Astronomers using the Hubble Space Telescope have made an unexpected finding.

They discovered a dwarf galaxy in our cosmic backyard, only 30 million light-years away.

An international team of astronomers recently used the telescope to study white dwarf stars, to measure the age of the globular cluster known as NGC 6752.

But in the process, they made the unexpected discovery of a compact collection of stars.

After a careful analysis of their brightnesses and temperatures, they 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.

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 NASA/ESA Hubble Space Telescope. The upper left one highlights the part containing the galaxy Bedin 1 | Image: ESA/Hubble, NASA, Bedin et al., Digitized Sky Survey 2

The newly-discovered cosmic neighbour has been nicknamed Bedin 1.

The European Space Agency (ESA) has said it is a "modestly sized, elongated galaxy" - measuring only around 3,000 light-years at its greatest extent.

This is a fraction of the size of the Milky Way.

It said: "Not only is it tiny, but it is also incredibly faint. These properties led astronomers to classify it as a dwarf spheroidal galaxy."

This image, taken with the NASA/ESA Hubble Space Telescope, shows a part of the globular cluster NGC 6752 | Image: ESA/Hubble, NASA, Bedin et al

Dwarf spheroidal galaxies are defined by their small size, low-luminosity, lack of dust and old stellar populations.

Some 36 galaxies of this type are already known to exist as 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 two million light-years from the nearest plausible large galaxy host, NGC 6744.

This image shows a ground-based wide-field view of the region around NGC 6752 from the Digitized Sky Survey 2 | Image: ESA/Digitized Sky Survey 2 | Acknowledgement: Davide De Martin

The ESA has said this makes it, possibly, the most isolated small dwarf galaxy discovered to date.

From the properties of its stars, astronomers were able to estimate 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 finding is reported in the journal Monthly Notices of the Royal Astronomical Society: Letters.

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.