![NGC 4993 map](https://upload.wikimedia.org/wikipedia/commons/2/23/NGC_4993_map.png)
NGC 4993 (also catalogued as NGC 4994 in the
New General Catalogue
The ''New General Catalogue of Nebulae and Clusters of Stars'' (abbreviated NGC) is an astronomical catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. The NGC contains 7,840 objects, including galaxies, star clusters and ...
) is a
lenticular galaxy
A lenticular galaxy (denoted S0) is a type of galaxy intermediate between an elliptical (denoted E) and a spiral galaxy in galaxy morphological classification schemes. It contains a large-scale disc but does not have large-scale spiral arms. ...
located about 140 million
light-year
A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...
s away
in the constellation
Hydra.
It was discovered on 26 March 1789
by
William Herschel
Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...
and is a member of the NGC 4993 Group.
NGC 4993 is the site of
GW170817
GW 170817 was a gravitational wave (GW) signal observed by the LIGO and Virgo detectors on 17 August 2017, originating from the shell elliptical galaxy . The signal was produced by the last minutes of a binary pair of neutron stars' insp ...
, the first astronomical event detected in both electromagnetic and gravitational radiation, the collision of two
neutron star
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. white ...
s, a discovery given the
Breakthrough of the Year
The Breakthrough of the Year is an annual award for the most significant development in scientific research made by the AAAS journal ''Science,'' an academic journal covering all branches of science. Originating in 1989 as the ''Molecule of the Ye ...
award for 2017 by the journal
''Science''. Detecting a gravitational wave event associated with the gamma-ray burst provided direct confirmation that binary neutron star collisions produce short gamma-ray bursts.
Physical characteristics
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 ~. These features in NGC 4993 may be the result of a recent merger with a gaseous late-type galaxy that occurred about 400 million years ago.
However, Palmese et al. suggested that the galaxy involved in the merger was a gas-poor galaxy.
Dark matter content
NGC 4993 has a
dark matter
Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ab ...
halo with an estimated mass of .
Globular clusters
NGC 4993 has an estimated population of 250
globular cluster
A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of membe ...
s.
The luminosity of NGC 4993 indicates that the globular cluster system surrounding the galaxy may be dominated by metal-poor globular clusters.
Supermassive black hole
NGC 4993 has a
supermassive black hole
A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical obj ...
with an estimated mass of roughly 80 to 100 million
solar mass
The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...
es ().
Galactic nucleus activity
The presence of weak
O III
In astronomy and atomic physics, doubly ionized oxygen is the ion O2+ (O III in spectroscopic notation). Its emission forbidden lines in the visible spectrum fall primarily at the wavelength 500.7 nm, and secondarily at 495.9 nm. Befor ...
,
NII and
SII emission lines in the nucleus of NGC 4993 and the relatively high ratio of
II»6583/Hα suggest that NGC 4993 is a low-luminosity
AGN (LLAGN).
The activity may have been triggered by gas from the late-type galaxy as it merged with NGC 4993.
Neutron star merger observations
In August 2017, rumors circulated
regarding a
short gamma-ray burst designated
GRB 170817A
GW 170817 was a gravitational wave (GW) signal observed by the LIGO and Virgo detectors on 17 August 2017, originating from the shell elliptical galaxy . The signal was produced by the last minutes of a binary pair of neutron stars' inspir ...
, of the type conjectured to be emitted in the
collision
In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great fo ...
of two
neutron star
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses, possibly more if the star was especially metal-rich. Except for black holes and some hypothetical objects (e.g. white ...
s.
On 16 October 2017, the
LIGO
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Two large ...
and
Virgo
Virgo may refer to:
*Virgo (astrology), the sixth astrological sign of the zodiac
* Virgo (constellation), a constellation
*Virgo Cluster, a cluster of galaxies in the constellation Virgo
*Virgo Stellar Stream, remains of a dwarf galaxy
* Virgo Su ...
collaborations announced that they had detected a
gravitational wave
Gravitational waves are waves of the intensity of gravity generated by the accelerated masses of an orbital binary system that propagate as waves outward from their source at the speed of light. They were first proposed by Oliver Heaviside in 1 ...
event, designated
GW170817
GW 170817 was a gravitational wave (GW) signal observed by the LIGO and Virgo detectors on 17 August 2017, originating from the shell elliptical galaxy . The signal was produced by the last minutes of a binary pair of neutron stars' insp ...
