As of February 2019[update], 10 mergers of binary black holes have been observed. In each case two black holes merged to a larger black hole. In addition, one
neutron star merger has been observed (
GW170817), forming a black hole. In addition, over 30 alerts have been issued since April 2019, of black hole merger candidates.
As of 2014, there are 5 triple black hole systems known.[27]
SDSS J150243.09+111557.3 (SDSS J1502+1115) core black holes — the three components are distant tertiary J1502P, and the close binary pair J1502S composed of J1502SE and J1502SW[27]
^Gerke, Brian F.; Newman, Jeffrey A.;
Lotz, Jennifer; Yan, Renbin; Barmby, P.; Coil, Alison L.; Conselice, Christopher J.; Ivison, R. J.; Lin, Lihwai; Koo, David C.; Nandra, Kirpal; Salim, Samir; Small, Todd; Weiner, Benjamin J.; Cooper, Michael C.; Davis, Marc; Faber, S. M.; Guhathakurta, Puragra; et al. (6 April 2007). "The DEEP2 Galaxy Redshift Survey: AEGIS Observations of a Dual AGN AT z p 0.7". The Astrophysical Journal Letters. 660 (1): L23–L26.
arXiv:astro-ph/0608380.
Bibcode:
2007ApJ...660L..23G.
doi:
10.1086/517968.
S2CID14320681.
^Schawinski, Kevin; Urry, Meg; Treister, Ezequiel; Simmons, Brooke; Natarajan, Priyamvada; Glikman, Eilat (29 November 2011). "Evidence for Three Accreting Black Holes in a Galaxy at z ~ 1.35: A Snapshot of Recently Formed Black Hole Seeds?". The Astrophysical Journal Letters. 743 (2) (published December 2011): 6.
arXiv:1111.6973.
Bibcode:
2011ApJ...743L..37S.
doi:
10.1088/2041-8205/743/2/L37.
S2CID118497392. L37.
^Liu, Xin; Shen, Yue; Strauss, Michael A. (18 April 2011). "Cosmic Train Wreck by Massive Black Holes: Discovery of a Kiloparsec-scale Triple Active Galactic Nucleus". The Astrophysical Journal Letters. 736 (1) (published July 2011): L7–L11.
arXiv:1104.3391.
Bibcode:
2011ApJ...736L...7L.
doi:
10.1088/2041-8205/736/1/L7.
S2CID118350891. L7.
As of February 2019[update], 10 mergers of binary black holes have been observed. In each case two black holes merged to a larger black hole. In addition, one
neutron star merger has been observed (
GW170817), forming a black hole. In addition, over 30 alerts have been issued since April 2019, of black hole merger candidates.
As of 2014, there are 5 triple black hole systems known.[27]
SDSS J150243.09+111557.3 (SDSS J1502+1115) core black holes — the three components are distant tertiary J1502P, and the close binary pair J1502S composed of J1502SE and J1502SW[27]
^Gerke, Brian F.; Newman, Jeffrey A.;
Lotz, Jennifer; Yan, Renbin; Barmby, P.; Coil, Alison L.; Conselice, Christopher J.; Ivison, R. J.; Lin, Lihwai; Koo, David C.; Nandra, Kirpal; Salim, Samir; Small, Todd; Weiner, Benjamin J.; Cooper, Michael C.; Davis, Marc; Faber, S. M.; Guhathakurta, Puragra; et al. (6 April 2007). "The DEEP2 Galaxy Redshift Survey: AEGIS Observations of a Dual AGN AT z p 0.7". The Astrophysical Journal Letters. 660 (1): L23–L26.
arXiv:astro-ph/0608380.
Bibcode:
2007ApJ...660L..23G.
doi:
10.1086/517968.
S2CID14320681.
^Schawinski, Kevin; Urry, Meg; Treister, Ezequiel; Simmons, Brooke; Natarajan, Priyamvada; Glikman, Eilat (29 November 2011). "Evidence for Three Accreting Black Holes in a Galaxy at z ~ 1.35: A Snapshot of Recently Formed Black Hole Seeds?". The Astrophysical Journal Letters. 743 (2) (published December 2011): 6.
arXiv:1111.6973.
Bibcode:
2011ApJ...743L..37S.
doi:
10.1088/2041-8205/743/2/L37.
S2CID118497392. L37.
^Liu, Xin; Shen, Yue; Strauss, Michael A. (18 April 2011). "Cosmic Train Wreck by Massive Black Holes: Discovery of a Kiloparsec-scale Triple Active Galactic Nucleus". The Astrophysical Journal Letters. 736 (1) (published July 2011): L7–L11.
arXiv:1104.3391.
Bibcode:
2011ApJ...736L...7L.
doi:
10.1088/2041-8205/736/1/L7.
S2CID118350891. L7.