A pair of neutron-star-cross’d lovers

Wondering what the big astrophysics announcement was about yesterday? It is a tale of love, tragedy, success and zombies. Let us begin…

130 million years ago, in a galaxy far far away, there were two stars. They were life partners, spending their lives orbiting around one another – held together by the sacred bond of gravity. One day, one of the stars died in a supernova explosion, leaving a neutron star weighing 1.7 times the mass of the sun. The other star kept living but was sad and wanted to join its partner in the stellar after-life. So after a while it too died in a huge supernova explosion. The remaining corpse was also a neutron star, this time weighing 1.1 times the mass of the sun. The second explosion sent these two remaining exotic objects on a chaotic orbit all around the galaxy in which they lived. They travelled all over the place and had many adventures.

But the two undead zombie stars were lonely. They really just wanted to be together as one. And eventually they got their wish. Slowly, over millions of years, the neutron stars got closer together by releasing gravitational waves. Then one day, they finally collided in a huuuuge kilanova explosion! This sent a gigantic burst of gravitational waves rippling across the universe. Almost at the same time, there was a huge burst of gamma-ray light that also went speeding across the universe (at the speed of light, obvs).

The explosion was so intense that gold, silver, platinum and many other heavy elements were forged in its bowels. And lots of it… ten thousand Earths worth of it! You may be wearing some of it right now!* What was left after the explosion remains a mystery. It was something weighing around 2.6 times the mass of the sun, and was probably a black hole. And so the two stars remained together as one, hidden from the rest of the universe for eternity.

Periodic table showing which elements were created by which dramatic astrophysical event. Credit: Robert Hurt/IPAC/Caltech.

130 million years later, the gravitational waves arrived on the Earth and were recorded by the VIRGO detector in Italy. A few milliseconds later, they were picked up by the LIGO detector in the USA which sounded the alarm.

Then only 1.7 seconds later, the FERMI satellite – which was chillin’ out in space and minding its own business – suddenly detected a burst of gamma rays. Then it was action stations for astronomers all around the world.

Within 10 hours, the little Swope telescope in Chile had spotted a bright dot in a galaxy which wasn’t there before – and so it was discovered that the explosion came from galaxy NGC4993.

Image: The galaxy NGC4993 before and after the new bright spot was visible. Image credit to Hubble/STScI (Left) and Photograph by 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley (Right)

Twelve days later, radio astronomer Jacinta Delhaize happened to be visiting the Australia Telescope Compact Array control centre in Sydney where she was supposed to do some training with the radio telescope to re-qualify for her remote observing licence. She was annoyed because she couldn’t do the training properly – the telescope was being used for something more important…

Me at the Australia Telescope Compact Array control room in Sydney while observations of NGC4993 were happening

It turned out they were searching for the radio ‘after glow’ of the neutron star merger. But Jacinta was slightly too early to join the excitement, nothing had been detected yet. Three days later, a team of Australian astronomers including Tara Murphy and Emil Lenc spotted the radio after-glow. More about that here: https://www.eurekalert.org/pub_re…/2017-10/uos-agw101617.php

In the days and weeks that followed the explosion, more than 3,500 astronomers all around the world worked together to detect the ‘after glow’ of the explosion in x-ray, optical, infrared and radio light. They used 70 telescopes on all seven continents (including Antarctica!) such as SALT in South Africa, ALMA in Chile and the good old Hubble telescope up in space.

Astronomers everywhere got goosebumps when they realised how super cool this discovery was. They now know that gravity travels at the speed of light (wow!), understand how heavy elements are produced in the universe and have the best evidence yet for what causes short-duration gamma-ray bursts.

The astronomers got warm fuzzy feelings knowing that they showed how awesome international collaboration can be. And they went to bed and slept very well the night after the big press release, feeling very relieved (and a tiny bit smug) that a large chunk of their funding was finally justified.

The end.

*Unless you are 130 million years old and originate very far from Earth, your gold, silver and platinum was probs formed in a different double neutron star collision, not this one.

Written by Dr Jacinta Delhaize.

There are many wonderful articles you can read for more information, including the inspiration for this post: http://news.nationalgeographic.com/2017/10/gravitational-waves-discovered-neutron-stars-pictures-science/

Feature image credit: Robin Dienel courtesy of the Carnegie Institution for Science.


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