From ARC Centres of Excellence for Gravitational Wave Discovery OzGrav (AU) via SciTechDaily : “Deciphering the Lives of Double Neutron Stars Using the Ripples in the Fabric of Space and Time”


From ARC Centres of Excellence for Gravitational Wave Discovery OzGrav (AU)



“Deciphering the Lives of Double Neutron Stars Using the Ripples in the Fabric of Space and Time”

May 26, 2021

Scientists from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) have described a way to determine the birth population of double neutron stars — some of the densest objects in the Universe formed in collapsing massive stars. The recently published study observed different life stages of these neutron star systems.

Scientists can observe the merging of double neutron star systems using gravitational waves — ripples in the fabric of space and time. By studying neutron star populations, scientists can learn more about how they formed and evolved. So far, there have been only two double neutron star systems detected by gravitational-wave detectors; however, many of them have been observed in radio astronomy.

One of the double neutron stars observed in gravitational wave signals, called GW190425, is far more massive than the ones in typical Galactic populations observed in radio astronomy, with a combined mass of 3.4 times that of our Sun. This raises the question: why is there a lack of these massive double neutron stars in radio astronomy? To find an answer, OzGrav PhD student Shanika Galaudage, from Monash University (AU), investigated how to combine radio and gravitational-wave observations.

The birth, mid-life and death of double neutron stars

Radio and gravitational-wave astronomy enables scientists to study double neutron stars at different stages of their evolution. Radio observations probe the lives of double neutron stars, while gravitational waves study their final moments of life. To achieve a better understanding of these systems, from formation to merger, scientists need to study the connection between radio and gravitational wave populations: their birth populations.

Shanika and her team determined the birth mass distribution of double neutron stars using radio and gravitational-wave observations. “Both populations evolve from the birth populations of these systems, so if we look back in time when considering the radio and gravitational-wave populations we see today, we should be able to extract the birth distribution,” says Shanika Galaudage.

The key is to understand the delay-time distribution of double neutron stars: the time between the formation and merger of these systems. The researchers hypothesised that heavier double neutron star systems may be fast-merging systems, meaning that they’re merging too fast to be visible in radio observations and could only be seen in gravitational-waves.

GW190425 and the fast-merging channel

The study [The Astrophysical Journal Letters] found mild support for a fast-merging channel, indicating that heavy double neutron star systems may not need a fast-merging scenario to explain the lack of observations in radio populations. “We find that GW190425 is not an outlier when compared to the broader population of double neutron stars,” says study co-author Christian Adamcewicz, from Monash University. “So, these systems may be rare, but they‘re not necessarily indicative of a separate fast-merging population.”

In future gravitational wave detections, researchers can expect to observe more double neutron star mergers. “If future detections reveal a stronger discrepancy between the radio and gravitational-wave populations, our model provides a natural explanation for why such massive double neutron stars are not common in radio populations,” adds co-author Dr Simon Stevenson, an OzGrav postdoctoral researcher at Swinburne University of Technology (AU).

See the full article here .


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OzGrav (AU)

ARC Centres of Excellence for Gravitational Wave Discovery OzGrav (AU)
A new window of discovery.
A new age of gravitational wave astronomy.
One hundred years ago, Albert Einstein produced one of the greatest intellectual achievements in physics, the theory of general relativity. In general relativity, spacetime is dynamic. It can be warped into a black hole. Accelerating masses create ripples in spacetime known as gravitational waves (GWs) that carry energy away from the source. Recent advances in detector sensitivity led to the first direct detection of gravitational waves in 2015. This was a landmark achievement in human discovery and heralded the birth of the new field of gravitational wave astronomy. This was followed in 2017 by the first observations of the collision of two neutron-stars. The accompanying explosion was subsequently seen in follow-up observations by telescopes across the globe, and ushered in a new era of multi-messenger astronomy.

The mission of the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) is to capitalise on the historic first detections of gravitational waves to understand the extreme physics of black holes and warped spacetime, and to inspire the next generation of Australian scientists and engineers through this new window on the Universe.

OzGrav is funded by the Australian Government through the Australian Research Council Centres of Excellence funding scheme, and is a partnership between Swinburne University of Technology (AU) (host of OzGrav headquarters), the ustralian National University (AU), Monash University (AU), University of Adelaide (AU), University of Melbourne (AU), and University of Western Australia (AU), along with other collaborating organisations in Australia and overseas.

The objectives for the ARC Centres of Excellence are to to:

undertake highly innovative and potentially transformational research that aims to achieve international standing in the fields of research envisaged and leads to a significant advancement of capabilities and knowledge

link existing Australian research strengths and build critical mass with new capacity for interdisciplinary, collaborative approaches to address the most challenging and significant research problems

develope relationships and build new networks with major national and international centres and research programs to help strengthen research, achieve global competitiveness and gain recognition for Australian research

build Australia’s human capacity in a range of research areas by attracting and retaining, from within Australia and abroad, researchers of high international standing as well as the most promising research students

provide high-quality postgraduate and postdoctoral training environments for the next generation of researchers

offer Australian researchers opportunities to work on large-scale problems over long periods of time

establish Centres that have an impact on the wider community through interaction with higher education institutes, governments, industry and the private and non-profit sector.