lead the bright, inquisitive and intelligent to the RIGHT answer.
Homer J Simpson said "D'oh!"
!!!
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---