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PSR J0952–0607

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PSR J0952–0607 is a massive millisecond pulsar in a binary system, located between 3,200–5,700 light-years (970–1,740 pc) from Earth in the constellation Sextans.[5] It holds the record for being the most massive neutron star known as of 2022, with a mass 2.35±0.17 times that of the Sun—potentially close to the Tolman–Oppenheimer–Volkoff mass upper limit for neutron stars.[4][6] The pulsar rotates at a frequency of 707 Hz (1.41 ms period), making it the second-fastest-spinning pulsar known, and the fastest-spinning pulsar known within the Milky Way.[7][5]

PSR J0952–0607

PSR J0952–0607 (center crosshair) imaged by the Fermi Gamma-ray Space Telescope
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sextans
Right ascension 09h 52m 08.319s[1]
Declination −06° 07′ 23.49″[1]
Characteristics
Spectral type Pulsar
Apparent magnitude (i) 22.0–24.4[2]
Astrometry
Distance970+1160
−530 pc[3]
or 1740+1570
−820 pc[3]
or 6260+360
−400 (optical) pc[4]
Details
PSR J0952–0607 A
Mass2.35±0.17[4] M☉
Rotation1.41379836 ms[3]
Age4.9[3] Gyr
PSR J0952–0607 B
Mass0.032±0.002[4] M☉
Luminosity9.96+1.20
−1.12[a] L☉
Temperature3085+85
−80[4] K
Metallicity [Fe/H]–0.5[2] dex
Orbit[3]
PrimaryPSR J0952–0607 A
CompanionPSR J0952–0607 B
Period (P)0.267461035 d
(6.41906484 h)
Semi-major axis (a)1600000 km[b]
Eccentricity (e)<0.004
Inclination (i)59.8+2.0
−1.9[4]°
Semi-amplitude (K2)
(secondary)		376.1±5.1[4] km/s
Other designations
PSR J0952–0607, 4FGL J0952.1–0607
Database references
SIMBADdata

PSR J0952–0607 was discovered by the Low-Frequency Array (LOFAR) radio telescope during a search for pulsars in 2016.[5] 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 winds and gamma-ray emissions.[4][8] The pulsar's high-energy emissions have been detected in gamma-ray and X-ray wavelengths.[9][3][10]

Discovery

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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's all-sky survey since 2008.[7]: 2  Because of its optimal location away from the crowded Galactic Center and its pulsar-like[11]: 8  gamma-ray emission peak at 1.4 GeV, it was deemed a prime millisecond pulsar candidate for follow-up.[7]: 2  The pulsar was reobserved and confirmed by the Low-Frequency Array (LOFAR) radio telescope in the Netherlands on 25 December 2016, which revealed a 707-Hz radio pulsation frequency alongside radial acceleration by an unseen binary companion.[7]: 3  Further LOFAR observations took place from January to February 2017, alongside radio observations by the Green Bank Telescope in Green Bank, West Virginia in March 2017.[7]: 3  Optical observations by the 2.54-meter Isaac Newton Telescope on La Palma detected and confirmed the pulsar's companion at a faint apparent magnitude of 23 in January 2017.[7]: 3  The discovery was published in The Astrophysical Journal Letters and was announced in a NASA press release in September 2017.[7][5]

Distance and location

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The distance of PSR J0952–0607 from Earth is highly uncertain.[2][3][4]

Binary system

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The PSR J0952–0607 binary system is composed of a massive pulsar and a substellar-mass (<0.1 M☉)[8]: 127  companion in close orbit around it.[4] 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.[6] The companion is continuously losing mass through ablation by intense high-energy solar winds and gamma-ray emissions from the pulsar, which then accretes some of the companion's lost material onto itself.[8]: 127 [4]: 1 

Companion

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Artist's impression of a black widow pulsar system, where a stellar-mass companion is being ablated by the intense radiation of its host pulsar

