Andrew Yee
January 5th 06, 07:46 PM
Press and Public Relations Department
Max Planck Society for the Advancement of Science
Munich, Germany
Contact:
Dr Roland Diehl
Max-Planck-Institute for Extraterrestrial Physics
Garching, Germany
Tel.: +49 (0)89 30000-3850 and +49 163 7916621
January 4th, 2006
SP / 2006 (1)
A Picture of Radioactivity from the Inner Part of Our Galaxy
Max Planck astronomers, using INTEGRAL, identify regions of new
atomic-nuclei production
Our environment is composed of "stardust", the chemical elements formed
long ago in stellar interiors and supernovae. This process of nuclear
fusion leads to the emission of gamma rays, which easily reach us from all
regions of the Milky Way Galaxy. An international team of researchers led
by Roland Diehl of the Max Planck Institute for Extraterrestrial Physics
in Garching, Germany now has been using ESA's INTEGRAL satellite to
determine that gamma rays from radioactive aluminium (26Al) originate from
the central regions of the Galaxy. This implies that production of new
atomic nuclei is an on-going process and occurs in star forming regions
galaxy-wide. From those new observations, the astronomers estimate that
the total amount of radioactive 26Al in the Galaxy is equivalent to three
solar masses. This amount of production corresponds to a galactic rate of
supernovae from gravitational collapse of about one every 50 years
(Nature, 5 January 2005).
We are familiar with radioactive isotopes from medical radiology tests and
treatments. Astrophysicists use penetrating gamma rays emitted during
radioactive decay to obtain direct messages from cosmic nuclear fusion
reactions, through special telescopes operated in near-Earth space.
Gamma-rays from decaying 26Al were detected in 1978, and because of its
known half life of 720,000 years, this provided direct proof of
currently-ongoing nucleosynthesis. Supernova 1987 in the Large Magellanic
Cloud galaxy was then observed through short-lived radioactive gamma rays.
This led scientists to believe that these nuclei had been produced within
this supernova event.
Astrophysicists from the Max Planck Institute for Extraterrestrial Physics
in Garching were part of the pioneering sky study on such radioactive
gamma rays. Roland Diehl and his MPE colleagues were able to show in the
mid-1990s that this relatively long-lived radioactivity is present over
large regions along the plane of the Galaxy. Hence, production of new
atomic nuclei is common in the Galaxy. This was a scientific surprise,
because at the end of the 1970s, traces of 26Al decay had been found in
meteorite samples originating from the early solar system. This finding
had been interpreted as evidence that the 26Al radioactivity was a key
ingredient in the formation of planetary bodies of the solar system;
radioactive heat is a necessary ingredient to melt cometary material to
form rocks. Therefore it was commonly believed at that time that 26Al
radioactivity was intimately related to the early solar system; now,
however, we have signals of currently-decaying 26Al all over the Galaxy. A
unifying picture emerged from nucleosynthesis theories of the 1950s, which
claimed that all nuclear species were produced inside stars, novae, and
supernovae. 26Al could be the result of such stellar processing,
occurring, with some enhancement, near the formation site of the solar
system 4.5 billion years ago. Alternatively, special conditions during the
formation of the solar system were thought to cause high-energy particle
collisions, which could produce 26Al locally. These two competing
scenarios are still debated and remain an unsolved puzzle. Although gamma
rays clearly show widespread cosmic nucleosynthesis, it remains to be
understood if only this, or additional local high-energy reactions, has
produced the amount of 26Al inferred for the early solar system. One key
to answering this question is the determination of the total 26Al content
of the Galaxy.
Gamma-Ray Spectroscopy with INTEGRAL
The new observational capabilities of ESA's INTEGRAL satellite now provide
fresh insights. INTEGRAL carries a spectrometer for gamma rays, which is
capable of recording the energy of gamma ray photons with unprecedented
precision. This is because its camera is composed of Ge semiconductor
detectors, similar to the ones which have been used in terrestrial nuclear
laboratories and are operated at temperatures below 90K (corresponding to
-183 C ) to reduce noise from thermal motions of atoms. The SPI satellite
telescope using this camera has been operated aboard INTEGRAL since
October 2002 in space at altitudes up to 150,000 kilometres above Earth.
