NGC 4993

Coordinates: Sky map 13h 09m 47.2s, −23° 23′ 4″
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NGC 4993
NGC 4993 and GRB 170817A afterglow as taken by Hubble Space Telescope[1]
Observation data (J2000 epoch)
Right ascension13h 09m 47.7s[2]
Declination−23° 23′ 02″[2]
Heliocentric radial velocity2916 km/s[2]
Distance44.1 Mpc (144 Mly)[2]
Group or clusterNGC 4993 Group[3]
Apparent magnitude (V)13.32[2]
Size~55,000 ly (17 kpc) (estimated)[2]
Apparent size (V)1.3 x 1.1[2]
Notable featuresHost of neutron star merger detected as gravitational wave GW170817 and gamma-ray burst GRB 170817A
Other designations
NGC 4994, ESO 508-18, AM 1307-230, MCG -4-31-39, PGC 45657, WH III 766[4]
NGC 4993 starmap near ψ Hydrae, near galaxies of NGC 4968, NGC 4970, NGC 5042, IC 4180, IC 4197

NGC 4993 (also catalogued as NGC 4994 in the New General Catalogue) is a lenticular galaxy[5] located about 140 million light-years away[2] in the constellation Hydra.[6] It was discovered on 26 March 1789[7] by William Herschel[6][7] and is a member of the NGC 4993 Group.[3]

NGC 4993 is the site of GW170817, the first astronomical event detected in both electromagnetic and gravitational radiation, the collision of two neutron stars, a discovery given the Breakthrough of the Year award for 2017 by the journal Science.[8][9] Detecting a gravitational wave event associated with the gamma-ray burst provided direct confirmation that binary neutron star collisions produce short gamma-ray bursts.[10]

Physical characteristics[edit]

NGC 4993 has several concentric shells of stars and large dust lane with diameter of approximately a few kiloparsecs which surrounds the nucleus and is stretched out into an "s" shape. The dust lane appears to be connected to a small dust ring with a diameter of ~330 ly (0.1 kpc).[11] These features in NGC 4993 may be the result[12] of a recent merger with a gaseous late-type galaxy that occurred about 400 million years ago.[13] However, Palmese et al. suggested that the galaxy involved in the merger was a gas-poor galaxy.[14]

Dark matter content[edit]

NGC 4993 has a dark matter halo with an estimated mass of 193.9×1010 M.[13]

Globular clusters[edit]

NGC 4993 has an estimated population of 250 globular clusters.[5]

The luminosity of NGC 4993 indicates that the globular cluster system surrounding the galaxy may be dominated by metal-poor globular clusters.[15]

Supermassive black hole[edit]

NGC 4993 has a supermassive black hole with an estimated mass of roughly 80 to 100 million solar masses (8×107 M).[16]

Galactic nucleus activity[edit]

The presence of weak O III, NII and SII emission lines in the nucleus of NGC 4993 and the relatively high ratio of [NII]λ6583/Hα suggest that NGC 4993 is a low-luminosity AGN (LLAGN).[16] The activity may have been triggered by gas from the late-type galaxy as it merged with NGC 4993.[13]

Neutron star merger observations[edit]

In August 2017, rumors circulated[17] regarding a short gamma-ray burst designated GRB 170817A, of the type conjectured to be emitted in the collision of two neutron stars.[18] On 16 October 2017, the LIGO and Virgo collaborations announced that they had detected a gravitational wave event, designated GW170817. The gravitational wave signal matched prediction for the merger of two neutron stars, two seconds before the gamma-ray burst. The gravitational wave signal, which had a duration of about 100 seconds, was the first gravitational wave detection of the merger of two neutron stars.[1][19][20][21][22]

An optical transient, AT 2017gfo (also known as SSS 17a), was detected in NGC 4993 11 hours after the gravitational wave and gamma-ray signals, allowing the location of the merger to be determined. The optical emission is thought to be due to a kilonova. The discovery of AT 2017gfo was the first observation (and first localisation) of an electromagnetic counterpart to a gravitational wave source.[19][21][22][23][24]

GRB 170817A was a gamma-ray burst (GRB) detected by NASA's Fermi and ESA's INTEGRAL on 17 August 2017.[17][25][26][27] Although only localized to a large area of the sky, it is believed to correspond to the other two observations,[23] in part due to its arrival time 1.7 seconds after the GW event.

