Andrew Yee
February 7th 06, 02:07 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-2006/pr-04-06.html
--------------------------------------------------------------
Contacts
Guido De Marchi
ESA, Noordwijk, The Netherlands
Phone: +31 71 565 8332
For immediate release: 7 February 2006
ESO Press Photo 04/06
How to Steal a Million Stars?
VLT Study Reveals Troubled Past of Globular Cluster Messier 12
Based on observations with ESO's Very Large Telescope, a team
of Italian astronomers reports [1] that the stellar cluster
Messier 12 must have lost to our Milky Way galaxy close to one
million low-mass stars.
"In the solar neighbourhood and in most stellar clusters, the
least massive stars are the most common, and by far", said
Guido De Marchi (ESA), lead author of the study. "Our
observations with ESO's VLT show this is not the case for
Messier 12."
The team, which also includes Luigi Pulone and Francesco Paresce
(INAF, Italy), measured the brightness and colours of more than
16,000 stars within the globular cluster Messier 12 [2] with
the FORS1 multi-mode instrument attached to one of the Unit
Telescopes of ESO's VLT at Cerro Paranal (Chile). The
astronomers could study stars that are 40 million times
fainter than what the unaided eye can see (magnitude 25).
Located at a distance of 23,000 light years in the constellation
Ophiuchus (The Serpent-holder), Messier 12 got its name by being
the 12th entry in the catalogue of nebulous objects compiled in
1774 by French astronomer and comet chaser Charles Messier. It
is also known to astronomers as NGC 6218 and contains about
200,000 stars, most of them having a mass between 20 and 80
percent of the mass of the Sun.
"It is however clear that Messier 12 is surprisingly devoid of
low-mass stars", said De Marchi. "For each solar-like star, we
would expect roughly four times as many stars with half that
mass. Our VLT observations only show an equal number of stars
of different masses."
Globular clusters move in extended elliptical orbits that
periodically take them through the densely populated regions
of our Galaxy, the plane, then high above and below, in the
'halo'. When venturing too close to the innermost and denser
regions of the Milky Way, the 'bulge', a globular cluster can
be perturbed, the smallest stars being ripped away.
"We estimate that Messier 12 lost four times as many stars as
it still has", said Francesco Paresce. "That is, roughly one
million stars must have been ejected into the halo of our
Milky Way."
The total remaining lifetime of Messier 12 is predicted to be
about 4.5 billion years, i.e. about a third of its present age.
This is very short compared to the typical expected globular
cluster's lifetime, which is about 20 billion years.
The same team of astronomers had found in 1999, another example
of a globular cluster that lost a large fraction of its original
content (see ESO PR 04/99).
The scientists hope to discover and study many more clusters
like these, since catching clusters while being disrupted
should clarify the dynamics of the process that shaped the
halo of our home galaxy, the Milky Way.
High resolution images and their captions are available at
http://www.eso.org/outreach/press-rel/pr-2006/phot-04-06.html
A press release on this is also issued by INAF in Italian and is available
at
http://www.inaf.it/comunicati_stampa/cs070206/Inaf-04-06.html
Notes
[1]: The article ("Why is the mass function of NGC 6218 flat?"
by Guido de Marchi, Luigi Pulone, and Francesco Paresce) to be
published in Astronomy and Astrophysics is available in PDF
format at
<http://www.edpsciences.org/articles/aa/pdf/press-releases/PRAA200601.pdf>
[2]: Messier 12 is one of about 200 globular clusters known in
our Galaxy. These are large groupings of 10,000 to more than
a million stars that were formed together in the youth of the
Milky Way, about 12 to 13 billion years ago. Globular clusters
are a key tool for astronomers, because all the stars in a
globular cluster share a common history. They were all born
together, at the same time and place, and only differ from one
another in their mass. By accurately measuring the brightness
of the stars, astronomers can determine their relative sizes
and stage of evolution precisely. Globular clusters are thus
very helpful for testing theories of how stars evolve.
ESO Media Contacts are on the Public Affairs Dept. Contact page,
http://www.eso.org/outreach/epr/epr-contact.html
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Finland: Ms. Riitta Tirronen, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vørnle, +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, benacchio @ inaf.it
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 the WWW at
http://www.eso.org/outreach/press-rel/
--------------------------------------------------------------
(c) 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-2006/pr-04-06.html
--------------------------------------------------------------
Contacts
Guido De Marchi
ESA, Noordwijk, The Netherlands
Phone: +31 71 565 8332
For immediate release: 7 February 2006
ESO Press Photo 04/06
How to Steal a Million Stars?
