Note: Gravitational waves had already been observed indirectly around a pair of neutron stars (one of which was a pulsar) orbiting each other. Joseph Taylor and Russell Hulse were awarded the 1993 Nobel Prize for their discovery. Today’s news is the first direct detection of gravitational waves.
The actual detection took place in the pre-dawn hours of September 14, 2015. Twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, one located in Livingston, Louisiana and the other in Hanford, Washington, detected the final moments of two black holes merging.
LIGO detector in Louisiana. Credit: LIGO
Two black holes merging had been predicted before but never observed. The detection of the gravitational waves also illustrates what makes them so special. By looking at the signals, LIGO scientists estimate the two black holes were about 29 and 36 times the mass of our Sun and merged 1.3 billion years ago.
Here’s LIGO describing the gravitational waves. “About 3 times the mass of the sun was converted into gravitational waves in a fraction of a second – with a peak power output about 50 times that of the whole visible universe.” If anything fits the description of mind-boggling, this is it!
Scientists can even tell the general location in the night’s sky the event originated from. Because the Livingston detector recorded the event 7 milliseconds before the Hanford detector, scientists know the source of the waves was located in the Southern Hemisphere.
The purple line indicates where the signal is believed to have come from with a 90% confidence level. The inner yellow lines represent a 10% confidence level. Credit: LIGO
And, you can even hear them!
A new era of astronomy
We hear this all the time about gravitational waves. But, it is true. Look at how we observe the final frontier today. Visible light, radio waves, X-rays and more. What if some cataclysmic event happens, but there’s no way for us to ‘see’ it. That’s where gravitational waves come in. Theoretical physicist Matt Strassler says it best, “you can try to hide in the shadows, but there’s no hiding from gravity.” Every object, every event – creates gravity.
Today’s news is just the beginning.
“With this discovery, we humans are embarking on a marvelous new quest: the quest to explore the warped side of the universe — objects and phenomena that are made from warped spacetime. Colliding black holes and gravitational waves are our first beautiful examples,” says Caltech’s Kip Thorne.
Plus, it’s a huge win for LIGO. Knowing the experiment works has to be a big relief for all those involved. And Australian National University’s David McClelland is optimistic about the future. “Hopefully this first observation will accelerate the construction of a global network of detectors to enable accurate source location in the era of multi-messenger astronomy.”
LIGO is working with scientists in India to build a third LIGO detector in that country. If everything works out, including Indian government approval, the third detector could go live in the early 2020s.
A huge congrats to all the folks involved with making this discovery happen! Gravitational waves have long promised a new era of astronomy and we already have our first result.