A Ghostly Galaxy Lacking Dark Matter (image)

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

For example, Ostriker has proposed a theory that does predict certain galaxies to have extremely low amounts of dark matter, in which dark matter particles are more than 10 times lighter than WIMPs.

Many galaxies in the universe, included our own, have an estimate of roughly 30 times more dark matter compared to the normal matter as we know it.

Although it has never been directly observed, scientists are confident that this elusive material exists because of the gravitational effects it appears to have on astronomical objects.

Based on this understanding, the team studying DF2 thought they had a pretty good idea how much dark matter it contained.

Van Dokkum plans to use Keck to search for more galaxies like NGC 1052-DF2. "It's so rare, particularly these days after so many years of Hubble, that you get an image of something and say, 'I've never seen that before.' This thing is astonishing, a huge blob that you can look through". It's a literally a transparent galaxy. The latest observations focused on an ultra-diffuse galaxy - ghostly galaxies that are large but have hardly any stars - called NGC 1052-DF2. When he and his team went to measure the speed of star clusters in the galaxy, which should have been moving about 67,000 miles per hour, they found the clusters were moving a sluggish 18,000 miles per hour instead.

"Finding a galaxy without dark matter is an oxymoron", says van Dokkum. These galaxies are more similar to the size of the known spiral galaxies but have less number of stars.

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

If you look around and out at the stars, what you see - and what astronomers can see using complex telescopes - accounts for just five per cent of what is contained in the universe.

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In recent decades, astronomers have believed that invisible, mysterious dark matter is the dominant aspect of any galaxy. NGC 1052-DF2 is considered to be some 10 billion years old.

"We thought all galaxies were made up of stars, gas and dark matter mixed together, but with dark matter always dominating", says Prof.

If NGC 1052-DF2 behaves as the new research describes, he wrote, that presents challenges to both explanations for the missing mass in the universe. Despite it being so elusive, its effects have been identified through several different methods, and there is very strong evidence to suggest that dark matter does exist.

Lying some 63 million light-years from the Milky Way, the elliptical galaxy NGC1052-DF2 seems to be completely made up of normal matter, defying all expectations. Yet in this odd galaxy, the projected signatures of these exotic effects are not seen. This would allow the gas to form stars away from clumps of dark matter.

It looked like a diffuse blob sprinkled with very compact star clusters. Already have suspicions of three, whom they will notice better.

"It is conventionally believed to be an integral part of all galaxies, the glue that holds them together and the underlying scaffolding on which they are built", said co-author Allison Merritt from the Max Planck Institute for Astronomy, in Germany. Thus, this leaves no speculative room for the existence of dark matter.

Stacy McGaugh, an astrophysicist at Case Western Reserve University in OH who has worked on both dark matter and MOND and did not work on the paper, disagreed with the idea that this galaxy refutes MOND or bolsters the case for dark matter. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope.



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