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Current Affairs > Science and Technology > 2018-12-05 > Science and Technology

Four new gravitational waves detected from black hole mergers

What in news:

·         Scientists have made four new detections of gravitational waves – ripples in the fabric of space and time – emanating from separate black hole mergers.

About news:

·         The position of the binary black holes, located by the LIGO and VIRGO observatories, were spotted 2.5 billion light-years from Earth, and identified with a precision of 39 square degrees

·         So far the US-based LIGO and Europe-based VIRGO gravitational-wave detectors have recorded gravitational waves from a total of 10 black hole mergers and one merger of neutron stars.

·           The new events are known as GW170729, GW170809, GW170818, and GW170823, in reference to the dates they were detected.

·         In this coalescence, which happened roughly 5 billion years ago, an equivalent energy of almost five solar masses was converted into gravitational radiation.

·         From September 12, 2015, to January 19, 2016, during the first LIGO observing, gravitational waves from three binary black hole mergers were detected.

·         The second observing run, yielded one binary neutron star merger and seven additional binary black hole mergers, including the four new gravitational-wave events being reported now.

·         GW170814 was the first binary black hole merger measured by the three-detector network, and allowed for the first tests of gravitational-wave polarization (analogous to light polarization).

Gravitational waves:

·         These are 'ripples' in the fabric of space-time caused by some of the most violent and energetic processes in the Universe.

·          Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity. Massive accelerating mass would disrupt space-time in such a way that 'waves' of distorted space would radiate from the source.

·         The strongest gravitational waves are produced by catastrophic events such as colliding black holes, the collapse of stellar cores (supernovae), coalescing neutron stars or white dwarf stars, the slightly wobbly rotation of neutron stars that are not perfect spheres, and possibly even the remnants of gravitational radiation created by the birth of the Universe.

Black holes

·         A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it.

·          The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole.

·          The boundary of the region from which no escape is possible is called the event horizon.

·         Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed.

·          In many ways a black hole acts like an ideal black body, as it reflects no light.

·         Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass.

·         This temperature is on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe.

The Laser Interferometer Gravitational-Wave Observatory (LIGO)

·         LIGO is a large-scale physics experiment and observatory to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool.

·         Two large observatories were built in the United States with the aim of detecting gravitational waves by laser interferometry.

·         These can detect a change in the 4 km mirror spacing of less than a ten-thousandth the charge diameter of a proton, equivalent to measuring the distance from Earth to Proxima Centauri (4.0208×1013 km with an accuracy smaller than the width of a human hair.

VIRGO:

·         The Virgo interferometer is a large interferometer designed to detect gravitational waves predicted by the general theory of relativity.

·          Virgo is a Michelson interferometer that is isolated from external disturbances: its mirrors and instrumentation are suspended and its laser beam operates in a vacuum.

·          The instrument's two arms are three kilometres long and located near Pisa, Italy.

Expected prelims question

Consider the following statements

1.       The strongest gravitational waves are produced by catastrophic events such as colliding black holes.

2.       VIRGO Observatory is located in Italy

3.       Theory of relativity was discovered by louis pasture

Which of the above statements are/ is correct.  

a)       Only 1 and 3

b)      Only 3

c)       Only 1 and 2

d)      All of above

Ans : C

Expected mains question

What do you understand by terms Gravitational waves, Black holes. Discuss how theory of relativity is connected with Gravitational waves.