Globular cluster Mayall II (M31 G1) is a possible candidate for hosting an intermediate-mass black hole at its center[1]

An intermediate-mass black hole (IMBH) is a class of black hole with mass in the range 102–105 solar masses: significantly more than stellar black holes but less than the 105–109 solar mass supermassive black holes.[2][3] Several IMBH candidate objects have been discovered in the Milky Way galaxy and others nearby, based on indirect gas cloud velocity and accretion disk spectra observations of various evidentiary strength.

Observational evidence

The gravitational wave signal GW190521, which occurred on 21 May 2019 at 03:02:29 UTC,[4] and was published on 2 September 2020,[5][6][7] resulted from the merger of two black holes, weighing 85 and 65 solar masses, with the resulting black hole weighing 142 solar masses, and 8 solar masses being radiated away as gravitational waves.[8][5][6][7]

Before that, the strongest evidence for IMBHs comes from a few low-luminosity active galactic nuclei.[9] Due to their activity, these galaxies almost certainly contain accreting black holes, and in some cases the black hole masses can be estimated using the technique of reverberation mapping. For instance, the spiral galaxy NGC 4395 at a distance of about 4 Mpc appears to contain a black hole with mass of about 3.6×105 solar masses.[10]

The largest up-to-date sample of intermediate-mass black holes includes 305 candidates[11] selected by sophisticated analysis of one million optical spectra of galaxies collected by the Sloan Digital Sky Survey.[12] X-ray emission was detected from 10 of these candidates[11] confirming their classification as IMBH.

Some ultraluminous X-ray sources (ULXs) in nearby galaxies are suspected to be IMBHs, with masses of a hundred to a thousand solar masses.[13] The ULXs are observed in star-forming regions (e.g., in starburst galaxy M82[14]), and are seemingly associated with young star clusters which are also observed in these regions. However, only a dynamical mass measurement from the analysis of the optical spectrum of the companion star can unveil the presence of an IMBH as the compact accretor of the ULX.

A few globular clusters have been claimed to contain IMBHs, based on measurements of the velocities of stars near their centers; the figure shows one candidate object. However none of the claimed detections has stood up to scrutiny.[9] For instance, the data for M31 G1, the object shown in the figure, can be fit equally well without a massive central object.[15]

Additional evidence for the existence of IMBHs can be obtained from observation of gravitational radiation, emitted from a binary containing an IMBH and a compact remnant or another IMBH.[16][17]

Finally, the M–sigma relation predicts the existence of black holes with masses of 104 to 106 solar masses in low-luminosity galaxies.. The smallest black holes from the M–sigma relation prediction is the nucleus of RGG 118 galaxy with only about 50,000 solar masses. [18]

Potential discoveries

RX J1140.1+0307 is a spiral galaxy, centered on a lighter, intermediate-mass black hole.[19]

In November 2004 a team of astronomers reported the discovery of GCIRS 13E, the first intermediate-mass black hole in the Milky Way galaxy, orbiting three light-years from Sagittarius A*.[20] This medium black hole of 1,300 solar masses is within a cluster of seven stars, possibly the remnant of a massive star cluster that has been stripped down by the Galactic Center. This observation may add support to the idea that supermassive black holes grow by absorbing nearby smaller black holes and stars. However, in 2005, a German research group claimed that the presence of an IMBH near the galactic center is doubtful, based on a dynamical study of the star cluster in which the IMBH was said to reside.[21] An IMBH near the galactic center could also be detected via its perturbations on stars orbiting around the supermassive black hole.[22]

In January 2006 a team led by Philip Kaaret of the University of Iowa announced the discovery of a quasiperiodic oscillation from an intermediate-mass black hole candidate located using NASA's Rossi X-ray Timing Explorer. The candidate, M82 X-1, is orbited by a red giant star that is shedding its atmosphere into the black hole.[23] Neither the existence of the oscillation nor its interpretation as the orbital period of the system are fully accepted by the rest of the scientific community, as the periodicity claimed is based on only about four cycles, meaning that it is possible for this to be random variation. If the period is real, it could be either the orbital period, as suggested, or a super-orbital period in the accretion disk, as is seen in many other systems.

In 2009, a team of astronomers led by Sean Farrell discovered HLX-1, an intermediate-mass black hole with a smaller cluster of stars around it,[24] in the galaxy ESO 243-49. This evidence suggested that ESO 243-49 had a galactic collision with HLX-1's galaxy and absorbed the majority of the smaller galaxy's matter.

