New light shed on massive black hole

Swinburne University of Technology scientists are part of an international team that has used observations of super-dense stars known as pulsars to probe the Universe in a completely new way.

Astronomers have known that at the heart of every galaxy, like our own Milky Way, there lurks a supermassive black hole.

But until now, the rate at which these black holes grow and collide has been poorly understood.

A paper in today’s issue of Science pits the front-running ideas about the growth of supermassive black holes against some of the most precise astrophysical measurements ever made.

The data for this experiment was derived from a long-standing collaboration established by the CSIRO and Swinburne using pulsar observations from the CSIRO Parkes 64 metre radio telescope.

The study was jointly led by Dr Ryan Shannon, a Postdoctoral Fellow with CSIRO, and Mr Vikram Ravi, a PhD student co-supervised by the University of Melbourne and CSIRO.

“For the first time, we’ve used information about gravitational waves as a tool in astrophysics,” Dr Shannon said.

“It’s a powerful new tool. These black holes are very hard to observe directly, so this is a new chapter in astronomy.”

“One model for black-hole growth has failed our test and we’re painting the others into a corner. They may not break, but they’ll have to bend,” Mr Ravi said.

Einstein predicted gravitational waves — ripples in spacetime, generated by bodies changing speed or direction. Bodies, for instance, such as pairs of black holes orbiting each other.

When galaxies merge, their resident black holes are doomed to meet. They first waltz together then enter a desperate embrace and merge.

“Towards the end of this dance they’re growling out gravitational waves at a frequency we’re set up to detect,” Dr Shannon said.

Armed with the Parkes Pulsar Timing Array data, the researchers tested four models of black-hole growth. They effectively ruled out black holes gaining mass only through mergers, but the other three models “are still in the game,” Dr Sarah Burke-Spolaor at the California Institute of Technology (Caltech) said.

For Swinburne’s Dr Willem van Straten, the result is particularly pleasing, as it exploits data processed on the Swinburne supercomputer from his PhD in the 1990s until today.