Cosmic radiation bombarding the telescope in space, however, leads to
destruction of the camera crystals. French team colleagues from CESR
Toulouse, who have been developing this instrument together with several
other European institutes, counteract the problem using a special trick.
Periodically, the camera is heated to ~100 C for a few days, which repairs
crystal damage and maintains the precision of the spectrometer over the
years. This is important because celestial 26Al gamma rays arrive at the
instrument at a rate of one every few minutes. Thus many months of
operation are required to make a precise spectral recording.
Roland Diehl and his colleagues were able to measure the recorded 26Al
gamma ray line energies along the plane of the inner Galaxy. They searched
for variations in the line energy, which could provide hints for the
location of the sources within the plane of the Galaxy. The disc of the
Galaxy rotates about its central axis, but not like a rotating wheel does.
Rather, inner regions move faster, to counteract gravitational pull from
the central gravity by increased centrifugal forces. Therefore, if we look
into the central regions, parts of the Galaxy have rather large relative
motions, compared to the sun on its path around the galactic centre.
Nuclear physics specifies that 26Al decay gamma rays have an intrinsic
energy value of 1808.65 kilo electron volts. They are moderated by the
Doppler effect in a characteristic way, if sources of 26Al gamma rays are
observed from inner regions of the Galaxy. This characteristic pattern is
what the researchers in Garching now found in their INTEGRAL data.
We learn from this measurement that indeed 26Al decay gamma rays reach us
from the inner regions of the Galaxy, rather than from foreground regions
along the same line of sight, which might have locally-enhanced 26Al
production. Foreground regions would not have the observed high relative
velocity. This leads us to conclude that observed 26Al gamma rays can be
attributed to Galaxy-wide regions of nucleosynthesis, and a geometrical
model of the Galaxy can be used to translate the observed intensity into
an amount of 26Al for the entire Galaxy.
The Garching team estimates that the Galaxy contains a radioactive 26Al
mass of about three solar masses. This is a lot, given that 26Al is an
extremely rare isotope; the fraction estimated for the early solar system
is 5/100,000 of 26Al , in proportion to its stable aluminium isotope (27Al
). From the observed distribution of 26Al gamma ray emission along the
plane of the Galaxy, astrophysicists had inferred that the likely sources
are mainly massive stars. Because massive stars terminate their evolution
in a supernova, the researchers could estimate the rate of such supernova
events, which correspond, on average, to the production of the observed
amount of 26Al . They obtained a rate of two supernovae per century. This
number is consistent with what indirectly had been inferred from
observations of other galaxies and their comparison to the Milky Way.
Thus, the new INTEGRAL results confirm both the production of 26Al in
massive stars and supernovae as well as the rate of supernovae, which is
one of the key parameters of our own Galaxy.
The INTEGRAL spectrometer for gamma rays will continue to operate for
several more years. Astrophysicists thus hope even to increase the
precision of such measurements. Project leader Roland Diehl explains,
"these gamma ray observations provide insights about our home galaxy,
which are difficult to obtain at other wavelengths due to interstellar
absorption."
These INTEGRAL based studies involve research by the Max Planck Institute
for Extraterrestrial Physics; the Centre d'Etude Spatiale des Rayonnements
and Université Paul Sabatier, Toulouse,France; the DSM/DAPNIA/Service
d'Astrophysique, CEA Saclay, Gif-Sur-Yvette,France; Clemson University,
Clemson,USA; ESA/ESTEC, Noordwijk, the Netherlands; and the Space Sciences
Laboratory, Berkeley,USA.
