Messier 108

Messier 108 (also known as NGC 3556, nicknamed the Surfboard Galaxy<ref name = guide/>) is a barred spiral galaxy about 46 million light-years away from Earth<ref name="Sorce2014" /><ref>Template:Cite web</ref> in the northern constellation Ursa Major. It was discovered by Pierre Méchain in 1781 or 1782.<ref name="NSOG">Template:Cite book</ref> From the Earth, this galaxy is seen almost edge-on.

This galaxy is an isolated<ref name="wang">Template:Cite journal</ref> member of the Ursa Major Cloud of galaxies in the local supercluster.<ref>Template:Cite book</ref> 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.<ref name="aaa54">Template:Cite journal</ref>

This galaxy has an estimated mass of 125 billion solar masses (Template:Solar mass)<ref name="Rhode" />Template:Refn and bears about 290 ± 80 globular clusters.<ref name="Rhode">Template:Cite journal</ref> 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.<ref>Template:Cite journal</ref>

Observations with the Chandra X-ray Observatory have identified 83 X-ray sources, including a source at the nucleus. The brightest of these is consistent with an intermediate-mass black hole accreting matter. The galaxy is also emitting a diffuse soft X-ray radiation within 2.6 arcminutes of the optical galaxy.<ref name="wang" />Template:Refn The spectrum of the source at the core is consistent with an active galactic nucleus, but an examination with the Spitzer Space Telescope showed no indication of activity. The supermassive black hole at the core has an estimated mass of 24 million solar masses (Template:Solar mass).<ref>Template:Cite journal</ref>

Supernovae

Three supernovae have been observed in M108:

• SN 1969B (type unknown, mag. 16) was discovered by Paul Wild on 6 February 1969,<ref>Template:Cite web</ref> and independently by Balázs on 10 February 1969.<ref>Template:Cite web</ref><ref>Template:Cite web</ref> It reached a brightness of mag. 13.9.<ref name = guide>Template:Cite web</ref>
• 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.<ref>Template:Cite journal</ref>
• SN 2023dbc (Type Ic, mag. 17) was discovered by the Zwicky Transient Facility on 13 March 2023.<ref>Template:Cite web</ref> 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.<ref name="AstroNote2023-66">Template:Cite web</ref>

Location of M108

See also

• List of Messier objects
• NGC 2403 - a similar spiral galaxy
• NGC 4631 - a similar spiral galaxy
• NGC 7793 - a similar spiral galaxy

External links

• SEDS: Spiral Galaxy M108
• Template:WikiSky