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Spider pulsar

From EverybodyWiki Bios & Wiki


Artist's impression of a spider pulsar system, where a pulsar's intense ionizing radiation ablates the atmosphere of a closely-orbiting companion.

Spider pulsars are a class of millisecond pulsars that belong in tight binary systems with a low-mass, non-degenerate companion, such as a star or substellar object. In these systems, the companion orbits the spider pulsar so closely that it experiences extreme heating and ablation by the pulsar's intense ionizing winds. Spider pulsars are divided into three broad subclasses, depending on the mass and orbital period of their companions: these are black widows, redbacks, and huntsmans. These subclasses are named after species of cannibalistic spiders, which consume their mates in a similar manner to how spider pulsars gradually destroy their companions.[1]

Background

See also: Millisecond pulsar and Binary pulsar
Artist's impression of a millisecond pulsar accreting matter from its stellar companion

Pulsars are rapidly-spinning neutron stars that form after a massive star ends its life in a core-collapse supernova.[2] While pulsars have a wide range of rotation periods, there is a distinct population of pulsars that have very short rotation periods on the order of milliseconds—these are known as millisecond pulsars.[2] Millisecond pulsars are observed to commonly occur in binary systems where they are orbited by a smaller-mass companion, which may be a star, substellar object, or a white dwarf.[3]

Millisecond pulsars are believed to have attained their rapid rotation from accreting matter from their companions.[2] This occurs when the companion orbits close enough for the pulsar to gravitationally pull matter directly from its atmosphere—a process known as Roche lobe overflow.[4] As the pulsar accretes matter from its companion, the pulsar acquires angular momentum and speeds up its rotation, while the companion shrinks in size and mass. Eventually, the companion shrinks enough that the pulsar can no longer pull matter from it, ceasing accretion in the pulsar. The stripped companion has now become a low-stellar-mass or substellar remnant that is significantly enriched in elements heavier than hydrogen; such objects may be a helium star, white dwarf, or a carbon-rich planet or brown dwarf.

Pulsars emit high amounts of ionizing radiation (X-rays, gamma rays, electrons, etc.) due to their extremely hot surface temperatures (few million kelvin) and extremely strong rotating magnetic fields (more than a billion gauss). Due to the high energy and intensity of the pulsar's radiation, it exerts a very strong radiation pressure that ionizes and blows gases away from the pulsar, creating an energetic stream of fast-moving charged particles known as pulsar wind (akin to the Sun's solar wind). In tight binary systems where the companion closely orbits a pulsar (orbital period less than 2 days), the pulsar's high-energy radiation and wind heats the companion up to temperatures of thousands of kelvin, resulting in the thermal inflation and evaporation (ablation) of the companion.[4] Ionized gases escaping from the ablating companion are blown away by the pulsar's wind, creating a dense stream of plasma emanating from the ablating companion.[5] At very far distances from the pulsar, the pulsar's wind becomes slow and diffuse enough that it begins interacting with the interstellar medium, producing a bow shock that glows in optical, ultraviolet, and X-ray light.

Definition and classification

Known spider pulsar systems as of November 2025, plotted by minimum companion mass and orbital period.[6] Datapoints are color-coded by spider pulsar subclass.

Spider pulsars refer to tight binary systems that contain a millisecond pulsar and a smaller, non-degenerate companion (which may be a star or substellar object, but not a white dwarf or neutron star). In the scientific literature, spider pulsars are commonly stated to have orbital periods less than 1 day.[7][8][9] Spider pulsar systems are typically observed exhibiting signs of pulsar accretion and companion ablation, though these are not necessary for the definition of spider pulsars.[citation needed]

The Norwegian University of Science and Technology maintains a public online catalogue of known spider pulsars, called "SpiderCat".[10][9] The SpiderCat catalogue was established by Karri Koljonen and Manuel Linares in 2025, who delineate a quantitative definition of spider pulsars with the following three criteria:[9][10]

  1. a pulsar spin period less than 30 milliseconds (< 30 ms)
  2. a companion orbital period less than or equal to 10 days (≲ 10 days)
  3. a non-degenerate or semi-degenerate companion star (inferred from radio eclipses, X-ray mode switching, optical spectra or X-ray/optical orbital modulation)

Based on the estimated minimum mass of their companion, spider pulsars are divided into two major subclasses: black widows and redbacks. Both of these subclasses describe compact binary systems with orbital periods less than 1 day.[9] A third minor class of spider pulsars, called huntsmans, have stellar-mass companions similar to redbacks, but have more distant orbits with periods between 2 and 10 days.[9][10]

Black widows

Composite image of the Black Widow pulsar (PSR B1957+20) in X-ray (red and white) and optical (green and blue) wavelengths. The pulsar's intense radiation creates a visible bow shock (in green) as it moves through the interstellar medium.

