Science & Environment

Black hole's blast stunts birth of stars

illustration of black hole emissions Image copyright NASA / JPL Caltech
Image caption The spherical shape of the wind, shown in this artist's impression, had been suspected but not observed

Winds blasted out by the giant black holes found at the centre of galaxies are strong enough to stunt the birth of new stars, astronomers have found.

By training two space telescopes on a supermassive black hole with the mass of a billion Suns, they measured the strength of its ferocious winds.

The team also confirmed that these winds blow outwards in every direction, an idea that had been tricky to prove.

The work shows how such black holes can affect the evolution of their galaxies.

It was conducted by an international team of astronomers using the telescopes XMM-Newton and Nustar, run by the European Space Agency (Esa) and Nasa respectively.

"We know that black holes in the centre of galaxies can feed on matter, and this process can produce winds. This is thought to regulate the growth of galaxies," said Prof Fiona Harrison of the California Institute of Technology, Nustar's principal investigator.

The two telescopes simultaneously recorded different wavelengths of light coming from their distant target: a black hole two billion light-years away known as PDS 456. It shines brightly with many types of light, making it a quasar.

Nustar specialises in high-energy X-rays while XMM-Newton views low-energy X-rays.

XMM-Newton had already detected a wind blowing from PDS 456 towards the earth, because iron atoms carried by the huge gusts block X-rays in a characteristic way. It had also allowed astronomers to calculate that the wind was travelling at one third of the speed of light.

But by adding high-energy observations from Nustar, the team was able to pick up a different signature of iron that was scattered to the sides, demonstrating that the wind rushes out in an almost spherical blast.

Image copyright NASA
Image caption Nasa's Nustar telescope is a high-energy X-ray specialist, sent into orbit in 2012

"Knowing the speed, shape and size of the winds, we can now figure out how powerful they are," Prof Harrison said.

That power is something to behold: about ten times the mass of the Sun is blown out every year, along with a trillion times more energy than our star emits.

Those quantities, and the shape of the wind, suggest that PDS 456 has quite some impact on the surrounding galaxy - and this is likely to be the case for other supermassive black holes, including "Sagittarius A*" at the heart of our very own Milky Way.

"Now we know that quasar winds significantly contribute to mass loss in a galaxy, driving out its supply of gas, which is fuel for star formation," said Dr Emanuele Nardini from Keel University in the UK, the study's lead author.

"This study provides a unique view of the possible mechanism that links the evolution of the central black holes to that of their host galaxies, over cosmic time."

The research is published in Science magazine.

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