PSR J1614–2230
Encyclopedia
PSR J1614–2230 is a neutron star
in a binary system with a white dwarf
. It was discovered in 2006 with the Parkes telescope
in a survey of unidentified gamma ray
sources in the Energetic Gamma Ray Experiment Telescope
catalog. PSR J1614–2230 is a millisecond pulsar
, a type of neutron star, that spins on its axis roughly 317 times per second, corresponding to a period of 3.15 milliseconds. Like all pulsars, it emits radiation in a beam, similar to a lighthouse
. Emission from PSR J1614–2230 is observed as pulses at the spin period of PSR J1614–2230. The pulsed nature of its emission allows for the arrival of individual pulses to be timed. By measuring the arrival time of pulses, astronomer
s observed the delay of pulse arrivals from PSR J1614–2230 when it was passing behind its companion from the vantage point of Earth
. By measuring this delay, known as the Shapiro delay
, astronomers determined the mass of PSR J1614–2230 and its companion. The team performing the observations found that the mass of PSR J1614–2230 is
. This mass makes PSR J1614–2230 the most massive known neutron star
, and rules out many neutron star equations of state
that include exotic matter
such as hyperon
s and kaon
condensates.
Pulsar
s were discovered in 1967 by Jocelyn Bell and her adviser Antony Hewish
using the Interplanetary Scintillation Array
. Franco Pacini and Thomas Gold
quickly put forth the idea that pulsars are highly magnetized
rotating neutron star
s, which form as a result of a supernova
at the end of the life of star
s more massive than about 10 times the mass of the Sun
. The radiation
emitted by pulsars is caused by interaction of the plasma
surrounding the neutron star with its rapidly rotating magnetic field. This interaction leads to emission "in the pattern of a rotating beacon," as emission escapes along the magnetic poles of the neutron star. The "rotating beacon" property of pulsars arises from the misalignment of their magnetic poles with their rotational poles. Historically, pulsars have been discovered at radio wavelength
s where emission is strong, but space telescopes that operate in the gamma ray
wavelengths have also discovered pulsars.
to conduct a survey of the EGRET sources located in the plane of the Milky Way
that lacked a known counterpart. In the search, they discovered PSR J1614–2230, and concluded that it might be a counterpart to a gamma ray source near the same location. The radio observations revealed that PSR J1614–2230 had a companion, likely a white dwarf
. The observed orbital parameters of the system indicated a minimum companion mass of
, and an orbital period of 8.7 days.
Paul Demorest et al. used the Green Bank Telescope
at the National Radio Astronomy Observatory
to observe the system through a complete 8.7 day orbit, recording the pulse arrival times from PSR J1614–2230 over this period. After accounting for factors that would alter pulse arrival times from exactly matching its period of 3.1508076534271 milliseconds, including the orbital parameters of the binary system, the spin of the pulsar, and the motion of the system, Demorest et al. determined the delay in the arrival of pulses that resulted from the pulse having to travel past the companion to PSR J1614–2230 on its way to Earth
. This delay is a consequence of general relativity
known as the Shapiro delay
, and the magnitude of the delay is dependent upon the mass of the white dwarf companion. The best fit companion mass was
. Knowing the companion mass and orbital elements then provided enough information to determine the mass of PSR J1614–2230 to be 
.
and gravity of neutron stars; their masses are of order the mass of a star
, but they have sizes around 10 kilometres (6.2 mi) in diameter, which is comparable to the size of the center of large cities such as London
. Neutron stars also have the property that as they become more massive, their diameter decreases. The mass of PSR J1614–2230 is the highest of any known neutron star
. The existence of a neutron star with such a high mass constrains the composition and structure of neutron stars, both of which are poorly understood. The reason for this is that the maximum mass of a neutron star is dependent upon its composition. A neutron star composed of matter such as hyperon
s or kaon
condensate
s would collapse to form a black hole
before it could reach the observed mass of PSR J1614–2230, meaning neutron star models that include such matter are strongly constrained by this result.
