Astronomers Find Galaxy Made Of Mostly Dark Matter

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Astronomers believed they have identified a galaxy roughly the same size as the Milky Way about 300 million light years from Earth that they think is make of about 99.99% dark matter. This dark Galaxy the researchers have found is only one-hundredth of one percent visible matter that makes up stars and planets. Thing is, astronomers really don’t know much about dark matter beyond the fact that they are near sure it exits.

Dragonfly 44 is 99.99% unknown material according to study

The researchers found the Dragonfly 44 galaxy in 2015, and it’s so named as it was found using the Dragonfly Telephoto Array in New Mexico which was developed by astronomers from both Yale University and the University of Toronto and uses a configuration of eight telephoto lenses. While scientists haven’t quite worked out what dark matter is nor has it ever been observed, scientists believe that it makes up about 80% of the universe. The identification of something invisible was made simply by the observance of the gravity from dark matter.

While 300 million miles may seem like quite the distance it really isn’t when you consider that the Hubble Space Telescope is able to see billions of light-years into space. Problem with the Hubble is it can’t see “in the dark” like the Dragonfly Array which was designed specifically for that purpose.

Understand that Dragonfly 44 was found in the largely dark Coma Cluster and while the size of the Milky Way it only emits one percent of the light of the Milky Way.

What seemed interesting to Pieter van Dokkum of Yale University and his colleagues is that there were far too few stars to hold the galaxy together and reasoned that something else’s gravity was doing the job, you guessed it…dark matter.

“They are so diffuse, these galaxies, so tenuous, that they would be ripped apart. There just wasn’t enough mass to hold them together,” van Dokkum said.

We have to go to Mauna Kea

The turned next to the W. M. Keck Observatory in Mauna Kea, Hawaii, which is home to one of the world’s most powerful earthbound telescopes. Specifically, they used the Deep Imaging Multi-Object Spectrograph (DEIMOS) on the Keck II telescope to study the movement of the stars to determine how much dark matter must surely be there.

“Motions of the stars tell you how much matter there is,” van Dokkum said in a statement. “They don’t care what form the matter is, they just tell you that it’s there. In the Dragonfly galaxy stars move very fast. So there was a huge discrepancy: using Keck Observatory, we found many times more mass indicated by the motions of the stars, than there is mass in the stars themselves.”

“This has big implications for the study of dark matter,” he continued. “It helps to have objects that are almost entirely made of dark matter so we don’t get confused by stars and all the other things that galaxies have. The only such galaxies we had to study before were tiny. This finding opens up a whole new class of massive objects that we can study.”

The researchers work was not done there and they stayed in Hawaii to use the Gemini Observatory where they turned to the Gemini Multi-Object Spectrometer (GMOS) in order to take a color “photo” of this strange galaxy. Ultimately, it’s far too far to visibly observe dark matter but the team hopes that someday they will find a similar galaxy much closer to Earth.

“Ultimately what we really want to learn is what dark matter is,” van Dokkum said. “The race is on to find massive dark galaxies that are even closer to us than Dragonfly 44, so we can look for feeble signals that may reveal a dark matter particle.”

The teams work was published yesterday in the journal Astrophysical Journal Letters.







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