Astronomers using the NASA/ESA Hubble Space Telescope have discovered a new dwarf galaxy in our cosmic neighborhood. Named Bedin 1, the galaxy is approximately 30 million light-years away. The object is classified as a dwarf spheroidal galaxy because it measures only around 3,000 light-years at its greatest extent, and it is roughly a thousand times dimmer than our own Milky Way Galaxy.
This image, taken with Hubble’s Advanced Camera for Surveys (ACS), shows a part the globular cluster NGC 6752. Behind the bright stars of the cluster a denser collection of faint stars is visible — the previously unknown dwarf spheroidal galaxy Bedin 1. Image credit: NASA / ESA / Hubble / Bedin et al.
Dwarf spheroidal galaxies are defined by their small size, low-luminosity, lack of dust and old stellar populations.
Thirty-six galaxies of this type are already known to exist in the Local Group, 22 of which are satellite galaxies of the Milky Way.
“We used Hubble to study white dwarf stars within the globular cluster NGC 6752,” explained Dr. Luigi Bedin from the INAF-Osservatorio Astronomico di Padova and colleagues.
“The aim of our observations was to use these stars to measure the age of the globular cluster, but in the process we made an unexpected discovery.”
“In the outer fringes of the area observed a compact collection of stars was visible.”
“After a careful analysis of their brightnesses and temperatures, we concluded that these stars did not belong to the cluster — which is part of the Milky Way — but rather they are millions of light-years more distant.”
While dwarf spheroidal galaxies are not uncommon, Bedin 1 has some notable features.
Not only is it one of just a few dwarf spheroidals that have a well established distance but it is also extremely isolated.
It lies about 30 million light-years from the Milky Way and 2 million light-years from the nearest plausible large galaxy host, NGC 6744. This makes Bedin 1 possibly the most isolated small dwarf galaxy discovered to date.
From the properties of its stars, Dr. Bedin and co-authors were able to infer that the galaxy is around 13 billion years old — nearly as old as the Universe itself.
Because of its isolation and its age, Bedin 1 is the astronomical equivalent of a living fossil from the early Universe.
The discovery is reported in the journal Monthly Notices of the Royal Astronomical Society: Letters.
_____
L.R. Bedin et al. 2019. The HST Large Programme on NGC 6752. I. Serendipitous discovery of a dwarf Galaxy in background. MNRASL 484 (1): L54-L58; doi: 10.1093/mnrasl/slz004
