Andrew Yee[_1_]
February 7th 07, 03:06 PM
Rob Gutro
Goddard Space Flight Center, Greenbelt, Md. February 6, 2007
(Phone: 301/286-4044)
High-Energy 'Relic' Wind Reveals Past Behavior of Dead Stars
A team of astronomers from France and South Africa announced the first
catalog of a new type of gamma-ray source, a dozen clouds of "relic"
radiation from dead stars that reveal information about the energetic past
of these celestial objects.
These findings were presented on Feb. 5, 2007 at the first Gamma Ray
Large-Area Space Telescope (GLAST) scientific Symposium meeting in Palo
Alto, Calif., by Dr. Arache Djannati-Ata an astrophysicist from the
Astroparticle & Cosmology (APC) laboratory in Paris, France.
Djannati-Ata Drs. Anne Lemie and Ris Terrier, also from the APC, and Prof.
Okkie de Jager from Space Unit, North Western University, in Potchefstroom,
South Africa, are members of the High Energy Stereoscopic System (H.E.S.S.),
a multi-national collaboration that made this finding. H.E.S.S. is a group
of four 40-foot telescopes located in Namibia, Africa.
This catalog of "relic" nebulae was obtained through detailed study and
modeling of sources discovered during 2004 and 2005 by the H.E.S.S.
collaboration.
The very high-energy gamma rays detected by H.E.S.S. appear to be coming
from regions near to pulsars -- rapidly spinning ultra-dense objects created
when a massive star explodes as a supernova -- but not close enough to be
produced directly by the pulsars themselves. While it has been known
previously that pulsars emit a "wind" of particles, it had not been thought
that the extent of gamma-ray emission from the wind could be on this large a
scale: many of these objects are surrounded by a gamma-ray glow many dozens
of light years across.
Djannati-Ataand other team members have shown that these winds, which are
powered by the pulsar over all its lifetime, are indeed the source of these
very energetic gamma rays.
Pulsars, first discovered in 1967, are the extremely dense remnants of
exploded stars, which typically have a mass that is 1.4 times that of the
Sun squeezed down into a ball only a few miles across. Pulsars have very
strong magnetic fields, billions and even trillions as times as powerful as
the Earth's. This incredible magnetism can accelerate electrons to speeds to
very nearly that of light. When such an electron slams into a particle of
light (a photon), the photon can pick up the energy of the electron in a
process known as "inverse Compton scattering." An ordinary photon of light
can be energized tremendously, becoming a super-high-energy gamma ray. The
gamma rays detected by H.E.S.S. have a trillion times the energy of visible
light.
Winds from pulsars have been known for many years. The most famous example
is that from the pulsar in the center of the Crab Nebula, a bright cloud of
expanding gas from a star that exploded in the year 1054. In that case, the
wind generates X-rays (which have less energy than gamma rays) through
synchrotron radiation and gamma rays through the inverse Compton scattering.
These X-rays and gamma rays are seen coming from gas a few light years
across at most.
The objects detected by the H.E.S.S. team are far more extended. The glow of
gamma rays seen from the pulsar PSR B1823-13, for example, is approximately
100 light years across. A light year is the distance a particle of light,
traveling 186,000 miles per second travels in one year.
The larger size of this gamma-ray emitting region means the electrons
producing the gamma rays have traveled further and so come from a period
earlier in the pulsar's history. This in turn means that studying the gamma
rays from pulsar winds can give astronomers insight into the history of the
pulsar itself and how its magnetic field has changed over the past tens of
thousands of years.
Commenting on these results, Djannati-Atasaid, "About half of the sources
discovered by H.E.S.S. in the central parts of the Galactic Plane are most
likely large relic gamma-ray nebulae associated with middle-aged pulsars:
these nebulae should then constitute a major component of the very high
energy gamma-ray sky. Further observations in radio, X-rays, gamma-rays and
detailed studies of these objects should confirm further these results and
yield precious insights on the evolution of the pulsars and their nebula
including constraints on the magnetic field evolution with time."
This presentation was made at the GLAST meeting, as the research is relevant
to this upcoming mission. Observations with GLAST would aid greatly in
understanding the physics of these objects, filling a gap in the energies
detected by other telescopes. GLAST is due for launch in late 2007. It is a
collaborative effort between NASA, the U.S. Department of Energy and
institutions in France, Germany, Japan, Italy and Sweden. General Dynamics
has been chosen to build the spacecraft.
