A quasar is a high energy object in the center of a galaxy that typically emits a gamma ray signature that is greater than the rest of the galaxy. They are the counterpart of blazars. Not all of the gamma rays detected can be traced to a specific celestial object, however, as extragalatic observation has shown. The field ofgamma ray astromony focuses upon the study of these unusual objects.


The discovery of quasars had to await advances in both radio astronomy and optical astronomy. It had long been known that galaxies outside our own emitted radio waves, investigation of one of these sources, 3C48 by Jodrell Bank radio telescope, showed the source to be somewhere in an area of the sky 1 arc second in size.

Advancement of the radio telescope at Caltech were able to refine the location of the souce to within 5 seconds of arc . This resolution was fine enough to allow the Palomar optical telescope lock the source down to a single object, a sharp point of light, apparently a star. Measurement of the stars spectrum gave a result unlike anything ever seen before, in astronomy or physics, the exact nature of the object remained a mystery.

In February 1963 a Dutch astronomer, Maarten Schimdt was investigating a similar object, 3C273 in the catalogue. It occured to him the strange spectrum could be explained if the object had a red shift of 16%, or in other words receeding from the earth at 16% of the speed of light. If this were the case then the spectrum of 3C48 showed it must be moving at 37% of the speed of light. This really ruled out the object being a star in, or near, our galaxy (and you can't observe individual stars in other galaxies, they're too far away). Further detailed work on the spectrum really proved it to be extremely unlikely the 'star' was hurled out at such speed from our galaxy.

What are they....?

The only explanation that made any sense was that these sources must be very far away, and their speed was due to the the expansion of space itself. (See the big bang). Calculations gave figures of 2 billion light years distance for 3C273 and 4.5 billion light years for 3C48. Now 3C273 was so bright it had be observed since 1895, with only (relatively) primitive telescopes, this distance meant it had to be giving out 100 times more energy that even the most luminous galaxy. Nobody had any real idea what such an energy source could be.

One more observation only made the problem worse; that 3C273's brightness had changed over periods at little as a month. Nothing can go faster than light, so whatever it was causing the change limited the size of the object to one light month. Our galaxy is about 100,000 light years in size, meaning this 'quasi-stellar' or quasar was emitting 100 times more energy from a region 10 18 times as small.

How do can they emit so much energy....?

The energy source driving this had to be massive to pack enough energy into such a small area, it had to be a super-massive black hole.

Detailed observations of the structure of material surrounding the light emitting core, made in the early 1980's convinced everybody that this must be the case. There are usually two large lobes of gas opposite each other outside the quasars, fed by perfectly straight jets up to a million light years in length leading from the core. This system had to be steady as a gyroscope over the lifetime of the jets; a million years. The only thing this stable, and able to pack so much power into such a small area has to be a gigantic, spinning black hole.
Also see the Blandford Znajek process for information on how a black hole could drive these jets.

Primary source:- Black Holes and Timewarps by Kip S. Thorne.

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