A small, ultra-faint satellite galaxy has been discovered orbiting the Milky Way.
According to Space.com, currently named Virgo 1, this cosmic wanderer isn't alone: There are about 50 known satellite galaxies orbiting our own (the largest of these are the Large Magellanic Cloud and Small Magellanic Cloud, which are visible from Earth with the naked eye).
But Virgo 1 is special because it is extremely faint — finding it required a very large telescope equipped with a very specialized instrument.
There should be many more of these faint satellite galaxies around the Milky Way, according to computer simulations that predict how the galaxy formed. And finding these galaxies will help scientists better understand a major ingredient in those computer models: dark matter, a material that makes up most of the mass in the universe, writes Space.com.
The extremely faint dwarf satellite was spotted by an international team led by astronomers from Tohoku University in Japan using the Subaru telescope, as part of the ongoing Subaru Strategic Survey using Hyper Suprime-Cam.
"We have carefully examined the early data of the Subaru Strategic Survey with HSC and found an apparent over density of stars in Virgo with very high statistical significance, showing a characteristic pattern of an ancient stellar system in the color-magnitude diagram," Daisuke Homma who found Virgo I said in a press release.
"Surprisingly, this is one of the faintest satellites, with absolute magnitude of -0.8 in the optical waveband. This is indeed a galaxy, because it is spatially extended with a radius of 124 light years - systematically larger than a globular cluster with comparable luminosity."
Earth Sky reported that the discovery of this satellite indicated the presence of a large number of yet-undetected dwarf satellites in the halo of the Milky Way. This would lead to the better understanding of how "dark matter" holds the numerous galaxies together.
"Our theories and simulations of how the Universe evolves tell us that the Milky Way should have many of these small, faint satellite galaxies," stated NASA's Jet Propulsion Laboratory astrophysicist Jason Rhodes as reported by Space.com. "However, they have been notoriously difficult to detect, prompting some people to say that they may not exist. This is called the 'missing satellite problem.'"
"As their survey gets bigger, more of these formerly missing satellites should be found. Likewise, with a new generation of instruments and telescopes in the 2020s, we will be able to push the sensitivity limits even further and find smaller and fainter 'missing satellites,'" Rhodes added.