Beacon Transcript – Researchers found a new, very faint, quite rare dwarf galaxy system which they named Virgo I and which is located at the edge of our galaxy, somewhere in the Milky Way’s halo.
Virgo I was the discovery of Daisuke Homma, a Japan-based, Tohoku University graduate student. He was helped by fellow colleague Masashi Chiba and a number of other international collaborators.
The extremely faint and rare dwarf system was located using the Subaru Telescope, 8.2-metre device. A large field-of-view was also obtained with the help of the HSC or Hyper Suprime-Cam.
The halo of our Milky Way is known to contain about 50 satellite galaxies. Amongst them, approximately 40 are so diffuse and faint that they have been classified as dwarf spheroidal galaxies.
As the halo and edges surrounding the Milky Way were explored, the study of the area came to be known as the Sloan Digital Sky Survey or SDSS.
Virgo I, the newest addition to the list of faint dwarf galaxies is located outsides the reach of the SDSS. Although the survey has analyzed the general area in which the system is located, it is so extremely faint and rare that it has only now been discovered.
Virgo I lies at a distance of 280,000 light years away from our galaxy’s center, the Sun. Its far away location is one the factors which explains its very faint brightness and the fact that it had not been previously located.
The dwarf galaxy received its name thanks to its shared direction towards the Virgo constellation. Also, the absolute magnitude it registers on the optical waveband is of just -0.8.
As such, it may also be the faintest galaxy to have been yet discovered. Before this latest discovery, the title of faintest dwarf galaxy belonged to Segue I and Cetus II.
Segue I, which was spotted in the SDSS, has an absolute optic wavelength magnitude of -1.5. Cetus II has a 0.0 absolute magnitude.
The researchers found the Virgo I galaxy after careful analysis of newly gathered and already existing data.
Early Subaru Strategic Survey data was compared to the HSC. Whilst doing so, the scientists observed what appeared to be an overdensity of stars.
This cluster was located in the Virgo constellation and had very high statistical significance according to Homma, the study’s lead.
Further analysis of the area revealed that the cluster was, in fact, a galaxy as it has a 124 light years radius. The value is systematically larger than what a cluster with a comparable luminosity could have achieved.
A difference between a cluster of stars and a galaxy does exist, but the line is so fine that even astronomers cannot limit a clear definition.
Typically, a cluster is made up of hundreds of stars whilst a galaxy is made up of millions.
Chiba, another of the study contributors, stated that the discovery of Virgo I could have important implications in relation to our understanding of the Milky Way.
As more such extremely faint dwarf galaxies may be hiding in its halo, further studies may help understand how the Milky Way formed.
Image Source: Wikimedia