List of lower mass gap objects

In astrophysics, the lower mass gap is a mass range between the maximum mass for a typical neutron star and the minimum mass for a typical black hole, often defined as roughly 2.5–5 solar masses (M☉). A compact object in this mass range often cannot be confidently determined to be a neutron star or a black hole due to uncertainties in measurement and in the maximum mass of a neutron star (the Tolman-Oppenheimer-Volkoff limit).

This list considers a "lower mass gap object" to be any compact object whose estimated mass or mass range overlaps with the range of 2.5–5 M☉.

List

Object Mass (M☉) Classification (if known) References
PSR J1641+3627F 1.4–3.7 Neutron star
Primary object in GW190425 1.60−2.52
Primary object in V1408 Aquilae 2.0–6.2 Likely black hole
Secondary object in GW190917_114630 2.1+1.1
−0.4
XMMU J013236.7+303228 2.2+0.8
−0.6		 Neutron star
PSR J0952−0607 2.35±0.17 Neutron star
Cygnus X-3 2.4+2.1
−1.1		 Likely black hole
PSR J2017−1614 2.4±0.6 Neutron star
PSR J1600−3053 2.5+0.9
−0.7		 Neutron star
Secondary object in GW190814 2.59+0.08
−0.09		 Likely black hole
GRO J0422+32 2.7+0.7
−0.5		 Black hole
4U 1543-475 2.7–7.5 Likely black hole
Secondary object in GW200210 2.83+0.47
−0.42
2MASS J05215658+4359220 3.3+2.8
−0.7		 Likely black hole
Primary object in Gaia DR3 3425577610762832384 3.6+0.8
−0.5		 Likely black hole
Primary object in GW230529 3.66+0.82
−1.21		 Likely black hole
GRO J1655−40 4.1−7.9 Likely black hole
GW230529 remnant 4.92+0.62
−0.63
Secondary object in GW190924_021846 5.0+1.4
−1.9
Primary object in GW200115_042309 5.7+1.8
−2.1		 Black hole
Primary object in GW190426_152155 5.7+3.9
−2.3
Secondary object in GW230627 5.79+0.95
−0.92		 Black hole
Secondary object in GW191113 5.9+4.4
−1.3		 Black hole
Secondary object in GW190725_174728 6.3+2.1
−2.5		 Likely black hole
Secondary object in GW191129 6.7+1.5
−1.7		 Black hole
Secondary object in GW231223_075055 6.80+2.00
−2.13		 Black hole
Secondary object in GW231118_090602 7.29+2.13
−3.27		 Black hole
Secondary object in GW231020 7.30+2.06
−2.85		 Black hole
Secondary object in GW230729 7.62+2.12
−2.63		 Black hole
Secondary object in GW190930_133541 7.8+1.7
−3.3		 Black hole
Secondary object in GW200316 7.8+2.0
−2.9		 Black hole

