From: LARRY KLAES (ljk4_at_msn.com)
Date: Mon Apr 28 2008 - 09:54:24 PDT
>From: "AAS Press Officer Dr. Steve Maran" <steve.maran_at_aas.org>
>To: "Steve Maran" <steve.maran_at_aas.org>
>Subject: CXC: Oldest Objects are Surprising Immature
>Date: Mon, 28 Apr 2008 12:02:28 -0400
>
THE FOLLOWING RELEASE WAS RECEIVED FROM THE CHANDRA X-RAY CENTER, IN
CAMBRIDGE, MASSACHUSETTS, AND IS FORWARDED FOR YOUR INFORMATION.
(FORWARDING DOES NOT IMPLY ENDORSEMENT BY THE AMERICAN ASTRONOMICAL
SOCIETY.) Steve Maran, American Astronomical Society
steve.maran_at_aas.org 1-202-328-2010 x116
For Release: April 28, 2008
Jennifer Morcone
Marshall Space Flight Center, Huntsville, Ala.
1-256-544-7199
jennifer.j.morcone_at_nasa.gov
Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
1-617-496-7998
mwatzke_at_cfa.harvard.edu
OLDEST KNOWN OBJECTS ARE SURPRISINGLY IMMATURE
Some of the oldest objects in the Universe may still have a long way
to go, according to a new study using NASA's Chandra X-ray
Observatory. These new results indicate that globular clusters might
be surprisingly less mature in their development than previously
thought.
Globular clusters are incredibly dense bunches of up to millions of
stars that are found in the outskirts of galaxies, including the Milky
Way. They are among the oldest known objects in the Universe, with
most estimates of their ages ranging from 9 to 13 billions of years
old. Understanding the nature of globular clusters is very important
as they are thought to contain some of the first stars to form in a
galaxy.
"For many years, globular clusters have been used as wonderful natural
laboratories to study the evolution and interaction of stars," said
John Fregeau of Northwestern University, who conducted the study.
"So, it's exciting to discover something that may be new and
fundamental about the way they evolve."
Conventional wisdom is that globular clusters pass through three
phases of development, corresponding to adolescence, middle age, and
old age. For years, it's been thought that most globular clusters are
middle-aged with a few being toward the end of the lives. However,
Chandra data along with theoretical work suggest this may not be the
case.
When single and double stars interact in the crowded centers of
globular clusters, new double stars can form that transfer mass and
give off X-rays.
Since such double stars are expected to mostly be formed in the middle
of a globular cluster's life and then lost in old age, the relative
number of X-ray sources gives clues about the stage of evolution the
cluster is in.
A new study by Fregeau of 13 globular clusters in the Milky Way shows
that three of them have unusually large number of X-ray sources, or
X-ray binaries, suggesting the clusters are middle-aged. Previously,
these globular clusters had been classified as being in old age
because they had very tight concentrations of stars in their centers,
another litmus test of age used by astronomers.
The implication is that most globular clusters, including the other
ten studied by Fregeau, are not in middle age, as previously thought,
but are actually in adolescence.
"It's remarkable that these objects, which are thought to be some of
the oldest in the Universe, may really be very immature," said Fregeau
whose paper appears in The Astrophysical Journal. "This would
represent a major change in thinking about the current evolutionary
status of globular clusters."
If confirmed, this result would help reconcile other observations with
recent theoretical work that suggest the tightness of the central
concentration of stars in the most evolved globular clusters is
consistent with them being in middle age, not old age. Other
theoretical studies have suggested it can take longer than the age of
the Universe for globular clusters to reach old age.
Besides improving the understanding of the basic evolution of globular
clusters, this result has implications for understanding stellar
interactions in dense environments. It also removes the need for
exotic mechanisms - some involving black holes - that were thought to
be needed to prevent the many middle-aged clusters from collapsing
into old age.
"Some exotic scenarios, including some of my own, have been invoked to
try to make sense of the observations and save the old theory," said
Fregeau. "If this result holds up, we don't have to worry about the
exotic scenarios any more."
Adolescence for a globular cluster is used here to describe a phase
after cluster formation when the stars near the center of the cluster
collapse inwards. Middle age refers to a phase when the interactions
of double stars and the formation of X-ray sources near the center of
the cluster prevents it from further collapse. Finally, old age
describes when binaries in the center of the cluster run out and the
center of the cluster collapses inwards.
NASA's Marshall Space Flight Center, Huntsville, Ala., manages the
Chandra program for the agency's Science Mission Directorate. The
Smithsonian Astrophysical Observatory controls science and flight
operations from the Chandra X-ray Center in Cambridge, Mass.
Additional information and images are available at:
http://chandra.harvard.edu and http://chandra.nasa.gov
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