Clusters of blue stars hanging in the void found near the Milky Way
An international team of astronomers has discovered four mysterious new class of star systems near the Milky Way that are composed of young blue stars and exist in isolation from their parent galaxies. Details of the discovery are published in the electronic archive of preprints arXiv.
Previously unknown stellar systems that look like spots of blue in a telescope are the size of dwarf galaxies and are located in the nearby Virgo galaxy cluster, 15-22 megaparsecs from the Milky Way. These objects “hang” in the intergalactic void, that is, they are more than 300 thousand light-years away from the galaxies closest to them.
Astronomers initially discovered gas clouds believed to be in the vicinity of or within the Milky Way, after which the search began for stars associated with them. However, the first group of blue stars discovered, called SECCO1, scientists have found, is much further away than expected. To better understand the nature of these star systems, the researchers made new observations using the Hubble Space Telescope, the Very Large Array radio telescope complex in New Mexico, and the VLT (Very Large Telescope) complex in Chile.
It turned out that each isolated star system in the Virgo cluster has the mass of a hundred thousand Suns and consists mainly of blue and very young stars that contain very little atomic hydrogen. Usually clouds of gas from atomic hydrogen turn into dense molecular clouds, where star formation processes are triggered. This suggests that the systems have lost atomic hydrogen, most likely recently. In addition, star systems are characterized by high metallicity, that is, an abundance of elements heavier than helium. Such elements are produced as a result of repeated episodes of star formation in large galaxies.
The absence of atomic hydrogen and high metallicity indicate that star systems formed from gas that was removed from a large galaxy. The most likely mechanism for this is tidal stripping (English ram pressure stripping), when hot intergalactic gas displaces interstellar gas from a galaxy that has fallen into the Virgo cluster. Left far behind, this gas serves as fuel for the formation of isolated star systems. In the future, star systems are expected to break up into separate clusters of stars and disperse throughout the galaxy cluster.