NGC 247

Galaxie
NGC 247
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NGC 247 aufgenommen mit dem Wide Field Imager am 2,2-Meter-Teleskop des MPG/ESO im La-Silla-Observatorium
AladinLite
SternbildWalfisch
Position
Äquinoktium: J2000.0, Epoche: J2000.0
Rektaszension00h 47m 08,55s[1]
Deklination−20° 45′ 37,4″[1]
Erscheinungsbild
Morphologischer TypSAB(s)d / HII[1]
Helligkeit (visuell)8,9 mag[2]
Helligkeit (B-Band)9,6 mag[2]
Winkel­ausdehnung21,4′ × 6,9′[1]
Positionswinkel172°[2]
Inklination75°
Flächen­helligkeit13,8 mag/arcmin²[2]
Physikalische Daten
ZugehörigkeitSculptor-Gruppe[1]
Rotverschiebung0.000520 ± 0.000007[1]
Radial­geschwin­digkeit(156 ± 2) km/s[1]
Hubbledistanz
H0 = 73 km/(s • Mpc)		(11 ± 2) · 106 Lj
(3,268 ± 0,62) Mpc [1]
Masseca. 1,8 · 1010 M☉
Durchmesser70.000 Lj[3]
Geschichte
EntdeckungWilhelm Herschel
Entdeckungsdatum20. Oktober 1784
Katalogbezeichnungen
NGC 247 • UGCA 11 • PGC 2758 • ESO 540-022 • MCG -04-03-005 • IRAS 00446-2101 • KUG 0044-210 • 2MASX J00470855-2045374 • GC 132 • H V 20 • h 57 • HIPASS J0047-20 • LDCE 26 NED005

NGC 247 ist eine leuchtschwache Balken-Spiralgalaxie vom Hubble-Typ SBcd mit ausgedehnten Sternentstehungsgebieten im Sternbild Walfisch südlich der Ekliptik. Sie ist schätzungsweise 11 Millionen Lichtjahre von der Milchstraße entfernt und hat einen Durchmesser von etwa 70.000 Lichtjahren. Die Galaxie gehört zu der unserer Lokalen Gruppe benachbarten Sculptor-Gruppe.

Eine Schwierigkeit bei der Entfernungsbestimmung von NGC 247 ist, dass wir von der Erde aus die Galaxie von der Seite sehen. Die Entfernung von Galaxien wird anhand der scheinbaren Helligkeit veränderlicher Sterne, der Cepheiden bestimmt. Durch die Seitenansicht wird das Licht von interstellarem Staub abgeschwächt und die Sterne scheinen weiter weg zu sein. Messungen des Araucaria-Projekts im Infrarot-Bereich aus dem Jahre 2009 zeigten, dass die Extinktion bei früheren Studien etwas unterschätzt worden war und führte zu einer um 7 % geringeren Entfernungsschätzung.[4]

Das Objekt wurde am 20. Oktober 1784 von dem deutsch-britischen Astronomen Wilhelm Herschel entdeckt.[5]

Literatur

  • König, Michael & Binnewies, Stefan (2019): Bildatlas der Galaxien: Die Astrophysik hinter den Astrofotografien, Stuttgart: Kosmos, S. 41

Weblinks

Commons: NGC 247 – Sammlung von Bildern, Videos und Audiodateien

Einzelnachweise

  1. ↑ a b c d e f NASA/IPAC EXTRAGALACTIC DATABASE
  2. ↑ a b c d SEDS: NGC 247
  3. ↑ NASA/IPAC
  4. ↑ W. Gieren et al.: The Araucaria Project. The Distance to the Sculptor Galaxy NGC 247 from Near-Infrared Photometry of Cepheid Variables. 16. Mai 2009, arxiv:0905.2699.
  5. ↑ Seligman

