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A team of American astronomers has announced the discovery of a quasar
which is the most distant object in the Universe. Rumours of the discovery,
made in April, have been in the air for months (New Å®ÉúСÊÓƵ, Science,
27 April).

The quasar, dubbed PC₁247+3406, has a red shift of 4.897.
The previous quasar to hold the distance record had a red shift of 4.733.
Distant objects have the light ‘red-shifted’ to longer wavelengths because
the Universe has expanded in the time their light has been travelling to
us.

Maarten Schmidt of the California Institute of Technology in Pasadena,
Donald Schneider of the Institute for Advanced Study in Princeton and James
Gunn of Princeton University, discovered the new quasar while searching
for distant objects with the 5-metre Hale telescope on Palomar Mountain
in California. According to Schmidt, light from the object has taken 93
per cent of the Universe’s age to reach us.

Schmidt is the astronomer credited with the discovery of the first quasar
in 1963. Ever since, he has been searching for quasars close to the edge
of the observable Universe.

Quasars are thought to be the prodigiously bright cores of young, ‘active’
galaxies. The consensus among astronomers is that they are probably powered
by the gravitational energy of matter as it falls onto a supermassive black
hole.

To search for distant objects, Schmidt and his colleagues used the Hale
telescope in conjunction with a square array of four light-sensitive chips
called charge coupled devices (CCDs). The astronomers’ search technique
involved pointing the telescope in a fixed direction and allowing the rotation
of the Earth to cause stars and galaxies to drift through the detectors’
field of view.

The light from these objects falls on each CCD after passing through
one of four different colour filters, and the output of each CCD is recorded
continuously by a computer. As the Earth turns, a narrow strip of sky is
observed, and every object in the strip leaves a trace at each of the four
CCDs.

What Schmidt and his colleagues end up with is the brightness of every
object in the strip in four different colours. ‘Effectively, we obtain very
low-resolution spectra for all objects,’ says Schmidt. A computer can then
look for the telltale signature of quasars.

This results in hundreds of quasar candidates, which Schmidt and his
colleagues then observe more closely to uncover their true nature and to
determine their red shifts.

According to Schmidt, the new technique ‘has proven very successful
in finding distant quasars’. However, he says that the limits of the technique
are not well known, which makes it difficult to analyse statistically the
sample of quasars that the technique yields. This is the real aim of Schmidt’s
work. ‘Breaking distance records is fun,’ he says, ‘but our aim is to get
a large, representative sample of high red shift quasars.’ Already, Schmidt
and his colleagues have found more than 140 distant quasars with red shifts
greater than 2.

Last month, Schmidt and his colleagues embarked on a new four-night-long
observing session with the Hale telescope. Schmidt says he sees no reason
why an even more distant quasar should not be discovered soon. ‘The main
limiting factor,’ he says, ‘is observing time on the telescope.’

The quasar discovery is to be announced in the September issue of The
Astronomical Journal.