Faintest dwarf satellite galaxy of Milky Way discovered

A new dwarf satellite galaxy has been discovered by scientists. This is believed to be the faintest galaxy till now in the Milky Way row. The satellite, named Virgo I, lies in the direction of the constellation Virgo.

Among the 50 satellite galaxies identified to the Milky Way, 40 are faint and belong to the category of “dwarf spheroidal galaxies.

The luminosity of the dwarf galaxies is very faint and is said to be in the optical waveband below minus 8 magnitude. Its discovery by researchers from Tohoku University in Japan suggests the presence of a large number of yet-undetected dwarf satellites in the halo of the Milky Way.

However, previous searches made use of telescopes with a diameter of 2.5 to four meters, so only satellites close to the Sun or those with higher magnitudes were identified.

Those that are more distant or faint ones in the halo of the Milky Way are yet to be detected.

The combination of the 8.2-metre Subaru Telescope and Hyper Suprime-Cam (HSC) instrument enabled an efficient search for very faint dwarf satellites over large areas of the sky.

“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 colour-magnitude diagram,” said Daisuke Homma, a graduate student at Tohoku University.

“Surprisingly, this is one of the faintest satellites, with absolute magnitude of minus 0.8 in the optical waveband,” said Homma, who found Virgo I under the guidance of Masashi Chiba.

“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,” Homma said.

The faintest dwarf satellites identified so far was Segue I, discovered by Sloan Digital Sky Survey (SDSS) and Cetus II in Dark Energy Survey (DES). Cetus II is yet to be confirmed, as it is too compact as a galaxy.

With PTI Inputs