When Stars Collide

On 17th August this year, a dramatic event occurred in deep space that has had the astronomers and astrophysicists of the world stuck to their telescopes in awestruck delight.

On that date, for only the fifth time in history, two purpose built observatories enabled scientists to hear the sound of gravitational wave bursts. A team of astronomers and astrophysicists had been listening for that sound for many months when it finally happened – a tiny bleep to their ears that could unlock many secrets of the universe. Previously, these wave bursts had been tracked back to the collision of black holes. But this time, researchers suspected – and hoped – for something different.

Approximately two seconds after the American LIGO detectors picked up the gravitational wave bursts, the FERMI telescope in Italy detected a gamma ray burst. Then 11 hours later, the Swope telescope in Chile first detected light from the collision.
Astronomers around the world trained their telescopes on the corresponding area of the sky, including Australian astrophysics teams who were amongst the first people in the world to see the 6,000oC fireball of light. This enabled them to track the source of the gravitational wave bursts in space to the dramatic collision of two neutron stars for the first time ever.

This rare event took place 130 million light years away and detecting it has been the goal of the LIGO Scientific Collaboration – a project involving thousands of astronomers around the world with the help of the LIGO and Virgo observatories.
David Reitze, Executive Director of LIGO, called this event “the most spectacular fireworks in the universe”.

What is a neutron star?
Very little is known about neutron stars. They are the smallest and densest stars in the universe that are essentially the heavy core left behind after the explosion of a supernova. The two that collided in August were each about the size of the city of Adelaide and about half the mass of the sun. In other words, about one quintillion kilograms each!

Scientists are excited because with the vision of the collision, they will be able to find out much more about the nature of neutron stars.

What is a gravitational wave?
Einstein first predicted the existence of gravitational waves back in 1916 as part of his General Theory of Relativity. They are vibrations of space and time, like ripples in the universe that you can think of as ‘spacequakes’.

Using triangulation, with the LIGO and Virgo observatories focussed on one part of the sky, scientists were finally able to first detect gravitational waves in 2015 – something that Einstein thought would never be possible.

It’s almost unbelievable that the gravitational waves were detected. Not only did they travel for 1.3 billion years to reach us, but they were so tiny by the time they got here that they only moved the LIGO’s mirrors by about one thousandth of the diameter of a proton.

Why is this an important discovery?
For the first time, astronomers could see events in the universe and as they usually do, but also feel or hear it them through the gravitational waves. This has only been possible through global collaboration with teams working in multiple observatories including the LIGO and VIRGO gravitational wave observatories. It was the nuetron neutron star collision’s unique combination of gravitational waves, gamma rays, electromagnetic waves, radio waves and light detected by multiple observatories that brought the global astronomical community together to monitor this event.

The discovery has many other ramifications.
First, it confirms Einstein’s theories concerning the speed of light. Einstein postulated that the speed of light and the speed of gravity would be the same. According to Professor David Blair from the University of WA, the observations show that gravitational waves and gamma rays travel at the same speed, which he says vindicates Einstein’s theories.

Second, it confirms that neutron star collisions are the source of gamma ray bursts – which was previously a mystery. Gamma ray bursts are rapid bursts of light energy that scientists only speculated were caused by neutron star collisions.

Third, it provides a more accurate estimate as to the size of the universe. That’s because researchers know in which galaxy the neutron star collision took place, and the gravitational waves from that collision produced a characteristic sound that tells them how far away the source of the sound (the collision) was. This is a much more definitive measure than physicists have ever had.

Finally, it appears that this massive explosion produced rare heavy elements, including gold. Professor Susan Scott, from the Australian National University, explained that analysis of the light from the explosion indicates the presence of precious metals such as gold, platinum and uranium.
Stars and Space School

While at Space School, students have the opportunity to hear speeches by a range of scientists and then to ask questions. If you are lucky enough to go to Space School and are lucky enough to have an astronomer or astrophysicist as a guest speaker, we hope this article has given you lots of questions to ask them!

The universe has many secrets and it’s thrilling when a discovery can begin to answer some of them. But there are so many more questions remaining to be answered. Will you be the one to make one of these incredible discoveries?

Dream big.