Astronomers using the NASA/ESA Hubble Space Telescope to study some of the oldest and faintest stars in the globular cluster NGC 6752 have made an unexpected finding. They discovered a dwarf galaxy in our cosmic backyard, only 30 million light-years away. The finding is reported in the journal Monthly Notices of the Royal Astronomical Society: Letters.
An international team of astronomers recently used the NASA/ESA Hubble Space Telescope to study white dwarf stars within the globular cluster NGC 6752. The aim of their observations was to use these stars to measure the age of the globular cluster, but in the process they 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. 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.
Our newly discovered cosmic neighbour, nicknamed Bedin 1 by the astronomers, is a modestly sized, elongated galaxy. It measures only around 3,000 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. 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. While similar to dwarf elliptical galaxies in appearance and properties, dwarf spheroidal galaxies are in general approximately spherical in shape and have a lower luminosity. 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. 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 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.
Media contacts
Mathias Jäger
ESA/Hubble, Public Information Officer
Garching, Germany
Tel: +49 176 6239 7500
Morgan Hollis
Royal Astronomical Society
London, UK
Tel: +44 (0)20 7292 3977
Mob: +44 (0)7802 877 700
Science contacts
Luigi Bedin
INAF-Osservatorio Astronomico di Padova
Padua, Italy
Tel: +49 8293 413
Images and captions
Further information
The new work appears in: “The HST Large Programme on NGC 6752. I. Serendipitous discovery of a dwarf Galaxy in background”, L.R. Bedin, M. Salaris, R.M. Rich et al., Monthly Notices of the Royal Astronomical Society: Letters (2019), 484 (1) (DOI: 10.1093/mnrasl/slz004).
A copy of the paper is available from: https://doi.org/10.1093/mnrasl/slz004
Notes for editors
The Royal Astronomical Society (RAS, www.ras.ac.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.
Twitter: https://twitter.com/royalastrosoc
Facebook: https://facebook.com/royalastrosoc
Instagram: https://www.instagram.com/royalastrosoc/
YouTube: https://www.youtube.com/user/RoyalAstroSoc/feed
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
The international team of astronomers that carried out this study consists of L. R. Bedin (INAF-Osservatorio Astronomico di Padova, Italy), M. Salaris (Liverpool John Moores University, UK), R. M. Rich (University of California Los Angeles, USA), H. Richer (University of British Columbia), J. Anderson (Space Telescope Science Institute, USA), B. Bettoni (INAF-Osservatorio Astronomico di Padova, Italy), D. Nardiello (Università di Padova, Italy), A. P. Milone (Università di Padova, Italy), A. F. Marino (Università di Padova, Italy), M. Libralato (Space Telescope Science Institute, USA), A. Bellini (Space Telescope Science Institute, USA), A. Dieball (University of Bonn, Germany), P. Bergeron (Université de Montréal, Canada), A. J. Burgasser (University of California San Diego, USA), D. Apai (University of Arizona, USA).