Dec 26, 2014 Amina Khan, Los Angeles Times
Astronomers searching the sky with NASA’s Hubble Space Telescope have discovered an odd little dwarf galaxy in our very own backyard — a mere 7 million light years away.
The findings, described in the Monthly Notices of the Royal Astronomical Society, add a new member to the more than 50 galaxies in our Local Group (part of the Laniakea supercluster), which includes Andromeda and our own Milky Way.
While only just recently discovered using Hubble’s Advanced Camera for Surveys, the galaxy known as KKs3 has been around a long while. Astronomers led by Igor Karachentsev of the Special Astrophysical Observatory in Karachai-Cherkessia, Russia, showed that some 74 percent of KKs3’s star mass was formed in the universe’s early years, at least 12 billion years ago. Most of the tiny galaxy’s stars are old and dim, making it a fascinating fossil that could help astronomers understand what ancient galactic environments looked like.
Carrying just 23 million solar masses’ worth of star-stuff, KKs3 holds just one ten-thousandth of the stellar mass of the Milky Way. As a dwarf spheroidal galaxy, it lacks any distinctive spiral arms.
The dwarf spheroidal galaxies that are found near massive galaxies are typically poor in gas and dust, because they’ve been stripped out by the gravitational pull of their much more massive neighbors (such as the Andromeda galaxy).
But KKs3 is far away from the thieving gravitational tug of a neighboring galaxy — and yet, for some reason, it also seems to be missing hydrogen gas. KKs3, in that way, is a much rarer breed, called an isolated dwarf spheroidal galaxy.
These isolated dwarf spheroidal galaxies are really hard to find, in part because they’re missing those telltale nebulae full of hydrogen gas that could have helped feed star formation. In fact, the only other one found in the Local Group, KKR 25, was found by the same research group way back in 1999.
KKs3 seems to have an interesting life history that could shed light on the strange processes that formed it. Though most of its stars are 12 billion years old or older, there appear to have been two smaller periods of star-formation around 5 billion years ago and even more recently, around 2 billion years ago or less.
Given that these isolated dwarf spheroidal galaxies are so hard to find, there could be many more of these fascinating galactic fossils just hanging out in the darkness of our own intergalactic neighborhood, just waiting to be found, the authors wrote.
"Since the detection of such objects is difficult, the number of them within (32.6 million light years) may be considerable," the study authors wrote.
Future space telescopes, including NASA’s James Webb Space Telescope set for launch in 2018, could help hunt down more of these mysterious objects in the heavens.
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