Andrew Yee[_1_]
April 29th 08, 12:19 AM
Jennifer Morcone
Marshall Space Flight Center, Huntsville, Ala. April 28, 2008
256-544-7199
Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
617-496-7998
News release: 08-054
Oldest Known Objects May Be 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, dense bunches of up to millions of stars found in all
galaxies, are among the oldest known objects in the Universe, with most
estimates of their ages ranging from 9 to 13 billions of years old. As such
they contain some of the first stars to form in a galaxy and understanding
their evolution is critical to understanding the evolution of galaxies.
"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
evolution or development of their structure, corresponding to adolescence,
middle age, and old age. These "ages" refer to the evolutionary state of the
cluster, not the physical ages of the individual stars.
In the adolescent phase, the stars near the center of the cluster collapse
inward. Middle age refers to a phase when the interactions of double stars
near the center of the cluster prevents it from further collapse. Finally,
old age describes when binaries in the center of the cluster are disrupted
or ejected, and the center of the cluster collapses inwards.
For years, it has been thought that most globular clusters are middle-aged
with a few being toward the end of their evolution. 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, 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 evolution 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 the middle age of their evolution, 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 in their development,"
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 a middle, rather than an advanced phase of evolution.
Other theoretical studies have suggested it can take longer than the current
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.
"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."
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/photo/2008/gclust/
and
http://chandra.nasa.gov
Marshall Space Flight Center, Huntsville, Ala. April 28, 2008
256-544-7199
Megan Watzke
Chandra X-ray Center, Cambridge, Mass.
617-496-7998
News release: 08-054
Oldest Known Objects May Be 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, dense bunches of up to millions of stars found in all
galaxies, are among the oldest known objects in the Universe, with most
estimates of their ages ranging from 9 to 13 billions of years old. As such
they contain some of the first stars to form in a galaxy and understanding
their evolution is critical to understanding the evolution of galaxies.
"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
evolution or development of their structure, corresponding to adolescence,
middle age, and old age. These "ages" refer to the evolutionary state of the
cluster, not the physical ages of the individual stars.
In the adolescent phase, the stars near the center of the cluster collapse
inward. Middle age refers to a phase when the interactions of double stars
near the center of the cluster prevents it from further collapse. Finally,
old age describes when binaries in the center of the cluster are disrupted
or ejected, and the center of the cluster collapses inwards.
For years, it has been thought that most globular clusters are middle-aged
with a few being toward the end of their evolution. 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, 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 evolution 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 the middle age of their evolution, 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 in their development,"
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 a middle, rather than an advanced phase of evolution.
Other theoretical studies have suggested it can take longer than the current
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.
"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."
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/photo/2008/gclust/
and
http://chandra.nasa.gov