| |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Sextans |
| Right ascension | 09h52m 08.319s[1] |
| Declination | −06° 07′ 23.49″[1] |
| Characteristics | |
| Spectral type | Pulsar |
| Apparent magnitude (i) | 22.0–24.4[2] |
| Astrometry | |
| Distance | 970+1160 −530 pc[3] or1740+1570 −820 pc[3] or6260+360 −400 (optical) pc[4] |
| Details | |
| PSR J0952–0607 A | |
| Mass | 2.35±0.17[4] M☉ |
| Rotation | 1.41379836 ms[3] |
| Age | 4.9[3] Gyr |
| PSR J0952–0607 B | |
| Mass | 0.032±0.002[4] M☉ |
| Luminosity | 9.96+1.20 −1.12[a] L☉ |
| Temperature | 3085+85 −80[4] K |
| Metallicity [Fe/H] | –0.5[2] dex |
| Orbit[3] | |
| Primary | PSR J0952–0607 A |
| Companion | PSR 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 | |
| SIMBAD | data |
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[update], 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 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]
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 TelescopeinGreen Bank, West Virginia in March 2017.[7]: 3 Optical observations by the 2.54-meter Isaac Newton TelescopeonLa 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]
The distance of PSR J0952–0607 from Earth is highly uncertain.[2][3][4]
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
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 planetorbrown dwarf,[6][3]: 12 with a present-day mass of 0.032±0.002 M☉or34±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
PSR J0952–0607 has a mass of 2.35±0.17 M☉, making it the most massive neutron star known as of 2022[update].[4] The pulsar likely acquired most of its mass by accreting up to 1 M☉ of lost material from its companion.[4]: 5
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
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[update].[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
PSR J0952–0607 appears very faint in gamma-rays and was not detected in July 2011.[10][3]: 2
![{\displaystyle a={\sqrt[{3}]{\frac {GMT^{2}}{4\pi ^{2}}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/acc0794d19344d83b82ba93518c68a0fccd0b31b)
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
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