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...
in a binary system with a white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
. It was discovered in 2006 with the Parkes telescope
Parkes Observatory
The Parkes Observatory is a radio telescope observatory, 20 kilometres north of the town of Parkes, New South Wales, Australia. It was one of several radio antennas used to receive live, televised images of the Apollo 11 moon landing on 20 July 1969....
in a survey of unidentified gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
sources in the Energetic Gamma Ray Experiment Telescope
Energetic Gamma Ray Experiment Telescope
The Energetic Gamma Ray Experiment Telescope was one of four instruments outfitted on NASA’s Compton Gamma Ray Observatory satellite. Since lower energy gamma rays cannot be accurately detected on Earth’s surface, EGRET was built to detect gamma rays while in space...
catalog. PSR J1614–2230 is a millisecond pulsar
Millisecond pulsar
A millisecond pulsar is a pulsar with a rotational period in the range of about 1-10 milliseconds. Millisecond pulsars have been detected in the radio, X-ray, and gamma ray portions of the electromagnetic spectrum. The origin of millisecond pulsars is still unknown...
, a type of neutron star, that spins on its axis roughly 317 times per second, corresponding to a period of 3.15 milliseconds. Like all pulsars, it emits radiation in a beam, similar to a lighthouse
Lighthouse
A lighthouse is a tower, building, or other type of structure designed to emit light from a system of lamps and lenses or, in older times, from a fire, and used as an aid to navigation for maritime pilots at sea or on inland waterways....
. Emission from PSR J1614–2230 is observed as pulses at the spin period of PSR J1614–2230. The pulsed nature of its emission allows for the arrival of individual pulses to be timed. By measuring the arrival time of pulses, astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
s observed the delay of pulse arrivals from PSR J1614–2230 when it was passing behind its companion from the vantage point of Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. By measuring this delay, known as the Shapiro delay
Shapiro delay
The Shapiro time delay effect, or gravitational time delay effect, is one of the four classic solar system tests of general relativity. Radar signals passing near a massive object take slightly longer to travel to a target and longer to return than it would if the mass of the object were not...
, astronomers determined the mass of PSR J1614–2230 and its companion. The team performing the observations found that the mass of PSR J1614–2230 is
. This mass makes PSR J1614–2230 the most massive known neutron starNeutron 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...
, and rules out many neutron star equations of state
Equation of state
In physics and thermodynamics, an equation of state is a relation between state variables. More specifically, an equation of state is a thermodynamic equation describing the state of matter under a given set of physical conditions...
that include exotic matter
Matter
Matter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...
such as hyperon
Hyperon
In particle physics, a hyperon is any baryon containing one or more strange quarks, but no charm quarks or bottom quarks.-Properties and behavior of hyperons:...
s and kaon
Kaon
In particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called strangeness...
condensates.
Background
Pulsar
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
s were discovered in 1967 by Jocelyn Bell and her adviser Antony Hewish
Antony Hewish
Antony Hewish FRS is a British radio astronomer who won the Nobel Prize for Physics in 1974 for his work on the development of radio aperture synthesis and its role in the discovery of pulsars...
using the Interplanetary Scintillation Array
Interplanetary Scintillation Array
The Interplanetary Scintillation Array was built at the Mullard Radio Astronomy Observatory in 1967 and originally covered four acres . It was extended in 1978 to nine, and re-furbished in 1989. It operates at 81.5 MHz , and is made up of 4096 dipoles in a phased array. 14 beams can map the...
. Franco Pacini and Thomas Gold
Thomas Gold
Thomas Gold was an Austrian-born astrophysicist, a professor of astronomy at Cornell University, a member of the U.S. National Academy of Sciences, and a Fellow of the Royal Society . Gold was one of three young Cambridge scientists who in the 1950s proposed the now mostly abandoned 'steady...
quickly put forth the idea that pulsars are highly magnetized
Magnetism
Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...
rotating neutron star
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...
s, which form as a result of a supernova
Type II supernova
A Type II supernova results from the rapid collapse and violent explosion of a massive star. A star must have at least 9 times, and no more than 40–50 times the mass of the Sun for this type of explosion. It is distinguished from other types of supernova by the presence of hydrogen in its spectrum...
