Quasars and Active Galaxies

How were quasars first identified as distant, super-bright objects?

In 1962 the Dutch American astronomer Maarten Schmidt (1929–), examining the spectrum of 3C 273, realized that its pattern of emission lines was unlike that of any known stars or planets. Furthermore, those emission lines were shifted far toward the red wavelengths of the electromagnetic spectrum. As Edwin Hubble had shown, such a redshift signature indicated that the object was likely to be very far away in the universe. Using the redshift, Schmidt showed that 3C 273 was nearly two billion light-years away from Earth. Another calculation showed that the object was far more luminous than the Milky Way galaxy; including its radio emission, 3C 273 was emitting more light each second than the Sun would in more than a million years. Soon, other radio sources in the 3C catalog were shown to be quasi-stellar objects, quasars that were all at distances of billions of light-years away from Earth.

An artist’s concept of a quasar in a distant galaxy. (NASA/JPL-Caltech/T. Pyle (SSC))


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