Quasara
Quasara (singular – Quasar) are astronomical objects with high brightness. It is thought that they are powered by supermassive black holes which are in the center of some massive galaxies. The luminosities of quasars are caused by a disk of gas and stars called accretion disk surrounding the black hole. The friction created from material that swirls around and into the black hole causes intense light and heat from the accretion disk. Quasars are brighter than the galaxies they are in. They also emit ‘jets’ (high-speed material) from the center, which are larger than their host galaxy. Radio waves are emitted when a quasar jet interacts with the gas around the galaxy. These radio waves can be detected by radio telescopes. Since quasars are more than a billion parsecs away from earth telescopes should be used to observe them.
Quasars were originally discovered in the 1950s with radio telescopes. The emissions of the optical spectrum of quasars are shifted towards the red end of the spectrum. (redshifted) The explanation for this redshift is stretching of the light waves due to traveling through the expanding universe, to earth. This is called ‘cosmological redshift’. More redshift means that quasar is farther away.
The use of quasars is using them as background light sources to study the intervening galaxies and diffuse gas. These intervening material absorb quasars’ light and what we get is an absorption spectrum. This leads to the detection of intervening material. Quasars being compact point-sources and being so bright which enables them to be observed from telescopes even from an enormous distance away, makes them suitable for this purpose.
Quasars are among the farthest objects known. As long as there is enough fuel for the accretion disk emissions are possible. Quasars can consume up to 1000-2000 solar masses of material per year. (one solar mass = mass of the sun = 1.989 × 1030 kg) The normal lifetime of a quasar is about 100-1000 million years. They will ‘turn off’ when the fuel is over. The presence of about 50 000 quasara has been estimated. The first quasar to be identified is 3C 273 and it is optically-brightest at magnitude +12.9. It is 2,443 million light-years distant.
©Dinithi M. Herath
Graphics by Deshan Rathnayake
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