Using the data from the Dark Energy Survey (DES), astronomers have found nine new ultra-faint Milky Way satellites. Based on the morphological properties, three of the new satellites are dwarf galaxies, one of which is located at the very outskirts of the Milky Way. The remaining six objects have sizes and luminosities comparable to an ultra-faint dwarf galaxy called Segue 1 and could be either dwarf galaxies or globular clusters.
This image shows the newly-discovered dwarf galaxy Eridanus 2.
Image credit: Sergey E. Koposov et al / Dark Energy Survey.
“The discovery of so many satellites in such a small area of the sky was completely unexpected. I could not believe my eyes,” said Dr Sergey Koposov of the Cambridge University’s Institute of Astronomy, UK, who is the first author of the paper submitted for publication in the Astrophysical Journal (arXiv.org preprint).
The newly-discovered satellites were found in the southern hemisphere near the Large and Small Magellanic Cloud, the largest and most well-known dwarf galaxies in the Milky Way’s orbit.
These objects – labeled Reticulum 2, Eridanus 2, Horologium 1, Pictoris 1, Phoenix 2, Indus 1, Grus 1, Eridanus 3, and Tucana 2 – are a billion times dimmer than the Milky Way, and a million times less massive.
The closest, Reticulum 2, is about 97,000 light-years away, while the most distant, Eridanus 2, is more than a million light-years away.
Eridanus 2 is a dwarf galaxy located at the very edge of the Milky Way halo, around 1.24 million light-years away. The galaxy shows signs of recent star formation and possibly even hosts a faint globular cluster.
With its location on the periphery of our Galaxy, high luminosity and a diameter of about 1,120 light-years, Eridanus 2 appears to be a twin of the Leo T dwarf galaxy.
This object is clearly visible in the DES color images as a group of faint blue stars embedded in a blue low surface-brightness cloud.
Tucana 2 lies at a distance of around 225,000 light-years from us. It can be classified as an ultra-faint dwarf galaxy due to its luminosity and the large diameter of 1,300 light-years.
Newly-discovered ultra-faint Milky Way satellites: Indus 1, left, and Eridanus 3.
Image credit: Sergey E. Koposov et al / Dark Energy Survey.
With a size of roughly 455 light-years, the dwarf galaxy Grus 1 is the third largest object in the sample. It is about 390,000 light-years away.
Reticulum 2 is a very elongated object located in the constellation Reticulum. It’s approximately 200 light-years long, with the measured axis ratio is around 0.6. Due to the massive tidal forces of our Galaxy, it is in the process of being torn apart.
The ultra-faint Milky Way satellite Horologium 1 has a diameter of about 195 light-years and lies at a distance of 325,000 light-years.
Eridanus 3, an ultra-faint object at 290,000 light-years away, has the smallest size in the sample, of only 117 light-years.
Phoenix 2 lies at a distance of about 270,000 light-years. It contains one or two blue horizontal-branch stars and a large number of blue straggler stars, and has a diameter of roughly 175 light-years.
Pictoris 1 is approximately 370,000 light-years away and has a diameter of about 200 light-years.
Similar to the bulk of the sample, Indus 1 lies at 325,000 light-years away and has a diameter of about 250 light-years.
“These results are very puzzling,” said co-author Dr Wyn Evans, also of the Cambridge University’s Institute of Astronomy.
“Perhaps they were once satellites that orbited the Magellanic Clouds and have been thrown out by the interaction of the Small and Large Magellanic Cloud.”
Read more: Sci-News.com