View source for Astronomy:NGC 3393

{{Short description|Galaxy in the constellation Hydra}}
{{Infobox galaxy
| name = [[Astronomy:New General Catalogue|NGC]] 3393
| image = [[File:Active Nucleus of NGC 3393.png|250px]]
| caption = NGC 3393 by [[Astronomy:Hubble Space Telescope|Hubble Space Telescope]]
| credit = NASA/JPL-Caltech
| epoch = [[Astronomy:J2000|J2000]]
| type = (R')SB(s)ab <ref name="ned">{{cite web
  | title=NASA/IPAC Extragalactic Database
  | work=Results for NGC 3393
  | url=http://ned.ipac.caltech.edu/cgi-bin/nph-objsearch?objname=NGC+3393
  | access-date=2016-01-18 }}</ref>
| ra = {{RA|10|48|23.5}}<ref name="ned" /> 
| dec = {{DEC|-25|09|43}}<ref name="ned" />
| dist_ly = 181 [[Astronomy:Light-year|Mly]] (56 [[Astronomy:Parsec|Mpc]])<ref name="ned" />
| z = 0.012509 ± 0.000017 <ref name="ned" />
| h_radial_v = 3,750 ± 5 km/s<ref name="ned" />
| appmag_v = 13.1
| size_v = 2.2{{prime}} × 2.0{{prime}}<ref name="ned" />
| constellation name = [[Astronomy:Hydra (constellation)|Hydra]]
| notes = Seyfert galaxy<br/>Hosts a pair of supermassive black holes
| names = ESO 501-G100, [[Astronomy:Morphological Catalogue of Galaxies|MCG]] -04-26-011, AM 1045-245, [[Astronomy:Principal Galaxies Catalogue|PGC]] 32300<ref name="ned" />
}}
'''NGC 3393''' is a [[Astronomy:Barred spiral galaxy|barred spiral galaxy]] located in the constellation [[Astronomy:Hydra (constellation)|Hydra]]. It is located at a distance of circa 180 million [[Astronomy:Light-year|light-year]]s from Earth, which, given its apparent dimensions, means that NGC 3393 is about 140,000 light-years across. It was discovered by [[Biography:John Herschel|John Herschel]] on March 24, 1835.<ref>[http://cseligman.com/text/atlas/ngc33a.htm#3393 NGC 3393] cseligman.com</ref> It is a Type II [[Astronomy:Seyfert galaxy|Seyfert galaxy]], known to host two [[Astronomy:Supermassive black hole|supermassive black hole]]s, which are the nearest known pair of supermassive black holes to Earth.<ref name="NASAH11278">{{cite web  |title=Spiral Galaxy NGC 3393 |url=https://www.nasa.gov/mission_pages/chandra/multimedia/photo-H-11-278.html |website=NASA |access-date=10 May 2020 |language=en |date=24 November 2015}}</ref>

== Characteristics ==
The galaxy is characterised as a barred spiral galaxy. At both ends of the bar [[Astronomy:H II region|H II region]]s are present. There is also evidence of a fainter inner bar. The fainter outer arms of the galaxy form a nearly complete [[Astronomy:Ring galaxy|ring]].<ref>{{cite journal |last1=Alonso-Herrero |first1=Almudena|last2=Simpson |first2=Chris |last3=Ward |first3=Martin J. |last4=Wilson |first4=Andrew S. |title=A Near-Infrared Imaging Study of Seyfert Galaxies with Extended Emission-Line Regions |journal=The Astrophysical Journal |date=March 1998 |volume=495 |issue=1 |pages=196–221 |doi=10.1086/305269|bibcode=1998ApJ...495..196A |doi-access=free }}</ref>

=== Active galactic nucleus ===
NGC 3393 has been characterised as a [[Astronomy:Seyfert galaxy|Seyfert galaxy]], a galaxy category which features bright point-like nuclei. NGC 3393 is a type II Seyfert galaxy. Its [[Physics:X-ray|X-ray]] spectrum is more consistent with a [[Physics:Compton scattering|Compton]]-thick cold reflection source, which means that the source is hidden behind dense material, mainly gas and dust, and the X-rays observed have been reflected.<ref>{{cite journal |author=Maiolino, R. |author2=Salvati, M. |author3=Bassani, L. |author4=Dadina, M. |author5=della Ceca, R. |author6=Matt, G. |author7=Risaliti, G. |author8=Zamorani, G. |title=Heavy obscuration in X-ray weak AGNs |journal=Astronomy and Astrophysics |date=October 1998 |volume=338 |pages=781–794 |arxiv=astro-ph/9806055|bibcode=1998A&A...338..781M }}</ref>

=== Supermassive black holes ===
The source of activity in the active galactic nuclei is a supermassive black hole (SMBH) lying at the centre of the galaxy. Observations by the [[Astronomy:Chandra X-ray Observatory|Chandra X-ray Observatory]] revealed evidence for a pair of [[Astronomy:Supermassive black hole|supermassive black hole]]s in the centre of NGC 3393. The observation in hard X-rays, including emission from iron, showed two separate peaks, which were identified as black holes that are actively growing, generating X-ray emission as gas falls towards the black holes and becomes hotter. The obscured regions around both black holes block the copious amounts of optical and ultraviolet light produced by infalling material. They are the first pair of black holes found in a spiral galaxy like our Milky Way. The two black holes are separated by only 490 light years.<ref name="NASAH11278"/><ref name="Fabbiano">{{cite journal |last1=Fabbiano |first1=G. |last2=Wang |first2=Junfeng |last3=Elvis |first3=M. |last4=Risaliti |first4=G. |title=A close nuclear black-hole pair in the spiral galaxy NGC 3393 |journal=Nature |date=31 August 2011 |volume=477 |issue=7365 |pages=431–434 |doi=10.1038/nature10364|pmid=21881560 |arxiv=1109.0483|bibcode=2011Natur.477..431F |s2cid=205226065 }}</ref>

