In a first, scientists connect gravitational waves and gamma rays to neutron stars

BENGALURU: For the first time, scientists working on different global projects have found conclusive evidence that short gamma ray bursts, often seen by orbiting satellites, are indeed created by colliding neutron stars, something that had only been speculated for decades. Joint observations have also given them an independent way of measuring the expansion rate of the universe.

Describing this as the "beginning of gravitational-wave multimessenger astronomy," scientists associated with the Laser Interferometer Gravitational-Wave Observatory (LIGO) say that all this began on August 17, 2017, when gravitational waves from a pair of colliding neutron stars were detected for the first time by US-Based LIGO and the Europe-based Virgo.

Parameswaran Ajith of Bengaluru-based ICTS, a scientist working with LIGO told TOI, that "this can be described as something as big as the detection of gravitational waves for the first time."

Till date, there have been four gravitational waves detected and the first such detection in 2015 led to the Nobel prize in physics being awarded this year.

The August 17 detection was the strongest gravitational wave signal detected so far, owing to the relatively close location of about 130 million light-years from earth and was confirmed by a large number of telescopes around the world that studied various forms of radiation from the merger.

Neutron Stars

Neutron stars are the smallest, densest stars known to exist and are formed when massive stars explode in supernovas.

"Typical neutron stars are heavier than the sun, but have a diameter of just about 20 kilometers: objects so dense that a teaspoon of neutron star material weighs more than Mount Everest," scientists explained in a statement shared with TOI.

Scientists could track these neutron stars, weighing about 1.1 to 1.6 times the mass of the sun, for about 100 seconds as they spiraled towards each other in a final deadly dance and collided.

"The collision created a flash of gamma rays that were detected by earth-orbiting satellites just two seconds after the gravitational waves, providing the first conclusive evidence that short gamma ray bursts, often seen by orbiting satellites, are indeed created by colliding neutron stars," the statement read.

Universe Expansion

The near-simultaneous arrival of gravitational waves and gamma rays from a source that is 130 million light years away confirms that gravitational waves indeed travel with the speed of light, as predicted by Einstein's theory.

"These joint observations also provided scientists an independent way of measuring the expansion rate of the universe. In the days that followed, astronomers pointed the source in the sky and studied it extensively in various forms of electromagnetic radiation, including X-ray, ultraviolet, optical, infrared, and radio waves," scientists said.

They added that these joint observations clearly show that at least some short gamma-ray bursts, the energetic flashes of gamma rays, are generated by the merging of neutron stars - something that was only theorized before.

These studies showed signatures of newly synthesized elements, confirming that such mergers are indeed the birthplaces of half of the elements heavier than iron - including most of the gold and platinum in the universe.