Dwarf galaxy, the Milky Way’s new neighbor, discovered

A Russian-American team of astronomers has discovered a tiny and isolated dwarf galaxy next door to our Milky Way. In astronomy, ‘next door’ can still be a very long distance. This dwarf galaxy is nearly 7 million light years away.

Their finding appears in Monthly Notices of the Royal Astronomical Society.

Using the Hubble Space Telescope Advanced Camera Surveys (ACS) in August 2014, team leader Prof Igor Karachentsev of the Special Astrophysical Observatory in Karachai-Cherkessia, Russia, and colleagues found the new galaxy, which they have called KKs 3.

KKs 3 is situated in the southern sky in the direction of the constellation of Hydrus. Its stars combined have just one ten-thousandth of the mass of the Milky Way.

This new galaxy does not have the spiral arms found in the Milky Way. KKs 3 is a “dwarf spheroidal” or dSph galaxy. This type of galaxy does not have the raw materials (dust and gas) required for new generations of stars to form, leaving behind older and fainter relics. Most of its raw materials have been stripped out by the massive Andromeda galaxy.

Dwarf Galaxy

KKs 3 seen with a negative image using the Advanced Camera for Surveys on the Hubble Space Telescope. The right hand dark object at the center of the image is the core of the galaxy, with its stars spreading out around it. The left hand of the two dark objects is another nearer globular star cluster. (Photo: astrobio.net)

Isolated objects must have formed differently, perhaps with an early burst of star formation that used up all the available gas. Astronomers are eager to find dSph objects to gain a better understanding of galaxy formation in the universe in general.

KKs 3 has no hydrogen gas clouds in nebulae, making it harder to spot in surveys. So instead, astronomers try finding them by picking out individual stars.

That is why only one other isolated dwarf spheroidal – KKR25 – has been found in the Local Group, a discovery the same team made in 1999.

Team member Prof Dimitry Makarov, said:

“Finding objects like Kks3 is painstaking work, even with observatories like the Hubble Space Telescope. 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 dwarf spheroidal galaxies out there, something that would have profound consequences for our ideas about the evolution of the cosmos.”

The researchers say they are going to seek out more dSph galaxies, a task which should get a little easier once instruments like the European Extremely Large Telescope and the James Webb Space Telescope come into service.