Pulsars are incredibly important. They have a wide range of applications in modern physics and astrophysics. They are used as extremely precise timekeepers, as their pulses are so regular that they can be used to measure time to within a few billionths of a second. They are also used as probes of the interstellar medium and as a tool to detect gravitational waves.
Pulsars are rapidly rotating neutron stars that emit beams of radiation that are observed as regular pulses of light. These intense sources of radiation were first discovered in 1967 by radio astronomer Jocelyn Bell Burnell, a graduate student at the University of Cambridge.
Pulsars are extremely dense, with a mass equal to that of the sun packed into a sphere the size of a city. They are formed when massive stars exhaust their nuclear fuel and their cores collapse under gravity, forming a neutron star. The intense gravity of a neutron star causes its electrons and protons to combine to form neutrons, giving the star its name.
The discovery of pulsars allowed astronomers to study an object never observed before, the neutron star. This kind of object is the only place where the behavior of matter at nuclear density can be observed (though not directly). Also, millisecond pulsars have allowed a test of general relativity in conditions of an intense gravitational field.
Pulsar maps have been included on the two Pioneer plaques as well as the Voyager Golden Record. They show the position of the Sun, relative to 14 pulsars, which are identified by the unique timing of their electromagnetic pulses, so that our position both in space and in time can be calculated by potential extraterrestrial intelligences. Because pulsars are emitting very regular pulses of radio waves, its radio transmissions do not require daily corrections. Moreover, pulsar positioning could create a spacecraft navigation system independently, or be used in conjunction with satellite navigation.
X-ray pulsar-based navigation and timing (XNAV) or simply pulsar navigation is a navigation technique whereby the periodic X-ray signals emitted from pulsars are used to determine the location of a vehicle, such as a spacecraft in deep space. A vehicle using XNAV would compare received X-ray signals with a database of known pulsar frequencies and locations. Similar to GPS, this comparison would allow the vehicle to calculate its position accurately to within 5 kilometers anywhere in the depths of space.
Nobel Prize controversy
When the Nobel Prize in Physics was awarded in 1974 for the discovery of pulsars, the person who actually discovered them, Jocelyn Bell, was not included.
The original paper announcing the discovery of pulsars had five authors. Bell’s thesis supervisor Antony Hewish was listed first, Bell second. But Hewish was awarded the Nobel Prize, along with the astronomer Martin Ryle. At the time fellow astronomer Sir Fred Hoyle criticised Bell’s omission.
The Royal Swedish Academy of Sciences, in its press release announcing the prize, cited Ryle and Hewish for their pioneering work in radio-astrophysics, with particular mention of Ryle’s work on aperture-synthesis technique and Hewish’s decisive role in the discovery of pulsars.
Feryal Özel, an astrophysicist at the University of Arizona, characterized Bell’s contributions as follows:
She helped build the array she used to make the observation. She is the one who noticed it. She is the one who argued it’s a real signal. When a graduate student takes that kind of lead in her project, it’s hard to play it down.
Washington Post
Bell later said that she had to be persistent in reporting the anomaly indicating the existence of pulsars in the face of scepticism from Hewish, who initially insisted it was due to interference and man-made. She spoke of meetings held by Hewish and Ryle to which she was not invited.
In later years she also said that “the fact that I was a graduate student and a woman, together, demoted my standing in terms of receiving a Nobel prize.”
She eventually received recognition that was rightfully hers.