Giant galaxies like the Milky Way are thought to form after smaller galaxies smash together. That suggests that hundreds of satellite galaxies would orbit our own, leftovers of the ones that formed our galaxy. But, so far, astronomers have found only about 50.
The new galaxy, named Virgo I, is the latest satellite to be discovered. It appeared as a team led by Daisuke Homma and Masashi Chiba of Tohoku University in Sendai, Japan, searched the sky with a new camera on the giant 8.2-meter Subaru Telescope in Hawaii.
“Virgo I might be the faintest galaxy,” Chiba says. It emits about half as much light as Segue 1, another satellite of the Milky Way and the previous faint-galaxy champ. A single bright star in our galaxy outshines all of Virgo I’s stars put together.
The Milky Way, as seen from the ISS NASA/Reid Wiseman
As many as half of all stars in the universe lie in the vast gulfs of space between galaxies, an unexpected discovery made in a new study using NASA rockets. These stars could help solve mysteries regarding missing light and particles that theory had suggested should exist, scientists say. The stars were ejected from their birthplaces by galaxy collisions or mergers.
Some estimations suggest up to 100,000 times more rogue planets than stars in the Milky Way.
We report the discovery of a new ultra-faint dwarf satellite companion of the Milky Way based on the early survey data from the Hyper Suprime-Cam Subaru Strategic Program. This new satellite, Virgo I, which is located in the constellation of Virgo, has been identified as a statistically significant (5.5 sigma) spatial overdensity of star-like objects with a well-defined main sequence and red giant branch in their color-magnitude diagram. The significance of this overdensity increases to 10.8 sigma when the relevant isochrone filter is adopted for the search. Based on the distribution of the stars around the likely main sequence turn-off at r ~ 24 mag, the distance to Virgo I is estimated as 87 kpc, and its most likely absolute magnitude calculated from a Monte Carlo analysis is M_V = -0.8 +/- 0.9 mag. This stellar system has an extended spatial distribution with a half-light radius of 38 +12/-11 pc, which clearly distinguishes it from a globular cluster with comparable luminosity. Thus, Virgo I is one of the faintest dwarf satellites known and is located beyond the reach of the Sloan Digital Sky Survey. This demonstrates the power of this survey program to identify very faint dwarf satellites. This discovery of VirgoI is based only on about 100 square degrees of data, thus a large number of faint dwarf satellites are likely to exist in the outer halo of the Milky Way.
SOURCES – Arxiv