PSR J0952–0607 is a massive

millisecond pulsar A millisecond pulsar (MSP) is a pulsar with a rotational period less than about 10 milliseconds. Millisecond pulsars have been detected in radio pulsar, radio, X-ray pulsar, X-ray, and gamma ray portions of the electromagnetic spectrum. The leadi ...

in a

binary system A binary system is a system of two astronomical bodies of the same kind that are comparable in size. Definitions vary, but typically require the center of mass to be located outside of either object. (See animated examples.) The most common ki ...

, located between from Earth in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Sextans Sextans is a faint, minor constellation on the celestial equator which was introduced in 1687 by Polish astronomer Johannes Hevelius. Its name is Latin for the astronomical sextant, an instrument that Hevelius made frequent use of in his obs ...

. , it holds the record for being the most massive

neutron star A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...

known, with a mass times that of the Sun—potentially close to the Tolman–Oppenheimer–Volkoff mass upper limit for neutron stars. The

pulsar A pulsar (''pulsating star, on the model of quasar'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its Poles of astronomical bodies#Magnetic poles, magnetic poles. This radiation can be obse ...

rotates at a frequency of (a period of ), making it the second-fastest-spinning pulsar known, and the fastest-spinning pulsar known within the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

. PSR J0952–0607 was discovered by the

Low-Frequency Array (LOFAR) The Low-Frequency Array (LOFAR) is a large radio telescope, with an antenna network located mainly in the Netherlands, and spreading across 7 other European countries as of 2019. Originally designed and built by ASTRON, the Netherlands Institute ...

radio telescope A radio telescope is a specialized antenna (radio), antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the r ...

during a search for pulsars in 2016. It is classified as a black widow pulsar, a type of pulsar harboring a closely-orbiting substellar-mass companion that is being ablated by the pulsar's intense high-energy

solar wind The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...

s and gamma-ray emissions. The pulsar's high-energy emissions have been detected in gamma-ray and

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

wavelengths.

Discovery

PSR J0952–0607 was first identified as an unassociated gamma-ray source detected during the first seven years of the

Fermi Gamma-ray Space Telescope The Fermi Gamma-ray Space Telescope (FGST, also FGRST), formerly called the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is ...

's all-sky survey since 2008. Because of its optimal location away from the crowded

Galactic Center The Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a ...

and its pulsar-like gamma-ray emission peak at 1.4 GeV, it was deemed a prime millisecond pulsar candidate for follow-up. The pulsar was reobserved and confirmed by the

in the

Netherlands , Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...

on 25 December 2016, which revealed a 707-Hz

radio Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connec ...

pulsation frequency alongside radial acceleration by an unseen binary companion. Further LOFAR observations took place from January to February 2017, alongside radio observations by the

Green Bank Telescope The Robert C. Byrd Green Bank Telescope (GBT) in Green Bank, West Virginia, US is the world's largest fully steerable radio telescope, surpassing the Effelsberg 100-m Radio Telescope in Germany. The Green Bank site was part of the National Rad ...

in Green Bank, West Virginia in March 2017. Optical observations by the 2.54-meter

Isaac Newton Telescope The Isaac Newton Telescope or INT is a 2.54 m (100 in) optical telescope run by the Isaac Newton Group of Telescopes at Roque de los Muchachos Observatory on La Palma in the Canary Islands since 1984. Originally the INT was situated at He ...

La Palma La Palma (, ), also known as ''La isla bonita'' () and historically San Miguel de La Palma, is the most northwesterly island of the Canary Islands, a Spanish autonomous community and archipelago in Macaronesia in the North Atlantic Ocean. La Pa ...

detected and confirmed the pulsar's companion at a faint

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

of 23 in January 2017. The discovery was published in ''

The Astrophysical Journal Letters ''The Astrophysical Journal'' (''ApJ'') is a peer-reviewed scientific journal of astrophysics and astronomy, established in 1895 by American astronomers George Ellery Hale and James Edward Keeler. The journal discontinued its print edition and b ...

'' and was announced in a

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

press release in September 2017.

Distance and location

The distance of PSR J0952–0607 from Earth is highly uncertain.

