Jamie Morton is the NZ Herald's science reporter.

NZ study could help the hunt for Einstein's cosmic ripples

Gravitational waves are cosmic ripples that travel through the universe at the speed of light. Image / 123RF
Gravitational waves are cosmic ripples that travel through the universe at the speed of light. Image / 123RF

Gravitational waves are among the most perplexing features of the universe.

Essentially cosmic ripples, comparable to sound, they zoom through space at the speed of light.

Our fascination with these mysterious disturbances in space-time has only grown since scientists physically observed them for the first time in 2015 – a century after Albert Einstein proposed their existence.

Thanks to Einstein, we've long understood space-time as a four-dimensional fabric able to be pushed or pulled as objects move through it.

If we thought of this fabric as a trampoline mat, gravitational waves might be likened to the ripples produced from dropping a bowling ball on to it.

Having captured them, we could now see how the universe worked in an entirely new way.

Last year, the science world was again abuzz with the announcement that more had been detected.

That chance signal, designated GW170817, emanated from the spectacular collision of two neutron stars – an event that lasted mere Earth seconds yet sprinkled gold across the heavens.

And just this week, scientists announced they'd confidently now detected gravitational waves from a total of 10 binary black hole mergers and one merger of neutron stars - which were the dense, spherical remains of stellar explosions.

A major study now being led by University of Auckland astrophysicist Dr JJ Eldridge aimed to understand the lifecycle of the stars that eventually produced such effects.

One way of understanding stars that have exploded into supernova – or so-called progenitor stars – was to learn more about the galaxies in which we saw gravitational wave events.

Unfortunately, the galaxies we'd recorded them in so far numbered just one.

Several groups of scientists have been studying this galaxy to calculate the time between the birth of the two stars and their eventual merging into a single, ultra-dense object that produced GW170817.

The problem was, Eldridge said, these studies assumed that all of the stars in the galaxy were single stars.

"And we know that the progenitor of the event must have been a binary star, as we needed two stars close to each other."

Fortunately, over the past decade, Eldridge and colleague Professor Elizabeth Stanway have been showing how these two-star systems could change the appearance of galaxies.

One of their papers, published earlier this year, demonstrated how ignoring binary stars meant we could be dating the age of stars incorrectly by billions of years.

In their new study, Eldridge, Stanway and Dr Anna McLeod would combine binary models with others showing how the universe and galaxies evolved.

What they learned could help predict which galaxies gravitational wave events would likely happen within - and narrow down the hunting ground for the next big discovery.

Their work could also offer a fundamental test of how light and gravity interact, while revealing more about how the abundance of elements - which we and everything around were made of - had changed over cosmic history.

And ultimately, Eldridge simply hoped to answer some of those basic questions we pondered when gazing upon the night sky.

How did stars live and die, for instance?

"This is important as every element that isn't hydrogen or helium around us was formed inside a star," Eldridge said.

"I think it is important to know how things are made - for example, we're now certain that most gold, platinum and silver were made in some gravitational wave events where two neutron stars merge.

"But we'll also have a code we'll be releasing publicly to the astronomical community that will allow them to perform similar studies using our models with their own observations.

"They'll use this code to study many things in the universe, beyond just gravitational wave events."

The study was supported with a $936,000 grant from the Marsden Fund.

- NZ Herald

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