Quasars

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Quasars

Since their discovery, the nature of quasars has been one of the most

intriguing and baffling problems as evidenced by the following quotations: "

the problem of understanding quasi-stellar objects… is one of the most

important and fascinating tasks in all physics" - G.Burbidge and Hoyle. "The

quasar continues to rank both as one of the most baffling objects in the

universe and one most capable of inspiring heated argument" - Morrison. "The

redshift problem is one of the most critical problems in astronomy today" -

G. Burbidge. "Quasars still remain the profoundest mystery in the heavens" -

Hazard and Mitton.

The conventional interpretation of the spectral lines observed in quasars is

based on the redshift hypothesis. Three hypotheses have been advanced to

account for the supposed redshifts: 1. Cosmological hypothesis; the redshifts

are due to the expansion of the universe, 2. Gravitational hypothesis, 3

Local-Doppler hypothesis; in this hypothesis the redshifts are due to the

Doppler effect, but the quasars are relatively nearby and have nothing to do

with the expansion of the universe. Of these hypotheses, the first one is

the most publicized one.

One is led to attribute to quasars very many mysterious properties if one

assumes the redshift hypothesis to be correct. A patient analysis of the

data on quasars over the years has led to the conclusion that the real source

of the trouble is in the assumption that the spectra of quasars have

redshifts.

In the early 1960's quasars were known as 'radio stars' because the method

used to discover the first quasars was based on coincidences between a strong

radio source and a point-like optical source. Since each radio source was

associated with a star it was originally thought that quasars were objects

within the galaxy hence the term 'radio stars'. Quasars or quasi-stellar

radio source, from the method by which they where originally discovered: as

stellar optical counterparts to small regions of strong radio emission. With

increasing spatial resolution of radio telescopes the strong radio emission

often seemed to come from a pair of lobes surrounding many of these faint

star-like emission line objects.

The initial method of selection was strong radio emission, and then later any

object with blue or ultraviolet excess wa...

... middle of paper ...

... between galaxies, either through direct collisions or near

encounters, can be important in turning on a quasar, by dumping fuel onto a

black hole. However some quasars look unperturbed, so there may be other,

more subtle mechanisms for feeding the black hole. Some of the galaxies we

observed don't appear to know they have a quasar in their core.

3. Quasars that are radio quiet are often in elliptical galaxies, not always

in spiral galaxies, as previously believed.

Advanced instruments planned for Hubble should also help pin down more

details. The Near Infrared Camera and Multi-Object Spectrometer (NICMOS), to

be installed in 1997, and the Advanced Camera, to be installed in 1999, will

have coronagraphic devices which will block out the glare of a quasar,

allowing astronomers to see closer into a galaxy's nucleus. By viewing

galactic structures in infrared light , the NICMOS should be able to provide

important new details about the host galaxies of quasars. The continued study

of quasars and the information that it will provide us with may help us to

develop a better understanding of space and how we fit in to this great

puzzle.

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