A team at the CSIRO radio telescope in Australia announced on 9 July 2012 that it had discovered the first intermediate-mass black hole.[25]

In 2015 a team at Keio University in Japan found a gas cloud (CO-0.40-0.22) with very wide velocity dispersion.[26] They performed simulations and concluded that a model with a black hole of around 100,000 solar masses would be the best fit for the velocity distribution.[27] However, a later work pointed out some difficulties with the association of high-velocity dispersion clouds with intermediate mass black holes and proposed that such clouds might be generated by supernovae.[28] Further theoretical studies of the gas cloud and nearby IMBH candidates have been inconclusive but have reopened the possibility.[29]

In 2017, it was announced that a black hole of a few thousand solar masses may be located in the globular cluster 47 Tucanae. This was based on the accelerations and distributions of pulsars in the cluster;[30] however, a later analysis of an updated and more complete data set on these pulsars found no positive evidence for this.[31]

In 2018, the Keio University team found several molecular gas streams orbiting around an invisible object near the galactic center, designated HCN-0.009-0.044, suggested that it is a black hole of 32,000 solar masses and, if so, is the third IMBH discovered in the region.[32]

Simulation of stellar motions in Messier 4
Simulation of stellar motions in Messier 4, where astronomers suspect that an intermediate-mass black hole could be present.[33][34] If confirmed, the black hole would be in the center of the cluster, and would have a sphere of influence (black hole) limited by the red circle.

Observations in 2019 found evidence for a gravitational wave event (GW190521) arising from the merger of two intermediate-mass black holes, with masses of 66 and 85 times that of the Sun.[35] In September 2020 it was announced that the resulting merged black hole weighed 142 solar masses, with 9 solar masses being radiated away as gravitational waves.[8][5][6][7]

In 2020, astronomers reported the possible finding of an intermediate-mass black hole, named 3XMM J215022.4-055108, in the direction of the Aquarius constellation, about 740 million light years from Earth.[36][37]

In 2021 the discovery of a 100,000 solar-mass intermediate-mass black hole in the globular cluster B023-G78 in the Andromeda Galaxy was posted to arXiv in a preprint.[38]

In 2023, an analysis of proper motions of the closest known globular cluster, Messier 4, revealed an excess mass of roughly 800 solar masses in the center, which appears to not be extended, and could thus be the best kinematic evidence for an IMBH (even if an unusually compact cluster of compact objects, white dwarfs, neutron stars or stellar-mass black holes cannot be completely discounted).[33][34]

Origin

Intermediate-mass black holes are too massive to be formed by the collapse of a single star, which is how stellar black holes are thought to form. Their environments lack the extreme conditions—i.e., high density and velocities observed at the centers of galaxies—which seemingly lead to the formation of supermassive black holes. There are three postulated formation scenarios for IMBHs. The first is the merging of stellar mass black holes and other compact objects by means of accretion. The second one is the runaway collision of massive stars in dense stellar clusters and the collapse of the collision product into an IMBH. The third is that they are primordial black holes formed in the Big Bang.[39][40][41]

Scientists have also considered the possibility of the creation of intermediate-mass black holes through mechanisms involving the collapse of a single star, such as the possibility of direct collapse into black holes of stars with pre-supernova helium core mass >133 M☉ (to avoid a pair instability supernova which would completely disrupt the star), requiring an initial total stellar mass of > 260 M☉, but there may be little chance of observing such a high-mass supernova remnant. Recent theories suggest that such massive stars which could lead to the formation of intermediate mass black holes may form in young star clusters via multiple stellar collisions.[42]

