Andrew Yee
May 19th 06, 04:25 AM
Press and Public Relations Department
Max Planck Society for the Advancement of Science
Munich, Germany
Contact:
Dr. Felix Aharonian
Max Planck Institute for Nuclear Physics, Heidelberg
Tel.: +49 6221 516-485 Fax: + 49 6221 516-324
Dr. Luigi Costamante
Max Planck Institute for Nuclear Physics, Heidelberg
Tel.: +49 6221 516-470 Fax: + 49 6221 516-324
Prof. Stefan Wagner
Landessternwarte Kigstuhl, Heidelberg
Tel.: +49 6221 541-712 Fax: +49 6221 541-702
May 8th, 2006
News SP / 2006 (46)
The Cosmos Does Not Glimmer As We Thought
The H.E.S.S. telescope shows that extragalactic background light hardly
dampens the gamma rays of distant quasars
All throughout space, a cosmic background light shimmers. Stars, galaxies --
all kinds of sources -- contribute to it; the light is their leftovers, in
fact. Now, astrophysicists have discovered that this light is hardly as
intense as anyone had guessed. The researchers used two distant quasars as
"probes", and recorded their gamma spectra using the H.E.S.S. telescopes in
Namibia. These spectra turned out to be just a bit reddened; the background
light seemed to only lightly obfuscate the quasars' radiation. These
observations do not just shed light on the background light -- but on topics
as great as the birth and development of galaxies (Nature, April 20, 2006).
Stars, galaxies, quasars, and many other objects contribute to the fog of
radiation in the universe. It permeates all of intergalactic space; it is
the "leftover" light that all these objects emit. Extragalactic background
light -- EBL -- covers up epochs worth of stellar activity, from the time
the first stars were created to the present. Scientists have been trying for
a long time to measure this emission. Doing that directly is not easy,
however, and extremely inaccurate, because Earth's atmosphere, the Solar
System, and the Milky Way send out radiation which gets in the way of
observing weak EBL.
One way out of this problem is observing quasars -- the cosmic energy
factories which have a huge black hole in their middle. These "gravity
traps" swallow up gas around them and spit some of it back as plasma,
accelerated to nearly the speed of light. It is radiation bundled out of
protons, electrons, and electromagnetic waves. Often, it can be hundreds of
times wider than its mother galaxy. If this "quasar spray" heads in the
direction of Earth, the radiation can appear quite strong -- astronomers
call this a "blazar".
The two objects which H.E.S.S. researchers observed are both blazars. How to
use them as probes? They send out very energetic gamma light particles,
which lose strength on their way to Earth when they hit EBL photons. This
causes the original blazar gamma spectrum to redden -- like when the Sun
nears the horizon at dusk and the Earth's atmosphere disperses more of the
blue part of the sunlight than the red. The thicker the atmosphere, the
redder the sun. Reddening depends on the thickness of the medium. This fact
is the key to investigating the composition of EBL.
Luigi Costamante of the Max Planck Institute for Nuclear Physics in
Heidelberg says: "the main problem is that energy distribution in quasars
can take many different forms. Until now, we could not really say whether
any observed spectrum looks red because it truly had a strong reddening, or
if it was that way from the beginning."
This problem has been solved thanks to the gamma spectra of two quasars -- H
2356-309 and 1ES 1101-232. These objects are more distant than any sources
observed until now. The sensitivity of the H.E.S.S. telescope made it
possible to investigate them. It turns out that EBL's intensity is not
strong enough to redden quasar light; the spectra are too blue, and contain
too many higher-energy gamma rays.
H.E.S.S. data has allowed the scientists to derive the maximum intensity of
the diffused light. It is near the lowest limit resulting from the sum of
the light of single galaxies visible in an optical telescope. That answers a
question that has puzzled astronomers for years: is diffuse light created
above all by the radiation from the first stars? The H.E.S.S. results seem
to eliminate this possibility. There is also little room for contributions
from other sources, like normal galaxies. Looking more closely at
intergalactic space gives new perspectives on investigating gamma rays
outside our own galaxy.
[EC]
Related links:
* The H.E.S.S. project
http://www.mpi-hd.mpg.de/hfm/HESS/HESS.html
Original work:
H.E.S.S. collaboration, Felix Aharonian et al.
A low level of extragalactic background light as revealed by gamma-rays from
blazars
Nature 440 (2006), 1018-1021
IMAGE CAPTION:
[http://www.mpg.de/bilderBerichteDokumente/multimedial/bilderWissenschaft/2006/05/Hoffmann0601_engl/Web_Zoom.jpeg
(187KB)]
Extragalactic Background Light comes into contact with gamma rays from a
distant quasar. At higher densities, EBL photons come into a number of
collisions with gamma light particles -- absorption is strong and the
spectrum clearly changes (above, right). At lesser EBL proton densities,
absorption is weaker and the spectrum changes only a little (below, right).
