NGC 4993

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NGC 4993
NGC 4993 and GRB170817A after glow.gif
NGC 4993 and GRB 170817A afterglow.[1]
Observation data (J2000 epoch)
Constellation Hydra
Right ascension 13h 09m 47.7s[2]
Declination −23° 23′ 02″[2]
Redshift 0.009727[2]
Helio radial velocity 2916 km/s[2]
Distance (comoving) 44.1 Mpc (144 Mly)[2]
Group or cluster NGC 4993 Group[3]
Apparent magnitude (V) 13.32[2]
Type (R')SAB0^-(rs)[2]
Size ~55,000 ly (17 kpc) (estimated)[2]
Apparent size (V) 1.3 x 1.1[2]
Notable features Host of Gravitational wave GW170817 and gamma-ray burst GW170817
Other designations
NGC 4994, ESO 508-18, AM 1307-230, MCG -4-31-39, PGC 45657[4]
See also: Galaxy, List of galaxies

Coordinates: Sky map 13h 09m 47.2s, −23° 23′ 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) is an elliptical galaxy or lenticular galaxy[5] located about 140 million light-years away[6] in the constellation Hydra.[7] It was discovered on 26 March 1789[8] by William Herschel[7][8] and is a member of the NGC 4993 Group.[3] In August 2017, astronomers reported[9] that the short gamma-ray burst GRB 170817A, of the sort conjectured to be emitted in the collision of two neutron stars,[10] was detected in this galaxy.

On 16 October 2017, the LIGO and Virgo collaborations officially announced the detection of a gravitational wave, named GW170817, associated with the merger of two neutron stars.[1][11][12][13][14] A gravitational wave event associated with this burst provided direct confirmation that binary neutron star collisions produce short gamma-ray bursts.[15]

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).[16] These features in NGC 4993 may be the result[17] of a recent merger with a gaseous late-type galaxy that occurred about 400 million years ago.[18] However, Palmese et al. suggested that the galaxy involved in the merger was a gas-poor galaxy.[19]

Dark Matter[edit]

NGC 4993 has a dark matter halo with an estimated mass of 193.9×1010 M.[18]

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.[20]

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).[21]


The presence of weak OIII, 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).[21] The activity may have been triggered by gas from the late-type galaxy as it merged with NGC 4993.[18]


AT 2017gfo (also known as SSS17a) is a transient astronomical event believed to be a kilonova, which was observed in NGC 4993 on 17 August 2017.

GW170817 is a gravitational wave signal observed by the LIGO/Virgo collaboration on 17 August 2017. It triggered a search for a corresponding electromagnetic signal, and the discovery of AT 2017gfo marked the first time one was observed.[11] The gravitational wave signal, which had a duration of about 100 seconds, is the first gravitational wave detection of the merger of two neutron stars, and was associated with GRB 170817A.[13][14][22][23]

