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Unveiling the mysteries of black holes

Exploring the extreme Universe using new X-ray technology.

Published: 
13 April 2016

The University of Southampton is part of an international collaboration set to harness observations from the Japan Aerospace Exploration Agency and NASA’s X-ray space telescope, Hitomi, to better understand how black holes grow.

Black holes were first identified in space over 40 years ago, but we are still a long way from understanding how they grow and evolve. Dr Poshak Gandhi, Associate Professor and Science and Technology Facilities Council Ernest Rutherford Fellow in the University’s Astronomy Group, aims to change that. He is part of a 200-strong international science team that has been developing the new telescope, which launched from Japan on 17 February.

So why study black holes? “Black holes are ubiquitous; every large galaxy hosts its own supermassive black hole at the centre,” says Poshak. “We now know that the growth of all these black holes goes hand-in-hand with the growth of the galaxies in which they sit: smaller black holes are hosted in smaller galaxies and larger galaxies tend to have much larger black holes.” There is now strong evidence to suggest that black holes have a much more profound impact on the Universe than once thought; galaxies themselves would have been much larger than they are today if black holes didn’t exist. Our own Milky Way galaxy may well have been much bigger than we see in the night sky.

The high precision 'X-ray colour vision' of the new Hitomi space telescope (which means ‘eye’ in Japanese) will be a huge step forward for such studies, and for understanding other hot and extreme objects in the Universe

Dr Poshak Gandhi - Associate Professor and Science and Technology Facilities Council Ernest Rutherford Fellow in the University’s Astronomy Group

As matter falls into black holes, it heats up to temperatures of many millions of degrees. This extreme environment is perfect for testing theories at the extremes of temperatures and gravity, which could not be achieved on Earth. The recent discovery of gravitational waves, in which Southampton researchers also participated, is a perfect example of the extreme physics that black holes allow us to probe.

While they are growing, black holes attract interstellar gas and dust, which radiates away its energy as it falls in, and can be detected using an X-ray telescope. “The high precision 'X-ray colour vision' of the new Hitomi space telescope (which means ‘eye’ in Japanese) will be a huge step forward for such studies, and for understanding other hot and extreme objects in the Universe,” says Poshak. “Hitomi has the best spectral resolution of any X-ray mission in space. It essentially splits up the X-ray spectrum into its individual energies, or ‘colours’, in the same way a prism splits light into its constituent colours.

“By studying this X-ray spectrum we will be able to learn a huge amount about the motions of gas around the black holes, about the temperatures of gas, the composition of gas, what the gas is actually made of. It is around 30 times better in its capability to distinguish these X-ray energies than previous missions. So that allows us much better precision to measure the speed of these gases, and all sorts of properties about the gases.”

Using observations from Hitomi, over the coming years Poshak will be involved in studies of supermassive black holes at the centre of nearby galaxies. “What we’re hoping to do is peer through the veils of absorbing clouds that we know to surround these supermassive black holes so that we can make closer observations of their behaviour. I am very excited to be part of this international collaborative effort, and look forward to solving mysteries that have long puzzled us.”

Poshak adds: “It was clear to me that the astronomy group here at Southampton is one of the best in the UK focused on the study of black holes across their full mass range. It is a very dynamic group and I am able to collaborate with many people who are very close to all my research areas.”

Update: On Easter Sunday, contact was lost with the Hitomi satellite and the Japan Space Agency is currently working to re-establish communications. The results from initial successful observations are also being prepared for publication.

For more information, visit www.astro.soton.ac.uk

Image credit: Akihiro Ikeshita - JAXA

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