Crab Pulsar
Encyclopedia
The Crab Pulsar (PSR B0531+21) is a relatively young neutron star
. The star is the central star in the Crab Nebula
, a remnant
of the supernova
SN 1054
, which was widely observed on Earth in the year 1054. Discovered in 1968, the pulsar was the first to be connected with a supernova remnant
.
The optical pulsar
is roughly 25 km in diameter and the pulsar "beams" rotate once every 33 milliseconds, or 30 times each second. The outflowing relativistic wind from the neutron star generates synchrotron emission, which produces the bulk of the emission from the nebula, seen from radio waves
through to gamma rays. The most dynamic feature in the inner part of the nebula is the point where the pulsar's equatorial wind slams into the surrounding nebula, forming a termination shock. The shape and position of this feature shifts rapidly, with the equatorial wind appearing as a series of wisp-like features that steepen, brighten, then fade as they move away from the pulsar into the main body of the nebula. The period of the pulsar's rotation is slowing by 38 nanosecond
s per day due to the large amounts of energy carried away in the pulsar wind.
The Crab Nebula
is often used as a calibration source in X-ray astronomy
. It is very bright in X-ray
s and the flux density
and spectrum
are known to be constant, with the exception of the pulsar itself. The pulsar provides a strong periodic signal that is used to check the timing of the X-ray detectors. In X-ray astronomy, 'crab' and 'millicrab' are sometimes used as units of flux density. A millicrab corresponds to a flux density of about 2.4x10−11 erg
s−1 cm−2 (2.4x10−14 W
m−2) in the 2–10 keV X-ray band, for a "crab-like" X-ray spectrum, which is roughly a powerlaw in photon energy, I(E)=9.5 E-1.1. Very few X-ray sources ever exceed one crab in brightness.
rules out the north following star but finds the evidence inconclusive for the south preceding. Rudolf Minkowski, in the same issue of Astrophysical Journal
as Baade, advances spectral arguments claiming the "evidence admits, but does not prove, the conclusion that the south preceding star is the central star of the nebula".
In late 1968, David H. Staelin and Edward C. Reifenstein III reported the discovery of two pulsating radio sources "near the crab nebula that could be coincident with it" using the 300-foot Green Bank radio antenna
. They were given the designations NP 0527 and NP 0532. The period and location of the Crab Nebula pulsar NP 0532 was discovered by Richard Lovelace and collaborators November 10, 1968 at the Arecibo radio observatory .
A subsequent study by them including William D. Brundage also found that the NP 0532 source is located at the Crab Nebula. A radio source was also reported coincident with the crab nebula in late 1968 by L. I. Matveenko in Soviet Astronomy.
Optical pulsations were reported by Nather, Warner, and Macfarlane in February 1969.
Jocelyn Bell Burnell
, who discovered the first pulsar PSR B1919+21 in 1967, relates that in the late 1950s a woman viewed the Crab Nebula source at the University of Chicago's telescope, then open to the public, and noted that it appeared to be flashing. The astronomer she spoke to, Elliot Moore, disregarded the effect as scintillation
, despite the woman's protestation that as a qualified pilot she understood scintillation and this was something else. Bell Burnell notes that the 30 Hz frequency of the Crab Nebula optical pulsar is difficult for many people to see.
es (i.e. 0.01 Jupiter mass
es or 3.3 Earth mass
es) and be located at 0.3 astronomical unit
s from the pulsar.
Neutron star
A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Such stars are composed almost entirely of neutrons, which are subatomic particles without electrical charge and with a slightly larger...
. The star is the central star in the Crab Nebula
Crab Nebula
The Crab Nebula is a supernova remnant and pulsar wind nebula in the constellation of Taurus...
, a remnant
Supernova remnant
A supernova remnant is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.There are two...
of the supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
SN 1054
SN 1054
SN 1054 is a supernova that was first observed as a new "star" in the sky on July 4, 1054 AD, hence its name, and that lasted for a period of around two years. The event was recorded in multiple Chinese and Japanese documents and in one document from the Arab world...
, which was widely observed on Earth in the year 1054. Discovered in 1968, the pulsar was the first to be connected with a supernova remnant
Supernova remnant
A supernova remnant is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.There are two...
.
Optical pulsar
An optical pulsar is a pulsar which can be detected in the visible spectrum. There are very few of these known: the Crab pulsar was detected by stroboscopic techniques in 1969, shortly after its discovery in radio waves, at the Steward Observatory...
is roughly 25 km in diameter and the pulsar "beams" rotate once every 33 milliseconds, or 30 times each second. The outflowing relativistic wind from the neutron star generates synchrotron emission, which produces the bulk of the emission from the nebula, seen from radio waves
Radio waves
Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers. Like all other electromagnetic waves,...
through to gamma rays. The most dynamic feature in the inner part of the nebula is the point where the pulsar's equatorial wind slams into the surrounding nebula, forming a termination shock. The shape and position of this feature shifts rapidly, with the equatorial wind appearing as a series of wisp-like features that steepen, brighten, then fade as they move away from the pulsar into the main body of the nebula. The period of the pulsar's rotation is slowing by 38 nanosecond
Nanosecond
A nanosecond is one billionth of a second . One nanosecond is to one second as one second is to 31.7 years.The word nanosecond is formed by the prefix nano and the unit second. Its symbol is ns....
s per day due to the large amounts of energy carried away in the pulsar wind.
