Discovery of a New Source of Gravitational Waves

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Scientists have picked up the ripples in space-time caused by the death spiral of two celestial juggernauts – a neutron star and a black hole – for the first time.

About

• There is huge excitement among scientists with the first confirmed detection of a neutron star-black hole (NS-BH) collision being reported. 
• Widely unequal mergers have very interesting effects that can be detected.
• This groundbreaking discovery of gravitational waves from a pair of NS-BH mergers.
• Until now, the LIGO-Virgo collaboration (LVC) of gravitational waves detectors has only been able to observe collisions between pairs of black holes or neutron stars. 

How were the detections made?

• As the two compact and massive bodies orbit around each other, they come closer, and finally merge, due to the energy lost in the form of gravitational waves. 
• The Gravitational Waves signals are buried deep inside a lot of background noise. 
• The technique used here to detect the signal is called matched filtering. This was also used for the first discovery of gravitational waves. 
  • In matched filtering, various expected gravitational waveforms predicted by Einstein’s theory of relativity, are compared with the different chunks of data to produce a quantity that signifies how well the signal in the data (if any) matches with any one of the waveforms. 
  • Whenever this match (in technical terms “signal-to-noise ratio” or SNR) is significant (larger than 8), an event is said to be detected. 
• Observing an event in multiple detectors separated by thousands of kilometres almost simultaneously gives scientists increased confidence that the signal is of astrophysical origin, which is the case for both events.
• Using Parameter Estimation tools, scientists find the probable masses, spins, distances, locations of these mergers from the data. 
• Both of these events occurred 1 billion light-years away. As the gravitational waves also travel with the speed of light, this means that we observed mergers that happened ~1 billion years ago — well before life appeared on earth!

Significance

• Inferring from data as to how often they merge will also give us clues about their origin and how they were formed.
• These observations help us understand the relative abundance of such binaries.
• Neutron stars are the densest objects in the Universe, so these findings can also help us understand the behaviour of matter at extreme densities. 
• Neutron stars are also the most precise ‘clocks’ in the Universe if they emit extremely periodic pulses. The discovery of pulsars going around Black Holes could help scientists probe effects under extreme gravity.

Blackhole

• A blackhole is a region in space where the pulling force of gravity is so strong that neither matter nor light can escape. This phenomenon occurs when a star is dying.
• For anything approaching a black hole, the point of no return is called the “event horizon” and anything that comes within the event horizon will be consumed forever.
• Since no light can escape from it, a black hole is invisible.
• However, advanced space telescopes can identify black holes by observing the behaviour of material and stars that are very close to black holes.
• This hot disk of material encircling a black hole shines bright and against this disk, a black hole appears to cast a shadow.
• This is how the photograph of the black hole was achieved.
• In 2019, NASA released the first-ever photograph of a black hole and its shadow, which was captured by an international network of radio telescopes called the Event Horizon Telescope (EHT).
  • The image shows the shadow of a supermassive black hole in the centre of Messier 87 (M87), an elliptical galaxy some 55 million light-years from Earth.
  • This black hole is 6.5 billion times the mass of the Sun.

Differences between Blackhole and Neutron Star:

• A neutron star has a surface and a Blackhole does not. 
• A neutron star is about 1.4-2 times the mass of the sun while the other black hole is much more massive.

Source: IE