The Hubble Space Telescope has discovered a dwarf galaxy in our own cosmic backyard, a mere 30 million light-years from the Milky Way. (That may sound like a far piece, but remember: the observable universe is a whopping 93 billion light-years across.)
The find was fortuitous. An international team of astronomers was using Hubble's Advanced Camera for Surveys instrument to study white dwarfs — superdense stellar corpses — in the globular cluster NGC 6752, which is part of the Milky Way. [Gallery: 65 All-Time Great Galaxy Hits]
The Hubble images revealed an odd clump of stars. Analyses of the stars' brightnesses and temperatures indicated that they lay beyond NGC 6752 and were, in fact, part of a previously unknown galaxy.
This image, taken with the Hubble Space Telescope's Advanced Camera for Surveys, shows a part the globular cluster NGC 6752. Behind the bright stars of the cluster a denser collection of faint stars is visible — a previously unknown dwarf spheroidal galaxy. This galaxy, nicknamed Bedin 1, is about 30 million light-years from Earth.
Credit: Bedin et al./ESA/Hubble/NASAThe researchers determined that this galaxy — nicknamed Bedin 1, after discovery team leader L. R. Bedin of the INAF-Osservatorio Astronomico di Padova in Italy — is a "spheroidal dwarf" just 3,000 light-years wide. (For comparison, the Milky Way's famous spiral disk has a diameter of about 100,000 light-years.) Dwarf spheroidal galaxies are not uncommon; astronomers already knew of more than 20 that are satellites of the Milky Way. But Bedin 1 is special in several ways, according to the discovery team.
For example, the dwarf is about 2 million light-years away from the closest big galaxy that could feasibly be its host (which is called NCG 6744), the researchers said. Bedin 1 may therefore be the most isolated small dwarf galaxy known.
And then there's Bedin 1's age.
This composite image shows the location of the accidentally discovered dwarf galaxy Bedin 1 behind the globular cluster NGC 6752. The lower image, depicting the complete cluster, is a ground-based observation from the Digitized Sky Survey 2. The upper right image shows the full field of view of the Hubble Space Telescope. The upper left one highlights the part containing the galaxy Bedin 1.
Credit: Bedin et al., Digitized Sky Survey 2/ESA/Hubble/NASA"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," Hubble team members wrote in a statement. "Because of 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 researchers published their findings online today (Jan. 31) in the journal Monthly Notices of the Royal Astronomical Society: Letters.
This image shows a ground-based wide-field view of the region around NGC 6752 from the Digitized Sky Survey 2.
Credit: ESA/Digitized Sky Survey 2; Acknowledgement: Davide De MartinThe Hubble Space Telescope, a joint project of NASA and the European Space Agency, launched to Earth orbit in April 1990 aboard the space shuttle Discovery. The scope's cosmic views were initially blurry — the result of a slight flaw in Hubble's primary mirror — but spacewalking astronauts fixed that problem in December 1993.
Astronauts maintained, repaired and upgraded Hubble on four additional servicing missions, the last of which occurred in May 2009.
Mike Wall's book about the search for alien life, "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate) is out now. Follow him on Twitter @michaeldwall. Follow us @Spacedotcom or Facebook. Originally published on Space.com.
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