This galaxy is an isolated[9] member of the Ursa Major Cluster of galaxies in the local supercluster. It has a morphological classification of type SBbc in the de Vaucouleurs system, which means it is a barred spiral galaxy with somewhat loosely wound arms. The maximum angular size of the galaxy in the optical band is 11′.1 × 4′.6, and it is inclined 75° to the line of sight.[5]
This galaxy has an estimated mass of 125 billion solar masses (M☉)[10][note 1] and bears about 290 ± 80 globular clusters.[10] Examination of the distribution of neutral hydrogen in this galaxy shows discrete shells of expanding gas extending for several kiloparsecs, known as H1 supershells. These may be driven by currents of dark matter, dust and gas contributing to large star formation, having caused supernovae explosions. Alternatively they may result from an infall from the intergalactic medium or arise from radio jets.[11]
SN 1969B (type unknown, mag. 16) was discovered by Paul Wild on 6 February 1969.[13][14] It reached a brightness of mag. 13.9.[6]
SPIRITS 16tn was discovered by the Spitzer Space Telescope in August 2016. The supernova was only visible in infrared light, because it was heavily obscured by dust. Its extinction was estimated to be 8–9 mag, making it one of the most heavily obscured supernovae ever observed.[15]
SN 2023dbc (Type Ic, mag. 17) was discovered by the Zwicky Transient Facility on 13 March 2023.[16] 2023dbc is likely a stripped-envelope supernova as there is no evidence for hydrogen in these spectra beyond narrow emission associated with the underlying HII region. It is among the nearest type Ic supernovae discovered to date.[17]
^Using an assumed distance of 7.1 Megaparsec to Messier 108, based on a 1986 study.[1]
^This is the angular size of the feature as it appears on the sky. The physical size depends on the distance to Messier 108, which is more difficult to measure. At the time of the study that discovered this feature (in 2003),[9] the accepted distance to Messier 108 was based on a 1988 work,[2] which gave a value of 14.1 Megaparsec (Mpc). This has been substantially revised down to 8.8 Mpc in a 2014 study.[3] At 14.1 Mpc, an angular size of 2.6 arcminutes would correspond to a physical size of kpc, or roughly 10 kiloparsec (kpc), which is the value given in the 2003 study. Using the more recent distance estimate, this would be kpc. Compare the list of distance measurements in the NASA/IPAC Extragalactic Database.[2]
^ ab"Messier 108: Surfboard Galaxy". Messier Objects: Guide to the Bright Galaxies, Nebulae and Clusters Listed in the Messier Catalogue. 26 September 2015.
^Marsden, Brian G. (12 February 1969). "Circular No. 2131". Central Bureau for Astronomical Telegrams. Smithsonian Astrophysical Observatory. Retrieved 2 December 2024.
^"SN1969B". Transient Name Server. IAU. Retrieved 2 December 2024.
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