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Science

Japan's Astro-H satellite to peek 8 billion years into the past

An X-ray image of the Centaurus cluster shows it is covered by high-temperature plasma. (Photo courtesy of JAXA, University of Tokyo)

TOKYO   A satellite capable of looking 8 billion years into the past is about to give astronomers a whole new glimpse of the universe.

     The Astro-H X-ray orbiting observatory, which was launched from the Tanegashima Space Center in Kagoshima Prefecture, southwest Japan, on Feb. 17,  will observe X-rays emitted by black holes and other cosmic bodies. With instruments 100 times more sensitive than those of its predecessor, the new satellite should help shed light on the history of the universe.

THE WHOLE PICTURE   Visible-light telescopes, which collect the light emanating from millions of stars, paint a stunning picture of the cosmos. But by also observing X-rays, "a completely different universe comes into view," says Tadayuki Takahashi, a professor at the Institute of Space and Astronautical Science and the Astro-H project manager at the Japan Aerospace Exploration Agency (JAXA).

     X-rays are emitted from plasma at super-high temperatures -- in the range of several millions to several hundreds of millions of degrees -- and from particles traveling at high speeds. The picture of the universe that emerges from X-ray observations will not be cool, quiet and dark, but rather hot, tempestuous and dynamic.

An image of the Centaurus cluster obtained using a visible-light telescope (Photo courtesy of NASA/SkyView)

     For example, when a galaxy cluster is viewed in the visible spectrum, it appears as a collection of thousands of galaxies, their cool white light shining serenely in space. In reality, however, super-heated plasma is flowing among -- and sometimes colliding with -- those galaxies. By observing the X-rays this plasma gives off, we can see that the cluster is more akin to a colossal fireball than a frozen beauty.

     There are other sources of X-rays. At the center of most galaxies is a massive black hole. Some of the gas swirling around this black hole is pulled into it, but a portion is violently expelled, emitting X-rays in the process.

     Astro-H, which was carried into space on one of Japan's H-IIA rockets, will orbit Earth at an altitude of around 575km for three years. The observations it makes will help scientists elucidate how galaxy clusters and black holes have affected each other over the 13.8 billion years of the universe's history.

BACK, BACK, BACK ...   To see further into the universe's past, we need to observe objects that are farther away from us. X-rays coming from an astronomical body 1 light-year away reflect the state of that heavenly body when the light was emitted one year ago. If we can observe objects 100 million light-years away, we can peer back in time 100 million years.

     Astro-H's sensors are 100 times more sensitive than those of its predecessor, Suzaku, which was launched in 2005. This will reportedly enable the new satellite to observe X-rays from black holes as far as 8 billion light-years away.

     The motion of an object has a slight effect on the energy of the X-rays it emits. Because Astro-H can observe X-ray energy with 30 times the precision of Suzaku, scientists should be able to better understand the movements of plasmas and gases.

     Suzaku's observations revealed that in the one-hundredth of a second before gas is sucked into a black hole, it is compressed so tightly that its temperature rises above 100 million degrees, causing it to emit powerful X-rays. Astro-H could help further elucidate the movement of such gas.

     The satellite's observations could also help verify the physics-related principles at play when X-rays are emitted under extreme conditions, such as super-high temperatures or pressures.

A YOUNG STUDY   The field of X-ray astronomy got its start around 50 years ago. Using instruments mounted on a rocket, a team led by American physicist Riccardo Giacconi discovered in 1962 that astronomical bodies emitting powerful X-rays exist outside our solar system. Just eight years later, NASA launched the world's first X-ray astronomy satellite.

     Japanese researchers, such as the late University of Tokyo Professor Emeritus Minoru Oda, have been involved in the field from its early days. Japan's first X-ray astronomy satellite, Hakucho, was launched in 1979. Among its achievements was the discovery of eight new sources of cosmic X-rays. Successive satellites -- Tenma, Ginga, Asca and Suzaku -- have given researchers even more data to work with.

     At present, two large satellites make the bulk of X-ray observations -- the U.S.'s 4.8-ton Chandra and Europe's 3.8-ton XMM-Newton, both launched in 1999. Weighing 2.7 tons, Astro-H is on the smaller side, but the precision of its X-ray energy measurements more than makes up for its relative diminutiveness.

     Eight countries participated in Astro-H's development, including Japan, the U.S., the Netherlands and Canada. Its observation plan will be made public and researchers around the globe will be able to use the data it gathers.

     Scientists believe the universe is made up largely of dark matter, which is invisible and cannot be observed with existing technology. And 80% of ordinary matter is plasma, which can only be observed with X-rays. "By being able to see the real shape of the universe by means of X-rays, we will be able to better understand how the present universe was formed," JAXA's Takahashi says.

     As to what mysteries of the universe's history Astro-H will unlock for us, only time will tell.

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