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Brightest Objects in Our Universe: Quasar

Quasars are among the brightest and most distant objects known to man. These astronomical objects of high luminosity are found in the centre of galaxies and shine so brightly that the brightest quasar in the universe can outshine all of the stars in their galaxy. A Quasar is powered by gas spiralling at velocities approaching the speed of light into an extremely large black hole. These black holes are a billion times as massive as our sun.

Quasar is among the brightest celestial objects that are crucial to the understanding of our early universe. Quasars are so luminous that they are visible even at a distance of billion light-years. A quasar is also known as a quasi-stellar object which is an extremely luminous galactic nucleus surrounded by a gaseous disk. The most distant and biggest quasar in the quasar universe is the J0313-1806, which has a mass of 1.6 billion times our sun and dates back to 670 million years ago after the Big Bang.


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Early Discovery and History

Around the 1930s, a physicist with bell and telephone laboratories, Karl Jansky discovered static interference on the transatlantic lines coming from the Milky Way. But it was only in the 1950s, these luminous objects were discovered by the early radio surveys of the sky. Most radio sources were identified as normal-looking galaxies but some, however, coincided with objects which appeared to be blue in colour and photographs showed them to be embedded in faint and fuzzy halos.  

Due to their starlike appearance, these luminous objects were termed “quasi-stellar radio sources” which was later changed to Quasar in 1964. But the optical spectra of Quasar represented a new mystery that was solved by a Dutch American astronomer by the name of Maarteen Schmidt in 1963. 

Maarteen discovered the pattern of the emission lines in the brightest Quasar 3C273 , coming from hydrogen atoms that had a redshift of 0.158. Redshift means the shifting of the emission lines towards the longer redder wavelengths because of the expansion of the universe. 

The wavelength of each emission line was 1.158 times longer than that measured in the laboratory and a redshift of this magnitude placed the 3C273 more than two billion light-years away according to Hubble’s law.  Nothing so bright had been ever seen at a distance so far away.  An even surprising finding was the significant variation in the brightness of these quasars, which implied that the total size of the quasar can’t be more than a few light-days across. 

The Quasar galaxy is galaxies with supermassive black holes. Quasar can only live in a galaxy with supermassive black holes. The Quasar galaxy also exhibits properties common to the other active galaxies. 


The Conundrum About Quasar 

The astronomers were faced with a difficult problem: how could an object about the size of the solar system have a mass of about a million stars and can outshine by 100 times a galaxy of a hundred billion stars. 

The answer was shortly proposed after Schmidt’s discovery by Russian astronomers Yakov Zel’dovich, Igor Novikov and Austrian American astronomer Edwin Salpeter who gave the right answer to the problem - accretion by gravity onto supermassive black holes. 

The redshift controversy was settled in the early 1980s that the fuzzy halos surrounding some of the quasars are starlight from the galaxy hosting the quasar and that these galaxies are at high redshifts.


Structure of the Quasar

In some of the quasar, gas tumbles into the deep gravitational well of the black hole which piles up in a rapidly rotating “accretion disk” close to the black hole. Other than accretion disk and supermassive black holes, quasars have other features as well such as clouds of gas that move at high velocities around the inner structure. Some quasars also have radio jets, which emit beams of radiation at X-ray and radio wavelengths.

The largest quasar in the quasar universe is formally designated J1107 + 2115 and has been given the Hawaiian name, Poniua’ena. 


Conclusion

Quasars are highly luminous objects which allow astronomers to understand the evolution of galaxies. The further the quasar is, it takes a longer time for light to reach us. So, any quasar billions of light-years old will provide information about life billions of light-years ago.  

FAQs (Frequently Asked Questions)

1. What are the Different Types of Quasars?

Ans- The quasars can be divided into subtypes having distinct properties:

  • Radio-Loud Quasar- These quasars are powerful jets that are strong sources of radio-wavelength emission and makeup around 10% of the quasar population.

  • Radio-Quiet Quasar- These quasars have a relatively weaker radio-emission as they lack powerful jets. Most quasars are radio-quiet.

  • Broad absorption line Quasar- These quasars exhibit broad absorption lines, resulting from gas flowing outward of the active nucleus. Most quasars are radio-quiet.

  • Type II quasar- In these quasars, the accretion disk and broad emission lines are highly obscured by dense gas and dust.

  • Red Quasar- These quasars have an optical colour that is redder than normal quasars. 

  • Optically Violent Variable Quasars- These are radio-loud quasars in which the jet is directed towards the observer. 

  • Weak emission Line Quasar- These have a faint emission line in the visible spectrum.

2. What are the Properties of Quasar?

Ans- Quasars are among the brightest and most distant objects in the universe. 

  • The power of quasars originates from the supermassive black holes that exist at the core of most galaxies. 

  • Although quasars appear faint, they are visible from extreme distances. 

  • The luminosities of quasars vary with time, ranging from months to hours, which suggest that quasars emit light from a very small region. 

  • Quasars exist in galaxies with supermassive black holes and these galaxies exhibit properties of other active galaxies.

  • The radiation from quasars is partially nonthermal.

  • The quasar redshifts are measured from the strong spectral lines that dominate their visible spectra. 

  • Radio-loud quasars can produce X-ray and gamma rays by the radio-emitting electrons in the jet.

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