Faintest Dwarf Satellite Galaxy Found Lurking In The Halo Of Milky Way

First Posted: Nov 23, 2016 04:40 AM EST

Astronomers have spotted, for the first time, a faint dwarf galaxy not so far away. It is lurking in the halo of the Milky Way. Dubbed as Virgo I, the satellite lies in the direction of the constellation Virgo at about 280,000 lightyears away from the Sun.

The discovery, which was published in The Astrophysical Journal, was announced by a team of international researchers from Tohoku University in Hawaii. The study is part of an ongoing Subaru Strategic Survey through the use of the Hyper Suprime-Cam.

The satellite galaxy was found at the absolute magnitude of -0.8 in the optical waveband, making it the faintest satellite galaxy ever found. The new discovery hints the presence of other dwarf satellites in the halo of the Milky Way, waiting to be found and detected.

"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, a graduate student at Tohoku University and the one who discovered the satellite galaxy, said in a press release by Subaru Telescope.

"Surprisingly, this is one of the faintest satellites, with an 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," he added.

Dwarf Satellite Discovery And Implications

Today, there are about 50 satellite galaxies lurking in the halo of the Milky Way that have been discovered. About 40 of these are diffuse and faint, belonging to the category called "dwarf spheroidal galaxies."

The formation of galaxies like the Milky Way is thought to be caused by the hierarchical assembly of dark matter. They form dark halos and with gas and stars falling due to gravity. Thus, this new discovery could pave way for more studies associated with the galaxy's dark matter.

"This discovery implies hundreds of faint dwarf satellites waiting to be discovered in the halo of the Milky Way," Homma's advisor, Masashi Chiba, said as reported by Wired.

"How many satellites are indeed there and what properties they have, will give us an important clue to understanding how the Milky Way formed and how dark matter contributed to it," he added.

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