VLT Study Reveals Troubled Past of Globular Cluster Messier 12
Based on observations with ESO's Very Large Telescope, a team
of Italian astronomers reports [1] that the stellar cluster
Messier 12 must have lost to our Milky Way galaxy close to one
million low-mass stars.
"In the solar neighbourhood and in most stellar clusters, the
least massive stars are the most common, and by far", said
Guido De Marchi (ESA), lead author of the study. "Our
observations with ESO's VLT show this is not the case for
Messier 12."
The team, which also includes Luigi Pulone and Francesco Paresce
(INAF, Italy), measured the brightness and colours of more than
16,000 stars within the globular cluster Messier 12 [2] with
the FORS1 multi-mode instrument attached to one of the Unit
Telescopes of ESO's VLT at Cerro Paranal (Chile). The
astronomers could study stars that are 40 million times
fainter than what the unaided eye can see (magnitude 25).
Located at a distance of 23,000 light years in the constellation
Ophiuchus (The Serpent-holder), Messier 12 got its name by being
the 12th entry in the catalogue of nebulous objects compiled in
1774 by French astronomer and comet chaser Charles Messier. It
is also known to astronomers as NGC 6218 and contains about
200,000 stars, most of them having a mass between 20 and 80
percent of the mass of the Sun.
"It is however clear that Messier 12 is surprisingly devoid of
low-mass stars", said De Marchi. "For each solar-like star, we
would expect roughly four times as many stars with half that
mass. Our VLT observations only show an equal number of stars
of different masses."
Globular clusters move in extended elliptical orbits that
periodically take them through the densely populated regions
of our Galaxy, the plane, then high above and below, in the
'halo'. When venturing too close to the innermost and denser
regions of the Milky Way, the 'bulge', a globular cluster can
be perturbed, the smallest stars being ripped away.
"We estimate that Messier 12 lost four times as many stars as
it still has", said Francesco Paresce. "That is, roughly one
million stars must have been ejected into the halo of our
Milky Way."
The total remaining lifetime of Messier 12 is predicted to be
about 4.5 billion years, i.e. about a third of its present age.
This is very short compared to the typical expected globular
cluster's lifetime, which is about 20 billion years.
The same team of astronomers had found in 1999, another example
of a globular cluster that lost a large fraction of its original
content (see ESO PR 04/99).
The scientists hope to discover and study many more clusters
like these, since catching clusters while being disrupted
should clarify the dynamics of the process that shaped the
halo of our home galaxy, the Milky Way.
High resolution images and their captions are available at
http://www.eso.org/outreach/press-rel/pr-2006/phot-04-06.html
A press release on this is also issued by INAF in Italian and is available
at
http://www.inaf.it/comunicati_stampa/cs070206/Inaf-04-06.html
Notes
[1]: The article ("Why is the mass function of NGC 6218 flat?"
by Guido de Marchi, Luigi Pulone, and Francesco Paresce) to be
published in Astronomy and Astrophysics is available in PDF
format at
<http://www.edpsciences.org/articles/aa/pdf/press-releases/PRAA200601.pdf>
[2]: Messier 12 is one of about 200 globular clusters known in
our Galaxy. These are large groupings of 10,000 to more than
a million stars that were formed together in the youth of the
Milky Way, about 12 to 13 billion years ago. Globular clusters
are a key tool for astronomers, because all the stars in a
globular cluster share a common history. They were all born
together, at the same time and place, and only differ from one
another in their mass. By accurately measuring the brightness
of the stars, astronomers can determine their relative sizes
and stage of evolution precisely. Globular clusters are thus
very helpful for testing theories of how stars evolve.
ESO Media Contacts are on the Public Affairs Dept. Contact page,
http://www.eso.org/outreach/epr/epr-contact.html
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Finland: Ms. Riitta Tirronen, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vørnle, +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, benacchio @ inaf.it
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 the WWW at
http://www.eso.org/outreach/press-rel/
--------------------------------------------------------------
(c) ESO Education & Public Relations Department
Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
--------------------------------------------------------------