Scientists detect gravitational waves produced by colliding neutron stars

Ability to observe an event via both gravitational waves and light is a revolution for modern astronomy.
By Laurel Kornfeld | Oct 17, 2017
Scientists using the Laser Interferometer Gravitational Wave Observatory (LIGO) observatory have for the first time detected gravitational waves produced by a collision of two neutron stars in the galaxy NGC4993, located in the constellation Hydra.

Predicted in 1916 by Albert Einstein's general theory of relativity, the ripples in the fabric of spacetime known as gravitational waves were first detected a century later by LIGO, caused by the merger of two black holes.

That detection led to three scientists winning the 2017 Nobel Prize in physics.

While gravitational waves have subsequently been detected several times since then, this is the first time they were observed coming from merging neutron stars rather than merging black holes.

Neutron stars are the stellar remnants of massive stars that died in supernova explosions. Extremely massive stars that die in supernova explosions leave behind black holes while less massive stars that die in these explosions produce neutron stars, which have cores somewhat less massive than black holes.

These extremely dense cores are capable of crushing protons and electrons to form neutrons.

Although neutron stars are small, with diameters of around 12 miles (19 km), they can be as dense as our Sun and have masses up to one billion tons.

Unlike black holes, which have gravitational pulls so strong that even light cannot escape them, neutron stars, in merging, emit light in multiple wavelengths.

This means their mergers can be observed both by the gravitational waves they produce and in various wavelengths of light.

Approximately 130 million years ago, two stars of between eight and 20 solar masses in the galaxy NGC4993 underwent supernova explosions, then orbited one another until they collided.

On August 17, LIGO and Virgo detected the gravitational waves produced by the collision, and a few minutes later, NASA's Fermi space telescope observed a flash of gamma rays the explosion produced.

Once the gamma rays were detected, scientists knew the direction from which the gravitational waves came, and astronomers worldwide aimed telescopes at the phenomenon to collect additional data.

The double detection confirms that both light and gravitational waves travel at the same universal speed of light, another Einstein prediction.

"This event has the most precise sky localization of all detected gravitational waves so far," said Virgo spokesman Jo van den Brand. "This record precision enabled astronomers to perform follow-up observations that led to a plethora of breathtaking results."

More than 3,500 astronomers worldwide observed the event with over 70 telescopes.

Researchers studying the light spectra of material emitted during the merger found the fingerprints of heavy elements, including gold, platinum, and lead, confirming theories that the periodic table's heaviest elements are forged in mergers of neutron stars.

 

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