See also

References

  1. ↑ Yang, Y.; Gayathri, V.; Bartos, I.; Haiman, Z.; Safarzadeh, M.; Tagawa, H. (2020). "Black Hole Formation in the Lower Mass Gap through Mergers and Accretion in AGN Disks". The Astrophysical Journal Letters. 901 (2): L34. arXiv:2007.04781. doi:10.3847/2041-8213/abb940.
  2. ↑ Gao, Shi-Jie; Li, Xiang-Dong (2023). "Can Cosmologically Coupled Mass Growth of Black Holes Solve the Mass Gap Problem?". The Astrophysical Journal. 956 (2): 128. arXiv:2307.10708. doi:10.3847/1538-4357/ace890.
  3. ↑ Wang, Song; et al. (2024). "A potential mass-gap black hole in a wide binary with a circular orbit". Nature Astronomy. 8 (12): 1583–1591. arXiv:2409.06352. doi:10.1038/s41550-024-02359-9.
  4. ↑ Tsokaros, Antonios; Ruiz, Milton; Shapiro, Stuart L.; Sun, Lunan; Uryū, Kōji (2020). "Great Impostors: Extremely Compact, Merging Binary Neutron Stars in the Mass Gap Posing as Binary Black Holes". Physical Review Letters. 124 (7) 071101. arXiv:1911.06865. doi:10.1103/PhysRevLett.124.071101. PMID 32142310.
  5. ↑ Hebeler, K.; Lattimer, J. M.; Pethick, C. J.; Schwenk, A. (2013). "Equation of State and Neutron Star Properties Constrained by Nuclear Physics and Observation". The Astrophysical Journal. 773: 11. arXiv:1303.4662. doi:10.1088/0004-637X/773/1/11.
  6. ↑ Cadelano, Mario; Chen, Jianxing; Pallanca, Cristina; Istrate, Alina G.; Ferraro, Francesco R.; Lanzoni, Barbara; Freire, Paulo C. C.; Salaris, Maurizio (2020). "PSR J1641+3627F: A Low-mass He White Dwarf Orbiting a Possible High-mass Neutron Star in the Globular Cluster M13". The Astrophysical Journal. 905: 63. arXiv:2010.09740. doi:10.3847/1538-4357/abc345.
  7. ↑ Abbott, B. P.; et al. (2020). "GW190425: Observation of a Compact Binary Coalescence with Total Mass ∼ 3.4 M⊙". The Astrophysical Journal Letters. 892: L3. arXiv:2001.01761. doi:10.3847/2041-8213/ab75f5. hdl:11245.1/a1d4c3da-e63f-4bf7-8502-5d1c342c3029.
  8. ↑ Gomez, Sebastian; Mason, Paul A.; Robinson, Edward L. (2015). "The Case for a Low Mass Black Hole in the Low Mass X-Ray Binary V1408 Aquilae (= 4U 1957+115)". The Astrophysical Journal. 809: 9. arXiv:1506.00181. doi:10.1088/0004-637X/809/1/9.
  9. 1 2 Abbott, R.; et al. (2024). "GWTC-2.1: Deep extended catalog of compact binary coalescences observed by LIGO and Virgo during the first half of the third observing run". Physical Review D. 109 (2) 022001. doi:10.1103/PhysRevD.109.022001. hdl:11245.1/7226562e-ae54-40dc-812e-32225b5c7320.
  10. ↑ Bhalerao, Varun B.; Van Kerkwijk, Marten H.; Harrison, Fiona A. (2012). "Constraints on the Compact Object Mass in the Eclipsing High-Mass X-Ray Binary Xmmu J013236.7+303228 in M 33". The Astrophysical Journal. 757: 10. arXiv:1207.0008. doi:10.1088/0004-637X/757/1/10.
  11. ↑ Romani, Roger W.; Kandel, D.; Filippenko, Alexei V.; Brink, Thomas G.; Zheng, Weikang (2022). "PSR J0952−0607: The Fastest and Heaviest Known Galactic Neutron Star". The Astrophysical Journal Letters. 934 (2): L17. arXiv:2207.05124. doi:10.3847/2041-8213/ac8007.
  12. ↑ Zdziarski, Andrzej A.; Mikołajewska, Joanna; Belczyński, Krzysztof (2013). "Cyg X-3: A low-mass black hole or a neutron star". Monthly Notices of the Royal Astronomical Society: Letters. 429: L104–L108. arXiv:1208.5455. doi:10.1093/mnrasl/sls035.
  13. ↑ Bobakov, A. V.; Kirichenko, A. Yu.; Zharikov, S. V.; Karpova, A. V.; Zyuzin, D. A.; Shibanov, Yu. A.; Mennickent, R. E.; Garcia-Álvarez, D. (2024). "Two black widow pulsars in the optical and X-rays". Astronomy & Astrophysics. 690: A173. arXiv:2407.17187. doi:10.1051/0004-6361/202450205.
