ACTIVE GALACTIC NUCLEI

21st February, 2022 Science and Technology

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Context:

Scientists said that their observations involving the supermassive black hole at the centre of galaxy Messier 77 and its surrounding cloud lend support to predictions made three decades ago about what are called “active galactic nuclei.”

Formation of AGN:

At the center of most galaxies, there’s a massive black hole.
The concentration of matter here is so dense that even light can’t escape from it.
They have mass of millions or even billions of Suns.
The black hole accretes gas, dust, and stellar debris around it.
As these material falls towards the black hole, their gravitational energy gets converted to light forming active galactic nuclei (AGN).
15 % of AGN emit charged particles called jets travelling at speeds close to the speed of light.

AGN characteristics:

An Active Galactic Nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum.
Such excess non-stellar (not from star) emission has been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an "active galaxy".
The observed characteristics of an AGN depend on several properties such as the mass of the central black hole, the rate of gas accretion onto the black hole, the orientation of the accretion disk, the degree of obscuration of the nucleus by dust, and presence or absence of jets.
Numerous subclasses of AGN have been defined based on their observed characteristics; the most powerful AGN are classified as quasars.
A blazar is an AGN with a jet pointed toward the Earth, in which radiation from the jet is enhanced by relativistic beaming.

Messier 77:

Messier 77 or M77, also known as NGC 1068 and the Squid Galaxy, is a barred spiral galaxy.
It is located 47 million light years from the Earth in the constellation Cetus.

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