See also[edit]


  1. ^ a b Chou, Felicia; Washington, Dewayne; Porter, Molly (16 October 2017). "Release 17-083 - NASA Missions Catch First Light from a Gravitational-Wave Event". NASA. Retrieved 21 October 2017.
  2. ^ a b c d e f g h i j "NASA/IPAC Extragalactic Database". Results for NGC 4993. Retrieved 3 June 2018.
  3. ^ a b Hjorth, Jens; Levan, Andrew J.; Tanvir, Nial R.; Lyman, Joe D.; Wojtak, Radosław; Schrøder, Sophie L.; Mandel, Ilya; Gall, Christa; Bruun, Sofie H. (16 October 2017). "The Distance to NGC 4993: The Host Galaxy of the Gravitational-wave Event GW170817". The Astrophysical Journal. 848 (2): L31. arXiv:1710.05856. Bibcode:2017ApJ...848L..31H. doi:10.3847/2041-8213/aa9110. hdl:2381/41880. S2CID 51812508.
  4. ^ Staff (2017). "Galaxy NGC 4993 - Galaxy in Hydra Constellation". Archived from the original on 16 September 2017. Retrieved 30 September 2017.
  5. ^ a b Abbott, B. P.; Abbott, R.; Abbott, T. D.; Acernese, F.; Ackley, K.; Adams, C.; Adams, T.; Addesso, P.; Adhikari, R. X. (1 December 2017). "On the Progenitor of Binary Neutron Star Merger GW170817". The Astrophysical Journal. 850 (2): L40. arXiv:1710.05838. Bibcode:2017ApJ...850L..40A. doi:10.3847/2041-8213/aa93fc. S2CID 29357210.
  6. ^ a b "NGC 4993". Deep Sky Observer's Companion. Retrieved 28 August 2017.
  7. ^ a b "New General Catalog Objects: NGC 4950 - 4999". Retrieved 5 June 2018.
  8. ^ "Breakthrough of the year 2017". Science | AAAS. 22 December 2017.
  9. ^ Cho, Adrian (2017). "Cosmic convergence". Science. 358 (6370): 1520–1521. Bibcode:2017Sci...358.1520C. doi:10.1126/science.358.6370.1520. PMID 29269456.
  10. ^ Overbye, Dennis (16 October 2017). "LIGO Detects Fierce Collision of Neutron Stars for the First Time". The New York Times. Retrieved 16 October 2017.
  11. ^ Blanchard, P. K.; Berger, E.; Fong, W.; Nicholl, M.; Leja, J.; Conroy, C.; Alexander, K. D.; Margutti, R.; Williams, P. K. G. (16 October 2017). "The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale". The Astrophysical Journal. 848 (2): L22. arXiv:1710.05458. Bibcode:2017ApJ...848L..22B. doi:10.3847/2041-8213/aa9055. S2CID 119336499.
  12. ^ Im, Myungshin; Yoon, Yongmin; Lee, Seong-Kook J.; Lee, Hyung Mok; Kim, Joonho; Lee, Chung-Uk; Kim, Seung-Lee; Troja, Eleonora; Choi, Changsu (26 October 2017). "Distance and Properties of NGC 4993 as the Host Galaxy of the Gravitational-wave Source GW170817". The Astrophysical Journal. 849 (1): L16. arXiv:1710.05861. Bibcode:2017ApJ...849L..16I. doi:10.3847/2041-8213/aa9367. S2CID 55716501.
  13. ^ a b c Ebrová, Ivana; Bílek, Michal (2020). "NGC 4993 the shell galaxy host of GW170817: constraints on the recent galactic merger". Astronomy & Astrophysics. 634: A73. arXiv:1801.01493. Bibcode:2020A&A...634A..73E. doi:10.1051/0004-6361/201935219. S2CID 56354361.
  14. ^ Palmese, A.; Hartley, W.; Tarsitano, F.; Conselice, C.; Lahav, O.; Allam, S.; Annis, J.; Lin, H.; Soares-Santos, M. (9 November 2017). "Evidence for Dynamically Driven Formation of the GW170817 Neutron Star Binary in NGC 4993". The Astrophysical Journal. 849 (2): L34. arXiv:1710.06748. Bibcode:2017ApJ...849L..34P. doi:10.3847/2041-8213/aa9660. S2CID 55049352.