[NOTE: Images and weblinks supporting this release are available at
http://www.nasa.gov/centers/goddard/news/topstory/2007/relic_wind.html ]
Goddard Space Flight Center, Greenbelt, Md. February 6, 2007
(Phone: 301/286-4044)
High-Energy 'Relic' Wind Reveals Past Behavior of Dead Stars
A team of astronomers from France and South Africa announced the first
catalog of a new type of gamma-ray source, a dozen clouds of "relic"
radiation from dead stars that reveal information about the energetic past
of these celestial objects.
These findings were presented on Feb. 5, 2007 at the first Gamma Ray
Large-Area Space Telescope (GLAST) scientific Symposium meeting in Palo
Alto, Calif., by Dr. Arache Djannati-Ata an astrophysicist from the
Astroparticle & Cosmology (APC) laboratory in Paris, France.
Djannati-Ata Drs. Anne Lemie and Ris Terrier, also from the APC, and Prof.
Okkie de Jager from Space Unit, North Western University, in Potchefstroom,
South Africa, are members of the High Energy Stereoscopic System (H.E.S.S.),
a multi-national collaboration that made this finding. H.E.S.S. is a group
of four 40-foot telescopes located in Namibia, Africa.
This catalog of "relic" nebulae was obtained through detailed study and
modeling of sources discovered during 2004 and 2005 by the H.E.S.S.
collaboration.
The very high-energy gamma rays detected by H.E.S.S. appear to be coming
from regions near to pulsars -- rapidly spinning ultra-dense objects created
when a massive star explodes as a supernova -- but not close enough to be
produced directly by the pulsars themselves. While it has been known
previously that pulsars emit a "wind" of particles, it had not been thought
that the extent of gamma-ray emission from the wind could be on this large a
scale: many of these objects are surrounded by a gamma-ray glow many dozens
of light years across.
Djannati-Ataand other team members have shown that these winds, which are
powered by the pulsar over all its lifetime, are indeed the source of these
very energetic gamma rays.
Pulsars, first discovered in 1967, are the extremely dense remnants of
exploded stars, which typically have a mass that is 1.4 times that of the
Sun squeezed down into a ball only a few miles across. Pulsars have very
strong magnetic fields, billions and even trillions as times as powerful as
the Earth's. This incredible magnetism can accelerate electrons to speeds to
very nearly that of light. When such an electron slams into a particle of
light (a photon), the photon can pick up the energy of the electron in a
process known as "inverse Compton scattering." An ordinary photon of light
can be energized tremendously, becoming a super-high-energy gamma ray. The
gamma rays detected by H.E.S.S. have a trillion times the energy of visible
light.
Winds from pulsars have been known for many years. The most famous example
is that from the pulsar in the center of the Crab Nebula, a bright cloud of
expanding gas from a star that exploded in the year 1054. In that case, the
wind generates X-rays (which have less energy than gamma rays) through
synchrotron radiation and gamma rays through the inverse Compton scattering.
These X-rays and gamma rays are seen coming from gas a few light years
across at most.
The objects detected by the H.E.S.S. team are far more extended. The glow of
gamma rays seen from the pulsar PSR B1823-13, for example, is approximately
100 light years across. A light year is the distance a particle of light,
traveling 186,000 miles per second travels in one year.
The larger size of this gamma-ray emitting region means the electrons
producing the gamma rays have traveled further and so come from a period
earlier in the pulsar's history. This in turn means that studying the gamma
rays from pulsar winds can give astronomers insight into the history of the
pulsar itself and how its magnetic field has changed over the past tens of
thousands of years.
Commenting on these results, Djannati-Atasaid, "About half of the sources
discovered by H.E.S.S. in the central parts of the Galactic Plane are most
likely large relic gamma-ray nebulae associated with middle-aged pulsars:
these nebulae should then constitute a major component of the very high
energy gamma-ray sky. Further observations in radio, X-rays, gamma-rays and
detailed studies of these objects should confirm further these results and
yield precious insights on the evolution of the pulsars and their nebula
including constraints on the magnetic field evolution with time."
This presentation was made at the GLAST meeting, as the research is relevant
to this upcoming mission. Observations with GLAST would aid greatly in
understanding the physics of these objects, filling a gap in the energies
detected by other telescopes. GLAST is due for launch in late 2007. It is a
collaborative effort between NASA, the U.S. Department of Energy and
institutions in France, Germany, Japan, Italy and Sweden. General Dynamics
has been chosen to build the spacecraft.
[NOTE: Images and weblinks supporting this release are available at
http://www.nasa.gov/centers/goddard/news/topstory/2007/relic_wind.html ]