Gravitational waves and light arrive on Earth 130 million years after their creation
There’s nothing like the first time.
A first kiss. Your first car. A baby’s first steps.
Laura Cadonati’s first chirp came on September 14, 2015.
It lasted just a fraction of second, passing through Earth 1.5 billion years after a violent collision of two massive black holes.
The signal confirmed the existence of gravitational waves, ripples in space-time, which the world had been hoping to detect since Albert Einstein predicted them a century ago.
On August 17 of this year, Cadonati and her LIGO colleagues heard another chirp — much different from the original. This chirp didn’t come and go in the blink of an eye. It stretched for 100 seconds.
“Groundbreaking,” said Cadonati, a professor in the College of Sciences. “It’s just as special as the first one, if not more.”
That’s because the gravitational wave that produced this chirp arrived with something else, something that couldn’t have been produced by colliding black holes. It arrived with light.
For the first time, scientists have detected a gravitational wave produced by the collision of two neutron stars.
The wave was born 130 million years ago when the stars spun around each other, creating warps in space and time. When the stars crashed together, they produced a burst of electromagnetic radiation — gamma radiation, to be precise.
Those gravitational waves and gamma rays raced through the cosmos at the speed of light, arriving at Earth at 8:41 a.m. on August 17.
The waves were first detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Italy’s Virgo observatory. NASA’s orbiting Fermi satellite saw the gamma ray flash two seconds later, and the European Science Agency also confirmed it.
In the days and weeks afterward, other forms of electromagnetic radiation — including X-ray, ultraviolet, optical, infrared and radio waves — were detected by nearly 70 ground- and space-based observatories around the world. The observations are allowing scientists to view a neutron star collision, and learn what happens next, for the first time.
“The 2015 detection was about discovery. This time it’s about understanding,” said Cadonati, who also serves as deputy spokesperson of the LIGO Scientific Collaboration (LSC), an international team of more than 1,200 researchers.
“We’re decoding the mysteries of the universe using our senses. We’re listening to the information within gravitational waves and combining it with what we’re seeing within electromagnetic radiation.”
A Golden Collision Neutron stars form when massive stars explode in supernovas and collapse upon themselves.
The August 17 neutron stars were about 12 miles in diameter — about the size of Atlanta — with an estimated mass within the range of 1.1 to 1.6 times that of our sun. Neutron stars are so incredibly dense that a teaspoon of their material would weigh a billion tons.
The gravitational waves they produced are gone forever, arriving and leaving the LIGO and Virgo detectors in less than two minutes. But the fragments of the collision remain in view for electromagnetic researchers, who have pointed their telescopes and instruments at the faraway galaxy.
Theorists have predicted that what follows the initial fireball is a “kilonova” — a phenomenon by which the material that is left over from the collision is blown out of the immediate region and far out into space and triggers a chain of nuclear reactions. The new light-based observations show that heavy elements, such as lead, gold and platinum, are created in these collisions and subsequently distributed throughout the universe. This solves a decades-long mystery of where about half of all elements heavier than iron are produced.
More findings are expected as scientists continue to monitor the smashup’s remnants in the weeks and months to come.
“This detection has genuinely opened the doors to a new way of doing astrophysics,” said Cadonati.
“I expect it will be remembered as one of the most studied astrophysical events in history.”
News source: Georgia Tech. The content is edited for length and style purposes.
Figure legend: This Knowridge.com image is credited to Karan Jani/Georgia Tech.