The companion orbits the pulsar at a distance of 1.6 million km (1 million mi)[b] with an orbital period of 6.42 hours.[4] Because it orbits so closely, the companion is presumably tidally locked, with one hemisphere always facing the pulsar.[3]: 8  The companion does not appear to eclipse the pulsar,[7]: 1 [3]: 12  indicating that its orbit is oriented nearly face-on with an inclination of 60° with respect to the plane perpendicular to Earth's line of sight.[4]: 4  The companion's orbital motion also does not appear to modulate the pulsar's pulsations, signifying a circular orbit with negligible orbital eccentricity.[3]: 4 

The companion was likely a former star that had been reduced to the size of a large gas giant planet or brown dwarf,[6][3]: 12  with a present-day mass of 0.032±0.002 M☉ or 34±2 MJ according to radial velocity measurements.[4]: 4  Due to intense irradiation and heating by the host pulsar, the companion's radius is bloated up to 80% of its Roche lobe[3]: 8 [4]: 4  and brightly glows with a thermal luminosity of about 10 L☉,[a] thereby accounting for much of the system's optical brightness.[4]: 1, 4 [2]: 1  As a result of bloating, the companion attains a low density likely around 10 g/cm3 (with significant uncertainty due to the system's unknown distance from Earth),[2]: 11  making it susceptible to tidal deformation by the pulsar.[3]: 12 

The companion's pulsar-facing irradiated hemisphere is continuously heated up to a temperature of 6,200 K, whereas the companion's unirradiated hemisphere experiences a uniform[2]: 4  temperature of 3,000 K.[4]: 4  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.[7]: 4 [3]: 8  This brightness variability is demonstrated in PSR J0952–0607's optical light curve, which exhibits an amplitude greater than one magnitude.[2]: 4 

Mass

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PSR J0952–0607 has a mass of 2.35±0.17 M☉, making it the most massive neutron star known as of 2022.[4] The pulsar likely acquired most of its mass by accreting up to 1 M☉ of lost material from its companion.[4]: 5 

Rotation and age

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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 Milky Way.[7][5] Assuming a standard neutron star radius of 10 km (6.2 mi),[3]: 11  the equator of PSR J0952–0607 rotates at a tangential velocity over 44,400 km/s (27,600 mi/s)—about 14% the speed of light.[12] 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 4.6×10−21 seconds per second, corresponding to a characteristic age of 4.9 billion years.[3]: 11 

Magnetic field

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Measurements of PSR J0952–0607's spin-down rate show that the pulsar has a remarkably weak surface magnetic field strength of 6.1×107 gauss (6.1×103 T), placing it among the 10 weakest pulsar magnetic fields known as of 2022.[4]: 1  For context, ordinary pulsar magnetic fields usually lie on the order of teragauss (1×1012 G, 1.0×108 T), over 10,000 times greater than that of PSR J0952–0607.[13][4]: 1  Other millisecond pulsars exhibit similarly weak magnetic fields, hinting at a common albeit unknown mechanism in these types of systems;[3]: 2  possible explanations range from accreted matter burying the pulsar's surface magnetic field to heat-driven evolution of the pulsar's solid crust.[13]: 1–2 [4]: 1 

Gamma-ray emissions

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PSR J0952–0607 appears very faint in gamma-rays and was not detected in July 2011.[10][3]: 2 

See also

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Notes

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  1. ^ a b Luminosity converted from erg/s to L☉, given 3.81+0.46
    −0.43    ×1034 erg/s     from Romani et al. (2022)[4] and the solar luminosity L☉ = 3.826×1033 erg/s.
  2. ^ a b Orbital semi-major axis calculated with Kepler's Third Law:   given primary mass   = 2.35 M☉ and orbital period   = 6.42 h.[4] Nieder et al. (2019) determined a minimum projected semi-major axis of 0.0626670 light seconds (18787 km) from gamma-ray and radio pulsation timing.[3]: 6 

