Our galactic neighbourhood has a new resident, with the new discovery of dwarf galaxy KKs 3. The galaxy has been described in The Monthly Notices of the Royal Astronomical Society and photographed with the Hubble Space Telescope.
Of course, KKs 3 is technically far from “new”. It has probably been in the area since the time the Milky Way was born but it has escaped our notice until now. Its discovery brings the membership of the Local Group to 55, and it is one of the most distant members from us.
Nevertheless, Kks 3 has some unusual features that make it of interest. Most dwarf galaxies lie near larger galaxies which are cannibalizing their gas and dust, spurring star formation in the predator galaxy. KKs 3 on the other hand, is very isolated. It has been found to be low on gas and dust, despite the lack of an obvious object to steal these raw materials. For the moment it is unclear whether at some previous time KKs3 lost its gas and dust to a large object, with which it has since parted ways, or if it never had much to start with: and what little it did have has been used up making stars.
As a result, “most stars (74%) were formed at an early epoch more than 12 Gyr ago," I.D Karachentsev and his co authors of Russia's Special Astrophysical Observatory writes.
The paper estimates the stellar mass at 23 million times that of the sun; by comparison the Sagittarius Dwarf Galaxy, our nearest galactic neighbor, is around a thousand times as massive. At that size KKs 3 is only five to six times the mass of Omega Centauri, the largest of the globular clusters orbiting the Milky Way.
Located in Hydrus KKs3 lies too far south to be seen by most northern hemisphere telescopes, and appears to sit next to a much nearer globular cluster (left object in the image above), obscuring its nature until now. It is only the second isolated dwarf spheroidal galaxy found in the Local Group, and astronomers hope it will help illuminate how small, isolated galaxies evolve.
“With persistence, we’re slowly building up a map of our local neighbourhood, which turns out to be less empty than we thought. It may be that are a huge number of dwarf spheroidal galaxies out there, something that would have profound consequences for our ideas about the evolution of the cosmos,” author Professor Dimitry Makarov of the Special Astrophysical Observatory told the Royal Astronomical Society's website.