Black widow pulsars have non-planetary substellar companions with masses between 0.004 and 0.1 solar masses (M☉).[9] This subclass derives its name from its prototype PSR B1957+20, which was discovered in 1986–1988 and nicknamed the "Black Widow pulsar" by David Eichler and Amir Levinson.[11][12] The Black Widow pulsar itself was named after the black widow spider, whose behavior of cannibalizing their mates resembles the pulsar's gradual destruction of its companion.[11][12]

Tidarrens

Tidarren pulsars are a subclass of black widow pulsars that have very small companion masses between 0.004 and 0.02 M☉ and orbital periods shorter than 2 hours.[9] This subclass is named after the black widow relative tidarren sisyphoides, which are known for having an extreme female-to-male mass ratio.[13] The name and classification of tidarren pulsars was introduced by Roger W. Romani and collaborators in 2016, after the first few tidarrens were discovered.[13] Tidarrens are believed to represent the late evolutionary stage of black widow systems, and may be the progenitors of planetary-mass objects around millisecond pulsars.[13]

Redbacks

Redback pulsars have main-sequence star companions that are more massive than 0.1 M☉.[9] This subclass is named after the redback spider, an Australian variant of black widows.[14] The first redback pulsar (PSR J1740−5340) was discovered by D'Amico et al. in 2001,[15][14] though the term "redback" was introduced later by Mallory Roberts in 2010.[14][lower-alpha 1]

Huntsmans

Huntsman pulsars have massive and distant stellar companions orbital periods between 2 and 10 days.[9]

Evolution

The companions of spider pulsars are generally thought to be remnants of former stars, stripped down by the pulsar via ablation and accretion.[16] It is hypothesized that the ablating companion's mass shrinks over time, which implies that redbacks should evolve into black widows.[citation needed] However, observations have shown that the masses of black widow companions are distinct from those of redback companions—there is lack of spider pulsars with companion masses at the 0.1 M☉ dividing line.[citation needed] For this reason, the evolutionary relation between black widows and redbacks remains controversial among astrophysicists.[17][18] Template:Tq is only for quoting in talk and project pages. Do not use it in actual articles.[18]

Detection methods

Eclipses in radio and gamma rays

Observational history

The first spider pulsar discovered was PSR B1957+20, an eclipsing binary black widow discovered in 1986 by the Arecibo Observatory.[19] The discovery of PSR B1957+20 was announced in May 1988 by Andrew S. Fruchter, Daniel R. Stinebring, and Joseph H. Taylor,[19] and it received the nickname of "Black Widow pulsar" by David Eichler and Amir Levinson in December 1988.[11][12]

Before the launch of NASA's Fermi Gamma-ray Space Telescope, only

The Norwegian University of Science and Technology maintains a public online catalogue of known spider pulsars, called "SpiderCat".[10][9] The SpiderCat catalogue was established by Karri Koljonen and Manuel Linares in 2025, and uses the three-criteria definition of spider pulsars from their 2025 study.[9] As of March 2026, 122 spider pulsars are known according to SpiderCat, with 32 confirmed redbacks (RB), 31 redback candidates (RBc), 52 confirmed black widows (BW), 4 black widow candidates (BWc), 2 huntsmans (HM), and 1 huntsman candidate (HMc).[10]

See also

Notes

  1. ↑ In a 2017 review paper on millisecond pulsars, Richard Manchester cites a 2013 conference paper by Mallory Roberts for the coining of "redback".[11] However, Roberts mentioned the term in an earlier conference paper from 2010.[14]

Citations

  1. ↑ Koljonen & Linares 2025, p. 1.
  2. ↑ 2.0 2.1 2.2 Manchester 2017, p. 1.
  3. ↑ Manchester 2017, p. 1–2.
  4. ↑ 4.0 4.1 Ginzburg & Quataert 2021.
  5. ↑ Hui & Li 2019.
  6. ↑ Koljonen & Linares 2025, p. 17.
  7. ↑ Kandel & Romani 2023, p. 1.
  8. ↑ Swihart et al. 2022, p. 1.
  9. ↑ 9.00 9.01 9.02 9.03 9.04 9.05 9.06 9.07 9.08 9.09 9.10 Koljonen & Linares 2025, p. 3.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 Koljonen, Karri; Linares, Manuel; Nedreaas, Iacob; Voaidas, Bogdan. "SpiderCat: A Catalog of Compact Binary Millisecond Pulsars". Norwegian University of Science and Technology. Retrieved 29 March 2026.
  11. ↑ 11.0 11.1 11.2 11.3 Manchester 2017, p. 2.
  12. ↑ 12.0 12.1 12.2 Eichler & Levinson 1988.
  13. ↑ 13.0 13.1 13.2 Romani et al. 2016, p. 1.
  14. ↑ 14.0 14.1 14.2 14.3 Roberts 2010, p. 40.
  15. ↑ D'Amico et al. 2001.
  16. ↑ Roberts 2010, p. 39.
  17. ↑ O'Doherty et al. 2023.
  18. ↑ 18.0 18.1 Disberg, Bahramian & Mandel 2026, p. 1.
  19. ↑ 19.0 19.1 Fruchter, Stinebring & Taylor 1988.

References

  • Disberg, Paul; Bahramian, Arash; Mandel, Ilya (March 2026). "Reconciling the Systemic Kicks of Observed Millisecond Pulsars, Spider Pulsars, and Low-mass X-Ray Binaries". The Astrophysical Journal Letters. 1000 (2): L56. arXiv:2601.12275. doi:10.3847/2041-8213/ae52f1.

Template:Neutron star


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