New isolated dwarf galaxy discovered in the Local Group

Chuck Bednar for – Your Universe Online

Don’t look now, Milky Way, but it appears that there’s a new dwarf galaxy in the neighborhood – at least, according to the authors of a paper published Sunday in the online edition of Monthly Notices of the Royal Astronomical Society.

A joint Russian-US team has discovered the tiny, isolated new galaxy located nearly seven million light years away, adding it to the cluster of over 50 galaxies that comprise the so-called Local Group. The new galaxy, named KKs3, was discovered in August using the Hubble Space Telescope’s Advanced Camera for Surveys (ACS) instrument.

According to the Royal Astronomical Society, lead investigator Professor Igor Karachentsev of the Special Astrophysical Observatory in Karachai-Cherkessia, Russia, and his colleagues found KKs3 in the southern sky in the vicinity of the constellation Hydrus.

Its stars have just one ten-thousandth the mass of the Milky Way, and it has been classified as a dwarf spheroidal (dSph) galaxy because it lacks features like our galaxy’s spiral arms. This type of galaxy also lacks the gas and dust needed to form new generations of stars, and in most cases, these raw materials were swiped by nearby massive galaxies, such as Andromeda.

As a result, these galaxies are typically filled with older stars and faint stellar remnants, and the vast majority of them are found near far bigger companion galaxies. However, isolated ones like KKs3 likely used up all of their available gas resources in an early burst of star formation, instead of having their raw materials stripped out by larger neighbors.

Only one other only isolated dwarf spheroidal, KKR 25, has ever been found in the Local Group – a discovery that was made by the same team 15 years ago. Astronomers are keen to find dSph objects in order to better understand galaxy formation, but the absence of hydrogen gas clouds in nebulae makes it difficult for them to be located in surveys.

“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,” said Professor Dimitry Makarov, a member of the research team who is also affiliated with the Special Astrophysical Observatory.

“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,” he added. Makarov and his colleagues plan to continue their search for dSph galaxies, and their efforts should get a boost when the James Webb Space Telescope and the European Extremely Large Telescope enter service within the next few years.

The Local Group, which was given its name by Edwin Hubble in the 1930s, has a binary or dumbbell shape and covers a 10 million light-year diameter. It is part of the Virgo Supercluster, and in addition to the Milky Way and Andromeda (and their satellite galaxies), it is home to the Triangulum Galaxy and several others that are gravitationally secluded from these large subgroups.