A Dying Satellite Helps Researchers Understand How Galaxies Grow

July 7, 2016 | Gillian Burrell

Artist's conception of Hitomi (ASTRO-H) in orbit
Photo credit: JAXA

Hitomi’s tragic end was not in vain.

The X-Ray Astronomy Satellite ASTRO-H (Hitomi) may have had a very brief lifespan, but what it accomplished in that time has astronomers rethinking the life history of galaxies.

The satellite launched on February 17 from the Tanegashima Space Center in Japan with a mission to observe black holes with a unique instrument: an X-ray calorimeter. This device receives X-ray photons from space and converts them into heat, which reveals the energy of the X-ray.

Scientists around the world have been trying for years to get an X-ray satellite into space equipped with a calorimeter, but the project seems to be cursed.

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The plans for NASA’s Chandra X-ray observatory, which launched in 1998, originally included a calorimeter, but it was cut from the final design for budgetary reasons. In 2000, NASA launched Astro-E, but the rocket exploded before it could make it into orbit. Finally, Japan’s Suzaku satellite successfully made it into space in 2005 but its calorimeter was soon destroyed by a leak in the cooling system.

Hitomi was expected to continue Suzaku’s mission, including a study of how matter moves as it approaches the event horizons of black holes, but its mission ended 5 weeks after launch when it spun out of control and disintegrated in the atmosphere.

Despite the brevity of its stint in space, Hitomi sent some highly valuable data back to Earth.

As published in Nature yesterday (July 6), the observatory collected X-ray data from a black hole at the center of the Perseus cluster, one of the largest known structures in the universe.

Specifically, Hitomi looked at the plasma bubbles being pumped out of the black hole at the center of Perseus. These bubbles are the result of vast amounts of heat being expelled by black holes and can only be seen using X-ray spectrometry. What researchers were most curious about was why plasma bubbles rarely cool down enough to form new galaxies.

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Now, data from Hitomi’s month-long journey explain that the turbulence in these plasma bubbles prevents the gas from cooling down. Brian McNamara, a researcher who collaborated on the Hitomi mission, explained that these plasma bubbles help to regulate the size of a galaxy cluster.

“It's like nature's thermostat, that keeps these galaxies from growing. If the galaxy tries to grow too fast, matter falls into the black hole, releasing an enormous amount of energy, which drives out the matter and prevents it from forming new stars."

Thanks to this self-regulating effect, the gas remains as a hot plasma that envelopes the galaxies at the core of Perseus.

“It's the raw material that in the next several billion years is going to make the next generation of suns and solar systems,” McNamara commented in a press release, “And how rapidly that happens is governed by the black hole."

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