Almost one quarter of these are members of a previously unknown class of X-ray bright, flat spectrum, radio-loud quasars.
Examples include the discovery of pulsars while studying interplanetary scintillation; finding quasars as stars with strange spectra.
Finding the powerful quasars responsible for the X-ray background radiation.
Further evidence comes from astronomical observation - astronomers look into the past when they look into space and have been measuring and observing quasars.
In several quasars, small, discrete sources have been found that change position from one observation to the next.
It is a suggestive coincidence that the space density of bright optical quasars also reached a peak sometime around z = 2-3.
Most types of cosmic object known to exist, from dwarf stars to the most distant quasars, are known to emit X-rays.
Several strong candidates for Type 2, or obscured quasars have been discovered.
Some astronomers supported this point of view, and have sought evidence for physical associations between high-redshift quasars and low-redshift normal galaxies.
The low and high redshift quasars are found very similar in their emission characteristics, although differences exist.
The objects called quasars are very strong point like radio sources, which can, like all radio objects, be detected in daylight.
The total number of ROSAT detected radio quasars from the above three sources is 654 objects.
Their spectra also have the same large redshift of the quasars in the cluster.