The universe contains about 20% more high-energy radiation than previously thought, according to a new and unusual set of observations. If confirmed, the data would bring the levels of high energy radiation into agreement with previous measurements of lower energy radiation.
The results come from observations in January and February 2006 of high-energy X-rays and gamma rays that contribute to the 鈥渃osmic high-energy background鈥�. Most of this radiation is thought to come from very distant, supermassive black holes.
NASA鈥檚 High Energy Astrophysics Observatory-1 last measured this radiation in the late 1970s. It found that the total amount of high-energy radiation was about 20% less than expected from extrapolations of studies of lower energy X-rays.
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快猫短视频s have now repeated the measurement by performing a highly unusual manoeuvre with Europe鈥檚 Integral gamma-ray observatory 鈥� turning the Earth-orbiting satellite, which normally points out into space, back towards the Earth. The move was only undertaken after months of risk analysis.
No procedure
In order to turn back toward the Earth, Integral could not use its sensitive star trackers to orient itself because the planet reflects too much radiation. 鈥淓arth observation was something we never planned to do,鈥� Parmar says. 鈥淲e didn鈥檛 have procedures in place to do it.鈥�
The team used Integral鈥檚 Sun sensor and gyroscopes onboard the spacecraft to control its attitude for a total of 10 hours of Earth observations.
As the planet drifted into the telescope鈥檚 field of view, it shielded the satellite from the high-energy background radiation. By comparing the amplitude and energy spectrum of the view before and after the Earth passed into view, scientists were able to derive a new measurement of the background.
Smooth transition
鈥淧reliminary analysis indicates we see around 20% more radiation, which is very interesting,鈥� Integral mission manager Arvind Parmar told 快猫短视频.
The result lines up well with predictions based on lower-energy X-ray data plots, says project scientist Chris Winkler at the European Space Agency. It is a 鈥渧ery smooth transition of the Integral data with the X-ray data鈥�, he says.
Future observations may pinpoint individual sources for this background radiation. Satellites such as ESA鈥檚 XMM-Newton and NASA鈥檚 Chandra X-ray Observatory have identified that individual sources are responsible for about 80% of the X-ray background at low energies. But that percentage drops drastically at higher energies, in the range Integral is equipped to detect. There, identified sources can only account for about 3% of the cosmic high-energy background.
Gamma rays provide astronomers with a particular challenge when it comes to identifying their sources. The high-energy rays cannot be focused with mirrors or lenses. 鈥淭hey pass through the material you鈥檙e trying to focus them with,鈥� Parmar explains.
So Integral employs a 鈥渕asking鈥� technique in which heavy bits of metal lie between the radiation sources and the telescope鈥檚 detectors. That way the sources cast 鈥渟hadows鈥� of the masks on the detectors and scientists can capture an indirect image of the sources.
