NGC 4993 | |
---|---|
Observation data (J2000 epoch) | |
Constellation | Hydra |
Right ascension | 13h 09m 47.7s [2] |
Declination | −23° 23′ 02″ [2] |
Redshift | 0.009727 [2] |
Heliocentric radial velocity | 2916 km/s [2] |
Distance | 44.1 Mpc (144 Mly) [2] |
Group or cluster | NGC 4993 Group [3] |
Apparent magnitude (V) | 13.32 [2] |
Characteristics | |
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 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 (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]
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]
NGC 4993 has a dark matter halo with an estimated mass of 193.9×1010 M☉ . [13]
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]
NGC 4993 has a supermassive black hole with an estimated mass of roughly 80 to 100 million solar masses (8×107 M☉ ). [16]
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]
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.
A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses (M☉), possibly more if the star was especially metal-rich. Except for black holes, neutron stars are the smallest and densest known class of stellar objects. Neutron stars have a radius on the order of 10 kilometers (6 mi) and a mass of about 1.4 M☉. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past white dwarf star density to that of atomic nuclei.
The following is a timeline of gravitational physics and general relativity.
Timeline of neutron stars, pulsars, supernovae, and white dwarfs
The Fermi Gamma-ray Space Telescope, formerly called the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor, is being used to study gamma-ray bursts and solar flares.
Einstein@Home is a volunteer computing project that searches for signals from spinning neutron stars in data from gravitational-wave detectors, from large radio telescopes, and from a gamma-ray telescope. Neutron stars are detected by their pulsed radio and gamma-ray emission as radio and/or gamma-ray pulsars. They also might be observable as continuous gravitational wave sources if they are rapidly spinning and non-axisymmetrically deformed. The project was officially launched on 19 February 2005 as part of the American Physical Society's contribution to the World Year of Physics 2005 event.
The gravitational wave background is a random background of gravitational waves permeating the Universe, which is detectable by gravitational-wave experiments, like pulsar timing arrays. The signal may be intrinsically random, like from stochastic processes in the early Universe, or may be produced by an incoherent superposition of a large number of weak independent unresolved gravitational-wave sources, like supermassive black-hole binaries. Detecting the gravitational wave background can provide information that is inaccessible by any other means, about astrophysical source population, like hypothetical ancient supermassive black-hole binaries, and early Universe processes, like hypothetical primordial inflation and cosmic strings.
Gamma-ray burst progenitors are the types of celestial objects that can emit gamma-ray bursts (GRBs). GRBs show an extraordinary degree of diversity. They can last anywhere from a fraction of a second to many minutes. Bursts could have a single profile or oscillate wildly up and down in intensity, and their spectra are highly variable unlike other objects in space. The near complete lack of observational constraint led to a profusion of theories, including evaporating black holes, magnetic flares on white dwarfs, accretion of matter onto neutron stars, antimatter accretion, supernovae, hypernovae, and rapid extraction of rotational energy from supermassive black holes, among others.
A neutron star merger is a type of stellar collision.
A kilonova 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 electromagnetic radiation, called "kilonovae", due to the radioactive decay of heavy r-process nuclei that are produced and ejected fairly isotropically during the merger process. The measured high sphericity of the kilonova AT2017gfo at early epochs was deduced from the blackbody nature of its spectrum.
Multi-messenger astronomy is astronomy based on the coordinated observation and interpretation of signals carried by disparate "messengers": electromagnetic radiation, gravitational waves, neutrinos, and cosmic rays. They are created by different astrophysical processes, and thus reveal different information about their sources.
James Michael Lattimer is a nuclear astrophysicist who works on the dense nuclear matter equation of state and neutron stars.
The first direct observation of gravitational waves was made on 14 September 2015 and was announced by the LIGO and Virgo collaborations on 11 February 2016. Previously, gravitational waves had been inferred only indirectly, via their effect on the timing of pulsars in binary star systems. The waveform, detected by both LIGO observatories, matched the predictions of general relativity for a gravitational wave emanating from the inward spiral and merger of a pair of black holes of around 36 and 29 solar masses and the subsequent "ringdown" of the single resulting black hole. The signal was named GW150914. It was also the first observation of a binary black hole merger, demonstrating both the existence of binary stellar-mass black hole systems and the fact that such mergers could occur within the current age of the universe.
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 NGC 4993. The signal was produced by the last minutes of a binary pair of neutron stars' inspiral process, ending with a merger. It is the first GW observation that has been confirmed by non-gravitational means. Unlike the five previous GW detections, which were of merging black holes not expected to produce a detectable electromagnetic signal, the aftermath of this merger was also seen by 70 observatories on 7 continents and in space, across the electromagnetic spectrum, marking a significant breakthrough for multi-messenger astronomy. The discovery and subsequent observations of GW 170817 were given the Breakthrough of the Year award for 2017 by the journal Science.
GW170608 was a gravitational wave event that was recorded on 8 June 2017 at 02:01:16.49 UTC by Advanced LIGO. It originated from the merger of two black holes with masses of and . The resulting black hole had a mass around 18 solar masses. About one solar mass was converted to energy in the form of gravitational waves.
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Daryl Haggard is an American-Canadian astronomer and associate professor of physics in the Department of Physics at McGill University and the McGill Space Institute.
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