Since humans first gazed at the heavens, they have observed the universe primarily through the window of the electromagnetic spectrum, including visible light waves, radio waves, and X-rays.
But it turns out that using light in its various forms is not the only way to peer into space.
Now, with the ability to detect gravitational waves, scientists say they will be able to document distant phenomena that would otherwise be obscured or hidden.
Gravitational waves are ripples in the fabric of space-time. They are produced in many ways but it takes the motions of dense and massive objects like black holes and neutron stars to produce strong enough waves to be detectable by instruments on Earth.
Unlike electromagnetic waves, gravitational waves do not get scattered or absorbed as they pass through matter. Part of what makes them so useful is that they can sail right through dense regions of space and come out the other side unaltered.
For example, the gravitational wave signal that was detected by two LIGO instruments in Washington and Louisiana first hit the Earth in the Southern Hemisphere and then passed right through our planet before being picked up by the two observatories, said Saul Teukolsky, an astrophysicist at Cornell University.
"That shows you how weakly these waves interact with matter," he added.
Gravitational waves may also allow scientists to "see" systems and objects that have never been detected before because they don't emit electromagnetic waves.
On Thursday, scientists announced that the first gravitational wave signal to be detected on Earth was caused by the collision of two black holes each with a mass roughly 30 times the mass of the sun. A collision like this one does not produce an electromagnetic signal, so it would not have been possible to detect with telescopes on Earth.
"No one had ever seen a system like this before," said Jonah Kanner, a LIGO research scientist at Caltech. "No one had ever seen a 30-solar-mass black hole period. "
He added that even this very first detection could help scientists better understand how galaxies and stars evolve.
Surabhi Sachdev, a graduate student at Caltech who works on LIGO data, said the most inspiring part of using gravitational waves to learn about the universe is the possibility of seeing something never seen before.
"That's what excites me," she said. "The idea that we may find objects we never imagined."
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