A pulsar is a rapidly spinning neutron star that emits electromagnetic radiation. This radiation is observed on Earth in the form of fast pulses. The name originally stood for pulsating radio source. Pulsars belong to the same class of celestial bodies as magnetars; the main difference is the strength of the magnetic field.
Their great regularity makes them useful as astronomical clocks. They sometimes approach the accuracy of atomic clocks, allowing accurate measurements of the pulsar's orbit. The first exoplanet was discovered in orbit around a pulsar. The high density causes an extremely strong gravitational pull and thus a curvature of space-time. Observations of the orbital decay of the double pulsar PSR B1913+16 provided evidence for the existence of the gravitational waves predicted by Albert Einstein.
The first known pulsar (PSR B1919+21) was discovered in August 1967 by student Jocelyn Bell and her mentor Antony Hewish when observed at a frequency of 81.5 MHz (wavelength 368 cm) with the Interplanetary Scintillation Array at the Mullard Radio Astronomy Observatory at Cambridge. PSR B1919+21 had a pulse time of 1.337 seconds. They ruled out that the signal came from Earth because it did not return to the same position in the sky after exactly 24 hours, but after a sidereal day. They initially named the object responsible for this LGM (Little Green Men) because it resembled a radio beacon used by aliens. Shortly after the discovery, the source of the signal was identified by Thomas Gold and Fred Hoyle as a rapidly rotating neutron star.
Since the discovery of this pulsar, much faster pulsing neutron stars have also been observed, down to the millisecond range. Also, some pulsars have a structure in the pulses that is much higher in frequency (nanoseconds); these parts must be emitted from pieces on the surface of the neutron star that are no larger than 60 centimeters. These structures are by far the smallest detail ever observed outside the Solar System.
In March 2018, 2636 pulsars were known.
Origin of a pulsar
A pulsar is the final stage of a star with a mass of around 10 solar masses. The formation of a pulsar is the result of a type II, type Ia or type Ib supernova. When the star has finally fused all the hydrogen in its core through a series of other elements to iron, it takes energy for the star to fuse it further (rather than producing energy). The star's hydrostatic equilibrium becomes unbalanced, and the star implodes under its own gravity. The enormous pressure fuses the protons and electrons of the iron atoms into neutrons. Due to the large amount of potential energy released, the outer layers of the star are blown into the universe with a large explosion. This causes the star to lose a large part of its mass. If the star had a small angular momentum during its lifetime, the shrinking of the star greatly increases the rotational speed, due to the conservation of angular momentum. The magnetic field of the star is also preserved, but greatly enhanced by the shrinking of the star. Under the influence of this rotating magnetic field, an electric field is generated, which accelerates charged particles at the magnetic poles. This causes the star to emit two electromagnetic jet streams near the poles.
Anatomy of a pulsar
A pulsar is a rapidly rotating, highly magnetic neutron star that emits an electromagnetic jet stream at both magnetic poles. A pulsar typically has a radius of 10 km, with a mass between 1.4 and 3 solar masses.
A neutron star does not consist entirely of neutrons, but it does consist largely of neutrons, and