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Space

Doomed Japanese satellite glimpsed galactic wind before it died

By Joshua Sokol

6 July 2016

Artist's impression of the satellite

Did sterling work on an all-too-brief stint

Akihiro Ikeshita/JAXA

It’s a taste of what might have been. In March, a software glitch caused the Japanese X-ray satellite Hitomi to spin itself to pieces just a month and a half after launch.

Efforts to rescue it have since been abandoned. But before it died, the probe mapped of one of the largest weather systems in the universe, the flowing plasma of a massive clump of galaxies known as the Perseus cluster.

We have long known that superheated plasma fills the spaces between galaxies in a cluster. This swirling material outweighs stars and other normal matter – that is, not dark matter made from exotic, unknown particles – by a factor of about five, making it a key part of the universe. But it is difficult to detect except in the X-ray wavelengths Hitomi was sensitive to, where it gives off a faint glow.

“We’re not just looking at some little fluffy atmosphere,” says Andrew Fabian of the University of Cambridge, a member of the Hitomi team and lead author of a paper detailing the spacecraft’s findings.

The new map shows mind-bogglingly large gusts of plasma, some larger than our own Milky Way. “There’s nothing like it,” Fabian says.

Within the cluster’s enormous central galaxy, an active black hole is generating jets of plasma particles that have been accelerated to close to the speed of light. On hitting cooler gas, the jets blow bubbles which then rise out of the cluster despite the tug of its gravity. Beyond explaining these flows, data from the probe should also help us understand how heavier elements formed inside supernovae have spread throughout the universe over aeons.

Roller coaster

For those following the Hitomi mission, the lead-up to this first publication has been something of a roller coaster. “I went through these three emotional stages,” says Eugene Churazov at the International Max Planck Research School on Astrophysics in Garching, Germany, who was not part of the team.

“One was the excitement in February from the successful launch of the first ever cryogenic spectrometer,” he says. “Then in late March the shock from the loss of the spacecraft. And today, another wave of excitement from reading the paper.”

The Perseus cluster observations were made over about three days a week after Hitomi launched, at a time when researchers were otherwise focused on calibrating the observatory. “It turns out the only good object that we looked at was this cluster,” Fabian says. “It was wise to get it done early.”

It’s a much smaller legacy than those working on Hitomi hoped it would leave, but should still result in a dozen or more papers as researchers dig into this data over the next year, Churazov thinks.

More importantly, it shows that the X-ray detector Hitomi pioneered is a way forward for the field. The next missions that will use similar detectors are ATHENA, an observatory the European Space Agency plans to launch in 2028, and the X-ray Surveyor, a mission concept being proposed to NASA.

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