Last updated November 9, 2017 at 2:57 pm
Australian scientists have announced that not only did they detect gravitational waves but, for the first time, they watched the event that led to their generation. This dual-detection has already provided a cascade of ground-breaking discoveries. Watch the video Scientists Watch Collision That Created Gravitational Waves
Astronomers and astrophysicists across Australia and around the world have announced a scientific bonanza delivered by the detection of gravitational waves from the violent collision of two neutron stars in a galaxy 130 million lightyears away. For the first time ever, they were able to watch the collision happen by the resulting gravitational waves. More incredibly, they were also able to visually observe the gigantic fireball created when the stars collided.
Scientists from the LIGO-Virgo Collaboration made the dual observation in August, they announced at a press conference this morning. Dr Eric Howell from the University of Western Australia (UWA) and a member of Australia’s Centre of Excellence for Gravitational Wave Detection (OzGrav) couldn’t believe their luck. “To find an event like this so early, so close, and so loud is just brilliant.” Professor Linqing Wen from the UWA/OzGrav collaboration described the event as “the discovery of the century!”
Making a splash in spacetime
LIGO made headlines around the world in early 2016 with the announcement of the successful detection of gravitational waves emitted by two black holes as they spiralled into each other, merging to create a larger black hole. The discovery earned three of the leading members of the collaboration the Nobel Prize in Physics less than a month ago.
This time, the gravitational waves were caused by the collision and merger of two neutron stars. Neutron stars are the super-dense remnants of giant stars that have run out of fuel and collapsed in on themselves in a supernova explosion. Neutron stars typically weigh two to three times the mass of the Sun, but are only about 10 km across, making them incredibly dense. A teaspoon of neutron star material would weigh 900 times more than the Great Pyramid of Giza.
Because not even light can escape from a black hole, collisions between black holes are invisible to telescopes and can only be observed using gravitational wave detectors. Collisions between neutron stars, on the other hand, create an immense fireball.
Professor Matthew Bailes, Director of OzGrav, explained that “this was the first time that any cosmic event was observed through both light it emitted and the gravitational ripples it caused in the fabric of spacetime. The subsequent avalanche of science was virtually unparalleled in modern astrophysics.”
Professor David Blair has worked on gravitational wave detectors for 40 years and was ecstatic when the first detection was announced, but is even more thrilled by the most recent discovery. “When the first detection came through (in 2015), we thought all our Christmases had come at once. But this is even more exciting!”
Seeing the light
Within minutes of the detection of the gravitational waves astronomers around the world were scrambling for their telescopes.
One problem with the current gravitational wave detectors is that their resolution is very poor, meaning the astronomers had to frantically sweep a large area of sky to track down the target. A “mad scramble” of messages were swapped between Howell and other astronomers around Australia in the search for the best coordinates. The Swope telescope in Chile eventually succeeded in identifying the target galaxy and alerting the astronomy community. “The teamwork between OzGrav and the wider astronomical community was absolutely fantastic to see,” said Howell.
Meanwhile, another team of astronomers swung CSIRO’s ATCA radio telescope into action and quickly confirmed that the fireball was emitting radio waves as well as visible light. And elsewhere around the world, research programs were interrupted so some of the world’s most powerful telescopes, such as the Hubble and ALMA, could also join in and gather crucial information about the fireball as it cooled and faded.
One of the unexpected findings that has the scientists involved even more excited was that the gravitational waves were followed less than two seconds later by a burst of gamma rays. Cosmic gamma ray bursts, which are extremely high energy light particles, were discovered 50 years ago and can last from fractions of a second to several hours. Astrophysicists had thought that collisions between two neutron stars could account for some of those shorter bursts. The new discovery “instantly confirmed that merging neutron stars were responsible for the so-called short-duration gamma ray bursts, solving a 50 year old mystery,” according to Professor Bailes.
Heart of gold
The telescopic observations of the fading fireball also explained another cosmic conundrum. Scientists have speculated that colliding neutron stars are the factories that create most of the gold and other precious metals in the universe. By comparing theoretical models and simulations with the telescope data, the scientists from the LIGO-Virgo Collaboration confirmed that these heavy metals are forged in the nuclear reactions that occur during the violent collision, before being scattered throughout the galaxy by the explosion. OzGrav’s Dr Kendall Ackley described it as “a scientific gold rush.”
A cascade of science
The LIGO-Virgo Collaboration scientists expect to be kept busy for a very long time, studying the wealth of fresh data to improve our understanding of the universe, and their results already lend further weight to well-established theories. When Albert Einstein predicted gravitational waves more than 100 years ago, his theory showed that the waves should move through space at the speed of light. Although the light from the gamma ray burst reached Earth after the gravitational waves, the difference was less than two seconds in a 130 million year journey. The difference in speed is due to light’s interaction with the thin gas found in intergalactic space.
The team also took the opportunity to measure the age of the universe by combining the gravitational wave data and measurements of the redshift of light from the host galaxy caused by the expansion of the universe. Their measurement agreed very closely with the age of 13.8 billion years established by previous scientific projects.
Eyes and ears open
The LIGO-Virgo Collaboration scientists have described the new discovery as the dawn of “multi-messenger” astronomy — the use of complementary information from both light and gravitational waves to study the universe in greater detail. “Before this event, it was like we were sitting in an IMAX theatre with blindfolds on. The gravitational wave detectors let us ‘hear’ the movies of black holes and neutron stars, but we couldn’t see anything,” explained Professor Cooke. “This event lifted the blindfolds and, wow, what an amazing show!”
Image of two neutron stars spiralling in to a collision, emitting gravitational waves in the process courtesy of NASA
Images of two neutron stars merging, producing an immense fireball courtesy of NASA
Illustration of a gamma ray burst courtesy of NASA/Goddard Space Flight Centre
Image of the LIGO facility courtesy of LIGO/Caltech