Binary system

The PSR J0952–0607

is composed of a massive pulsar and a substellar-mass (<) companion in close orbit around it. Because of this configuration, this system falls under the category of black widow pulsars that "consume" their companion, by analogy with the mating behavior of the eponymous

black widow spider ''Latrodectus'' is a broadly distributed genus of spiders with several species that are commonly known as the true widows. This group is composed of those often loosely called black widow spiders, brown widow spiders, and similar spiders. However ...

. The companion is continuously losing mass through

ablation Ablation ( – removal) is the removal or destruction of something from an object by vaporization, chipping, erosion, erosive processes, or by other means. Examples of ablative materials are described below, including spacecraft material for as ...

by intense high-energy

s and gamma-ray emissions from the pulsar, which then accretes some of the companion's lost material onto itself.

Companion

The companion orbits the pulsar at a distance of with an

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

of 6.42 hours. Because it orbits so closely, the companion is presumably

tidally locked Tidal locking between a pair of co-orbiting astronomical bodies occurs when one of the objects reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit. In the case where a tidally locked ...

, with one hemisphere always facing the pulsar. The companion does not appear to

eclipse An eclipse is an astronomical event which occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three ...

the pulsar, indicating that its orbit is oriented nearly face-on with an

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...

of 60° with respect to the plane perpendicular to Earth's line of sight. The companion's orbital motion also does not appear to modulate the pulsar's pulsations, signifying a circular orbit with negligible

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values be ...

. The companion was likely a former

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

that had been reduced to the size of a large

gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" was originally synonymous with "giant planet". However, in the 1990s, it became known that Uranu ...

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...

, with a present-day mass of or according to

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

measurements. Due to intense

irradiation Irradiation is the process by which an object is exposed to radiation. An irradiator is a device used to expose an object to radiation, most often gamma radiation, for a variety of purposes. Irradiators may be used for sterilizing medical and p ...

and heating by the host pulsar, the companion's radius is bloated up to 80% of its

Roche lobe In astronomy, the Roche lobe is the region around a star in a binary system within which orbiting material is gravitationally bound to that star. It is an approximately teardrop-shaped region bounded by a critical gravitational equipotential, ...

and brightly glows with a

thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

luminosity Luminosity is an absolute measure of radiated electromagnetic radiation, electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electroma ...

of about , thereby accounting for much of the system's optical brightness. As a result of bloating, the companion attains a low density likely around (with significant uncertainty due to the system's unknown distance from Earth), making it susceptible to tidal deformation by the pulsar. The companion's pulsar-facing irradiated hemisphere is continuously heated up to a temperature of , whereas the companion's unirradiated hemisphere experiences a uniform temperature of . This hemispherical temperature difference corresponds to a difference in hemisphere luminosities, which in turn causes significant variability in apparent brightness as the companion rotates around the pulsar. This brightness variability is demonstrated in PSR J0952–0607's optical

light curve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

, which exhibits an

amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...

greater than one

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

Mass

PSR J0952–0607 has a mass of , making it the most massive

known . The pulsar likely acquired most of its mass by accreting up to of lost material from its companion.

Rotation and age

PSR J0952–0607 rotates at a frequency of 707 Hz (1.41 ms period), making it the second-fastest-spinning pulsar known, and the fastest-spinning pulsar that is located in the

. Assuming a standard neutron star radius of , the equator of PSR J0952–0607 rotates at a tangential velocity over —about 14% the

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant exactly equal to ). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time i ...

. Based on 7 years of precise pulsation timing data from gamma-ray and radio observations, the pulsar's rotation period is estimated to be slowing down at a spin-down rate less than seconds per second, corresponding to a characteristic age of 4.9 billion years.

Magnetic field

Measurements of PSR J0952–0607's spin-down rate show that the pulsar has a remarkably weak surface

magnetic field A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...

strength of , placing it among the 10 weakest pulsar magnetic fields known . For context, ordinary pulsar magnetic fields usually lie on the order of teragauss (), over 10,000 times greater than that of PSR J0952–0607. Other millisecond pulsars exhibit similarly weak magnetic fields, hinting at a common albeit unknown mechanism in these types of systems; possible explanations range from accreted matter burying the pulsar's surface magnetic field to heat-driven evolution of the pulsar's solid crust.

Gamma-ray emissions

PSR J0952–0607 appears very faint in gamma-rays and was not detected in July 2011.

Notes

References

{{DEFAULTSORT:PSR J0952-0607 Millisecond pulsars Binary stars X-ray binaries Sextans Astronomical objects discovered in 2016