The core of galaxy Kks3 is the right hand dark object in the top centre of this negative image. Credit: D. Makarov
The Milky Way has a new neighbour.
A team of observers have found a dwarf galaxy that is believed to be part of the Local Group, a gravitationally bound group of galaxies which the Milky Way is a part of.
The new galaxy, named Kks3, was found using the Hubble Space Telescope Advanced Camera for Surveys (ACS) in August 2014.
It is a tiny dwarf spheroidal galaxy; its stars have only one ten thousandth of the mass of the Milky Way and lacks the distinctive spiral arms.
The new galaxy is joined in the Local Group by the Milky Way and Andromeda Galaxies, as well as a handful of smaller galaxies.
Though the new addition is very isolated, located 7 million lightyears away, it is still bound by the gravity of the Local Group.
Finding a galaxy like this is a major step in understanding how galaxies formed.
Usually dwarf galaxies have their growth stunted as nearby large galaxies rip out all of their gas and dust.
Deprived of the raw materials for growing stars, the galaxies are left with an old and faint population.
But isolated objects, like Kks3, which are too far away from the nearest large galaxy must have formed in a different way.
One possibility is that an initial flush of star formation used up all the available gas, so that no new stars could form as the galaxy grew.
Finding more dwarf spheroidal galaxies is vital to understanding how these various process effects the growth of galaxies across the Universe.
But finding them beyond the Local Group is incredibly difficult as they are very faint and the absence of hydrogen makes them hard to pick out in surveys.
Instead astronomers attempt to pick out the individual stars.
“Finding objects like Kks3 is painstaking work, even with observatories like the Hubble Space Telescope,” says Prof Dimitry Makarov of the Special Astrophysical Observatory.
“But 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.”