New dwarf galaxy detected orbiting the Milky Way

The Milky Way (Earth's galaxy) is not alone in the vastness of intergalactic space. Several nearby objects exert gravitational forces upon it, and there may be up to 50 of these objects out there.

A new object has been detected by astrophysicists from Tohoku University (Japan). This object is orbiting the Milky Way. The object has been detected using the advanced Subaru Telescope. At present, the best description of the object is a miniature (or dwarf) galaxy. A dwarf galaxy is a small galaxy composed of anything from 100 million up to several billion stars; while this seems big it is a far smaller number than the Milky Way's 200 - 400 billion stars.

The outside object is too small to be classed as a 'real galaxy' and scientists are debating whether 'dwarf galaxy' is a better descriptor. In terms of size, the Milky Way, according to latest estimates is some 100,000 light years in diameter. In contrast, the orbiting dwarf galaxy is probably only around 124 light years in diameter. It is located over 280,000 light years away from Earth. There is no other information about Virgo's origins.

The detection via the Subaru Telescope is very faint (absolute magnitude of -0.8 in the optical waveband), even accounting for the telescope's power. The Subaru Telescope is a 8.2-metre flagship telescope of the National Astronomical Observatory of Japan. It is located at the Mauna Kea Observatory on Hawaii. The telescope structure includes an instrument called the Hyper Suprime-Cam, and it was this device that detected the ultra-faint dwarf galaxy.

The dwarf galaxy has been given the name Virgo. The dwarf galaxy is 1.5 billion times dimmer than another recognizable object just outside the Milky Way: the Large Magellanic Cloud.

More about the discovery of Virgo is shown in the following video:

As well as the detection of Virgo, it is thought there are similar objects out there. These could be detected as optical technology advances. In a way it was only by chance that Virgo was detected given its faintness in space and the vast distance from Earth. The identification of Virgo is based only on about 100 square degrees of data.

The findings about Virgo have been published in the Astrophysical Journal. The research paper is titled (in capital letters): "A NEW MILKY WAY SATELLITE DISCOVERED IN THE SUBARU/HYPER SUPRIME-CAM SURVEY."