What is a Quasar?

The brightest objects in the universe: Quasars

Yes, you've read it right. Not the neutron stars, nor those huge bright galaxies, it's the quasars that are known as the most powerful sources of light and radio waves. Quasars are so powerful and bright that we might be able to see them even if they were a billion light-years away, well for a fact, most of them ARE billions of light-years away!!  

Quasars were first discovered in the 1950s when scientists observed an unknown radio source. But it was only in the early 1960s that it was finally found that these emissions of light and radio waves were coming from an Active Galactic Nuclei (AGN) or in other words, a quasar.

A quasar can mostly be found in the nucleus of an active galaxy, whose centre consists of a supermassive black hole (which has about 1 billion solar masses). An active galaxy means a galaxy whose centre host (or black hole) should be having an accretion disk around it, indicating that the black hole is actively intaking matter (like stars and gases nearby it). Only active galaxies can be found to produce quasars or AGNs. Quasars that are being produced from such galactic centres actually seem brighter than the host galaxy itself.

How are Quasars formed?

Quasars are formed when the supermassive black hole at the centre starts to gulp in neighbouring stars, planets and gases, which were hovering too near to its event horizon. As they get drawn towards the black hole, an accretion disk is formed, where all the infalling matter is swirling around the black hole. These matter particles accelerate at high velocities and intense heat is created due to the high friction of these particles in motion. Ripping up of matter in the accretion disk releases an abundant amount of energy in the form of radiation and light. Also, some of the particles tend to escape from the event horizon at nearly light speed. This sudden blast of energy emerging from the centre of large galaxies is what we call quasars. It is clear that quasars actually depend on the host black holes because it's only when the black holes suck in the matter, that the quasars are produced.

There's a supermassive black hole present in the centre of our galaxy, called the Sagittarius A*, but it's not an Active Galactic Nuclei. It may become an AGN in the future, probably after billions of years, so we're safe for now. Even if it happened, the quasar will stay on that way for another million years till the black hole becomes inactive.

Quasars are often accompanied by a phenomenon called Red-Shift, where the emitted light seems a little shifted to the redder end of the spectrum. This happens because the light source is a billion light-years away and by the time it reaches our telescopes on earth, it'll seem more stretched than when it left the source. This implies that the universe is expanding as time goes on. Quasars play an important role in determining the expansion rate of our universe. The farther the quasar comes from, the further we look back into the beginning of the universe.

 The most recent quasar which we found is one among the earliest in the universe, which opens a whole new window to understand the early universe.