NGC 613 is abarred spiral galaxy located 67 millionlight years away in the southernconstellation ofSculptor.[6][9] The galaxy was discovered by German-English astronomerWilliam Herschel on 9 December 1798, then re-discovered and catalogued by Scottish astronomerJames Dunlop on 5 August 1826.[10][11] It was first photographed in 1912, which revealed the spiral form of the nebula.[7] During the twentieth century,radio telescope observations showed that a linear feature in the nucleus was a relatively strong source of radio emission.[12]
Hubble image of NGC 613 showing the prominent bar and loosely wound arms[13]
NGC 613 is inclined by an angle of 37° to theline of sight from theEarth along aposition angle of 125°.[14] Themorphological classification of NGC 613 is SBbc(rs),[15] indicating that it is a spiral galaxy with a bar across the nucleus (SB), a weak inner ring structure circling the bar (rs), and moderate to loosely wound spiral arms (bc).[16] The bar is relatively broad but irregular in profile with a position angle that varies from 115–124° and dust lanes located along the leading edges. Star formation is occurring at the ends of the bar and extending along the well-defined spiral arms. The central bulge is readily apparent, with a radius of 14″.[14]
The classification of the nucleus is of type HII, indicating a match to the spectrum of anH II region. Near the core, the stars have avelocity dispersion of 136 ± 20 km/s. The nucleus is a source of radio emission with the form of an inner ring with a radius of about 1,100 ly (350 pc) and a linear feature that is perhaps perpendicular to it. The latter consists of three discrete blobs spanning approximately 2,000 ly (600 pc).[17] Observations suggest the presence of asupermassive black hole at the core with a mass in the range(1.9–9.6) × 107 times themass of the Sun.[15]
On September 20, 2016, Argentinian amateur astronomer Victor Buso capturedsupernova SN 2016gkg in NGC 613, just as it was starting to erupt.[18][19] This was a Type IIb supernova, a supernova that initially shows a hydrogen envelope like aType II supernova,[18] but later loses the hydrogen lines in its spectrum to appear like aType Ib supernova. It showed the double peak that is common to many Type IIb supernovae, rising to aroundmagnitude 15.5 shortly after discovery and then again about 20 days later. The progenitor star has been identified inHubble Space Telescope images from before its collapse, and it is likely to have been ayellow supergiant.[20]
^Hummel, E.; et al. (January 1987), "The central region of NGC 613. Evidence for an accelerated collimated outflow",Astronomy and Astrophysics,172 (1–2):51–54,Bibcode:1987A&A...172...51H.
^abBaumgart, C. W.; Peterson, C. J. (January 1986), "Near-infrared surface photometry of barred spiral galaxies",Publications of the Astronomical Society of the Pacific,98:56–69,Bibcode:1986PASP...98...56B,doi:10.1086/131721.
