Barely-visible galaxy made from 99.9pc dark matter found

26 Aug 2016

It took the world’s most powerful telescopes, but astronomers have just about managed to spot a distant galaxy that is almost entirely made up of dark matter.

While astronomers continue to try and figure out the workings of the mysterious phenomenon that is dark matter, spotting something in the universe that defies what we know about how galaxies operate is usually a sign that it’s present there.

Case in point, the recent discovery of a distant, faint galaxy referred to as Dragonfly 44 that appears to be almost entirely made up of dark matter.

Publishing its findings in Astrophysical Journal Letters, a team of astronomers from Yale University revealed that, despite being overlooked for over a year, Dragonfly 44 was finally observed using two of the world’s most powerful telescopes: the W.M. Keck Observatory and the Gemini North telescope.

What became instantly noticeable about the galaxy was that it was almost entirely dark with only a very small number of stars, meaning something strange was going on.

“Very soon after its discovery, we realised this galaxy had to be more than meets the eye. It has so few stars that it would quickly be ripped apart unless something was holding it together,” said Yale University astronomer Pieter van Dokkum.

Dragonfly 44 dark matter

The original image taken of the galaxy (left) compared to a long exposure with the Gemini telescope (right). Image via Pieter van Dokkum, Roberto Abraham, Gemini, Sloan Digital Sky Survey

No idea how it formed

Of the two tredecillion kilogram mass of the galaxy – or 1trn-times the mass of our sun – it’s estimated that 99.99pc of its mass is made from dark matter, the other 0.01pc being comprised of stars and ‘normal’ matter.

While galaxies almost entirely made of dark matter are not new in the field of astronomy, Dragonfly 44 is unprecedented simply because of its scale, with a mass 10,000-times that of anything discovered before.

“We have no idea how galaxies like Dragonfly 44 could have formed,” said co-author of the paper, Roberto Abraham.

“The Gemini data shows that a relatively large fraction of the stars is in the form of very compact clusters, and that is probably an important clue. But at the moment we’re just guessing.”

Distant galaxy image via Shutterstock

Colm Gorey was a senior journalist with Silicon Republic