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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: 4, Interesting) by stormwyrm on Sunday March 19 2017, @12:40AM (1 child)
Numquam ponenda est pluralitas sine necessitate.
(Score: 2) by requerdanos on Sunday March 19 2017, @12:57AM
No one took phlogiston theory seriously after Lavoisier showed how oxidation worked
Well, even Joseph Priestley, discoverer of the key ingredient (oxygen) that led Lavoisier to his breakthroughs in oxidation, took phlogiston seriously enough to call oxygen 'pure air' and "believed his 'pure air' enhanced respiration and caused candles to burn longer because it was free of phlogiston.... [calling] the gas that he obtained from decomposing mercury calx 'dephlogisticated air.'" [https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/lavoisier.html [acs.org]]