Pulsars and Quasars

Pulsars and quasars are celestial objects that often emit radio waves but can also emit energy in the visible light, X-ray, and gamma-ray ranges of wavelengths. Unlike quasars, pulsars are rapidly spinning neutron stars that often have a rotational period so regular that, as timepieces, they are more accurate than atomic clocks. Although quasars are neither stars nor timepieces, they are among the most distant observable objects in space, so distant that observing them is akin to looking at the past.

First discovered in 1967 by English radio astronomer Antony Hewish and his Irish graduate student Jocelyn Bell, pulsars are the result of a supernova explosion of a midsized star. The ensuing gravitational collapse of such a star forms a neutron star. Pulsars get their name from the regular pulses of radio waves that emit from their magnetic poles. They behave like lighthouses, but with radio waves in place of flashes of light. Each pulsar has a period, the time it takes for it to rotate once; this period can range from a millisecond to 8.5 seconds. As time passes, and the pulsar ages, the period will grow longer, meaning that the pulsar's spinning slows as its magnetic force increases. One type of pulsar is the millisecond pulsar, which has the shortest period. Its weak magnetic field allows for greater rotation speed. The periods of millisecond pulsars are stable and predictable enough to trump the timekeeping of atomic clocks. Another type of pulsar is the binary pulsar, which is one star in a binary star system in which two stars revolve around each other. Because of their atomic makeup—neutron-saturated nuclei—pulsars may have the mass of the sun but are extremely dense, sometimes less than 20 miles in diameter. For this reason, identification of their periodic pulses is often the only way these objects are discovered and observed.

Another source of radio emissions, quasars are pragmatically named, the term originating from the acronym QSRS (quasi-stellar radio source). Some can be radio-quiet, instead emitting X-rays or [Page 1068]gamma rays. Quasars appear starlike in that they can be observed optically as a point, or star, of light. However, their emissions are redshifted, which refers to their spectra's longer wavelengths. Redshift is a quality often attributed to objects that are accelerating away from the observer, and cosmological redshift refers to the infinite expansion of space-time and matter since the big bang. Because quasars are the most distant objects observed, their optical light appears faint. However, calculations including distance and speed led to figures of great magnitude, and quasars are sometimes posited to emit a trillion times the radiation of the sun. The most popular theory of the source behind this energy is that quasars are spinning disks of dust that surround a massive black hole. Given the great distance and theorized relationship to the big bang, quasar emissions are arriving from the cosmological past. Unlike the timepiece pulsar, the quasar is a preserver of time, displaying a picture of long ago.

This artist's concept depicts the pulsar planet system discovered by AleksanderWolszczan in 1992. Pulsars are rapidly rotating neutron stars that are the collapsed cores of exploded massive stars. They spin and pulse with radiation, much like a lighthouse

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