Quasars and pulsars represent a new class of objects in space, a new kind of massive, extraordinarily bright object. Massive, exceedingly dense, and producing powerful radio and light transmissions, quasars and pulsars radically expanded and altered scientists’ view of space and space structures.
Quasars are some of the brightest and most distant objects in the universe. Pulsars provide hints of the life path and life expectancy of stars. Their discovery led to a greater understanding of the life and death of stars and opened up new fields of study in astronomy, super-dense matter, gravitation, and super-strong magnetic fields.
In the fall of 1960, American astronomer Allan Rex Sandage noticed a series of dim objects that looked like stars. He cross checked them with a radio telescope to see if they transmitted radio signals as well as dim light.
Each of these dim objects produced amazingly powerful radio signals. No known object could do that. Maybe they weren’t really stars, at least not stars like other stars. Sandage called these mystery objects quasi-stellar radio sources. Quasi-stellar quickly shortened to quasar.
Sandage studied the spectrographic lines of these strange objects (lines that identify the chemical makeup of a distant star). The lines didn’t match any known chemical elements and could not be identified.
Sandage and Dutch-born American astronomer Maarten Schmidt finally realized that the spectral lines could be identified as normal and common elements if they were viewed as spectrograph lines that normally occurred in the ultraviolet range and had been displaced by a tremendous red shift (Doppler shift) into the visible range. (Doppler shifts are changes in the frequency of light or sound caused by the motion of an object.)
While that explanation solved one mystery, it introduced another. What could cause such a giant Doppler shift? In 1963 they decided that the only plausible answer was distance and that the quasars must be over a billion light years away, the most distant objects ever detected.
But now the dim light of the quasars was too bright for a single star at that distance, often 1,000 times as bright as whole galaxies. Sandage and Schmidt proposed that each quasar must really be a distant galaxy. However, the measured radio signals varied too much (on the order of days and hours) to be a galaxy of separate stars. That indicated a compact mass, not a galaxy.
Quasars remained a perplexing mystery until, in 1967, it was proposed that they were really the material surrounding massive black holes. Quasars instantly became the most interesting and important objects in distant space.
That same year (in July 1967) Cambridge University Astronomy professor Antony Hewish completed a 4.5-acre radio antenna field to detect radio frequency transmissions from the farthest corners of space. This gargantuan maze of wire would be the most sensitive radio frequency receiver on Earth.
The radio telescope printed 100 feet of output chart paper each day. Graduate assistant Jocelyn Bell had the job of analyzing this chart paper. She compared the chart’s squiggly lines to the position of known space objects and then compared the known electromagnetic emissions of these bodies to the chart’s squiggles and spikes in order to account for each mark on the chart.
Two months after the telescope started up, Bell noticed an unusual, tight-packed pattern of lines that she called a “bit of scruff”, a squiggling pattern she couldn’t explain. She marked it with a question mark and moved on.
Four nights later, she saw the same pattern. One month later she found the same pattern of scruff and recognized that the antenna was focused on the same small slice of sky. She took the extra time to expand and measure the squiggles. Whatever it was, this radio signal regularly pulsed every 1 1/3 seconds. No natural body in the known universe emitted regular signals like that.
Before Hewish publicly announced their discovery, Bell found another bit of scruff on chart printouts from a different part of the sky. The pulses of this second signal came 1.2 seconds apart and at almost the exact same frequency.
Every theoretician at Cambridge was brought in to explain Jocelyn’s scruff. After months of study and calculation the science team concluded that Bell had discovered super-dense, rotating stars. Astronomers had mathematically theorized that when a huge star runs out of nuclear fuel, all matter in the star collapsed inward, creating a gigantic explosion, called a supernova.
What remained became a hundred million times denser than ordinary matter , a neutron star. If the star rotated, its magnetic and electric fields would broadcast beams of powerful radio waves. From Earth, a rapidly rotating neutron star would appear to pulse and so these were named “pulsars.”
The more distant the quasar is, the redder its light appears on Earth. The light from the most distant quasar known takes 13 billion light-years to reach Earth. Thirteen billion light-years is how far away that quasar was 13 billion years ago when the light we now see first left the star and headed toward where Earth is now.
Quasars are the most distant objects in the universe.