Related links:
[1] Further information about INTEGRAL
http://www.mpe.mpg.de/gamma/instruments/integral/www/integral.html
[2] MPG Annual Report 2005 "More than hot: Sources of Cosmic Gamma-Rays"
(in German)
<http://www.mpg.de/bilderBerichteDokumente/dokumentation/jahrbuch/2005/extraterrestrische_physik/forschungsSchwerpunkt/index.html>
[3] Additional informations and images
http://www.mpe.mpg.de/gamma/science/lines/26Al/26Al.html
Original work:
Roland Diehl, Hubert Halloin, Karsten Kretschmer, Giselher G. Lichti,
Volker Schönfelder, Andrew W.Strong, Andreas von Kienlin, Wei Wang, Pierre
Jean, Jürgen Knödlseder, Jean-Pierre Roques, Georg Weidenspointner,
Stephane Schanne, Dieter H. Hartmann, Christoph Winkler, and Cornelia
Wunderer
Radioactive 26Al and massive stars
Nature, 5 January 2005
IMAGE CAPTIONS:
[Image 1:
<http://www.mpg.de/bilderBerichteDokumente/multimedial/bilderWissenschaft/2005/12/Diehl0501/presselogin/Web_Zoom.jpeg>
(193KB)]
Radioactive decay of unstable isotopes leads to emission of gamma rays
with a characteristic energy (coloured) being determined by properties of
the atomic nucleus. ESA¹s INTEGRAL satellite observatory has been
measuring such gamma rays since October 2002. Radioactive isotopes are
by-products of nuclear fusion reactions, which produce new atomic nuclei
in stellar interiors and in supernovae. In the gamma ray light of 26Al
isotopes, which decay after about a million years to magnesium, one sees
the radioactive glow of regions of the Galaxy with recent production of
new nuclei. Visible light, on the other hand, often cannot reach us from
stars in those regions, due to occulting interstellar gas clouds.
Image: Max Planck Institute for Extraterrestrial Physics
[Image 2:
<http://www.mpg.de/bilderBerichteDokumente/multimedial/bilderWissenschaft/2005/12/Diehl0502/presselogin/Web_Zoom.jpeg>
(121KB)]
Expected line shifts from the Doppler effect along the plane of the
Galaxy, as they result from galactic rotation. The modelled distribution
of sources (coloured) agree with the measured line position changes from
INTEGRAL (crosses).
Image: Max Planck Institute for Extraterrestrial Physics
Max Planck Society for the Advancement of Science
Munich, Germany
Contact:
Dr Roland Diehl
Max-Planck-Institute for Extraterrestrial Physics
Garching, Germany
Tel.: +49 (0)89 30000-3850 and +49 163 7916621
January 4th, 2006
SP / 2006 (1)
A Picture of Radioactivity from the Inner Part of Our Galaxy
Max Planck astronomers, using INTEGRAL, identify regions of new
atomic-nuclei production
Our environment is composed of "stardust", the chemical elements formed
long ago in stellar interiors and supernovae. This process of nuclear
fusion leads to the emission of gamma rays, which easily reach us from all
regions of the Milky Way Galaxy. An international team of researchers led
by Roland Diehl of the Max Planck Institute for Extraterrestrial Physics
in Garching, Germany now has been using ESA's INTEGRAL satellite to
determine that gamma rays from radioactive aluminium (26Al) originate from
the central regions of the Galaxy. This implies that production of new
atomic nuclei is an on-going process and occurs in star forming regions
galaxy-wide. From those new observations, the astronomers estimate that
the total amount of radioactive 26Al in the Galaxy is equivalent to three
solar masses. This amount of production corresponds to a galactic rate of
supernovae from gravitational collapse of about one every 50 years
(Nature, 5 January 2005).
We are familiar with radioactive isotopes from medical radiology tests and
treatments. Astrophysicists use penetrating gamma rays emitted during
radioactive decay to obtain direct messages from cosmic nuclear fusion
reactions, through special telescopes operated in near-Earth space.
Gamma-rays from decaying 26Al were detected in 1978, and because of its
known half life of 720,000 years, this provided direct proof of
currently-ongoing nucleosynthesis. Supernova 1987 in the Large Magellanic
Cloud galaxy was then observed through short-lived radioactive gamma rays.
This led scientists to believe that these nuclei had been produced within
this supernova event.