References

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  1. ^ a b "PSR J0952-0607 -- Pulsar". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 26 July 2022.
  2. ^ a b c d e f g Draghis, Paul; Romani, Roger W.; Filippenko, Alexei V.; Brink, Thomas G.; Zheng, WeiKang; Halpern, Jules P.; Fernando, Camilo (September 2019). "Multiband Optical Light Curves of Black-widow Pulsars". The Astrophysical Journal. 883 (1): 13. arXiv:1908.00992. Bibcode:2019ApJ...883..108D. doi:10.3847/1538-4357/ab378b. 108.
  3. ^ a b c d e f g h i j k l m n o p q r s Nieder, L.; Clark, C. J.; Bassa, C. G.; Wu, J.; Singh, A.; Donner, J. Y.; et al. (September 2019). "Detection and Timing of Gamma-Ray Pulsations from the 707 Hz Pulsar J0952-0607". The Astrophysical Journal. 883 (1): 17. arXiv:1905.11352. Bibcode:2019ApJ...883...42N. doi:10.3847/1538-4357/ab357e. 42.
  4. ^ a b c d e f g h i j k l m n o p q r s t u v w x Romani, Roger W.; Kandel, D.; Filippenko, Alexei V.; Brink, Thomas G.; Zheng, WeiKang (August 2022). "PSR J0952-0607: The Fastest and Heaviest Known Galactic Neutron Star". The Astrophysical Journal Letters. 934 (2): 6. arXiv:2207.05124. Bibcode:2022ApJ...934L..17R. doi:10.3847/2041-8213/ac8007. L18.
  5. ^ a b c d e Reddy, Francis (5 September 2017). "'Extreme' Telescopes Find the Second-fastest-spinning Pulsar". NASA. Retrieved 26 July 2022.
  6. ^ a b c Sanders, Robert (26 July 2022). "Heaviest neutron star to date is a 'black widow' eating its mate". Berkeley News. University of California Berkeley. Retrieved 26 July 2022.
  7. ^ a b c d e f g h i j Bassa, C. G.; Pleunis, Z.; Hessels, J. W. T.; Ferrara, E. C.; Breton, R. P.; Gusinskaia, N. V.; et al. (September 2017). "LOFAR Discovery of the Fastest-spinning Millisecond Pulsar in the Galactic Field". The Astrophysical Journal Letters. 846 (2): 7. arXiv:1709.01453. Bibcode:2017ApJ...846L..20B. doi:10.3847/2041-8213/aa8400. L20.
  8. ^ a b c Roberts, Mallory S. E. (March 2013). "Surrounded by spiders! New black widows and redbacks in the Galactic field". Proceedings of the International Astronomical Union. 291: 127–132. arXiv:1210.6903. Bibcode:2013IAUS..291..127R. doi:10.1017/S174392131202337X.
  9. ^ Ho, Wynn C. G.; Heinke, Craig O.; Chugunov, Andrey I. (September 2019). "XMM-Newton Detection and Spectrum of the Second Fastest Spinning Pulsar PSR J0952-0607". The Astrophysical Journal. 882 (2): 7. arXiv:1905.12001. Bibcode:2019ApJ...882..128H. doi:10.3847/1538-4357/ab3578. 128.
  10. ^ a b Kohler, Susanna (11 December 2019). "An Extreme Pulsar Seen in Gamma Rays". AAS Nova Highlights. American Astronomical Society. Bibcode:2019nova.pres.6048K. Retrieved 26 July 2022.
  11. ^ Abdollahi, S.; Acero, F.; Ackermann, M.; Ajello, M.; Atwood, W. B.; Axelsson, M.; et al. (March 2020). "Fermi Large Area Telescope Fourth Source Catalog". The Astrophysical Journal Supplement Series. 247 (1): 37. arXiv:1902.10045. Bibcode:2020ApJS..247...33A. doi:10.3847/1538-4365/ab6bcb. 33.
  12. ^ Starr, Michelle (24 September 2019). "Astronomers Detect Gamma Rays From an Extreme Pulsar Spinning 707 Times Per Second". ScienceAlert. Retrieved 27 July 2022.
  13. ^ a b Mukherjee, Dipanjan (September 2017). "Revisiting Field Burial by Accretion onto Neutron Stars". Journal of Astrophysics and Astronomy. 38 (3): 10. arXiv:1709.07332. Bibcode:2017JApA...38...48M. doi:10.1007/s12036-017-9465-6. hdl:1885/247814. 48.
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