From ARC Centres of Excellence for Gravitational Wave Discovery via “Future space detector LISA could reveal the secret life and death of stars”


From ARC Centres of Excellence for Gravitational Wave Discovery


Artist’s illustration of an ‘isolated neutron star’—one without associated supernova remnants, binary companions or radio pulsations. Credit: Casey Reed – Penn State University

A team of astrophysicists led by Ph.D. student Mike Lau, from the ARC Centre of Excellence in Gravitational Wave Discovery (OzGrav), recently predicted that gravitational waves of double neutron stars may be detected by the future space satellite LISA. The results were presented at the 14th annual Australian National Institute for Theoretical Astrophysics (ANITA) science workshop 2020. These measurements may help decipher the life and death of stars.

Lau, first author of the paper, compares his team to astro-paleontologists: “Like learning about a dinosaur from its fossil, we piece together the life of a binary star from their double neutron star fossils.”

A neutron star is the remaining ‘corpse’ of a huge star after the supernova explosion that occurs at the end of its life. A double neutron star, a system of two neutron stars orbiting each other, produces periodic disturbances in the surrounding space-time, much like ripples spreading on a pond surface. These ‘ripples’ are called gravitational waves, and made headlines when the LIGO/Virgo Collaboration detected them for the first time in 2015. These gravitational waves formed when a pair of black holes spiraled too close together and merged.

However, scientists still haven’t found a way to measure the gravitational waves given off when two neutron stars or black holes are still far apart in their orbit. These weaker waves hold valuable information about the lives of stars and could reveal the existence of entirely new object populations in our Galaxy.

The recent study [below] shows that the Laser Interferometer Space Antenna (LISA) could potentially detect these gravitational waves from double neutron stars.


ESA/NASA eLISA space based, the future of gravitational wave research

LISA is a space-borne gravitational-wave detector that is scheduled for launch in 2034, as part of a mission led by the European Space Agency. It’s made of three satellites linked by laser beams, forming a triangle that will orbit the Sun. Passing gravitational waves will stretch and squeeze the 40 million-kilometer laser arms of this triangle. The highly sensitive detector will pick up the slowly-oscillating waves—these are currently undetectable by LIGO and Virgo.

MIT /Caltech Advanced aLigo

VIRGO Gravitational Wave interferometer, near Pisa, Italy

Using computer simulations to model a population of double neutron stars, the team predicts that in four years of operation, LISA will have measured the gravitational waves emitted by dozens of double neutron stars as they orbit each other. Their results were published in the Monthly Notices of the Royal Astronomical Society.

A supernova explosion kicks the neutron star it forms and makes the initial circular orbit oval-shaped. Usually, gravitational wave emission rounds off the orbit—that is the case for double neutron stars detected by LIGO and Virgo. But LISA will be able to detect double neutron stars when they’re still far apart, so it may be possible to catch a glimpse of the oval orbit.

How oval the orbit is, described as the eccentricity of the orbit, can tell astronomers a lot about what the two stars looked like before they became double neutron stars. For example, their separation and how strongly they were ‘kicked’ by the supernova.

The understanding of binary stars—stars that are born as a pair—is plagued with many uncertainties. Scientists hope that by the 2030s, LISA’s detection of double neutron stars will shed some light on their secret lives.

See the full article here .


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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 (host of OzGrav headquarters), the Australian National University, Monash University, University of Adelaide, University of Melbourne, and University of Western Australia, 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.