For the first time, astronomers were able to register oscillations of space-time, which lasted 100 seconds, and occurred when two exotic stars approached and merged.
On August 17, 2017, the LIGO automatic observatory detected the gravitational wave GW170817. This is already the fifth wave of this kind, registered since 2015, when the observatory was launched. The wave came from a 35 square degree sector of the sky. Observations of the same sector with telescopes made it possible to notice a flare in the gamma range. It was caused by a powerful burst of fusion and decay of nuclei on the surface of two neutron stars when they merge. The opening is reported by a press release from the European Southern Observatory.
Immediately after the registration of the gravitational wave, more than fifty telescopes around the world were connected to the observation of this sector of the sky. The telescope of the European Southern Observatory in Chile was the first to obtain an image of the region of events in the visible range. The flash could also be seen in the electromagnetic range, but only from the southern hemisphere - observation from the northern one was hampered by the tilt of the Earth.
Comparing images in all available ranges, astronomers concluded that the gravitational wave came from the same event as the gamma-ray burst, as well as the visible flare. The source of the waves and flares was located in the galaxy NGC 4993, 130 million light-years away. This is the first time a gravitational wave event has happened this close to Earth.
Analysis of the LIGO data showed that the gravitational wave was caused by the merger of two bodies of relatively small mass - from 1.1 to 1.6 solar masses. This means that they were two neutron stars. Ordinary stars can also have a similar mass, but are not capable of generating a gravitational wave of such strength.
The fact is that any gravitational wave is a ripple of space-time, a distortion that two massive and compact bodies cause when they are sharply accelerated next to each other. Neutron stars with a mass greater than the sun have a diameter of not 1.4 million kilometers, like our star, but only 20-25 kilometers. They are hundreds of thousands of times smaller, which is why their density is colossal, and the gravity on the surface is 200 billion times greater than that of the Earth (the Sun has only 28 times higher). The superposition of the gravitational fields of two such objects, rapidly rotating around each other, generates the strongest waves, comparable to those formed when two black holes merge.
Until August 2017, LIGO gravimeters observed only mergers of black holes that are extremely distant from our planet. And these events were never accompanied by outbreaks in any other ranges. With neutron stars detected by LIGO, everything is different - a kilonova was seen at the site of their outburst in the galaxy NGC 4993. This is the name for a powerful flash caused by the process of rapid capture of neutrons by atoms and their subsequent radioactive decay. Until now, it has not been possible to unequivocally find out what causes kilonova. New observations have shown that their cause is precisely the merger of neutron stars.
IVAN ORTEGA
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