CANBERRA, (PNA/Xinhua) — A paper in Friday’s issue of the journal Science pits the front-running ideas about the growth of supermassive black holes against observational data — a limit on the strength of gravitational waves from pairs of black holes, obtained with Australia’s national science body CSIRO’s 64m Parkes radio telescope in eastern Australia.
The study was jointly led by Dr. Ryan Shannon, a Postdoctoral Fellow with CSIRO, and 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 in the statement. “It’s a powerful new tool. These black holes are very hard to observe directly, so this is a new chapter in astronomy.”
Einstein predicted gravitational waves — ripples in space-time, generated by bodies changing speed or direction. Bodies, for instance, such as pairs of black holes orbiting each other.
When galaxies merge, their resident central black holes are doomed to meet. They first waltz together then enter a desperate embrace and merge.
“Theorists predict that towards the end of this dance they’re growling out gravitational waves at a frequency we’re set up to detect,” Dr. Shannon said.
Played out again and again across the Universe, such encounters create a background of gravitational waves, like the noise from a restless crowd.
Astronomers have been searching for gravitational waves with the Parkes radio telescope and a set of 20 small, spinning stars called pulsars.
Pulsars act as extremely precise clocks in space. We measure when their pulses arrive on Earth to within a tenth of a microsecond.
As gravitational waves roll through an area of space-time, they temporarily swell or shrink the distances between objects in that region.
The Parkes Pulsar Timing Array (PPTA) project and an earlier collaboration between CSIRO and Swinburne University in Melbourne together provide nearly 20 years’ worth of timing data.
“We haven’t yet detected gravitational waves outright, but we’ re now into the right ballpark to do so,” CSIRO’s project leader Dr. George Hobbs said.
According to Dr. Hobbs, combining pulsar-timing data from Parkes with that from other telescopes in Europe and the U.S. — a total of about 50 pulsars — should give researchers the accuracy to detect gravitational waves “within 10 years”.
Meanwhile, the PPTA results are showing researchers how low the background rate of gravitational waves is.
The strength of the gravitational wave background depends on how often supermassive black holes spiral together and merge, how massive they are, and how far away they are. So if the background is low, that puts a limit on one or more of those factors.
Armed with the PPTA 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”, said Dr. Sarah Burke-Spolaor, formerly with NASA’s Jet Propulsion Laboratory and now at the California Institute of Technology (Caltech) IN PASADENA, CALIFORNIA.