. 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.
An
optical transient
Time-domain astronomy is the study of how astronomical objects change with time. Though the study may be said to begin with Galileo's ''Letters on Sunspots'', the term now refers especially to variable objects beyond the Solar System. This may be ...
, (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
A kilonova (also called a macronova) is a transient astronomical event that occurs in a compact binary system when two neutron stars or a neutron star and a black hole merge. These mergers are thought to produce gamma-ray bursts and emit bright e ...
. The discovery of AT 2017gfo was the first observation (and first localisation) of an electromagnetic counterpart to a gravitational wave source.
GRB 170817A
GW 170817 was a gravitational wave (GW) signal observed by the LIGO and Virgo detectors on 17 August 2017, originating from the shell elliptical galaxy . The signal was produced by the last minutes of a binary pair of neutron stars' inspir ...
was a
gamma-ray burst
In gamma-ray astronomy, gamma-ray bursts (GRBs) are immensely energetic explosions that have been observed in distant galaxies. They are the most energetic and luminous electromagnetic events since the Big Bang. Bursts can last from ten milli ...
(GRB) detected by
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
's
Fermi
Enrico Fermi (; 29 September 1901 – 28 November 1954) was an Italian (later naturalized American) physicist and the creator of the world's first nuclear reactor, the Chicago Pile-1. He has been called the "architect of the nuclear age" and ...
and
ESA
, owners =
, headquarters = Paris, ÃŽle-de-France, France
, coordinates =
, spaceport = Guiana Space Centre
, seal = File:ESA emblem seal.png
, seal_size = 130px
, image = Views in the Main Control Room (120 ...
's
INTEGRAL
In mathematics
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented i ...
on 17 August 2017.
Although only localized to a large area of the sky, it is believed to correspond to the other two observations, in part due to its arrival time 1.7 seconds after the GW event.
See also
*
Gravitational-wave astronomy
Gravitational-wave astronomy is an emerging branch of observational astronomy which aims to use gravitational waves (minute distortions of spacetime predicted by Albert Einstein's theory of general relativity) to collect observational data about ...
*
List of gamma-ray bursts
*
List of gravitational wave observations
This is a list of observed/candidate gravitational wave events. Direct observation of gravitational waves, which commenced with the detection of an event by LIGO in 2015, constitutes part of gravitational wave astronomy. LIGO has played a role in ...
*
Neil Gehrels Swift Observatory
Neil Gehrels Swift Observatory, previously called the Swift Gamma-Ray Burst Explorer, is a NASA three-telescope space observatory for studying gamma-ray bursts (GRBs) and monitoring the afterglow in X-ray, and UV/Visible light at the location o ...
*
Ultra-Fast Flash Observatory Pathfinder
The Ultra-Fast Flash Observatory (UFFO) Pathfinder is a space observatory measuring prompt emission of gamma-ray bursts (GRB) both in optical/UV and in X-ray range down to sub-second timescales for the first time. Instead of turning the whole sate ...
References
External links
*
*
*
*
GRB 170817A–
NASA/IPAC Extragalactic Database The NASA/IPAC Extragalactic Database (NED) is an online astronomical database for astronomers that collates and cross-correlates astronomical information on extragalactic objects (galaxies, quasars, radio, x-ray and infrared sources, etc.). NED was ...
(NED)
GRB 170817A–
Max Planck Institute for Extraterrestrial Physics (MPE)
GRB 170817A-
INTEGRAL Science Data Center (ISDC)
The galaxy NGC 4993 in the constellation of Hydra Starmap
{{DEFAULTSORT:NGC 4993
Active galaxies
Astronomical objects discovered in 1789
Elliptical galaxies
Lenticular galaxies
Shell galaxies
Hydra (constellation)
4993
45657