Astrophysicists from the Max Planck Institute for Extraterrestrial Physics
in Garching were part of the pioneering sky study on such radioactive
gamma rays. Roland Diehl and his MPE colleagues were able to show in the
mid-1990s that this relatively long-lived radioactivity is present over
large regions along the plane of the Galaxy. Hence, production of new
atomic nuclei is common in the Galaxy. This was a scientific surprise,
because at the end of the 1970s, traces of 26Al decay had been found in
meteorite samples originating from the early solar system. This finding
had been interpreted as evidence that the 26Al radioactivity was a key
ingredient in the formation of planetary bodies of the solar system;
radioactive heat is a necessary ingredient to melt cometary material to
form rocks. Therefore it was commonly believed at that time that 26Al
radioactivity was intimately related to the early solar system; now,
however, we have signals of currently-decaying 26Al all over the Galaxy. A
unifying picture emerged from nucleosynthesis theories of the 1950s, which
claimed that all nuclear species were produced inside stars, novae, and
supernovae. 26Al could be the result of such stellar processing,
occurring, with some enhancement, near the formation site of the solar
system 4.5 billion years ago. Alternatively, special conditions during the
formation of the solar system were thought to cause high-energy particle
collisions, which could produce 26Al locally. These two competing
scenarios are still debated and remain an unsolved puzzle. Although gamma
rays clearly show widespread cosmic nucleosynthesis, it remains to be
understood if only this, or additional local high-energy reactions, has
produced the amount of 26Al inferred for the early solar system. One key
to answering this question is the determination of the total 26Al content
of the Galaxy.
Gamma-Ray Spectroscopy with INTEGRAL
The new observational capabilities of ESA's INTEGRAL satellite now provide
fresh insights. INTEGRAL carries a spectrometer for gamma rays, which is
capable of recording the energy of gamma ray photons with unprecedented
precision. This is because its camera is composed of Ge semiconductor
detectors, similar to the ones which have been used in terrestrial nuclear
laboratories and are operated at temperatures below 90K (corresponding to
-183 C ) to reduce noise from thermal motions of atoms. The SPI satellite
telescope using this camera has been operated aboard INTEGRAL since
October 2002 in space at altitudes up to 150,000 kilometres above Earth.
Cosmic radiation bombarding the telescope in space, however, leads to
destruction of the camera crystals. French team colleagues from CESR
Toulouse, who have been developing this instrument together with several
other European institutes, counteract the problem using a special trick.
Periodically, the camera is heated to ~100 C for a few days, which repairs
crystal damage and maintains the precision of the spectrometer over the
years. This is important because celestial 26Al gamma rays arrive at the
instrument at a rate of one every few minutes. Thus many months of
operation are required to make a precise spectral recording.
Roland Diehl and his colleagues were able to measure the recorded 26Al
gamma ray line energies along the plane of the inner Galaxy. They searched
for variations in the line energy, which could provide hints for the
location of the sources within the plane of the Galaxy. The disc of the
Galaxy rotates about its central axis, but not like a rotating wheel does.
Rather, inner regions move faster, to counteract gravitational pull from
the central gravity by increased centrifugal forces. Therefore, if we look
into the central regions, parts of the Galaxy have rather large relative
motions, compared to the sun on its path around the galactic centre.
Nuclear physics specifies that 26Al decay gamma rays have an intrinsic
energy value of 1808.65 kilo electron volts. They are moderated by the
Doppler effect in a characteristic way, if sources of 26Al gamma rays are
observed from inner regions of the Galaxy. This characteristic pattern is
what the researchers in Garching now found in their INTEGRAL data.
We learn from this measurement that indeed 26Al decay gamma rays reach us
from the inner regions of the Galaxy, rather than from foreground regions
along the same line of sight, which might have locally-enhanced 26Al
production. Foreground regions would not have the observed high relative
velocity. This leads us to conclude that observed 26Al gamma rays can be
attributed to Galaxy-wide regions of nucleosynthesis, and a geometrical
model of the Galaxy can be used to translate the observed intensity into
an amount of 26Al for the entire Galaxy.