See also

References

  1. ↑ Gebhardt, Karl; Rich, R. M.; Ho, Luis C. (December 2005), "An Intermediate-Mass Black Hole in the Globular Cluster G1: Improved Significance from New Keck and Hubble Space Telescope Observations", The Astrophysical Journal, 634 (2): 1093–1102, arXiv:astro-ph/0508251, Bibcode:2005ApJ...634.1093G, doi:10.1086/497023, S2CID 119049663
  2. ↑ Jiang, Yan-Fei; Greene, Jenny E.; Ho, Luis C.; Xiao, Ting; Barth, Aaron J. (2011), "The Host Galaxies of Low-mass Black Holes"
  3. ↑ Graham, Alister W.; Scott, Nicholas (2015), "The (Black Hole)-bulge Mass Scaling Relation at Low Masses"
  4. ↑ "GW trigger S190521g ('GW 190521')". University of Leicester. 2020. Archived from the original on 28 June 2020. Retrieved 26 June 2020.
  5. 1 2 3 Abbott, R.; et al. (2 September 2020). "Properties and Astrophysical Implications of the 150 M ⊙ Binary Black Hole Merger GW190521". The Astrophysical Journal. 900 (1): L13. arXiv:2009.01190. Bibcode:2020ApJ...900L..13A. doi:10.3847/2041-8213/aba493.
  6. 1 2 3 Abbott, R.; et al. (2 September 2020). "GW190521: A Binary Black Hole Merger with a Total Mass of 150 M ⊙". Physical Review Letters. 125 (10): 101102. arXiv:2009.01075. Bibcode:2020PhRvL.125j1102A. doi:10.1103/PhysRevLett.125.101102. PMID 32955328.
  7. 1 2 3 Martin (2 September 2020). "GW190521: The Most Massive Black Hole collision Observed To Date" (PDF). LIGO Scientific Collaboration. Archived (PDF) from the original on 4 September 2020. Retrieved 2 September 2020.
  8. 1 2 Siegel, Ethan (3 September 2020). "LIGO's Biggest Mass Merger Ever Foretells A Black Hole Revolution". Forbes. Archived from the original on 4 September 2020. Retrieved 5 September 2020.
  9. 1 2 Merritt, David (2013). Dynamics and Evolution of Galactic Nuclei. Princeton, NJ: Princeton University Press. ISBN 9781400846122.
  10. ↑ Peterson, Bradley; et al. (2005). "Multiwavelength Monitoring of the Dwarf Seyfert 1 Galaxy NGC 4395. I. A Reverberation-based Measurement of the Black Hole Mass". The Astrophysical Journal. 632 (2): 799–808. arXiv:astro-ph/0506665. Bibcode:2005ApJ...632..799P. doi:10.1086/444494. S2CID 13886279.
  11. 1 2 Chilingarian, Igor; et al. (2018). "A Population of Bona Fide Intermediate-mass Black Holes Identified as Low-luminosity Active Galactic Nuclei". The Astrophysical Journal. 863 (1): 799–808. arXiv:1805.01467. Bibcode:2018ApJ...863....1C. doi:10.3847/1538-4357/aad184. S2CID 119093965.
  12. ↑ Sloan Digital Sky Survey https://www.sdss.org
  13. ↑ Maccarone, T.J.; Kundu, A; Zepf, SE; Rhode, KL (2007). "A black hole in a globular cluster". Nature. 445 (7124): 183–185. arXiv:astro-ph/0701310. Bibcode:2007Natur.445..183M. doi:10.1038/nature05434. PMID 17203062. S2CID 4323113.
  14. ↑ Patruno, A.; Portegies Zwart, S.; Dewi, J.; Hopman, C. (2006). "The ultraluminous X-ray source in M82: an intermediate-mass black hole with a giant companion". Monthly Notices of the Royal Astronomical Society: Letters. 370 (1): L6–L9. arXiv:astro-ph/0506275. Bibcode:2006MNRAS.370L...6P. doi:10.1111/j.1745-3933.2006.00176.x. S2CID 10694200.
  15. ↑ Baumgardt, H.; et al. (2003). "A Dynamical Model for the Globular Cluster G1". The Astrophysical Journal. 589 (1): L25–L28. arXiv:astro-ph/0301469. Bibcode:2003ApJ...589L..25B. doi:10.1086/375802. S2CID 119464795.
  16. ↑ Hopman, Clovis; Simon Portegies Zwart (2005). "Gravitational waves from remnants of ultraluminous X-ray sources". Mon. Not. R. Astron. Soc. Lett. 363 (1): L56–L60. arXiv:astro-ph/0506181. Bibcode:2005MNRAS.363L..56H. doi:10.1111/j.1745-3933.2005.00083.x. S2CID 6904146.
  17. ↑ "Measuring Intermediate-Mass Black-Hole Binaries with Advanced Gravitational Wave Detectors". Gravitational Wave Group. University of Birmingham. Retrieved 28 November 2015.
  18. ↑ Baldassare, Vivienne F.; Reines, Amy E.; Gallo, Elena; Greene, Jenny E. (2015). "A ~50,000 M ⊙ Solar Mass Black Hole in the Nucleus of RGG 118". The Astrophysical Journal. 809 (1): L14. arXiv:1506.07531. Bibcode:2015ApJ...809L..14B. doi:10.1088/2041-8205/809/1/L14. S2CID 84177579.
  19. ↑ "A black hole of puzzling lightness". www.spacetelescope.org. Retrieved 9 January 2017.
  20. ↑ S2 and Central Black Hole