GRB 170817A is a gamma-ray burst (GRB) detected by NASA's Fermi and ESA's INTEGRAL on 17 August 2017.[9][24][25][26] Although only localized to a large area of the sky, it is believed to correspond to the other two observations,[22] 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 "NASA/IPAC Extragalactic Database". Results for NGC 4993. Retrieved 2018-06-03. 
  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. (2017-10-16). "The Distance to NGC 4993: The Host Galaxy of the Gravitational-wave Event GW170817". The Astrophysical Journal. 848 (2): L31. arXiv:1710.05856Freely accessible. Bibcode:2017ApJ...848L..31H. doi:10.3847/2041-8213/aa9110. hdl:2381/41880. 
  4. ^ Staff (2017). "Galaxy NGC 4993 - Galaxy in Hydra Constellation". 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. (2017-12-01). "On the Progenitor of Binary Neutron Star Merger GW170817". The Astrophysical Journal. 850 (2): L40. arXiv:1710.05838Freely accessible. Bibcode:2017ApJ...850L..40A. doi:10.3847/2041-8213/aa93fc. 
  6. ^ "Your NED Search Results". Retrieved 2018-06-05. 
  7. ^ a b "NGC 4993". Deep Sky Observer's Companion. Retrieved 28 August 2017. 
  8. ^ a b "New General Catalog Objects: NGC 4950 - 4999". Retrieved 2018-06-05. 
  9. ^ a b Drake, Nadia (25 August 2017). "Strange Stars Caught Wrinkling Spacetime? Get the Facts". National Geographic. Retrieved 27 August 2017. 
  10. ^ Nakar, E. (2007). "Short-hard gamma-ray bursts". Physics Reports. 442: 166–236. arXiv:astro-ph/0701748Freely accessible. Bibcode:2007PhR...442..166N. CiteSeerX accessible. doi:10.1016/j.physrep.2007.02.005. 
  11. ^ 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. 
  12. ^ Abbott, B. P.; et al. (16 October 2017). "GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral". Physical Review Letters. 119 (16): 161101. arXiv:1710.05832Freely accessible. Bibcode:2017PhRvL.119p1101A. doi:10.1103/PhysRevLett.119.161101. PMID 29099225. 
  13. ^ 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. 
  14. ^ 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. 
  15. ^ Overbye, Dennis (16 October 2017). "LIGO Detects Fierce Collision of Neutron Stars for the First Time". The New York Times. Retrieved 16 October 2017. 
  16. ^ Blanchard, P. K.; Berger, E.; Fong, W.; Nicholl, M.; Leja, J.; Conroy, C.; Alexander, K. D.; Margutti, R.; Williams, P. K. G. (2017-10-16). "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:1710.05458Freely accessible. Bibcode:2017ApJ...848L..22B. doi:10.3847/2041-8213/aa9055. 
  17. ^ Im, Myungshin; Yoon, Yongmin; Lee, Seong-Kook J.; Lee, Hyung Mok; Kim, Joonho; Lee, Chung-Uk; Kim, Seung-Lee; Troja, Eleonora; Choi, Changsu (2017-10-26). "Distance and Properties of NGC 4993 as the Host Galaxy of the Gravitational-wave Source GW170817". The Astrophysical Journal. 849 (1): L16. arXiv:1710.05861Freely accessible. Bibcode:2017ApJ...849L..16I. doi:10.3847/2041-8213/aa9367. 
  18. ^ a b c Ebrová, Ivana; Bílek, Michal (1 January 2018). "NGC 4993 the shell galaxy host of GW170817: constraints on the recent galactic merger". arXiv:1801.01493Freely accessible [astro-ph.GA]. 
  19. ^ Palmese, A.; Hartley, W.; Tarsitano, F.; Conselice, C.; Lahav, O.; Allam, S.; Annis, J.; Lin, H.; Soares-Santos, M. (2017-11-09). "Evidence for Dynamically Driven Formation of the GW170817 Neutron Star Binary in NGC 4993". The Astrophysical Journal. 849 (2): L34. arXiv:1710.06748Freely accessible. Bibcode:2017ApJ...849L..34P. doi:10.3847/2041-8213/aa9660. 
  20. ^ 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: 1–8. arXiv:1805.01127Freely accessible. Bibcode:2018ApJ...859L...6L. doi:10.3847/2041-8213/aac2e9. 
  21. ^ 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: 1–7. arXiv:1710.09590Freely accessible. Bibcode:2018ApJ...855...46W. 
  22. ^ 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. 
  23. ^ 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:1710.05832Freely accessible. Bibcode:2017PhRvL.119p1101A. doi:10.1103/PhysRevLett.119.161101Freely accessible. PMID 29099225. 
  24. ^ Kienlin, Andreas von (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. 
  25. ^ Castelvecchi, Davide (25 August 2017). "Rumours swell over new kind of gravitational-wave sighting". Nature News. doi:10.1038/nature.2017.22482. Retrieved 27 August 2017. 
  26. ^ Sokol, Joshua (25 August 2017). "What Happens When Two Neutron Stars Collide?". Wired. Retrieved 28 August 2017. 

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