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Stony Brook deep-space hunter discovers ultra dark galaxies far, far away

This image was made from the Subaru Telescope

This image was made from the Subaru Telescope at the National Astronomical Observatory of Japan. A small region of 6 x 6 arcmin is cut out from large Coma Cluster images. Yellow circles show two of the 47 dark galaxies discovered last year, and green circles are the ones discovered in this new study. Credit: NAOJ

A vast community of ultra-dark galaxies that are new to science have been discovered by a Stony Brook University deep-space hunter who searched the cosmos millions of light-years away to find them.

All told, Jin Koda and collaborators at the National Astronomical Observatory of Japan found 854 new galaxies in the Coma Cluster, a region in deep space 330 light-years from Earth. One light-year is equivalent to nearly 6 trillion miles.

"We call them dark galaxies because they are very faint and are characterized by so-called dark matter," said Koda, an assistant professor in the department of astronomy and physics and the project's lead investigator.

He describes each of the newfound galaxies as being about the size of our Milky Way.

The key difference between any one of the distant 854 and the Milky Way, where tiny Earth and its sibling planets revolve around the sun, is the degree of light, Koda said.

Anywhere in the Coma Cluster the average amount of brightness is only 1/1,000th the amount of light emitted from the Milky Way, noteworthy for its liberal sprinkling of stars. Despite the Coma Cluster's immense distance, Koda calls the new galaxies the Milky Way's neighbors.

"We call them local because they're at the very edge of the local universe," Koda said. "There are still objects that are much farther away. We can see to the beginning of the universe. That's about 14 billion light-years."

The new findings come on the heels of the discovery of 47 different Coma Cluster galaxies pinpointed by Yale University astronomer Pieter van Dokkum last year.

Koda, and his collaborators, who are mapping the Coma Cluster, say the galaxies are elliptical in shape compared with the Milky Way's famous bright spiral.

The Coma Cluster's absence of brightness, Koda said, may have resulted from a loss of gases required to create new stars billions of Earth years ago.

Stony Brook scientists identified the new deep space regions by scouring archival data captured by the gargantuan Subaru Telescope atop Hawaii's dormant Mauna Kea volcano 13,803 feet above sea level.

Koda had journeyed to the giant telescope in 2013 on a different mission. At that time he was tracking the movement of Comet Lovejoy, a 6-mile-wide ball of ice and dirt hurtling toward a close encounter with our sun.

Yet, it is the mystifying phenomenon of dark matter contained within Coma Cluster galaxies that makes them intriguing for scientists who hunt the heavens. Dark matter is invisible, but scientists know that it exists.

"The big thing is the dark matter. We don't understand much about it and that's why dark matter is such a mystery," Koda said.

Dark matter is so mystifying that it has never been captured, but researchers insist that it makes up more than 90 percent of the matter in the universe. Koda said its existence is calculated based on its gravitational pull on visible matter, such as stars.

There may even be black holes -- collapsed stars -- within the new galaxies' dark matter, but black holes, with their own potent gravitational strength, do not explain many of the unanswered questions involving dark matter -- or the Coma Cluster, Koda said.

Peter Capak, a staff scientist at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, called the discovery by Koda and his team important because it provides insight into dark matter and the evolution of galaxies.

"Of course these findings will have to be replicated," Capak said, but emphasized that Koda and colleagues have helped further explain the existence of dark matter.

"As astronomers, the only things we can see are objects that are luminous, things that glow, like stars. But when looking at how galaxies move around -- and move around each other -- that tells us the universe is filled with dark matter," he said.

At Yale, van Dokkum, who chairs the department of astronomy and published his findings about the Coma Cluster last year, describes their appearance from Earth-based telescopes as "fluffy."

"If the Milky Way is a sea of stars, then these newly discovered galaxies are like wisps of clouds," van Dokkum said.

Scientists, according to van Dokkum, are beginning to form hypotheses about how these galaxies were born, and the region where they took shape, he said, is anything but benign.

"They are found in a dense, violent region of space filled with dark matter and galaxies whizzing around, so we think they must be cloaked in their own invisible dark matter shields that are protecting them from this intergalactic assault," van Dokkum said.

Koda likewise describes the Coma Cluster as a violent deep-space region typified by strong tidal forces. And also like van Dokkum, Koda insists that something invisible must be protecting fragile star systems within these galaxies, something with a high mass. He believes that the unknown protective force is probably an excessive amount of dark matter.

As additional evidence unfolds, Koda said, findings from the Coma Cluster may help scientists understand how key elements of the universe itself came to be.

"Follow-up spectroscopic observations in the future may reveal the history of star formation in these dark galaxies," he said.

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