The two black holes in NGC 3393 are likely the remnant of a merger of two galaxies of unequal mass a billion or more years ago.<ref name="Fabbiano"/> Other evidence that supports the hypothesis of the galaxy merger include high pre-shock densities in the narrow-line region and low O/H and Mg/H abundances. However the N/H is more than predicted, probably due to the creation of [[Astronomy:Wolf–Rayet star|Wolf–Rayet star]]s in the central region of the galaxy during the merger.<ref>{{cite journal |last1=Contini |first1=M. |title=Evidence of merging in the Seyfert galaxy NGC 3393, revealed by modelling the spectra |journal=Monthly Notices of the Royal Astronomical Society |date=11 September 2012 |volume=425 |issue=2 |pages=1205–1214 |doi=10.1111/j.1365-2966.2012.21504.x|arxiv=1206.3060 |bibcode=2012MNRAS.425.1205C |doi-access=free }}</ref>

The total mass of the pair is estimated to be between 21 and 35 million {{solar mass|link=yes}}.<ref>{{cite journal |last1=Davis |first1=Benjamin L. |last2=Graham |first2=Alister W. |last3=Cameron |first3=Ewan |title=Black Hole Mass Scaling Relations for Spiral Galaxies. I. I. M BH–M *,sph |journal=The Astrophysical Journal |date=6 March 2019 |volume=873 |issue=1 |pages=85 |doi=10.3847/1538-4357/aaf3b8|arxiv=1810.04887 |bibcode=2019ApJ...873...85D |hdl=1959.3/448397 |s2cid=119211505 |hdl-access=free |doi-access=free }}</ref>

== Supernova ==
One [[Astronomy:Supernova|supernova]] has been observed in NGC 3393, SN 2018aqi. The supernova was discovered by ASAS-SN on April 6, 2018, and had an apparent magnitude of 16.4 at discovery.<ref>{{cite web |title=SN 2018aqi |url=https://wis-tns.weizmann.ac.il/object/2018aqi |website=Transient Name Server |publisher=wis-tns.weizmann.ac.il}}</ref> By its spectrum, it was identified as a [[Astronomy:Type Ia supernova|type Ia supernova]] 6 days before maximum brightness.<ref>{{cite web |title=ATel #11516: ePESSTO spectroscopic classification of optical transients |url=http://www.astronomerstelegram.org/?read=11516 |website=ATel|date= 8 April 2018}}</ref>

== Nearby galaxies ==
NGC 3393 is the brightest galaxy in the NGC 3393 group, which also includes [[Astronomy:NGC 3369|NGC 3369]], NGC 3383, and ESO 501-086.<ref>{{cite journal|last1=Makarov|first1=Dmitry|last2=Karachentsev|first2=Igor|title=Galaxy groups and clouds in the local (z~ 0.01) Universe|journal=Monthly Notices of the Royal Astronomical Society|date=21 April 2011|volume=412|issue=4|pages=2498–2520|doi=10.1111/j.1365-2966.2010.18071.x|url=http://www.sao.ru/hq/dim/groups/galaxies.dat|bibcode=2011MNRAS.412.2498M|arxiv=1011.6277|s2cid=119194025|access-date=10 May 2020|archive-date=31 January 2016|archive-url=https://web.archive.org/web/20160131020344/http://www.sao.ru/hq/dim/groups/galaxies.dat|url-status=dead}}</ref> NGC 3463 has also been proposed to be a member of the group.<ref name="garcia1993">{{cite journal
  | author=A. Garcia
  | title=General study of group membership. II – Determination of nearby groups
  | journal=Astronomy and Astrophysics Supplement
  | date=1993
  | volume=100
  | pages=47–90
  | bibcode=1993A&AS..100...47G}}</ref> The group is part of the [[Astronomy:Hydra–Centaurus Supercluster|Hydra Supercluster]].<ref>{{cite web |title=The Hydra Supercluster |url=http://www.atlasoftheuniverse.com/superc/hya.html |website=www.atlasoftheuniverse.com}}</ref>

== References ==
{{Reflist}}

== External links ==
{{WikiSky}}

{{Catalogs|NGC=3393|PGC=32300}}

{{DEFAULTSORT:NGC 3393}}
[[Category:Barred spiral galaxies]]
[[Category:Ring galaxies]]
[[Category:Seyfert galaxies]]
[[Category:Hydra (constellation)]]
[[Category:NGC objects|3393]]
[[Category:Principal Galaxies Catalogue objects|32300]]
[[Category:Hydra-Centaurus Supercluster]]
[[Category:ESO objects|501-G100]]
[[Category:MCG objects|-04-26-011]]

{{Sourceattribution|NGC 3393}}