Scientists have found what
looks like an exceedingly small galaxy in the orbit around our own Milky Way
Galaxy, which had previously avoided detection. Named Hydrus 1, it’s located
about 90,000 light-years from Earth, between two other satellites of our galaxy
– the Small and Large Magellanic Clouds (SMC and LMC).
It was found using the Dark
Energy Camera (DECam) on the Blanco Telescope in Chile. A paper describing the
findings, available on arXiv, has been submitted to the Monthly Notices of the
Royal Astronomical Society for publication. It was led by Sergey Koposov from
Carnegie Mellon University (CMU) in Pennsylvania.
“We report the discovery of
a nearby dwarf galaxy in the constellation of Hydrus, between the Large and the
Small Magellanic Clouds,” the authors wrote in their paper.
Hydrus 1 is a dwarf galaxy,
described as being ultra-faint. It’s only about 326 light-years across, which
is pretty paltry when compared to our Milky Way, which is 100,000 light-years
across. It’s so small that it might actually be a globular cluster, a loose
collection of stars. This will help astronomers understanding the surroundings of milky way more easily.
It was discovered within the
Magellanic Bridge, a stream of gas that links both the SMC and the LMC. Being
found in the Hydrus constellation, which means “male water snake”, it was
described as a “snake in the clouds”.
The researchers found that
Hydrus 1 has stars that are relatively metal-poor, which is similar to other
suspected dwarf galaxies like this. Galaxies are described as “dwarfs” if they
have about 100 million to a few billion stars, much less than the up to 400
billion or so stars in our own galaxy.
The team also noted that the
galaxy is rotating, making it the “first rotating ultra-faint dwarf galaxy”
ever detected, they wrote in their paper. And they also said it was probably
dominated by dark matter, which may be quite easy to study due to its
proximity.
At the moment the connection
between Hydrus 1 and the nearby SMC and LMC isn't quite clear. But it’s hoped
that data from the Gaia mission, which recently released a stunning map of
nearby stars, could give us some vital clues and tell us a bit more about it.