The Garching team estimates that the Galaxy contains a radioactive 26Al
mass of about three solar masses. This is a lot, given that 26Al is an
extremely rare isotope; the fraction estimated for the early solar system
is 5/100,000 of 26Al , in proportion to its stable aluminium isotope (27Al
). From the observed distribution of 26Al gamma ray emission along the
plane of the Galaxy, astrophysicists had inferred that the likely sources
are mainly massive stars. Because massive stars terminate their evolution
in a supernova, the researchers could estimate the rate of such supernova
events, which correspond, on average, to the production of the observed
amount of 26Al . They obtained a rate of two supernovae per century. This
number is consistent with what indirectly had been inferred from
observations of other galaxies and their comparison to the Milky Way.
Thus, the new INTEGRAL results confirm both the production of 26Al in
massive stars and supernovae as well as the rate of supernovae, which is
one of the key parameters of our own Galaxy.
The INTEGRAL spectrometer for gamma rays will continue to operate for
several more years. Astrophysicists thus hope even to increase the
precision of such measurements. Project leader Roland Diehl explains,
"these gamma ray observations provide insights about our home galaxy,
which are difficult to obtain at other wavelengths due to interstellar
absorption."
These INTEGRAL based studies involve research by the Max Planck Institute
for Extraterrestrial Physics; the Centre d'Etude Spatiale des Rayonnements
and Université Paul Sabatier, Toulouse,France; the DSM/DAPNIA/Service
d'Astrophysique, CEA Saclay, Gif-Sur-Yvette,France; Clemson University,
Clemson,USA; ESA/ESTEC, Noordwijk, the Netherlands; and the Space Sciences
Laboratory, Berkeley,USA.
Related links:
[1] Further information about INTEGRAL
http://www.mpe.mpg.de/gamma/instruments/integral/www/integral.html
[2] MPG Annual Report 2005 "More than hot: Sources of Cosmic Gamma-Rays"
(in German)
<http://www.mpg.de/bilderBerichteDokumente/dokumentation/jahrbuch/2005/extraterrestrische_physik/forschungsSchwerpunkt/index.html>
[3] Additional informations and images
http://www.mpe.mpg.de/gamma/science/lines/26Al/26Al.html
Original work:
Roland Diehl, Hubert Halloin, Karsten Kretschmer, Giselher G. Lichti,
Volker Schönfelder, Andrew W.Strong, Andreas von Kienlin, Wei Wang, Pierre
Jean, Jürgen Knödlseder, Jean-Pierre Roques, Georg Weidenspointner,
Stephane Schanne, Dieter H. Hartmann, Christoph Winkler, and Cornelia
Wunderer
Radioactive 26Al and massive stars
Nature, 5 January 2005
IMAGE CAPTIONS:
[Image 1:
<http://www.mpg.de/bilderBerichteDokumente/multimedial/bilderWissenschaft/2005/12/Diehl0501/presselogin/Web_Zoom.jpeg>
(193KB)]
Radioactive decay of unstable isotopes leads to emission of gamma rays
with a characteristic energy (coloured) being determined by properties of
the atomic nucleus. ESA¹s INTEGRAL satellite observatory has been
measuring such gamma rays since October 2002. Radioactive isotopes are
by-products of nuclear fusion reactions, which produce new atomic nuclei
in stellar interiors and in supernovae. In the gamma ray light of 26Al
isotopes, which decay after about a million years to magnesium, one sees
the radioactive glow of regions of the Galaxy with recent production of
new nuclei. Visible light, on the other hand, often cannot reach us from
stars in those regions, due to occulting interstellar gas clouds.
Image: Max Planck Institute for Extraterrestrial Physics
[Image 2:
<http://www.mpg.de/bilderBerichteDokumente/multimedial/bilderWissenschaft/2005/12/Diehl0502/presselogin/Web_Zoom.jpeg>
(121KB)]
Expected line shifts from the Doppler effect along the plane of the
Galaxy, as they result from galactic rotation. The modelled distribution
of sources (coloured) agree with the measured line position changes from
INTEGRAL (crosses).
Image: Max Planck Institute for Extraterrestrial Physics