astro.wikisort.org - Star

PSR J0952–0607 is a massive millisecond pulsar in a binary system, located between 3,200–5,700 light-years (970–1,740 pc) away 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 as much as 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 that is located in 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
Distance	970+1160 −530 pc[3] or 1740+1570 −820 pc[3] or 6260+360 −400 (optical)[4] pc
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[lower-alpha 1] 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[lower-alpha 2]
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 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

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

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

Binary system

The PSR J0952–0607 binary system comprises 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

The companion orbits the pulsar closely at a distance of 1.6 million km (1 million mi)[lower-alpha 2] 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 since 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 M_J 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_☉,[lower-alpha 1] 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 Such brightness variability has been observed in its optical light curve, which exhibits fluctuations greater than 2 magnitudes.[2]^: 4

Mass

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

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 Milky Way.[7][5] Assuming a standard neutron star radius of 10 km (6.2 mi),[3]^: 11 the equator of PSR J0952–0607 would be rotating 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

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

Gamma-ray emissions

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

See also

• Tolman–Oppenheimer–Volkoff limit
• Black Widow Pulsar, the prototypical namesake for the class of binary pulsars with ablating companions
• PSR J1748−2446ad, the fastest-spinning pulsar located in the globular cluster Terzan 5

Notes

References

---