University of St Andrews

Computer simulation shows stars form around black holes after all

A new computer simulation has suggested that stars can form in the hostile environment around a black hole after all.

London, August 22 : A new computer simulation has suggested that stars can form in the hostile environment around a black hole after all.

The area around a black hole was thought to be too violent to form stars, since intense gravitational forces there could rip apart gas clouds in which stars are born.

But, according to a report in New Scientist, a new computer simulation shows a gas cloud on a near-collision course with a black hole could survive these forces.

The black hole would eventually flatten some of this gas into a stable disc from which stars could form.

Though initially, the process would inhibit star formation, in the end, though, knots of gas within the disc would gravitationally attract enough surrounding gas to trigger the formation of new stars.

If the simulation is correct, and a black hole can capture a molecular gas cloud and turn it into a stellar nursery, the effect could help explain the origin of an unusual population of young, massive stars orbiting the centre of the Milky Way.

There, stars orbit a supermassive black hole weighing 3.6 million times the mass of the Sun.

One such stellar population, known as S stars, takes as little as 10 years to orbit the black hole.

Astronomers suspect that these stars may have originally been members of binary systems. As the stellar pairs flew past the black hole, one star was captured and the other was cast outwards at high speed.

But the origin of a second group of stars is harder to explain. These young stars appear to fall within a disc surrounding the black hole.

One theory suggests the stars were pulled from a pre-existing star cluster that happened to wander near the black hole. But this violent capture should have pulled apart the cluster and left a trail of stars in its wake, and no such trail has been found.

The new simulation bolsters an alternative explanation: that the disc formed when a black hole captured an errant cloud of gas.

In the simulation, study author Ian Bonnell of the University of St Andrews in the UK, and colleague Ken Rice of the University of Edinburgh placed a cloud of gas 10 light years away from a black hole on a path that would take it near the edge of the black hole.

After moving towards the hole for 20,000 years, the gas cloud finally reached the galactic centre. There, most of the gas whipped back outwards, but 10 per cent of it slowed down and condensed to form an oval disc.

According to Mitchell Begelman of the University of Colorado, Boulder, this research may very well advance the understanding of how stars form close to black holes.

ANI