  15. ^ Lee, Myung Gyoon; Kang, Jisu; Im, Myungshin (20 May 2018). "A Globular Cluster Luminosity Function Distance to NGC 4993 Hosting a Binary Neutron Star Merger GW170817/GRB 170817A". The Astrophysical Journal Letters. 859 (1): L6. arXiv:1805.01127. Bibcode:2018ApJ...859L...6L. doi:10.3847/2041-8213/aac2e9. S2CID 73713875.
  16. ^ a b Wu, Qingwen; Feng, Jianchao; Fan, Xuliang (6 March 2018). "The Possible Submillimeter Bump and Accretion-jet in the Central Supermassive Black Hole of NGC 4993". The Astrophysical Journal. 855 (1): 46. arXiv:1710.09590. Bibcode:2018ApJ...855...46W. doi:10.3847/1538-4357/aaac28. S2CID 89606053.
  17. ^ a b Drake, Nadia (25 August 2017). "Strange stars caught wrinkling spacetime? Get the facts". National Geographic. Archived from the original on 27 August 2017. Retrieved 27 August 2017.
  18. ^ Nakar, E. (2007). "Short-hard gamma-ray bursts". Physics Reports. 442 (1–6): 166–236. arXiv:astro-ph/0701748. Bibcode:2007PhR...442..166N. CiteSeerX doi:10.1016/j.physrep.2007.02.005. S2CID 119478065.
  19. ^ a b Landau, Elizabeth; Chou, Felicia; Washington, Dewayne; Porter, Molly (16 October 2017). "NASA Missions Catch First Light from a Gravitational-Wave Event". NASA. Retrieved 16 October 2017.
  20. ^ Abbott, B.P.; et al. (16 October 2017). "GW 170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral". Physical Review Letters. 119 (16): 161101. arXiv:1710.05832. Bibcode:2017PhRvL.119p1101A. doi:10.1103/PhysRevLett.119.161101. PMID 29099225. S2CID 217163611.
  21. ^ a b Cho, Adrian (16 October 2017). "Merging neutron stars generate gravitational waves and a celestial light show". Science. doi:10.1126/science.aar2149. Retrieved 16 October 2017.
  22. ^ a b Krieger, Lisa M. (16 October 2017). "A Bright Light Seen Across The Universe, Proving Einstein Right - Violent collisions source of our gold, silver". The Mercury News. Retrieved 16 October 2017.
  23. ^ a b Overbye, Dennis (16 October 2017). "LIGO Detects Fierce Collision of Neutron Stars for the First Time". The New York Times. Retrieved 16 October 2017.
  24. ^ Abbott, B. P.; et al. (LIGO Scientific Collaboration & Virgo Collaboration) (16 October 2017). "GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral". Physical Review Letters. 119 (16): 161101. arXiv:1710.05832. Bibcode:2017PhRvL.119p1101A. doi:10.1103/PhysRevLett.119.161101. PMID 29099225.
  25. ^ von Kienlin, Andreas (17 August 2017). "GCN Circular Number 21520; GRB 170817A: Fermi GBM detection; 2017-08-17 20:00:07 GMT". Max Planck Institute for Extraterrestrial Physics. Retrieved 28 August 2017.
  26. ^ Castelvecchi, Davide (25 August 2017). "Rumours swell over new kind of gravitational-wave sighting". Nature. Nature News. doi:10.1038/nature.2017.22482. Retrieved 27 August 2017.
  27. ^ Sokol, Joshua (25 August 2017). "What Happens When Two Neutron Stars Collide?". Wired. Retrieved 28 August 2017.

External links[edit]