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, X-ray, and gamma ray portions of the electromagnetic spectrum. The leading theory for the origin of ...

in a

binary system A binary system is a system of two astronomical bodies which are close enough that their gravitational attraction causes them to orbit each other around a barycenter ''(also see animated examples)''. More restrictive definitions require that thi ...

, located between away 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 origins of the e ...

Sextans Sextans is a minor celestial equator, equatorial constellation which was introduced in 1687 by Johannes Hevelius. Its name is Latin for the sextant (astronomical), astronomical sextant, an instrument that Hevelius made frequent use of in his ob ...

. It holds the record for being the most massive

neutron star A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. white ...

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

pulsar A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Ea ...

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

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

. PSR J0952–0607 was discovered by the

Low-Frequency Array (LOFAR) The Low-Frequency Array, or 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 Instit ...

radio telescope A radio telescope is a specialized 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 radio frequency ...

during a search for pulsars in 2016. It is classified as a

black widow pulsar The Black Widow Pulsar (PSR B1957+20) is an eclipsing binary millisecond pulsar in the Milky Way. Discovered in 1988, it is located roughly away from Earth. It orbits with a brown dwarf or Super-Jupiter companion with a period of 9.2 hou ...

, 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 upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...

s and

gamma-ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nucleus, atomic nuclei. It consists of the shortest wavelength electromagnetic wav ...

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

and

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

wavelengths.

Discovery

PSR J0952–0607 was first identified as an unassociated

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 or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact rad ...

and its pulsar-like gamma-ray emission peak at 1.4

GeV GEV may refer to: * ''G.E.V.'' (board game), a tabletop game by Steve Jackson Games * Ashe County Airport, in North Carolina, United States * Gällivare Lapland Airport, in Sweden * Generalized extreme value distribution * Gev Sella, Israeli-Sou ...

, it was deemed a prime millisecond pulsar candidate for follow-up. The pulsar was reobserved and confirmed by the

in the

Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...

on 25 December 2016, which revealed a 707-Hz

radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmit ...

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 Radio ...

Green Bank, West Virginia Green Bank is a census-designated place in Pocahontas County in West Virginia's Potomac Highlands inside the Allegheny Mountain Range. Green Bank is located along WV 28. Green Bank is home to the Green Bank Observatory and is also close to the S ...

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 Her ...

La Palma La Palma (, ), also known as ''La isla bonita'' () and officially San Miguel de La Palma, is the most north-westerly island of the Canary Islands, Spain. La Palma has an area of making it the fifth largest of the eight main Canary Islands. The ...

detected and confirmed the pulsar's companion at a faint

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

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

The Astrophysical Journal Letters ''The Astrophysical Journal'', often abbreviated ''ApJ'' (pronounced "ap jay") in references and speech, is a peer-reviewed scientific journal of astrophysics and astronomy, established in 1895 by American astronomers George Ellery Hale and James ...

'' and was announced in a

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

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

comprises a massive pulsar and a substellar-mass (<) companion in close orbit around it. Because of this configuration, this system falls under the category of

s 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. Howeve ...

. The companion is continuously losing mass through

ablation Ablation ( la, ablatio – removal) is 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, and include spacecraft materi ...

by intense high-energy

s and

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 body, 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 ...

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

eclipse An eclipse is an astronomical event that 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 ce ...

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 Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...

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 betwee ...

. The companion was likely a former

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

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. Gas giants are also called failed stars because they contain the same basic elements as a star. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" ...

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

, with a present-day mass of or according to

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

measurements. Due to intense

irradiation Irradiation is the process by which an object is exposed to radiation. The exposure can originate from various sources, including natural sources. Most frequently the term refers to ionizing radiation, and to a level of radiation that will serve ...

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, wit ...

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 power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

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 of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequ ...

, 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 amplit ...

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 In everyday use and in kinematics, the speed (commonly referred to as ''v'') of an object is the magnitude of the change of its position over time or the magnitude of the change of its position per unit of time; it is thus a scalar quantity. ...

over —about 14% the

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit ...

. 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 is a vector 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 to its own velocity and to ...

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

{{Sextans Millisecond pulsars Binary stars X-ray binaries Sextans (constellation) Astronomical objects discovered in 2016