Andrew Yee[_1_]
March 14th 07, 03:19 PM
ESO Education and Public Relations Dept.
----------------------------------------------------------------------------
Text with all links and the photos are available on the ESO Website at URL:
http://www.eso.org/outreach/press-rel/pr-2007/pr-12-07.html
----------------------------------------------------------------------------
Contact:
Dirk Froebrich
University of Kent, Canterbury, UK
Phone: +44-1227-827346
Helmut Meusinger
Thuringer Landessternwarte Tautenburg, Germany
Phone: +49-36427-86362
Aleks Scholz
University of St. Andrews, Scotland, UK
Phone: +44-1334-461666
For Immediate Release: 13 March 2007
ESO Science Release 12/07
Star Family Seen Through Dusty Fog
New Globular Cluster Found in Milky Way
Images made with ESO's New Technology Telescope at La Silla by a team of
German astronomers reveal a rich circular cluster of stars in the inner
parts of our Galaxy. Located 30,000 light-years away, this previously
unknown closely-packed group of about 100,000 stars is most likely a new
globular cluster.
Star clusters provide us with unique laboratory conditions to investigate
various aspects of astrophysics. They represent groups of stars with similar
ages, chemical element abundances and distances. Globular clusters, in
particular, are fossils in the Milky Way that provide useful information.
With ages of about 10 billion years, they are among the oldest objects in
our Galaxy -- almost as old as the Universe itself. These massive, spherical
shaped star clusters are therefore witnesses of the early, mysterious ages
of the Universe.
"Moreover, the properties of globular clusters are deeply connected with the
history of their host galaxy," says Dirk Froebrich from the University of
Kent, and lead-author of the paper presenting the results. "We believe today
that galaxy collisions, galaxy cannibalism, as well as galaxy mergers leave
their imprint in the globular cluster population of any given galaxy. Thus,
when investigating globular clusters we hope to be able to use them as an
acid test for our understanding of the formation and evolution of galaxies,"
he adds.
In our own Galaxy about 150 globular clusters are known, each containing
many hundreds of thousands of stars. In contrast to their smaller and less
regularly shaped siblings -- open clusters -- globular clusters are not
concentrated in the galactic disc; rather they are spherically distributed
in the galactic halo, with increasing concentration towards the centre of
the Galaxy. Until the mid-1990s, globular clusters were identified mostly by
eye -- from visual inspection of photographic plates. However, these early
searches are likely to have missed a significant number of globular
clusters, particularly close to the disc of the Galaxy, where dense clouds
of dust and gas obscure the view. In the early times of extragalactic
astronomy this area was called the 'Zone of Avoidance' because extragalactic
stellar systems appeared to be very rare in this part of the sky.
Searching for the missing globular clusters in our Galaxy requires
observations in the infrared, because infrared radiation is able to
penetrate the thick 'galactic fog'. Using modern, sensitive infrared
detectors, this is now possible.
Completing the census is not only a challenge for its own sake, as finding
new globular clusters is useful for several additional reasons. For example,
analysing their orbits allows astronomers to draw conclusions about the
distribution of mass in the Galaxy. Star clusters can therefore be used as
probes for the large-scale structure of the Milky Way.
"It has been estimated that the region close to the Galactic Centre might
contain about 10 so far unknown globular clusters and we have started a
large campaign to unveil and characterise them," explains Helmut Meusinger,
from the Thuringer Landessternwarte Tautenburg, Germany, and part of the
team.
The astronomers carried out a systematic and automated large-scale (14,400
square degrees) search for globular cluster candidates in the entire
Galactic Plane, based on the near-infrared Two Micron All Sky Survey
(2MASS). Eventually, only about a dozen candidate objects remained.
The astronomers observed these candidates with the SofI instrument attached
to ESO's New Technology Telescope (NTT) at La Silla (Chile), taking images
through three different near-infrared filters. The new images are ten times
deeper and have a much better angular resolution than the original 2MASS
images, thereby allowing the astronomers to resolve at least partly the
dense accumulation of stars in the globular cluster candidates.
One of these candidates had the number 1735 in the list of Froebrich,
Scholz, and Raftery, and is therefore denoted as FSR 1735.
"The unique images we have obtained reveal that the nebulous appearance of
the cluster in previous images is in fact due to a large number of faint
stars," says Froebrich. "The images show a beautiful, rich, and circular
accumulation of stars."
