A new neighbor of our Milky Way Galaxy has been discovered with the Advanced Camera for Surveys (ACS) instrument on NASA’s Hubble Space Telescope.
This image shows the newly discovered dwarf galaxy Kks3. The core of the galaxy is the right hand object at the top center of the image, with its stars spreading out over a large section around it; the left hand of the two objects is a much nearer globular star cluster. Image credit: Dimitry Makarov.
The galaxy, named Kks3, is a dwarf spheroidal (dSph) galaxy, lacking features like the spiral arms found in our Galaxy.
It is located in the southern constellation Hydrus, approximately 7 million light-years away, and has a stellar mass about 1/10,000 of Milky Way’s.
DSph galaxies like Kks3 have an absence of the raw materials needed for new generations of stars to form, leaving behind older and fainter relics. In almost every case, these raw materials seem to have been stripped out by nearby massive galaxies like Andromeda, so the vast majority of dSph objects are found near much bigger companions.
Isolated objects must have formed in a different way, with one possibility being that they had an early burst of star formation that used up the available gas resources.
Astronomers are particularly interested in finding dSph galaxies to understand galaxy formation in the Universe in general.
“Finding objects like Kks3 is painstaking work, even with observatories like the Hubble,” said Prof Dimitry Makarov from the Special Astrophysical Observatory in Karachai-Cherkessia, who is the lead author of a paper published in the Monthly Notices of the Royal Astronomical Society (arXiv.org version).
“But with persistence, we’re slowly building up a map of our local neighborhood, which turns out to be less empty than we thought.”
“It may be that are a huge number of dSphs out there, something that would have profound consequences for our ideas about the evolution of the cosmos.”
Prof Makarov and his colleagues from the University of Hawaii and W. M. Keck Observatory will continue to look for more dSph galaxies, a task that will become a little easier in the next few years, once instruments like the James Webb Space Telescope and the European Extremely Large Telescope begin service.
_____
I. D. Karachentsev et al. 2015. A new isolated dSph galaxy near the Local Group. MNRAS 447 (1): L85-L89; doi: 10.1093/mnrasl/slu181
