Ghostly galaxy without dark matter stuns astronomers
30 Марта, 2018, 00:45 | Author: Tracy Craig
When observing a collection of galaxies called the NGC 1052 group, the array spotted an object that had shown up in other surveys of that region of the sky.
In view of the proportion in different galaxies, a confined galaxy such as NGC1052-DF2 ought to have around a hundred times more dark matter than ordinary matter.
"I spent an hour just staring at this image", lead researcher Pieter van Dokkum of Yale University says as he recalls first seeing the Hubble image of NGC 1052-DF2.
Based on these data the team discovered that the newly discovered galaxy is larger than the Milky Way, but contains about 250 times fewer stars, leading it to be classified as an ultra diffuse galaxy. After that everything else happens: gas falls into the dark matter halos, the gas turns into stars, they slowly build up, then you end up with galaxies like the Milky Way. But physicists contacted by Live Science to discuss this paper mostly said the finding made dark matter (already the dominant explanation for the universe's weirdness) look a lot more likely. "This result also suggests that there may be more than one way to form a galaxy".
Up to now, the analysis of galaxies has shown a fairly tight ratio of dark to ordinary matter.
"There is no theory that predicts these types of galaxies - how you actually go about forming one of these things is completely unknown", added co-author Allison Merritt from Yale University and the Max Planck Institute for Astronomy, Germany. For instance, dwarf galaxies have 400 times more dark matter than regular matter, whereas a galaxy like the Milky Way has about 30 times less.
There have been several ideas that have floated around regarding the true nature of dark matter, and discoveries like this will only push astronomers to unlocking its secrets.
Instead, DF2 is a rare ultra-diffuse galaxy. That would only make sense if there was no dark matter at all acting on them, a finding confirmed when the researchers subsequently calculated the mass of the galaxy.
This is weird-and it could change what astrophysicists think dark matter is, in addition to upending their understanding of how galaxies form, says van Dokkum. Or would the current appearance of the galaxy be the result of a cataclysmic event within it? When van Dokkum and his team found NGC 1052-DF2, they expected to see something similar. Yet in this unusual galaxy, the projected signatures of these exotic effects are not seen.
Bottom line: The galaxy NGC 1052-DF2 appears to have no dark matter.
These ideas, however, still do not explain how this galaxy formed. That stellar sparseness means it does not look much like a typical spiral galaxy, but rather a loosely connected, ghostly blob of star-pocked gas and dust. They can't agree on what it's made of, how much a single particle weighs, or the best way to construct a Play-Doh diorama of it.
NGC 1052-DF2 is missing its dark matter. "In those theories, every galaxy should show a dark matter signature, as it's not due to dark matter at all but due to the laws of physics", van Dokkum explained.
We don't really know what dark matter is and why it exists... or why it doesn't. Because there's some regular issue right here, any kind of variation of customized gravity would certainly have that issue generate dark-matter-like impacts. Future observatories under construction, such as the European Extremely Large Telescope in Chile's Atacama Desert, or NASA's James Webb Space Telescope, should be able to take such measurements.
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