Thursday, February 11th saw the announcement of the first direct detection of gravitational waves (not to be confused with “gravity waves”, as some in the media initially took to calling them, but which are something else entirely*), which are ripples in the fabric of space-time whose existence was first proposed by Albert Einstein, in 1916.
The detection came about partly as happenstance, in that the Large Interferometer Gravitational Wave Observatory (LIGO), a world-wide operation established in 1992 and involving 900 scientists from 80 institutions in 15 countries. However, the detectors in use up until recently had failed to provide direct evidence of gravitational waves.
Enter the National Science Foundation in the United States. Over the last five years, they have funded the development and construction of two “Advanced LIGO” detectors, themselves massive feats of technology and engineering, located 3,000 km apart in the United States. One resides Livingston, Louisiana, and the other in Hanford, Washington State.
These detectors started running in February2015, in what was called an “engineering mode”. However, in September 2015 work started on running them up to full operational status when, and completely unexpectedly and within milliseconds of one another, both appeared to detect gravitational passing through them.
The odds of such an event occurring almost precisely at the time when the detectors were starting to do the work for which they have been designed would seem to be – and no pun intended – astronomical. As a result the LIGO investigators wanted to be sure of what had just happened and verify what they had apparently detected; hence why the news was only released on February 11th, 2016, several months after the actual detection had been made.
Since the initial detection, the LIGO teams have deduced the gravitational waves were created by two black holes, each barely 150km across, but each travelling at around half the speed of light and massing around 30 times as much as our on Sun, spinning around one another and merging together some 1.3 billion light years away. As such, the detection marked two things: the first direct proof of gravitational waves and the conformation of a another theory: that black holes can meet and coalesce to create much larger black holes.
But what are “gravitational waves”, and why are they important?
Predicted over a century ago by Einstein in his theory of general relativity, gravitational waves are at their most basic, ripples in spacetime, generated by the acceleration or deceleration of massive objects in the cosmos. So, for example, if a star goes supernova or two black holes collide or if two super-massive neutron stars orbit closely about one another, they will distort spacetime, creating ripples which propagate outwards from their source, like ripples across the surface of a pond. The problem has been that these ripples are incredibly hard to detect, although the proof that they may well exist has been available since 1974.
It was in that year, two decades after Einstein’s passing, that astronomers at the Arecibo Radio Observatory in Puerto Rico discovered a binary pulsar (two rapidly rotating neutron stars orbiting one another). Over the ensuing years, astronomers measured how the period of the stars’ orbits changed over time. By 1982 it had been determined the stars were getting closer to each other at exactly the rate Einstein’s of general theory relativity predicted would be required for the generation of gravitational waves. In the 40 years since its discovery, the system has continued to fit so precisely with the theory, and astronomers have had little doubt it is emitting gravitational waves.
The LIGO detection however, provides the first direct evidence of gravitational waves, and with it comes the ability to see the universe in a totally new way.
“It’s like Galileo pointing the telescope for the first time at the sky,” LIGO team member Vassiliki Kalogera, a professor of physics and astronomy at Northwestern University in Illinois, said. “You’re opening your eyes — in this case, our ears — to a new set of signals from the universe that our previous technologies did not allow us to receive, study and learn from.”
Just as we’re able to study the universe in various wavelengths of light, using them to reveal things we otherwise would not be able to see, so gravitational waves will allow us to see the more of the dynamics in cosmic events which have so far remained hidden from us. We would in theory be able to see precisely what is happening in the heart of a supernova for example, and be able to detect the collisions and mergers of black holes, and more. So gravitational waves offer us a further means to increase our understanding of the cosmos.
(*In case you were wondering, gravity waves are physical perturbations driven by the restoring force of gravity in a planetary environment; that is, they are specific to planetary atmospheres and bodies of water, not cosmological events.)
Continue reading “Space Sunday: of Einstein, waves, landers and honours”
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