  21. ↑ Schoedel, R.; A. Eckart; C. Iserlohe; R. Genzel; T. Ott (2005). "A Black Hole in the Galactic Center Complex IRS 13E?". Astrophysical Journal. 625 (2): L111–L114. arXiv:astro-ph/0504474. Bibcode:2005ApJ...625L.111S. doi:10.1086/431307. S2CID 10250848.
  22. ↑ Gualandris, A.; Merritt, D. (2009). "Perturbations of Intermediate-mass Black Holes on Stellar Orbits in the Galactic Center". Astrophys. J. 705 (1): 361–371. arXiv:0905.4514. Bibcode:2009ApJ...705..361G. doi:10.1088/0004-637X/705/1/361. S2CID 17649160.
  23. ↑ Dying Star Reveals More Evidence for New Kind of Black Hole | Science Blog
  24. ↑ Soria, Roberto; Hau, George K. T.; Graham, Alister W.; Kong, Albert K. H.; Kuin, N. Paul M.; Li, I.-Hui; Liu, Ji-Feng; Wu, Kinwah (2010), "Discovery of an optical counterpart to the hyperluminous X-ray source in ESO 243-49"
  25. ↑ Nease, Eric (9 July 2012). "Astronomers spot the very first intermediate-mass black hole". The Bunsen Burner. Phillips Cronkite Media Group. Archived from the original on 13 July 2012. Retrieved 9 July 2012.
  26. ↑ Oka, Tomoharu; Mizuno, Reiko; Miura, Kodai; Takekawa, Shunya (December 28, 2015). "Signature of an Intermediate-Mass Black Hole in the Central Molecular Zone of Our Galaxy". Astrophysical Journal. 816 (1): L7. arXiv:1512.04661. Bibcode:2016ApJ...816L...7O. doi:10.3847/2041-8205/816/1/L7. S2CID 119228384.
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  30. ↑ Kızıltan, Bülent; Baumgardt, Holger; Loeb, Abraham (2017). "An intermediate-mass black hole in the centre of the globular cluster 47 Tucanae". Nature. 542 (7640): 203–205. arXiv:1702.02149. Bibcode:2017Natur.542..203K. doi:10.1038/nature21361. PMID 28179649. S2CID 1289123.
  31. ↑ Freire, Paulo; Ridolfi, Alessandro; Kramer, Michael (2017). "Long-term observations of the pulsars in 47 Tucanae - II. Proper motions, accelerations and jerks". Monthly Notices of the Royal Astronomical Society. 471 (7640): 857–876. arXiv:1706.04908. Bibcode:2017MNRAS.471..857F. doi:10.1093/mnras/stx1533. S2CID 119240682.
  32. ↑ Takekawa, Shunya; Oka, Tomoharu; Iwata, Yuhei; Tsujimoto, Shiho; Nomura, Mariko (16 January 2019). "Indication of Another Intermediate-mass Black Hole in the Galactic Center". The Astrophysical Journal. 871 (1): L1. arXiv:1812.10733. Bibcode:2019ApJ...871L...1T. doi:10.3847/2041-8213/aafb07. ISSN 2041-8213. S2CID 119418223.
  33. 1 2 Vitral, E.; et al. (2023). "An elusive dark central mass in the globular cluster M4". Monthly Notices of the Royal Astronomical Society. 522 (4): 5740–5757. arXiv:2305.12702. Bibcode:2023MNRAS.522.5740V. doi:10.1093/mnras/stad1068.
  34. 1 2 "NASA's Hubble Hunts for Intermediate-Sized Black Hole Close to Home". NASA. 23 May 2023. Retrieved 23 May 2023.
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  37. ↑ Lin, Dachenge; et al. (2020). "Multiwavelength Follow-up of the Hyperluminous Intermediate-mass Black Hole Candidate 3XMM J215022.4−055108". The Astrophysical Journal. 892 (2): L25. arXiv:2002.04618. Bibcode:2020ApJ...892L..25L. doi:10.3847/2041-8213/ab745b. S2CID 211082676.
  38. ↑ Starr, Michelle (19 November 2021). "Astronomers May Have Detected a Rare 'Missing Link' Black Hole in Our Closest Neighbor". ScienceAlert.
  39. ↑ Bean, Rachel; Magueijo, Joao (2002). "Could supermassive black holes be quintessential primordial black holes?". Physical Review D. 66 (6): 063505. arXiv:astro-ph/0204486. Bibcode:2002PhRvD..66f3505B. doi:10.1103/PhysRevD.66.063505. S2CID 36067101.
  40. ↑ Kawasaki, M.; Kusenko, A.; Yanagida, T. (2012). "Primordial seeds of supermassive black holes". Physics Letters B. 711 (1): 1–5. arXiv:1202.3848. Bibcode:2012PhLB..711....1K. doi:10.1016/j.physletb.2012.03.056. S2CID 119229231.
  41. ↑ Clesse, S.; Garcia-Bellido, J. (2015). "Massive Primordial Black Holes from Hybrid Inflation as Dark Matter and the seeds of Galaxies". Physical Review D. 92 (2): 023524. arXiv:1501.07565. Bibcode:2015PhRvD..92b3524C. doi:10.1103/PhysRevD.92.023524. hdl:10486/674729. S2CID 118672317.
  42. ↑ Di Carlo, U. N. (2019). "Merging black holes in young star clusters". Monthly Notices of the Royal Astronomical Society: Letters. 487 (2): 2947–2960. arXiv:1901.00863v1. Bibcode:2019MNRAS.487.2947D. doi:10.1093/mnras/stz1453. S2CID 119252415.
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