The Crab Nebula
Crab Nebula
The Crab Nebula is a supernova remnant and pulsar wind nebula in the constellation of Taurus...
is often used as a calibration source in X-ray astronomy
X-ray astronomy
X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and...
. It is very bright in X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s and the flux density
Flux density
-Formal Statement:The flux density is simply defined as the amount of flux passing through a unit-area. -Mathematical Statement:The flux density would essentially be the number of field lines passing through a defined unit-area...
and spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
are known to be constant, with the exception of the pulsar itself. The pulsar provides a strong periodic signal that is used to check the timing of the X-ray detectors. In X-ray astronomy, 'crab' and 'millicrab' are sometimes used as units of flux density. A millicrab corresponds to a flux density of about 2.4x10−11 erg
Erg
An erg is the unit of energy and mechanical work in the centimetre-gram-second system of units, symbol "erg". Its name is derived from the Greek ergon, meaning "work"....
s−1 cm−2 (2.4x10−14 W
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
m−2) in the 2–10 keV X-ray band, for a "crab-like" X-ray spectrum, which is roughly a powerlaw in photon energy, I(E)=9.5 E-1.1. Very few X-ray sources ever exceed one crab in brightness.
History
The modern history of the Crab Pulsar begins with the identification of the central star of the nebula in optical light. Focus was made on two stars near the center of the nebula (referred to in the literature as the "north following" and "south preceding" stars). In September 1942, Walter BaadeWalter Baade
Wilhelm Heinrich Walter Baade was a German astronomer who worked in the USA from 1931 to 1959.-Biography:He took advantage of wartime blackout conditions during World War II, which reduced light pollution at Mount Wilson Observatory, to resolve stars in the center of the Andromeda galaxy for the...
rules out the north following star but finds the evidence inconclusive for the south preceding. Rudolf Minkowski, in the same issue of Astrophysical Journal
Astrophysical Journal
The Astrophysical Journal is a peer-reviewed scientific journal covering astronomy and astrophysics. It was founded in 1895 by the American astronomers George Ellery Hale and James Edward Keeler. It publishes three 500-page issues per month....
as Baade, advances spectral arguments claiming the "evidence admits, but does not prove, the conclusion that the south preceding star is the central star of the nebula".
In late 1968, David H. Staelin and Edward C. Reifenstein III reported the discovery of two pulsating radio sources "near the crab nebula that could be coincident with it" using the 300-foot Green Bank radio antenna
Green Bank Telescope
The Robert C. Byrd Green Bank Telescope is the world's largest fully steerable radio telescope and the world's largest land-based movable structure. It is part of the National Radio Astronomy Observatory site at Green Bank, West Virginia, USA. The telescope honors the name of the late Senator...
. They were given the designations NP 0527 and NP 0532. The period and location of the Crab Nebula pulsar NP 0532 was discovered by Richard Lovelace and collaborators November 10, 1968 at the Arecibo radio observatory .
A subsequent study by them including William D. Brundage also found that the NP 0532 source is located at the Crab Nebula. A radio source was also reported coincident with the crab nebula in late 1968 by L. I. Matveenko in Soviet Astronomy.
Optical pulsations were reported by Nather, Warner, and Macfarlane in February 1969.
Jocelyn Bell Burnell
Jocelyn Bell Burnell
Susan Jocelyn Bell Burnell, DBE, FRS, FRAS , is a British astrophysicist. As a postgraduate student she discovered the first radio pulsars with her thesis supervisor Antony Hewish. She was president of the Institute of Physics from October 2008 until October 2010, and was interim president...
, who discovered the first pulsar PSR B1919+21 in 1967, relates that in the late 1950s a woman viewed the Crab Nebula source at the University of Chicago's telescope, then open to the public, and noted that it appeared to be flashing. The astronomer she spoke to, Elliot Moore, disregarded the effect as scintillation
Scintillation (astronomy)
Scintillation or twinkling are generic terms for rapid variations in apparent brightness or color of a distant luminous object viewed through a medium, most commonly the atmosphere ....
, despite the woman's protestation that as a qualified pilot she understood scintillation and this was something else. Bell Burnell notes that the 30 Hz frequency of the Crab Nebula optical pulsar is difficult for many people to see.
A planetary companion?
In 1970, astronomer Curtis Michel proposed the presence of a planetary companion to explain certain variations observed in pulsar timing. The hypothesized object would have a mass of 0.00001 Solar massSolar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
es (i.e. 0.01 Jupiter mass
Jupiter mass
Jupiter mass , is the unit of mass equal to the total mass of the planet Jupiter . Jupiter mass is used to describe masses of the gas giants, such as the outer planets and extrasolar planets. It is also used in describing brown dwarfs....
es or 3.3 Earth mass
Earth mass
Earth mass is the unit of mass equal to that of the Earth. 1 M⊕ = 5.9722 × 1024 kg. Earth mass is often used to describe masses of rocky terrestrial planets....
es) and be located at 0.3 astronomical unit
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
s from the pulsar.