Jamie Morton is the NZ Herald's science reporter.

Kiwi John Bray's star gazing may lead to breakthrough

Astrophysics doctoral student John Bray. Photo / Supplied
Astrophysics doctoral student John Bray. Photo / Supplied

John Bray might have just solved a long-standing mystery about what happens when massive stars die - yet it's not the most impressive thing one might say about the University of Auckland researcher.

Only a few years ago, he was sitting in his office at an Auckland manufacturing company, wondering what had happened to his teenaged dream of becoming an astrophysicist.

In the 1980s, his curiosity led him through a Bachelor of Science in physics, but he instead followed a different career path, into the somewhat duller world of production management.

By the age of 48, he'd worked in plants in New Zealand, Hong Kong and Australia and had landed a general manager's role.

But his urge to study the stars still niggled.

"There probably was a moment when I'd gone through the third or fourth round of redundancies that I decided there must be something more interesting to do," he told the Herald.

"Then I thought back to the fun I had doing physics."

It was enough to spur a dramatic course change from the boardroom back to the lecture theatre.

While the landscape of astrophysics had transformed dramatically since the 1980s -- much of today's theory revolved around computer models -- he worked his way through a post-graduate diploma, then a masters which he later changed to a PhD.

Bray recently published a paper that put forward an explanation of what it is that sends some neutron stars whizzing across the universe at speeds of millions of kilometres an hour, while others are almost motionless.

The answer lies in the spectacular explosions -- supernovae -- that end the lives of massive stars that are much larger and shorter-lived than our sun.

Like all stars, these goliath stars can be formed on their own or in multiples where they orbit around one another, and while some are born in isolation, it's thought that most are created in groups, with pairs or binary star systems being the most common.

Supernovae are incredibly bright, briefly out-shining entire galaxies while creating almost all of the elements that we are made of, and many leave behind either a black hole or a neutron star.

While it's widely accepted that speeding neutron stars gain their high velocities by being blown out in the supernovae, despite three decades of research, scientists remain unsure exactly how this happens.

Bray and his colleagues suspected it was the distinct characteristics of individual explosions that could explain how certain neutron stars were propelled out into space.

They proposed that when exploding stars blew off their outer layer slightly more in one direction, resulting neutron stars were shot off in the opposite direction, much like the way a gun recoiled when it fired a bullet.

The theory was then tested with two specially-developed computer models.

"While we find that the velocity of neutron stars formed from single star supernovae do not match the velocities observed, we find the velocities of those formed by supernovae in binary pairs are a very good match to the observations," he said.

"If our proposal is correct, researchers carrying out detailed simulations of exploding stars will be able to focus on how such an uneven ejection of the outer shell could occur - and finally explain exactly how neutron stars get their kicks."

Bray, who expects to receive his PhD within two years, believed his story showed it was never too late to pursue a different career path.

"If you have that interest and that desire, it'll make up for any cobwebs in the old brain matter."

- NZ Herald

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