A Swinburne astronomer is part of an international discovery effort bringing scientists one step closer to understanding the physics of binary neutron star mergers and the universe at large.

The discovery, made by an international team of astronomers, suggests that a narrow and super-fast 'jet' of material blasted out during the cataclysmic neutron star merger, slammed into the environment surrounding the merging neutron stars and inflated a bubble-like cocoon.

The findings, published in Nature, contradict a popular theory describing the aftermath of the recently observed neutron star merger — namely, that the beam-like jet thought to be associated with highly energetic phenomena called gamma-ray bursts had been seen directly, immediately after the merger.
“The burst of gamma-rays from this merger didn't come directly from a tightly focused, high-speed jet that just grazed our line of sight; instead, we attribute them to a more slowly moving outflow of material that had absorbed some of the jet’s energy,” says Swinburne astronomer Dr Adam Deller, ARC Future Fellow at the Centre for Astrophysics and Supercomputing and Associate Investigator at the ARC Centre of Excellence for Gravitational Wave Discovery.

“We confirmed this by studying the radio emission produced by this outflowing material weeks and months after the merger.”

Dr Deller believes this finding will impact astronomy in two important ways.

“The 'canonical' model of what happens when neutron stars merge will be revised and improved,” he says. “And when LIGO detects more binary neutron star mergers in the future, we now expect to see an 'afterglow' counterpart more frequently than previously expected, which will help us pin down their locations and is good news for learning more about the extreme physics of these merger events.”

Australia and the world looking to the skies
The findings were made possible by the cooperative efforts of a team of astronomers and facilities
world-wide, and Dr Deller stresses the importance of having radio telescopes in Australia and the
world monitoring these events.

"As we've kept our radio telescopes trained on the site of this event, we've continued to learn more
and more about the nature of the explosion that accompanied the neutron star merger,” he says.

"Having a suite of radio telescopes world-wide, including in Australia, has underpinned this
monitoring effort. By observing at a range of times and radio frequencies, we've learnt much more
about the explosion than any one facility could have provided alone."

Dr Tara Murphy, an ARC fellow at University of Sydney who led observations with the Australia
Telescope Compact Array, says that detecting and monitoring radio waves is critical to understand
what happens when two neutron stars merge.

“We now know that what we’re observing is not what we expected - we haven’t seen anything quite
like it before.”

“Australian facilities have played a vital role in monitoring radio waves from the merger. We’re able
to detect this high energy event, 130 million light years away, tracking it as the explosion evolves
with time.”

Looking to the future
The research team say that future observations with international telescopes LIGO, Virgo, and
others will help further clarify the origins and mechanisms of these extreme events.

The observatories should be able to detect additional neutron-star mergers—and perhaps
eventually, mergers of neutron stars and black holes.

The findings were made with the Karl G. Janksy Very Large Array in New Mexico, the CSIRO Australia
Telescope Compact Array, and the Giant Meter-wave Radio Telescope in India. The lead author is Kunal Mooley, formerly of the University of Oxford and now a Jansky Fellow at
Caltech.

To view the complete findings, see: A mildly relativistic wide-angle outflow in the neutron star
merger GW170817

Image credit: NRAO/AUI/NSF: D. Berry.
The image shows a radio telescope (upper right) observing GW170817 (lower left). The jet within GW170817 (narrow bright beam emanating from GW170817) has dissipated its energy into the dynamical ejecta (shown in brown/yellow) and thus given rise to a wide-angle outflow (shown in red/pink) - a scenario called the choked-jet cocoon.

Scientists searching for gravitational waves have confirmed yet another detection from their fruitful observing run earlier this year. Dubbed GW170608, the latest discovery was produced by the merger of two relatively light black holes, 7 and 12 times the mass of the sun, at a distance of about a billion light-years from Earth. The merger left behind a final black hole 18 times the mass of the sun, meaning that energy equivalent to about 1 solar mass was emitted as gravitational waves during the collision. 

GW170608 is the lightest black hole binary that LIGO and Virgo have observed – and so is one of the first cases where black holes detected through gravitational waves have masses similar to black holes detected indirectly via electromagnetic radiation, such as X-rays.​ 

Prof Matthew Bailes delivers a history of gravitational waves in virtual and augmented reality to a packed theatre at Swinburne University of Technology. We were delighted to have Prof Brian Schmidt as our MC, and a personal message from Prof Barry Barish to launch our Centre of Excellence for Gravitational Wave Discovery (OzGrav).