Auf dieser Seite verwendete Medien

Caldwell Catalogue.jpg
Autor/Urheber: Roberto Mura, Lizenz: CC BY-SA 3.0
Caldwell Catalogue objects.
GALEX-NGC247.jpg
This image of the dwarf spiral galaxy NGC 247 was taken by Galaxy Evolution Explorer on October 13, 2003, in a single orbit exposure of 1600 seconds. The region that looks like a "hole" in the upper part of the galaxy is a location with a deficit of gas and therefore a lower star formation rate and ultraviolet brightness. Optical images of this galaxy show a bright star on the southern edge. This star is faint and red in the Galaxy Evolution Explorer ultraviolet image, revealing that it is a foreground star in our Milky Way galaxy. The string of background galaxies to the North-East (upper left) of NGC 247 is 355 million light years from our Milky Way galaxy whereas NGC 247 is a mere 9 million light years away. The faint blue light that can be seen in the Galaxy Evolution Explorer image of the upper two of these background galaxies may indicate that they are in the process of merging together.
NGC 247 - Potw1640a.tif
(c) ESA/Hubble, CC BY 4.0

The centre of NGC 247

This Hubble image shows the central region of a spiral galaxy known as NGC 247. NGC 247 is a relatively small spiral galaxy in the southern constellation of Cetus (The Whale). Lying at a distance of around 11 million light-years from us, it forms part of the Sculptor Group, a loose collection of galaxies that also contains the more famous NGC 253 (otherwise known as the Sculptor Galaxy).

NGC 247’s nucleus is visible here as a bright, whitish patch, surrounded by a mixture of stars, gas and dust. The dust forms dark patches and filaments that are silhouetted against the background of stars, while the gas has formed into bright knots known as H II regions, mostly scattered throughout the galaxy’s arms and outer areas.

This galaxy displays one particularly unusual and mysterious feature — it is not visible in this image, but can be seen clearly in wider views of the galaxy, such as this picture from ESO’s MPG/ESO 2.2-metre telescope. The northern part of NGC 247’s disc hosts an apparent void, a gap in the usual swarm of stars and H II regions that spans almost a third of the galaxy’s total length.

There are stars within this void, but they are quite different from those around it. They are significantly older, and as a result much fainter and redder. This indicates that the star formation taking place across most of the galaxy’s disc has somehow been arrested in the void region, and has not taken place for around one billion years. Although astronomers are still unsure how the void formed, recent studies suggest it might have been caused by gravitational interactions with part of another galaxy.

Credit:

ESA/Hubble & NASA 

Coordinates
Position (RA):	0 47 10.46
Position (Dec): -20° 46' 6.67"
Field of view:	3.41 x 3.16 arcminutes
Orientation:	North is 80.6° right of vertical 

Colours & filters Band	Wavelength	Telescope
Optical B	475 nm	Hubble Space Telescope ACS
Optical V	606 nm	Hubble Space Telescope ACS
Infrared I	814 nm	Hubble Space Telescope ACS
.
Wide Field Imager view of the spiral galaxy NGC 247.jpg
Autor/Urheber: ESO, Lizenz: CC BY 4.0
This picture of the spiral galaxy NGC 247 was taken using the Wide Field Imager (WFI) at ESO’s La Silla Observatory in Chile. NGC 247 is thought to lie about 11 million light-years away in the constellation of Cetus (The Whale). It is one of the closest galaxies to the Milky Way and a member of the Sculptor Group. 
Coordinates
Position (RA):	0 47 1.99
Position (Dec):	-20° 44' 45.83"
Field of view:	33.77 x 21.00 arcminutes
Orientation:	North is 90.0° right of vertical

Colours & filters
Band	Telescope
Optical B	MPG/ESO 2.2-metre telescope WFI
Optical V	MPG/ESO 2.2-metre telescope WFI
Optical H-alpha	MPG/ESO 2.2-metre telescope WFI
Optical R	MPG/ESO 2.2-metre telescope WFI
.