From a detailed analysis of the properties of the cluster, the astronomers
arrive at the conclusion that the cluster is about 30,000 light-years away
from us and only 10,000 light-years away from the Galactic Centre, close to
the Galactic Plane.
"All the evidence supports the interpretation that FSR 1735 is a new
globular cluster in the inner Milky Way," says Aleks Scholz, from the
University of St Andrews, UK, and another member of the team. "However, to
be sure, we now need to measure the age of the cluster accurately, and this
requires still deeper observations."
The cluster is about 7 light-years wide (slightly less than twice the
distance between the Sun and its nearest star, Proxima Centauri) but
contains about 100,000 stars for a total estimated mass of 65,000 times the
mass of the Sun. The stars contain between 5 and 8 times less heavy elements
than the Sun.
"On its way to our Solar System, the light coming from the stars in the FSR
1735 cluster has to penetrate a thick cloud of dust and gas," says
Meusinger. "This is one of the reasons why this cluster was hard to find in
previous surveys."
"Is this now the last missing globular cluster in our galaxy?," asks Scholz.
"We really can't be sure. The opaque interiors of the Milky Way may well
have more surprises in store."
More Information:
The team is composed of Dirk Froebrich (University of Kent, UK), Helmut
Meusinger (Thuringer Landessternwarte Tautenburg, Germany), and Aleks Scholz
(University of St Andrews, Scotland, UK).
This research is presented in an article in press in the Monthly Notices of
the Royal Astronomical Society ("FSR 1735 - A new globular cluster candidate
in the inner Galaxy", by Froebrich et al.).
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Finland: Ms. Tiina Raivo, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vnle, +45-33-18 19 97
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-347-230 26 51
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Sweden: Dr. Jesper Sollerman, +46-8-55 37 85 54
Switzerland: Dr. Martin Steinacher, +41-31-324 23 82
United Kingdom: Mr. Peter Barratt, +44-1793-44 20 25
----------------------------------------------------------------------------
ESO Press Information is available on Receive email notification
the WWW at about important news from
http://www.eso.org/outreach/press-rel/ ESO - subscribe to the
ESO-NEWS Mailing List.
----------------------------------------------------------------------------
Copyright ESO Education & Public Relations Department
Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
----------------------------------------------------------------------------
----------------------------------------------------------------------------
Text with all links and the photos are available on the ESO Website at URL:
http://www.eso.org/outreach/press-rel/pr-2007/pr-12-07.html
----------------------------------------------------------------------------
Contact:
Dirk Froebrich
University of Kent, Canterbury, UK
Phone: +44-1227-827346
Helmut Meusinger
Thuringer Landessternwarte Tautenburg, Germany
Phone: +49-36427-86362
Aleks Scholz
University of St. Andrews, Scotland, UK
Phone: +44-1334-461666
For Immediate Release: 13 March 2007
ESO Science Release 12/07
Star Family Seen Through Dusty Fog
New Globular Cluster Found in Milky Way
Images made with ESO's New Technology Telescope at La Silla by a team of
German astronomers reveal a rich circular cluster of stars in the inner
parts of our Galaxy. Located 30,000 light-years away, this previously
unknown closely-packed group of about 100,000 stars is most likely a new
globular cluster.
Star clusters provide us with unique laboratory conditions to investigate
various aspects of astrophysics. They represent groups of stars with similar
ages, chemical element abundances and distances. Globular clusters, in
particular, are fossils in the Milky Way that provide useful information.
With ages of about 10 billion years, they are among the oldest objects in
our Galaxy -- almost as old as the Universe itself. These massive, spherical
shaped star clusters are therefore witnesses of the early, mysterious ages
of the Universe.
"Moreover, the properties of globular clusters are deeply connected with the
history of their host galaxy," says Dirk Froebrich from the University of
Kent, and lead-author of the paper presenting the results. "We believe today
that galaxy collisions, galaxy cannibalism, as well as galaxy mergers leave
their imprint in the globular cluster population of any given galaxy. Thus,
when investigating globular clusters we hope to be able to use them as an
acid test for our understanding of the formation and evolution of galaxies,"
he adds.
