The first galaxy was discovered without dark matter

30 March, 2018, 00:44 | Author: Grady Montgomery
  • Galaxy without any dark matter baffles astronomers

Astrophysicists have come up with two main solutions to this problem.

"We thought all galaxies were made up of stars, gas and dark matter mixed together, but with dark matter always dominating", said Prof. "What we found is that there is no dark matter at all".

"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. They then used the W.M. Keck Observatory in Hawaii to measure the motions of 10 giant groupings of stars called globular clusters in the galaxy. The researchers then set about measuring the movements of the clusters as a way to estimate the galaxy's total mass.

The galaxy was discovered using the Dragonfly Telephoto Array, a telescope in New Mexico that's custom-made to seek out these elusive targets.

Dark matter and dark energy comprise the rest, and scientists have yet to directly observe either.

On the off chance that astronomers truly have discovered an "undark" galaxy, it's a solid piece of information that dark matter is genuine.

The thing about dark matter, or whatever's causing outer space to move so weirdly, is that it's predictably distributed throughout the universe. Those expected speeds factor in the existence of dark matter and its gravitational effects, but because the scientists believe all the gravity present in the galaxy is accounted for by the mass of the stars, there must be no (or at least very, very little) dark matter present there. 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. Gemini revealed that the galaxy does not show signs of an interaction with another galaxy.

"In other words, no dark matter, no galaxy", says National Geographic.

About a year ago, University of Waterloo researchers captured a composite image that strongly supports the existence of dark matter. In fact, it's now thought that galaxies wouldn't even form it if wasn't for dark matter; that it's dark matter that keeps the normal matter together as the galaxy coalesces, allowing the normal matter to gather into the forms we see it in. However you wouldn't expect that galaxy to be as big as this object (it's nearly the size of the Milky Way), and you'd also expect to see some other remnants around from the merger event.

Dark matter does not emit electromagnetic radiation, and remains immune to direct observation. And over time, those clumps attracted the gas with their gravity. Another idea is that it formed from matter spewed out by quasars. It was made up of thoroughly normal matter. His stars are enough to explain his whole mass, and there seems to be no extra space for dark matter, "he added". "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. "That doesn't make it wrong, just really weird". So the enigma of NGC 1052-DF2, may not be an enigma for long. Sure, MOND doesn't easily explain a galaxy behaving as if there is no missing mass. Galaxies like the Milky Way have some 30 times more dark matter than normal matter.

"I don't find that [point of view] at all compelling", Bauer said. "This result also suggests that there may be more than one way to form a galaxy". "It's very hard to argue against the data", says Geha. The team are now turning to look at other ultra-diffuse galaxies to see whether any others are similarly deficient in dark matter. One idea suggests it's a result of a galaxy merger, and that the gas concentrated after being ejected. "So, this is at the hairy edge of credible".

Instead, DF2 is a rare ultra-diffuse galaxy.



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