When worlds collide

We have proof, at last, that cataclysmic events deep in intergalactic space are the source of mysterious bursts of gamma rays that we’ve been witnessing for half a century.

IT WAS TOUTED as the dawning of a new era in astronomy – a game changer. Textbooks would be rewritten. Scientists were jubilant.

I’m referring to last October’s announcement of the collision of two neutron stars in a galaxy 130 million light-years away. For the first time, a complete set of observations of a cataclysmic event deep in intergalactic space had been obtained. It was dramatic, but I suspected many ordinary folk felt in the dark.What are neutron stars? Why is a collision so exciting?

Neutron stars are remnants of old stars that have exploded, leaving behind a highly magnetised 20km ball of subatomic particles that weighs as much as a normal star.We’ve long believed that when such objects collide, they release copious radiation as light, radio waves, X-rays and high-energy gamma rays. And for almost 50 years, we’ve observed mysterious gamma-ray bursts from space and speculated that their source might be distant colliding neutron stars. Now we have proof.

It has come from our new-found capability to sense the massive gravitational disturbance that such a collision generates. Rippling through empty space at the speed of light, gravitational waves were predicted by Einstein, but detectors only became sensitive enough in 2015 to sense the infinitesimally small vibrations as they wash over Earth.There are now two such detectors in the USA and one in Italy, enabling astronomers to reveal details of the source of gravitational waves and also pinpoint its position in space.

On 17 August 2017, astronomers were alerted by a gravitational signal that betrayed the collision of the two neutron stars. Seconds later, its gammaray flash was detected and the world’s visible-light and radio telescopes locked onto it in unprecedented international collaboration. With the microscopic view provided by the gravitational wave detectors, this is the most complete analysis of such an event ever achieved. No wonder its announcement was such a big deal. Nobel prizes are sure to follow.

This artist’s impression of neutron stars colliding captures the brief but powerful burst of gamma rays that new observations reveal are produced during such impacts. Earth’s gold, and other rare heavy elements, are thought to have come from events...

FRED WATSON is an astronomer at the Australian Astronomical Observatory.