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Department of Physics

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Galaxy cluster keeps calm and carries on radiating x-rays

(11 July 2016)

Hitomi Perseus Cluster

Hitomi Perseus Cluster

An international scientific collaboration, including Durham University, has discovered that gas in the Perseus cluster of galaxies is much less turbulent than expected.

Writing in the prestigious journal Nature, the scientists say the result is surprising because the Perseus cluster is home to a highly energetic, active, galaxy called NGC1275.

The discovery was made using the Hitomi X-ray observatory. Led by the Japan Aerospace Exploration Agency (JAXA), it is a collaboration of over 60 institutes and 200 scientists and engineers from Japan, the US, Canada, and Europe.

Celestial objects

The result indicates that the cluster gas has very little turbulent motions within. The study of such chaotic behaviour is also a powerful tool for astronomers to understand the behaviour of celestial objects.

Turbulent energy in Perseus is just four per cent of the energy stored in the gas as heat.

Scientists previously thought that bubbles of extremely hot gas, created by energy being pumped out by the NGC1275 galaxy brought about turbulence, which keeps the central gas hot.

Are sound waves the answer?

The researchers are now examining the mystery of what is keeping the cluster's widespread gas hot. One theory is that sound waves spread the energy evenly throughout the gas.

Professor Chris Done, in the Centre for Extragalactic Astronomy, Department of Physics, Durham University, is part of the Hitomi Collaboration, which carried out the work.

She said: “We’ve known for some time that the black holes in the centres of the most massive galaxies are keeping their surrounding gas hot. The major question is how are they able to do this?

“Turbulence generated by the jets from the black hole stirring up the cluster gas was a possible answer, until these transformational results from Hitomi. Now it’s back to the drawing board!”

Unfortunately, just a few weeks after the Perseus observation, a malfunction in the attitude control system put Hitomi into an uncontrollable spin that resulted in the break up and loss of the satellite.

The next mission that will be capable of fully following up the Hitomi programme is the European Space Agency's (ESA’s) Athena, an X-ray observatory scheduled for launch in the 2020s.

Image: X-ray view of the Perseus cluster. Credit: Background: NASA/CXO; Spectrum: Hitomi Collaboration/JAXA, NASA, ESA, SRON, CSA

* ESA’s media release about this research can be read here.