Image: H.E.S.S. collaboration
Max Planck Society for the Advancement of Science
Munich, Germany
Contact:
Dr. Felix Aharonian
Max Planck Institute for Nuclear Physics, Heidelberg
Tel.: +49 6221 516-485 Fax: + 49 6221 516-324
Dr. Luigi Costamante
Max Planck Institute for Nuclear Physics, Heidelberg
Tel.: +49 6221 516-470 Fax: + 49 6221 516-324
Prof. Stefan Wagner
Landessternwarte Kigstuhl, Heidelberg
Tel.: +49 6221 541-712 Fax: +49 6221 541-702
May 8th, 2006
News SP / 2006 (46)
The Cosmos Does Not Glimmer As We Thought
The H.E.S.S. telescope shows that extragalactic background light hardly
dampens the gamma rays of distant quasars
All throughout space, a cosmic background light shimmers. Stars, galaxies --
all kinds of sources -- contribute to it; the light is their leftovers, in
fact. Now, astrophysicists have discovered that this light is hardly as
intense as anyone had guessed. The researchers used two distant quasars as
"probes", and recorded their gamma spectra using the H.E.S.S. telescopes in
Namibia. These spectra turned out to be just a bit reddened; the background
light seemed to only lightly obfuscate the quasars' radiation. These
observations do not just shed light on the background light -- but on topics
as great as the birth and development of galaxies (Nature, April 20, 2006).
Stars, galaxies, quasars, and many other objects contribute to the fog of
radiation in the universe. It permeates all of intergalactic space; it is
the "leftover" light that all these objects emit. Extragalactic background
light -- EBL -- covers up epochs worth of stellar activity, from the time
the first stars were created to the present. Scientists have been trying for
a long time to measure this emission. Doing that directly is not easy,
however, and extremely inaccurate, because Earth's atmosphere, the Solar
System, and the Milky Way send out radiation which gets in the way of
observing weak EBL.
One way out of this problem is observing quasars -- the cosmic energy
factories which have a huge black hole in their middle. These "gravity
traps" swallow up gas around them and spit some of it back as plasma,
accelerated to nearly the speed of light. It is radiation bundled out of
protons, electrons, and electromagnetic waves. Often, it can be hundreds of
times wider than its mother galaxy. If this "quasar spray" heads in the
direction of Earth, the radiation can appear quite strong -- astronomers
call this a "blazar".
The two objects which H.E.S.S. researchers observed are both blazars. How to
use them as probes? They send out very energetic gamma light particles,
which lose strength on their way to Earth when they hit EBL photons. This
causes the original blazar gamma spectrum to redden -- like when the Sun
nears the horizon at dusk and the Earth's atmosphere disperses more of the
blue part of the sunlight than the red. The thicker the atmosphere, the
redder the sun. Reddening depends on the thickness of the medium. This fact
is the key to investigating the composition of EBL.
Luigi Costamante of the Max Planck Institute for Nuclear Physics in
Heidelberg says: "the main problem is that energy distribution in quasars
can take many different forms. Until now, we could not really say whether
any observed spectrum looks red because it truly had a strong reddening, or
if it was that way from the beginning."
This problem has been solved thanks to the gamma spectra of two quasars -- H
2356-309 and 1ES 1101-232. These objects are more distant than any sources
observed until now. The sensitivity of the H.E.S.S. telescope made it
possible to investigate them. It turns out that EBL's intensity is not
strong enough to redden quasar light; the spectra are too blue, and contain
too many higher-energy gamma rays.
H.E.S.S. data has allowed the scientists to derive the maximum intensity of
the diffused light. It is near the lowest limit resulting from the sum of
the light of single galaxies visible in an optical telescope. That answers a
question that has puzzled astronomers for years: is diffuse light created
above all by the radiation from the first stars? The H.E.S.S. results seem
to eliminate this possibility. There is also little room for contributions
from other sources, like normal galaxies. Looking more closely at
intergalactic space gives new perspectives on investigating gamma rays
outside our own galaxy.
[EC]
Related links:
* The H.E.S.S. project
http://www.mpi-hd.mpg.de/hfm/HESS/HESS.html
Original work:
H.E.S.S. collaboration, Felix Aharonian et al.
A low level of extragalactic background light as revealed by gamma-rays from
blazars
Nature 440 (2006), 1018-1021
IMAGE CAPTION:
[http://www.mpg.de/bilderBerichteDokumente/multimedial/bilderWissenschaft/2006/05/Hoffmann0601_engl/Web_Zoom.jpeg
(187KB)]
Extragalactic Background Light comes into contact with gamma rays from a
distant quasar. At higher densities, EBL photons come into a number of
collisions with gamma light particles -- absorption is strong and the
spectrum clearly changes (above, right). At lesser EBL proton densities,
absorption is weaker and the spectrum changes only a little (below, right).
Image: H.E.S.S. collaboration