Pulsars
Pulsars are a type of neutron star, the collapsed core of a massive star. At the end of their lifetime, the most massive of stars collapse into stellar black holes. In stars that are 8 times more massive than our Sun, but with stellar cores weighing less than 3 solar masses, the collapse of the core is stopped by neutron pressure. In this case, the core becomes a neutron star, and the outer layers crash inward resulting in a core-collapse supernova. Neutron stars are extremely dense objects. A neutron star's mass is typically about 40% more than the mass of the Sun, but packed into a radius of only about ten to twelve kilometers. A teaspoon of neutron star material on Earth would weigh about 10 million tons.
All neutron stars are born spinning, because all stars have angular momentum. Neutron stars can also have very strong magnetic fields and powerful, focused beams of electromagnetic radiation that emerge from their magnetic poles. Since the spin axis and the magnetic poles are often not aligned, beams of radio emission sweep across space and can be detected by radio telescopes whenever the magnetic pole faces Earth. The first pulsar was discovered that way in 1976 by Jocelyn Bell under the supervision of Anthony Hewish. The rapid spinning of the neutron star creates pulsed, regular emissions with periods ranging from seconds down to milliseconds. Pulsar periods are highly exact and stable, meaning that they can be used to measure time almost like atomic clocks.
The Vela Pulsar
The Vela Pulsar, PSR J0835-4510, was discovered in 1986 near the site of the Vela supernova remnant, providing early evidence that pulsars are formed from supernova explosions. The Type II supernova that created the Vela Pulsar exploded 11,000 - 12,300 years ago. Vela has the strongest radio emission of all discovered pulsars and a period of 89.33 milliseconds (or 11.2 pulses per second). The Vela pulsar is a glitching pulsar, meaning that it sometimes undergoes sudden increases in its rotation speed. The first time it glitched was December 12, 2016, and Vela glitched again on July 22, 2021. Astronomers do not currently understand when or why pulsars glitch.
Below is a sonified video of the Vela Pulsar made with the Parkes radio telescope in Australia, provided by the Jodrell Bank Centre for Astrophysics at the University of Manchester. The 60 second video shows the radio intensity of the pulsar over time, for 5 seconds (56 pulses) before the image refreshes, showing the next 5 seconds.
PSR J0437-4715
PSR J0437-4715 was discovered in 1993 by the Parkes 70 cm radio survey, and it is the brightest and nearest millisecond pulsar. Millisecond pulsars are pulsars with rotation periods less than 10 milliseconds. The rotation period of PSR J0437-4715 is 5.75 milliseconds, (or 189 pulses per second) and it is known as the most stable celestial timekeeper. Millisecond pulsars are thought to be older neutron stars that have sped up when their intense gravity tears mass away from a companion star. The binary companion of PSR J0437-4715 is most likely a low-mass helium white dwarf.
Below is a sonified video of the PSR J0437-4715 made with the Parkes radio telescope in Australia, provided by the Jodrell Bank Centre for Astrophysics at the University of Manchester. The 60 second video shows the radio intensity of the pulsar over time, for 5 seconds (948 pulses) before the image refreshes, showing the next 5 seconds. Here, the beats come so rapidly (at the frequency of 189 Hertz) that it sounds more like a buzz than separate pulses.