The accidentally discovered galaxy Bedin I
Bedin 1 in NGC 6752
Globular cluster NGC 6752
Wide-field view of NGC 6752 (ground-based view)
Videos
Videos
Zooming in on NGC 6752 and Bedin 1
Flight to Bedin 1
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 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. 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 [1]. 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.
Notes
[1] 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.
More Information
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
The results were presented in the letter The HST Large Programme on NGC 6752. I. Serendipitous discovery of a dwarf galaxy in background, published in the journal Monthly Notices of the Royal Astronomical Society: Letters.
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).
Image credit: NASA, ESA, Bedin et al.
Links
Links
Contact
L. R. Bedin
INAF-Osservatorio Astronomico di Padova
Padua, Italy
Tel: +49 8293 413
Email: luigi.bedin@oapd.inaf.it
Mathias Jäger
ESA/Hubble, Public Information Officer
Garching, Germany
Tel: +49 176 62397500
Email: mjaeger@partner.eso.org
Source: ESA/Hubble/News
