3. Space News | Integral -The Cosmic Eye
With eyes that peer into mysterious gamma-ray s-the most energetic phenomena in the cosmos- ESA’s Integral Gamma-Ray Observatory, launched on 17 October 2002, has helped scientists make great strides in understanding the gamma-ray universe.
Integral's gamma-ray vision can peer into the hearts of solar flares, supernovae, neutron stars, black holes, and active galaxies. By exploring the universe at these high energies, scientists can search for new physics, testing theories and performing experiments which are not possible in earth-bound laboratories.
Surveying the entire galaxy looking for the radioactive isotope aluminium 26 with Integral, scientists have been able to calculate that a supernova goes off in our galaxy, once every 50 years.
We have learned that based on findings from Integral, something is creating massive bursts of gamma rays at the center of the Milky Way - the suspect is positrons, the antimatter counterparts of electrons. Scientists have been baffled as to how vast numbers of such particles can be generated every second and how these sources would be distributed over the sky to match the gamma-ray map (above).
Gamma-ray bursts in our Milky Way galaxy are indeed rare, but the scientists estimate that at least one nearby likely hit the Earth in the past billion years. Life on Earth is thought to have appeared at least 3.5 billion years ago.
"A gamma-ray burst originating within 6,000 light years from Earth would have a devastating effect on life," said Dr. Adrian Melott of the Department of Physics and Astronomy at the University of Kansas, Lawrence. "We don't know exactly when one came, but we're rather sure it did come -- and left its mark. What's most surprising is that just a 10-second burst can cause years of devastating ozone damage," Melott added.
Within months of its launch, Integral solved a thirty-year-old mystery by showing that the broadband gamma-ray emission observed towards the center of the galaxy was produced by a hundred individual sources. A catalog of close to 500 gamma-ray sources from all over the sky, most of them new, was then complied.
Scientists now know that a rare class of anomalous X-ray pulsars, or neutron stars, also called magnetars, generates magnetic fields a thousand million times stronger than the strongest steady magnetic field achievable in a laboratory on Earth. These sources show, unexpectedly, strong emission in the Integral energy range.
Neutron stars are extremely dense remnants of exploded stars about the size of Manhattan consisting of tightly packed neutrons.
Neutrons stars rank at or near the top of freaky phenomena found in our Universe. In the early 1930s, California Institute of Technology astrophysicist, Fred Zwicky, an immigrant from Bulgaria, focused his attention on a question that had long troubled astronomers: the appearance of random, unexplained points of light, new stars.
It occurred to Zwicky that if a star collapsed to the sort of density found in the core of atoms, the result would be an unimaginably compacted core: atoms would be crushed together with their electrons squeezed into the nucleus, forming neutrons and a neutron star, with a core so dense that a single spoonful would weigh 200 billion pounds. But there's more, Zwicky concluded: with the collapse of the star there would be huge amounts of leftover energy that would result in a massive explosion, the biggest in the known universe that we called today supernovas.
Most neutron stars house incredibly large magnetic fields. If they are spinning rapidly they make fabulous clocks, cosmic radio beacons we call pulsars. Pulsars can keep time to an accuracy better that one microsecond per year. Some pulsars generate more than 1000 pulses per second, which means that an object with the mass of the Sun packed into an object 10 to 20 kilometers across is rotating over 1000 times per second, or more that half the speed of light!
Integral revealed that a sub-class of X-ray binary stars, called super-giant fast X-ray transients, previously thought to be extremely rare, is actually common in our galaxy. The satellite has also discovered a completely new class of high-mass X-ray binaries, called highly absorbed X-ray binaries.
Integral has seen about 100 of the brightest supermassive black holes, the main producers of gamma radiation in our universe, in other galaxies. But while looking for them in nearby galaxies, surprisingly few have been found. They are either too well-hidden or are only present in the younger galaxies which populate the more distant universe.
Galaxies throughout the universe are believed to be responsible for creating the diffuse background glow of gamma rays, observed over the entire sky. Integral used the Earth as a giant shield to disentangle this faint glow. The data will help understand the origin of the highest energy background radiation and possibly, provide new clues to the history of growth of supermassive black holes since the early epochs of the Universe.
Although not designed to be a gamma-ray-burst ‘watchdog’, scientists realized that Integral could perform this task if assisted by sufficiently powerful software. ESA set a new record for speed and accuracy with the Integral Burst Alert System on 3 December 2003 when a burst was detected, localized and astronomers were alerted in 18 seconds.
The event, called GRB 031203, was faint and close, in cosmological terms, which suggests that an entire population of low energy gamma-ray bursts has so far gone unnoticed.
On 27 December 2004 Integral was hit by the strongest flux of gamma rays ever measured by any spacecraft and it even measured radiation that bounced off the Moon. The culprit was a magnetar, SGR 1806-20, located 50 000 light years away on the other side of our Milky Way. Thanks to this outburst, astronomers now think that some gamma-ray bursts might come from similar magnetars in other galaxies.
Posted by Casey Kazan, adapted from an ESA release and a release issued by NASA/Goddard Space Flight Center.
http://www.dailygalaxy.com/my_weblog/2007/10/integral--the-e.html
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