Astronomers find first ever gamma ray clock

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 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=mc²) 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).

Source: Particle Physics & Astronomy Research Council

The Quiet Explosion: Object intermediate between normal supernovae and gamma-ray bursts found
A European-led team of astronomers are providing hints that a recent supernova may not be as normal as initially thought. Instead, the star that exploded is now understood to have collapsed into a black hole, producing a weak jet, typical of much more violent events, the so-called gamma-ray bursts. The object, SN 2008D, is thus probably among the weakest explosions that produce very fast moving jets. This discovery represents a crucial milestone in the understanding of the most violent phenomena observed in the Universe.
UO plays key role in LIGO's new view of a cosmic event
An international team of physicists, including University of Oregon scientists, has concluded that last February's intense burst of gamma rays possibly coming from the Andromeda Galaxy lacked a gravitational wave. That absence, they say, rules out an initial interpretation that the burst came from merging neutron stars or black holes within Andromeda.
LIGO Sheds Light on Cosmic Event
An analysis by the international LIGO (Laser Interferometer Gravitational-Wave Observatory) Scientific Collaboration has excluded one previously leading explanation for the origin of an intense gamma-ray burst that occurred last winter. Gamma-ray bursts are among the most violent and energetic events in the universe, and scientists have only recently begun to understand their origins.
Robotic Telescope unravels mystery of cosmic blasts
Scientists have used the world's largest robotic telescope to make the earliest-ever measurement of the optical polarisation of a Gamma Ray Burst (GRB) just 203 seconds after the start of the cosmic explosion. This finding, which provides new insight into GRB physics, is published in Science today.
Newfound diversity in gamma-ray bursts puzzles astronomers
Two brilliant flashes of light from nearby galaxies are puzzling astronomers and could indicate that gamma-ray bursts, which signal the birth of a black hole, are more diverse than once thought.
Most distant cosmic explosion was a star collapsing into a black hole
It came from the edge of the visible universe, the most distant explosion ever detected. In this week's issue of Nature, scientists at Penn State University and their U.S. and European colleagues discuss how this explosion, detected on 4 September 2005, was the result of a massive star collapsing into a black hole.
Milky Way Churns Out Seven New Stars Per Year, Scientists Say
In an investigation smacking of forensic detective work, scientists have measured the rate of star death and rebirth in our galaxy by combing through the sparse remains of exploded stars from the last few million years.
Science's Breakthrough of the Year: Watching evolution in action
Evolution has been the foundation and guiding theory of biology since Darwin gave the theory its proper scientific debut in 1859. But Darwin probably never dreamed that researchers in 2005 would still be uncovering new details about the nuts and bolts of his theory -- how does evolution actually work in the world of influenza genes and chimpanzee genes and stickleback fish armor? Studies that follow evolution in action claim top honors as the Breakthrough of the Year, named by Science and its publisher AAAS, the nonprofit science society.

Astronomers find first ever gamma ray clock

Related stories:

News discussion: