The light emitted from all objects in the Universe during its entire history - stars, galaxies, quasars etc. forms a diffuse sea of photons that permeates intergalactic space, referred to as "diffuse extragalactic background light" (EBL). Scientists have long tried to measure this fossil record of the luminous activity in the Universe in their quest to decipher the history and evolution of the Cosmos, but its direct determination from the diffuse glow of the night sky is very difficult and uncertain.
Very high energy (VHE) gamma-rays, some 100,000,000,000 times more energetic than normal light, offer an alternative way to probe this background light, and UK researchers from Durham University in collaboration with international partners used the High Energy Stereoscopic System (HESS) gamma-ray telescopes in the Khomas Highlands of Namibia to observe several quasars (the most luminous VHE gamma-ray sources known) with this goal in mind. The results, to be published in the April 20 issue of
Nature, turned out to be rather striking.
Gamma-rays, which are produced in the most violent objects in the Universe, are absorbed in their journey from distant objects to Earth if they happen to hit a photon of "normal" background light. This fog of light in which the Universe is bathed is a fossil record of all the light emitted in the Universe over its lifetime, from the glare of the first stars and galaxies up to the present time.
So, using the distant quasars as a probe and studying the effect of the fossil light on the energy distribution of the initial gamma-rays, astrophysicists used HESS to derive a limit on the maximum amount of this 'extragalactic background light', which is remarkably lower than what previous estimates had suggested.
This result, published in the April 20 issue of Nature, has important consequences for our understanding of galaxy formation and evolution, and expands the horizon of the gamma-ray Universe which is clearly more transparent to gamma-rays than previously believed
Commenting in the findings, Dr Lowry McComb of Durham University, said, "HESS has in the last few years achieved a number of important discoveries concerning high-energy gamma-ray sources in our own Galaxy and has revolutionized high-energy gamma-ray astronomy.
These new HESS results illustrate the power of the instrument for extragalactic astronomy and cosmology. The discovery of lower levels of intergalactic starlight has the interesting side effect that the Universe becomes more transparent to gamma rays and that the telescopes can look deeper into the cosmos, increasing their reach for further discoveries!"
Source: PPARC
Related stories:
Liquid Mirror Telescopes on the Moon
A team of internationally renowned astronomers and opticians may have found a way to make "unbelievably large" telescopes on the Moon.
Spallation Neutron Source sends first neutrons to 'Big Bang' beam line
New analytical tools coming on line at the Spallation Neutron Source, the Department of Energy's state-of-the-art neutron science facility at Oak Ridge National Laboratory, include a beam line dedicated to nuclear physics studies.
Cosmic strings might emit cosmic sparks, answer cosmological questions
(PhysOrg.com) -- For astronomers, understanding what happened in the early moments of the universe could answer many questions in physics and astronomy. One possible player in the early universe is cosmic strings, which arise naturally in particle physics models. However, cosmic strings are quite strange hypothetical entities: they’re thinner than a proton, but can be as long as the universe. Cosmic strings might have formed as imperfections when the early universe was undergoing drastic phase changes.
Cosmic eye sheds light on early galaxy formation
A Cosmic Eye has given scientists a unique insight into galaxy formation in the very early Universe. Using gravity from a foreground galaxy as a zoom lens the team was able to see a young star-forming galaxy in the distant Universe as it appeared only two billion years after the Big Bang.
Japan ready to host new 'Big-Bang' project
Boosted by its win of the 2008 Nobel Physics Prize, Japan said Wednesday it hoped to play host to a major international scientific organisation's new machine exposing the secrets of the cosmos.
Stars stop forming when big galaxies collide
Astronomers studying new images of a nearby galaxy cluster have found evidence that high-speed collisions between large elliptical galaxies may prevent new stars from forming, according to a paper to be published in a November 2008 issue of The
Astrophysical Journal Letters.
Bad connection caused atom smasher shutdown
(AP) -- A bad electrical connection likely caused the malfunction that sidelined the world's largest atom smasher days after it was launched with great fanfare, a senior scientist said Monday.
NASA Selects Science Teams for Astrobiology Institute
(PhysOrg.com) -- NASA has awarded five-year grants, averaging $7 million each, to 10 research teams from across the country, including two from NASA's Jet Propulsion Laboratory in Pasadena, to study the origins, evolution, distribution and future of life in the universe.