Read our media announcement here, or watch the OzGrav Director Professor Matthew Bailes explain the discovery:

MEDIA ADVISORY:
Australian scientists to discuss new developments in gravitational-wave astronomy

NEWS BRIEFING: Tue 17 Oct 2017 at 09:00 AEDT at Old Parliament House, Canberra and online

Scientists from OzGrav (The ARC Centre of Excellence for Gravitational Wave Discovery), CAASTRO (The ARC Centre of Excellence for All-sky Astrophysics) and the LIGO-Virgo Collaboration will reveal new details and discoveries made in the ongoing search for gravitational waves.

Join us for this media briefing, moderated by Australia's Chief Scientist Dr Alan Finkel, when Australian experts will discuss the research and its implications.

The Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav) is delighted to congratulate the winners of this year’s Nobel prize in Physics for the leadership roles they played in the discovery of gravitational waves by the Advanced LIGO detector.

The three winners are Rainer Weiss, from the Massachusetts Institute of Technology, Kip Thorne and Barry Barish, both of whom are from the California Institute of Technology.  OzGrav is very fortunate to have Barry Barish serve on our Scientific Advisory Committee. 

Australia’s Minister for Education and Training, Simon Birmingham, also congratulated the 2017 Nobel Prize winners. “OzGrav is helping Australia stay at the cutting edge of this new and rapidly advancing field,” said Senator Birmingham. “It will capitalise on the first detections of gravitational waves, to understand the extreme physics of black holes and warped space-time.”

​The LIGO Scientific Collaboration and the Virgo collaboration report the first joint detection of gravitational waves with both the LIGO and Virgo detectors. This is the fourth announced detection of a binary black hole system and the first significant gravitational-wave signal recorded by the Virgo detector, and highlights the scientific potential of a three-detector network of gravitational-wave detectors.
 
The three-detector observation was made on August 14, 2017 at 10:30:43 UTC. The two Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, and funded by the National Science Foundation (NSF), and the Virgo detector, located near Pisa, Italy, detected a transient gravitational-wave signal produced by the coalescence of two stellar mass black holes.
 
A paper about the event, known as GW170814, has been accepted for publication in the journal Physical Review Letters.

OzGrav headquarters is pleased to call for applications for the following two travel funding programs.

Applications for both programs closed Friday 22nd September 2017.

International Visitor Funding Program
The OzGrav International Visitor Program has been established to support travel by leading international scientists to collaborate on OzGrav projects with OzGrav CIs and other members within Australia. This is a competitive funding program, with potential visitors to be nominated by OzGrav CIs. Visitors will be  encouraged to visit multiple nodes, participate in node and theme meetings, and give seminars or public talks during their visit. At least one third of the budget should come from the hosting or sponsoring node(s). 

Further details, guidelines, and application instructions are contained in the international visitor funding application form.

Student/Postdoc Travel or Placement Awards
We are inviting applications from OzGrav students and postdocs for travel awards to enable them to spend time working at other nodes or collaborating organizations on OzGrav projects, and/or to attend national or international conferences to communicate OzGrav research. This is a competitive funding program. Successful applicants may be awarded up to $3,000 for international placements/travel or up to $2,000 for domestic placements/travel. At least one third of the budget should come from the applicant’s home or host institution.

Further details, guidelines, and application instructions are contained in the student/postdoc travel award application form. 

The Laser Interferometer Gravitational-wave Observatory (LIGO) has made a third detection of gravitational waves, ripples in space and time, demonstrating that a new window in astronomy has been firmly opened.

As was the case with the first two detections, the waves were generated when two black holes merged to form a larger black hole. In the latest merger, the final black hole was some 50 times the mass of our Sun. The recent detection, called GW170104, is the farthest yet, with the black holes located about three billion light-years away.

Einstein's theory of general relativity predicts that colliding black holes and neutron stars generate ‘gravitational waves’ that cause ripples in the fabric of space-time. After such an event, space-time does not return to its original state, instead it stays permanently warped. The astonishing prediction of Monash University researchers (and OzGrav investigators) Eric Thrane and Paul Lasky, along with student Lucy McNeill is that this warping could be detected using the advanced LIGO detector - even when the signal that caused the warping was not observed.
More details in the Press Release, New Scientist article, and the full publication.