This Galaxy Has Almost No Dark MatterAnd Scientists Are Baffled

[Judi Lynn]

If astronomers really have found an "undark" galaxy, it’s a strong clue that dark matter is real.



Galaxies litter the cosmos in a picture of the deep universe taken by the Hubble
Space Telescope. A closer look at a galaxy 65 million light-years away suggests
that it is missing a fundamental part of the usual galactic recipe: the mysterious
substance known as dark matter.
PHOTOGRAPH COURTESY NASA, ESA AND THE HST FRONTIER FIELDS TEA

By Nadia Drake
PUBLISHED MARCH 28, 2018

An unusual galaxy far, far away is stumping astronomers not because of what’s there, but because of what’s missing.

What is this thing?

About 65 million light-years away, the galaxy called NGC1052-DF2 is dim and diffuse, coming in at about one two-hundredths the mass of our Milky Way.

Normally, not all of a galaxy’s mass is visible. In addition to a mix of ordinary matter—like stars and planets and manatees—galaxies are expected to contain dark matter, an invisible substance that makes up most of the mass in the universe. Although we can’t directly observe it, we know dark matter is there because we can see how its gravity affects ordinary matter.

Based on the ratio in other galaxies, an isolated galaxy like NGC1052-DF2 should have about a hundred times more dark matter than ordinary matter. But this one appears to have … almost none, scientists report today in Nature.

More:
https://news.nationalgeographic.com/2018/03/dark-matter-galaxy-gravity-dragonfly-physics-space-science/

[Judi Lynn]

1. (Older article) Canadian astronomer discovers Milky Way-size galaxy that's 99.99% dark matter

Dragonfly 44 is almost entirely invisible, University of Toronto prof and UBC astronomy grad tells Metro, but it has the mass of our own galaxy.



COURTESY PIETER VAN DOKKUM

Dragonfly 44 galaxy was initially spotted in the Coma constellation using Dragonfly Telephoto Array,
a multi-lens telescope invented by University of Toronto’s Roberto Abraham and Yale’s
Pieter van Dokkum.


By: David P. Ball Metro Published on Thu Sep 01 2016

Many a discovery or idea was hatched over a pint of ale: DNA, the existence of carbon dioxide, Pet Rocks among them.

But a “beery” conversation four years ago has led two astronomers, including a Canadian observational cosmologist, to stumble upon a gigantic galaxy that’s as heavy as our own — but has almost no visible stars.

It’s named “Dragonfly 44,” and University of Toronto’s Roberto Abraham estimates it is made of 99.99 per cent dark matter, a mysterious cosmic material only observable through its gravitational effects.

“This is a really massive galaxy, about same mass as our Milky Way, but it’s almost pure dark matter,” Abraham, who completed an astronomy degree at the University of B.C., told Metro in a phone interview. “Dragonfly 44 is a different type of galaxy.

More:
http://www.metronews.ca/news/vancouver/2016/09/01/canadian-prof-discovers-dark-matter-milky-way-size-galaxy.html

[Salviati]

2. Very cool

Though this poses a lot of new questions about dark matter, it seems to bolster it in the sense that it seems to make explaining both "regular" galaxies and these two difficult to do with any sort of MOND theory.