  14. ↑ Arzoumanian, Zaven; et al. (2018). "The NANOGrav 11-year Data Set: High-precision Timing of 45 Millisecond Pulsars". The Astrophysical Journal Supplement Series. 235 (2): 37. arXiv:1801.01837. doi:10.3847/1538-4365/aab5b0.
  15. ↑ Abbott, R.; et al. (2020). "GW190814: Gravitational Waves from the Coalescence of a 23 Solar Mass Black Hole with a 2.6 Solar Mass Compact Object". The Astrophysical Journal Letters. 896 (2): L44. arXiv:2006.12611. doi:10.3847/2041-8213/ab960f.
  16. ↑ Casares, J.; Muñoz-Darias, T.; Torres, M A P.; Mata Sánchez, D.; Britt, C. T.; Armas Padilla, M.; Álvarez-Hernández, A.; Cúneo, V. A.; González Hernández, J. I.; Jiménez-Ibarra, F.; Jonker, P. G.; Panizo-Espinar, G.; Sánchez-Sierras, J.; Yanes-Rizo, I. V. (2022). "A correlation between H α trough depth and inclination in quiescent X-ray transients: Evidence for a low-mass black hole in GRO J0422+32". Monthly Notices of the Royal Astronomical Society. 516 (2): 2023–2037. arXiv:2207.01628. doi:10.1093/mnras/stac1881. hdl:2066/253645.
  17. ↑ Orosz, Jerome A.; Jain, Raj K.; Bailyn, Charles D.; McClintock, Jeffrey E.; Remillard, Ronald A. (1998). "Orbital Parameters for the Soft X-Ray Transient 4U 1543−47: Evidence for a Black Hole". The Astrophysical Journal. 499: 375–384. arXiv:astro-ph/9712018. doi:10.1086/305620.
  18. 1 2 3 4 Abbott, R.; et al. (2023). "GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo during the Second Part of the Third Observing Run". Physical Review X. 13 (4) 041039. arXiv:2111.03606. doi:10.1103/PhysRevX.13.041039. hdl:1721.1/154852.
  19. ↑ Thompson, Todd A.; Kochanek, Christopher S.; Stanek, Krzysztof Z.; Badenes, Carles; Post, Richard S.; Jayasinghe, Tharindu; Latham, David W.; Bieryla, Allyson; Esquerdo, Gilbert A.; Berlind, Perry; Calkins, Michael L.; Tayar, Jamie; Lindegren, Lennart; Johnson, Jennifer A.; Holoien, Thomas W.-S.; Auchettl, Katie; Covey, Kevin (2019). "A noninteracting low-mass black hole–giant star binary system". Science. 366 (6465): 637–640. arXiv:1806.02751. doi:10.1126/science.aau4005. PMID 31672898.
  20. ↑ Wang, Song; et al. (2024). "A potential mass-gap black hole in a wide binary with a circular orbit". Nature Astronomy. 8 (12): 1583–1591. arXiv:2409.06352. doi:10.1038/s41550-024-02359-9.
  21. 1 2 3 4 5 6 7 The LIGO Scientific Collaboration; et al. (2025). "GWTC-4.0: Updating the Gravitational-Wave Transient Catalog with Observations from the First Part of the Fourth LIGO-Virgo-KAGRA Observing Run". arXiv:2508.18082. {{cite journal}}: Cite journal requires |journal= (help)
  22. ↑ Chaty, S.; Mirabel, I. F.; Goldoni, P.; Mereghetti, S.; Duc, P.- A.; Marti, J.; Mignani, R. P. (2002). "Near-infrared observations of Galactic black hole candidates". Monthly Notices of the Royal Astronomical Society. 331 (4): 1065–1071. arXiv:astro-ph/0112329. doi:10.1046/j.1365-8711.2002.05267.x.
  23. 1 2 3 Abbott, R.; et al. (2021). "GWTC-2: Compact Binary Coalescences Observed by LIGO and Virgo during the First Half of the Third Observing Run". Physical Review X. 11 (2) 021053. arXiv:2010.14527. doi:10.1103/PhysRevX.11.021053.
  24. ↑ Abbott, R.; et al. (2021). "Observation of Gravitational Waves from Two Neutron Star–Black Hole Coalescences". The Astrophysical Journal Letters. 915: L5. arXiv:2106.15163. doi:10.3847/2041-8213/ac082e. hdl:2434/1111308.