Elusive Dwarf Galaxy Found Orbiting Our Milky Way

It's the fourth largest circling our Milky Way, astronomers say.

17/04/2016 5:38 AM AEST | Updated 18/04/2016 9:59 PM AEST
Loop Images via Getty Images
Our Milky Way galaxy, as seen from the French island of Reunion in the Indian Ocean.  There are about four dozen galaxies that we know of which circle it.

We have a newfound galactic neighbor.

Astronomers say they've recently discovered an elusive dwarf galaxy orbiting our own Milky Way. There are about four dozen galaxies that we know of circling our own, New Scientist reported.

Our newly named neighbor, Crater 2, is the fourth largest, according to a paper published in the Monthly Notices of the Royal Astronomical Society on Wednesday. (The biggest satellite galaxy of the Milky Way is the Large Magellanic Cloud, nearly 200,000 light years away.)

Crater 2 sits some 400,000 light years away, said paper co-author Dr. Vasily Belokurov, an astrophysicist at the University of Cambridge's Institute of Astronomy. 

"This is indeed a very rare discovery," Belokurov told The Huffington Post. "A galaxy like Crater 2 is a sort of invisible object."

It seems to be aligned with a handful of other astronomically nearby objects, which may be teaching us how our group of galaxies formed.

Researchers at Cambridge’s Institute of Astronomy discovered the dwarf galaxy in January when they used a computer algorithm to pinpoint where there might be a significant clustering of stars in images taken of space beyond our Milky Way.

They identified a never-before-seen cluster of stars -- and concluded that this was evidence of a dwarf galaxy.

Analysis of the data revealed that Crater 2 is roughly the same age as the universe, and its angular size is at least twice that of our own moon.

V. Belokurov, S. Koposov & G. Torrealba, IoA Cambridge, VST ATLAS, Simon C. Smith
An artist's illustration of what Crater 2 would look like if it was a few thousand times more luminous than actually it is. The Moon is shown to scale for comparison.

"We have found many similar objects in the last 10 years, but never such a large beast," Belokurov said. "It is orders of magnitude less luminous compared to most objects of similar size. It is extremely diffuse. We believe it was born that fluffy. But why, we do not yet know."

Dr. Jay Pasachoff, an astronomer at Williams College in Massachusetts, who was not involved in the new discovery, said that to find such a faint and diffuse galaxy is a nice piece of research.

"It is always fun to discover a nearby neighbor about which we didn't know before, and the dwarf galaxy Crater 2 falls into that category," said the co-author of The Cosmos. "It seems to be aligned with a handful of other astronomically nearby objects, which may be teaching us how our group of galaxies formed."

V. Belokurov, S. Koposov (IoA, Cambridge). Photo: Y. Beletsky (Carnegie Observatories)
The Large Magellanic Cloud and other orbiting galaxies are seen at the Paranal Observatory in the Atacama Desert in Chile.

The same research team discovered a treasure trove of nine new dwarf galaxies orbiting our Milky Way last year.

At the time, Dr. Sergey Koposov of Cambridge’s Institute of Astronomy, who led that previous study, said in a statement, "The discovery of so many satellites in such a small area of the sky was completely unexpected ... I could not believe my eyes."

Until 10 years ago, only a dozen dwarf satellite galaxies had been identified around the Milky Way. But Belokurov said that he and his colleagues have since found several tens more.

"In the last two years alone, the number of known Milky Way satellite galaxies has doubled, largely thanks to the Dark Energy Camera on the Blanco 4 meter telescope in Chile," Dr. Evan Kirby, assistant professor at Caltech Department of Astronomy & Astrophysics, who was not involved in the research, told HuffPost.

"These galaxies are intense concentrations of dark matter," he added. "If there's a place in the universe where we can look to learn about dark matter, it's dwarf galaxies. How is it distributed? What is it made of?  Future observations, especially spectroscopy, will help answer those questions."

Dwarf galaxies are the most numerous type of galaxy in the universe.

"While we cannot say for sure this particular dwarf is the oldest in the universe, dwarf galaxies in general are," Belokurov said.

"They are the first systems to be assembled, so they contain the information about the gas densities and the efficiencies of turning that gas into stars," he added. "As we have seen with the follow-up studies of similar objects, many stars in them look like the direct descendants of the very first stars in the universe."

Also on HuffPost
Stunning Milky Way

More On This Topic