at the end of the life of star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s more massive than about 10 times the mass of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. The radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
emitted by pulsars is caused by interaction of the plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
surrounding the neutron star with its rapidly rotating magnetic field. This interaction leads to emission "in the pattern of a rotating beacon," as emission escapes along the magnetic poles of the neutron star. The "rotating beacon" property of pulsars arises from the misalignment of their magnetic poles with their rotational poles. Historically, pulsars have been discovered at radio wavelength
Radio Wave
Radio Wave may refer to:*Radio frequency*Radio Wave 96.5, a radio station in Blackpool, UK...
s where emission is strong, but space telescopes that operate in the gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
wavelengths have also discovered pulsars.
Observations
The Energetic Gamma-Ray Experiment Telescope (EGRET) identified a half dozen known pulsars at gamma ray wavelengths. Many of the sources it detected had no known counterparts at other wavelengths. In order to see whether any of these sources were pulsars, Fronefield Crawford et al. used the Parkes telescopeParkes Observatory
The Parkes Observatory is a radio telescope observatory, 20 kilometres north of the town of Parkes, New South Wales, Australia. It was one of several radio antennas used to receive live, televised images of the Apollo 11 moon landing on 20 July 1969....
to conduct a survey of the EGRET sources located in the plane of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
that lacked a known counterpart. In the search, they discovered PSR J1614–2230, and concluded that it might be a counterpart to a gamma ray source near the same location. The radio observations revealed that PSR J1614–2230 had a companion, likely a white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
. The observed orbital parameters of the system indicated a minimum companion mass of
, and an orbital period of 8.7 days.Paul Demorest et al. used the Green Bank Telescope
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...
at the National Radio Astronomy Observatory
National Radio Astronomy Observatory
The National Radio Astronomy Observatory is a Federally Funded Research and Development Center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc for the purpose of radio astronomy...
to observe the system through a complete 8.7 day orbit, recording the pulse arrival times from PSR J1614–2230 over this period. After accounting for factors that would alter pulse arrival times from exactly matching its period of 3.1508076534271 milliseconds, including the orbital parameters of the binary system, the spin of the pulsar, and the motion of the system, Demorest et al. determined the delay in the arrival of pulses that resulted from the pulse having to travel past the companion to PSR J1614–2230 on its way to Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. This delay is a consequence of general relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...
known as the Shapiro delay
Shapiro delay
The Shapiro time delay effect, or gravitational time delay effect, is one of the four classic solar system tests of general relativity. Radar signals passing near a massive object take slightly longer to travel to a target and longer to return than it would if the mass of the object were not...
, and the magnitude of the delay is dependent upon the mass of the white dwarf companion. The best fit companion mass was
. Knowing the companion mass and orbital elements then provided enough information to determine the mass of PSR J1614–2230 to be .Significance
The conditions in neutron stars are very different from those encountered on Earth, as a result of the high densityDensity
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
and gravity of neutron stars; their masses are of order the mass of a star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
, but they have sizes around 10 kilometres (6.2 mi) in diameter, which is comparable to the size of the center of large cities such as London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
. Neutron stars also have the property that as they become more massive, their diameter decreases. The mass of PSR J1614–2230 is the highest of any known neutron star
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 existence of a neutron star with such a high mass constrains the composition and structure of neutron stars, both of which are poorly understood. The reason for this is that the maximum mass of a neutron star is dependent upon its composition. A neutron star composed of matter such as hyperon
Hyperon
In particle physics, a hyperon is any baryon containing one or more strange quarks, but no charm quarks or bottom quarks.-Properties and behavior of hyperons:...
s or kaon
Kaon
In particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called strangeness...
condensate
Condensate
Condensate may refer to:* The liquid phase produced by the condensation of steam or any other gas* The product of a chemical condensation reaction, other than water* Natural gas condensate, in the natural gas industry- Quantum physics :...
s would collapse to form a black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
before it could reach the observed mass of PSR J1614–2230, meaning neutron star models that include such matter are strongly constrained by this result.