From ARC Centres of Excellence for Gravitational Wave Discovery – OzGrav (AU) via : “Exploring the mysterious origins of the most extreme light flashes in the universe”


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


October 18, 2021

Artist’s illustration of a gamma ray burst. Credit: Carl Knox, OzGrav-The Swinburne University of Technology (AU).

Our universe shines bright with light across the electromagnetic spectrum. While most of this light comes from stars like our sun in galaxies like our own, we are often treated with brief and bright flashes that outshine entire galaxies themselves. Some of these brightest flashes are believed to be produced in cataclysmic events, such as the death of massive stars or the collision of two stellar corpses known as neutron stars. Researchers have long studied these bright flashes or “transients” to gain insight into the deaths and afterlives of stars and the evolution of our universe.

Astronomers are sometimes greeted with transients that defy expectations and puzzle theorists who have long predicted how various transients should look. In October 2014, a long-term monitoring program of the southern sky with the Chandra telescope—NASA’s flagship X-Ray telescope—detected one such enigmatic transient called CDF-S XT1: a bright transient lasting a few thousandths of a second.

The amount of energy CDF-S XT1 released in X-rays was comparable to the amount of energy the sun emits over a billion years. Ever since the original discovery, astrophysicists have come up with many hypotheses to explain this transient; however, none have been conclusive.

In a recent study, a team of astrophysicists led by OzGrav postdoctoral fellow Dr. Nikhil Sarin (Monash University (AU)) found that the observations of CDF-S XT1 match predictions of radiation expected from a a high-speed jet traveling close to the speed of light. Such “outflows” can only be produced in extreme astrophysical conditions, such as the disruption of a star as it gets torn apart by a massive black hole, the collapse of a massive star or the collision of two neutron stars.

Sarin et al’s study found that the outflow from CDF-S XT1 was likely produced by two neutron stars merging together.

This insight makes CDF-S XT1 similar to the momentous 2017 discovery called GW170817—the first observation of gravitational-waves, cosmic ripples in the fabric of space and time—although CDF-S XT1 is 450 times further away from Earth. This huge distance means that this merger happened very early in the history of the universe; it may also be one of the furthest neutron star mergers ever observed.

Neutron star collisions are the main places in the universe where heavy elements such as gold, silver and plutonium are created. Since CDF-S XT1 occurred early on in the history of the universe, this discovery advances our understanding of Earth’s chemical abundance and elements.

Recent observations of another transient AT2020blt in January 2020—primarily with the Zwicky Transient Facility—have puzzled astronomers.

This transient’s light is like the radiation from high-speed outflows launched during the collapse of a massive star. Such outflows typically produce higher energy gamma-rays; however, they were missing from the data—they were not observed. These gamma rays can only be missing due to one of three reasons: 1) The gamma-rays were not produced, 2) The gamma rays were directed away from Earth, 3) The gamma-rays were too weak to be seen.

In a separate study [The Astrophysical Journal Letters], led again by OzGrav researcher Dr. Sarin, the Monash University astrophysicists teamed up with researchers in Alabama, Louisiana, Portsmouth and Leicester to show that AT2020blt probably did produce gamma-rays pointed toward Earth, they were just really weak and missed by our current instruments.

Dr. Sarin says: “Together with other similar transient observations, this interpretation means that we are now starting to understand the enigmatic problem of how gamma-rays are produced in cataclysmic explosions throughout the Universe.”

The class of bright transients collectively known as gamma-ray bursts, including CDF-S XT1, AT2020blt, and AT2021any, produce enough energy to outshine entire galaxies in just one second.

“Despite this, the precise mechanism that produces the high-energy radiation we detect from the other side of the universe is not known,” explains Dr. Sarin. “These two studies have explored some of the most extreme gamma-ray bursts ever detected. With further research, we’ll finally be able to answer the question we’ve pondered for decades: How do gamma ray bursts work?”

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 Australian 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:

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.