The Hubble Space Telescope has made an unexpected discovery of a dwarf galaxy in our cosmic backyard, located just 30 million light-years away, scientists say.
Researchers used the NASA/ESA Hubble Space Telescope to study white dwarf stars within the globular cluster NGC 6752.
According to the European Space Agency (ESA), the aim of the observations was to use these stars to measure the age of the globular cluster, but in the process researchers made an unexpected discovery.
In the outer fringes of the area observed with Hubble's Advanced Camera for Surveys a compact collection of stars was visible, according to a study published in the journal Monthly Notices of the Royal Astronomical Society: Letters.
After a careful analysis of their brightnesses and temperatures, the astronomers 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.
The cosmic neighbour, nicknamed Bedin 1, is a modestly sized, elongated galaxy. It measures only around 3000 light-years at its greatest extent—a fraction of the size of the Milky Way.
Not only is it tiny, but it is also incredibly faint, researchers said. These properties led astronomers to classify it as a dwarf spheroidal galaxy.
Dwarf spheroidal galaxies are defined by their small size, low-luminosity, lack of dust and old stellar populations. 36 galaxies of this type are already known to exist in the Local Group of Galaxies, 22 of which are satellite galaxies of the Milky Way.
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 it possibly the most isolated small dwarf galaxy discovered to date.
From the properties of its stars, astronomers were able to infer that the galaxy is around 13 billion years old—nearly as old as the Universe itself.
Due to its isolation—which resulted in hardly any interaction with other galaxies—and its age, Bedin 1 is the astronomical equivalent of a living fossil from the early Universe.
The discovery of Bedin 1 was a truly serendipitous find. Very few Hubble images allow such faint objects to be seen, and they cover only a small area of the sky.
Future telescopes with a large field of view, such as the WFIRST telescope, will have cameras covering a much larger area of the sky and may find many more of these galactic neighbours.
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