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Astronomers find first ever gamma ray clock
November 28, 2006Astronomers using the H.E.S.S. telescopes have discovered the first ever modulated signal from space in Very High Energy Gamma Rays - the most energetic such signal ever observed. Regular signals from space have been known since the 1960s, when the first radio pulsar (nicknamed Little Green Men-1 for its regular nature) was discovered. This is the first time a signal has been seen at such high energies - 100,000 times higher than previously known-and is reported today (24th November) in the Journal Astronomy and Astrophysics.
The signal comes from a system called LS 5039 which was discovered by the H.E.S.S. team in 2005. LS5039 is a binary system formed of a massive blue star (20 times the mass of the Sun) and an unknown object, possibly a black hole. The two objects orbit each other at very short distance, varying between only 1/5 and 2/5 of the separation of the Earth from the Sun, with one orbit completed every four days.
"The way in which the gamma ray signal varies makes LS5039 a unique laboratory for studying particle acceleration near compact objects such as black holes." Explained Dr Paula Chadwick from the University of Durham, a British team member of H.E.S.S.
Different mechanisms can affect the gamma-ray signal that reaches Earth and by seeing how the signal varies, astronomers can learn a great deal about binary systems such as LS 5039 and also the effects that take place near black holes.
As it dives towards the blue-giant star, the compact companion is exposed to the strong stellar 'wind' and the intense light radiated by the star, allowing on the one hand particles to be accelerated to high energies, but at the same time making it increasingly difficult for gamma rays produced by these particles to escape, depending on the orientation of the system with respect to us. The interplay of these two effects is at the root of the complex modulation pattern.
The gamma-ray signal is strongest when the compact object (thought to be a black hole) is in front of the star as seen from Earth and weakest when it is behind the star. The gamma rays are thought to be produced as particles which are accelerated in the star's atmosphere (the stellar wind) interact with the compact object. The compact object acts as a probe of the star's environment, showing how the magnetic field varies depending on distance from the star by mirroring those changes in the gamma ray signal.
In addition, a geometrical effect adds a further modulation to the flux of gamma-rays observed from the Earth. We know since Einstein derived his famous equation (E=mc˛) that matter and energy are equivalent, and that pairs of particles and antiparticles can mutually annihilate to give light. Symmetrically, when very energetic gamma rays meet the light from a massive star, they can be converted into matter (an electron-positron pair in this case). So, the light from the star resembles, for gamma rays, a fog which masks the source of the gamma rays when the compact object is behind the star, partially eclipsing the source. "The periodic absorption of gamma-rays is a nice illustration of the production of matter-antimatter pairs by light, though it also obscures the view to the particle accelerator in this system" (Guillaume Dubus, Astrophysical Laboratory of the Grenoble Observatory, LAOG).
Particle Physics & Astronomy Research Council
Different mechanisms can affect the gamma-ray signal that reaches Earth and by seeing how the signal varies, astronomers can learn a great deal about binary systems such as LS 5039 and also the effects that take place near black holes.
As it dives towards the blue-giant star, the compact companion is exposed to the strong stellar 'wind' and the intense light radiated by the star, allowing on the one hand particles to be accelerated to high energies, but at the same time making it increasingly difficult for gamma rays produced by these particles to escape, depending on the orientation of the system with respect to us. The interplay of these two effects is at the root of the complex modulation pattern.
The gamma-ray signal is strongest when the compact object (thought to be a black hole) is in front of the star as seen from Earth and weakest when it is behind the star. The gamma rays are thought to be produced as particles which are accelerated in the star's atmosphere (the stellar wind) interact with the compact object. The compact object acts as a probe of the star's environment, showing how the magnetic field varies depending on distance from the star by mirroring those changes in the gamma ray signal.
In addition, a geometrical effect adds a further modulation to the flux of gamma-rays observed from the Earth. We know since Einstein derived his famous equation (E=mc˛) that matter and energy are equivalent, and that pairs of particles and antiparticles can mutually annihilate to give light. Symmetrically, when very energetic gamma rays meet the light from a massive star, they can be converted into matter (an electron-positron pair in this case). So, the light from the star resembles, for gamma rays, a fog which masks the source of the gamma rays when the compact object is behind the star, partially eclipsing the source. "The periodic absorption of gamma-rays is a nice illustration of the production of matter-antimatter pairs by light, though it also obscures the view to the particle accelerator in this system" (Guillaume Dubus, Astrophysical Laboratory of the Grenoble Observatory, LAOG).
Particle Physics & Astronomy Research Council
Gamma Rays News and Current Gamma Rays Events RSSGLAST Observatory renamed for Fermi, reveals entire gamma-ray sky
The U.S. Department of Energy (DOE) and NASA announced today that the Gamma-Ray Large Area Space Telescope (GLAST) has revealed its first all-sky map in gamma rays.
Study shows clumps and streams of dark matter in inner regions of the Milky Way
Using one of the most powerful supercomputers in the world to simulate the halo of dark matter that envelopes our galaxy, researchers found dense clumps and streams of the mysterious stuff lurking in the inner regions of the halo, in the same neighborhood as our solar system.
GLAST Safely in Orbit, Getting Check-ups
Less than a week after launch, NASA's Gamma-ray Large Area Space Telescope, or GLAST, is safely up-and-running well in orbit approximately 350 miles (565 kilometers) above Earth's surface.
First semiconductor-based PET scanner demonstrates potential to aid in early diagnosis of disease
Evaluations of the first-ever prototype positron emission tomography (PET) brain scanner that uses semiconductor detectors indicate that the scanner could advance the quality and spatial resolution of PET imaging, according to researchers at SNM's 55th Annual Meeting.
UC Santa Cruz physicists eagerly await launch of NASA space telescope they helped build
When NASA launches its newest space observatory, physicists at the University of California, Santa Cruz, will be watching as the product of nearly 16 years of hard work blasts into orbit.
CSI: Milky Way team works scene of dead star
Like a team of forensic detectives in a television show that could be called "CSI: Milky Way," a University of Chicago astrophysicist and his associates are piecing together how a mysterious infrared ring got left around a dead star that displays a magnetic field trillions of times more intense than Earth's.
A scientific first: A supernova explosion is observed in real time
An ordinary observation with NASA's Swift research satellite recently led to the first real-time sighting of a star in the process of exploding. Astronomers have surveyed thousands of these supernova explosions in the past, but their observations have always begun some time after the main event is underway.
NASA's Swift satellite catches first 'normal' supernova in the act of exploding
Thanks to a fortunate observation with NASA's Swift satellite, astronomers, for the first time, have caught a normal supernova at the moment of its birth--the first instant when an exploding star begins spewing its energy into space, transforming into a supernova that during its brief lifetime will shine brighter than billions of stars combined.
Searching the heavens
A new space mission, due to launch this month, is going to shed light on some of the most extreme astrophysical processes in nature - including pulsars, remnants of supernovae, and supermassive black holes.
Researchers bridge the 'terahertz gap' with new tunable metamaterial
A frequency-agile metamaterial that for the first time can be tuned over a range of frequencies in the so-called "terahertz gap" has been engineered by a team of researchers from Boston College, Los Alamos National Laboratory and Boston University.
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