In our own Galaxy about 150 globular clusters are known, each containing
many hundreds of thousands of stars. In contrast to their smaller and less
regularly shaped siblings -- open clusters -- globular clusters are not
concentrated in the galactic disc; rather they are spherically distributed
in the galactic halo, with increasing concentration towards the centre of
the Galaxy. Until the mid-1990s, globular clusters were identified mostly by
eye -- from visual inspection of photographic plates. However, these early
searches are likely to have missed a significant number of globular
clusters, particularly close to the disc of the Galaxy, where dense clouds
of dust and gas obscure the view. In the early times of extragalactic
astronomy this area was called the 'Zone of Avoidance' because extragalactic
stellar systems appeared to be very rare in this part of the sky.
Searching for the missing globular clusters in our Galaxy requires
observations in the infrared, because infrared radiation is able to
penetrate the thick 'galactic fog'. Using modern, sensitive infrared
detectors, this is now possible.
Completing the census is not only a challenge for its own sake, as finding
new globular clusters is useful for several additional reasons. For example,
analysing their orbits allows astronomers to draw conclusions about the
distribution of mass in the Galaxy. Star clusters can therefore be used as
probes for the large-scale structure of the Milky Way.
"It has been estimated that the region close to the Galactic Centre might
contain about 10 so far unknown globular clusters and we have started a
large campaign to unveil and characterise them," explains Helmut Meusinger,
from the Thuringer Landessternwarte Tautenburg, Germany, and part of the
team.
The astronomers carried out a systematic and automated large-scale (14,400
square degrees) search for globular cluster candidates in the entire
Galactic Plane, based on the near-infrared Two Micron All Sky Survey
(2MASS). Eventually, only about a dozen candidate objects remained.
The astronomers observed these candidates with the SofI instrument attached
to ESO's New Technology Telescope (NTT) at La Silla (Chile), taking images
through three different near-infrared filters. The new images are ten times
deeper and have a much better angular resolution than the original 2MASS
images, thereby allowing the astronomers to resolve at least partly the
dense accumulation of stars in the globular cluster candidates.
One of these candidates had the number 1735 in the list of Froebrich,
Scholz, and Raftery, and is therefore denoted as FSR 1735.
"The unique images we have obtained reveal that the nebulous appearance of
the cluster in previous images is in fact due to a large number of faint
stars," says Froebrich. "The images show a beautiful, rich, and circular
accumulation of stars."
From a detailed analysis of the properties of the cluster, the astronomers
arrive at the conclusion that the cluster is about 30,000 light-years away
from us and only 10,000 light-years away from the Galactic Centre, close to
the Galactic Plane.
"All the evidence supports the interpretation that FSR 1735 is a new
globular cluster in the inner Milky Way," says Aleks Scholz, from the
University of St Andrews, UK, and another member of the team. "However, to
be sure, we now need to measure the age of the cluster accurately, and this
requires still deeper observations."
The cluster is about 7 light-years wide (slightly less than twice the
distance between the Sun and its nearest star, Proxima Centauri) but
contains about 100,000 stars for a total estimated mass of 65,000 times the
mass of the Sun. The stars contain between 5 and 8 times less heavy elements
than the Sun.
"On its way to our Solar System, the light coming from the stars in the FSR
1735 cluster has to penetrate a thick cloud of dust and gas," says
Meusinger. "This is one of the reasons why this cluster was hard to find in
previous surveys."
"Is this now the last missing globular cluster in our galaxy?," asks Scholz.
"We really can't be sure. The opaque interiors of the Milky Way may well
have more surprises in store."
More Information:
The team is composed of Dirk Froebrich (University of Kent, UK), Helmut
Meusinger (Thuringer Landessternwarte Tautenburg, Germany), and Aleks Scholz
(University of St Andrews, Scotland, UK).
This research is presented in an article in press in the Monthly Notices of
the Royal Astronomical Society ("FSR 1735 - A new globular cluster candidate
in the inner Galaxy", by Froebrich et al.).
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Finland: Ms. Tiina Raivo, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vnle, +45-33-18 19 97
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-347-230 26 51
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Sweden: Dr. Jesper Sollerman, +46-8-55 37 85 54
Switzerland: Dr. Martin Steinacher, +41-31-324 23 82
United Kingdom: Mr. Peter Barratt, +44-1793-44 20 25
----------------------------------------------------------------------------
ESO Press Information is available on Receive email notification
the WWW at about important news from
http://www.eso.org/outreach/press-rel/ ESO - subscribe to the
ESO-NEWS Mailing List.
----------------------------------------------------------------------------
Copyright ESO Education & Public Relations Department
Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
----------------------------------------------------------------------------