Messier 108

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Galaxy in the constellation Ursa Major

title: "Messier 108" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["barred-spiral-galaxies", "ursa-major", "messier-objects", "ngc-objects", "ugc-objects", "principal-galaxies-catalogue-objects", "astronomical-objects-discovered-in-1781", "discoveries-by-pierre-méchain", "virgo-supercluster", "field-galaxies"] description: "Galaxy in the constellation Ursa Major" topic_path: "science/astronomy" source: "https://en.wikipedia.org/wiki/Messier_108" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Galaxy in the constellation Ursa Major ::

::data[format=table title="Infobox Galaxy"]

FieldValue
nameMessier 108
imageMessier108 - SDSS DR 14 (panorama).jpg
captionA Sloan Digital Sky Survey image of M108.
epochJ2000
constellation nameUrsa Major
typeSB(s)cd
ra
dec
z696.1 ± 0.6 km/s
dist_ly14.1 Mpc (46 Mly)
appmag_v10.0
size_v8′.7 × 2′.2
namesNGC 3556, PGC 34030, UGC 6225
::

| name=Messier 108 | image=Messier108 - SDSS DR 14 (panorama).jpg | caption=A Sloan Digital Sky Survey image of M108. | credit= | epoch=J2000 | constellation name=Ursa Major | type=SB(s)cd | ra= | dec= | z=696.1 ± 0.6 km/s | dist_ly=14.1 Mpc (46 Mly) | appmag_v=10.0 | size_v=8′.7 × 2′.2 | names=NGC 3556, PGC 34030, UGC 6225}}

Messier 108 (also known as NGC 3556, nicknamed the Surfboard Galaxy in the northern constellation Ursa Major. It was discovered by Pierre Méchain in 1781 or 1782. From the Earth, this galaxy is seen almost edge-on.

This galaxy is an isolated member of the Ursa Major Cloud 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.

This galaxy has an estimated mass of 125 billion solar masses () and bears about 290 ± 80 globular clusters. 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.

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. 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 ().

Supernovae

Four supernovae have been observed in M108:

  • SN 1969B (type unknown, mag. 16) was discovered by Paul Wild on 6 February 1969,{{cite journal | url = http://www.cbat.eps.harvard.edu/IAUCs/IAUC2131.jpg | title = SUPERNOVA IN NGC 3556 | last = Wild | first = P. | editor-last = Marsden | editor-first = Brian G. | date = 12 February 1969 | journal = Central Bureau for Astronomical Telegrams | volume = 2131 | pages = 2 | publisher = IAU | access-date = 2 December 2024 | url = http://www.cbat.eps.harvard.edu/IAUCs/IAUC2134.jpg | title = SUPERNOVAE | last1 = Detre | first1 = Dr. L. | last2 = Balázs | editor-last = Marsden | editor-first = Brian G. | date = 14 February 1969 | website = Central Bureau for Astronomical Telegrams | volume = 2134 | pages = 1 | publisher = IAU | access-date = 2 August 2025}} It reached a brightness of mag. 13.9.
  • 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.
  • SN 2023dbc (Type Ic, mag. 17) was discovered by the Zwicky Transient Facility on 13 March 2023. 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.
  • SN 2025ahqr ([TypeIax02cx-like], mag. 20.0269) was discovered by the Zwicky Transient Facility on 23 November 2025. It is highly reddened, suggesting that it is strongly extincted by dust. At the time of discovery, it is the closest low luminosity Type Iax supernova known.

::figure[src="https://upload.wikimedia.org/wikipedia/commons/2/29/M108map.png" caption="Location of M108"] ::

Notes

References

References

  1. (1988). "The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer". [[Sky Publishing Corporation]]/[[Cambridge University Press]].
  2. "NASA/IPAC Extragalactic Database". Results for NGC 3556.
  3. Sorce, J. G.. (2014). "From Spitzer Galaxy photometry to Tully–Fisher distances". [[Monthly Notices of the Royal Astronomical Society]].
  4. "Messier 108".
  5. "Messier 108".
  6. Kepple, George Robert. (1998). "The Night Sky Observer's Guide". [[Willmann-Bell]].
  7. Wang, Q. Daniel. (2003). "Chandra Observation of the Edge-on Galaxy NGC 3556 (M 108): Violent Galactic Disk-halo Interaction Revealed". The Astrophysical Journal.
  8. Tully, R. Brent. (1988). "Nearby galaxies catalog". Cambridge University Press.
  9. Tully, R. B.. (1977). "A new method of determining distances to galaxies". [[Astronomy and Astrophysics]].
  10. Rhode, Katherine L.. (2007). "Global Properties of the Globular Cluster Systems of Four Spiral Galaxies". [[Astronomical Journal]].
  11. Gopal-Krishna. (2000). "Radio jet-blown neutral hydrogen supershells in spiral galaxies?". [[Astronomy and Astrophysics]].
  12. Satyapal, S.. (2008). "Spitzer Uncovers Active Galactic Nuclei Missed by Optical Surveys in Seven Late-Type Galaxies". [[Astrophysical Journal]].
  13. "SN{{nbsp}}1969B". [[International Astronomical Union.
  14. (26 September 2015). "Messier 108: Surfboard Galaxy". Messier Objects: Guide to the Bright Galaxies, Nebulae and Clusters Listed in the Messier Catalogue.
  15. Jencson, Jacob E.. (2018). "SPIRITS 16tn in NGC 3556: A Heavily Obscured and Low-luminosity Supernova at 8.8 Mpc". [[The Astrophysical Journal]].
  16. "SN 2023dbc". [[International Astronomical Union.
  17. (2023). "Spectroscopic Classification of SN 2023dbc as a Highly Extinguished Stripped-Envelope Supernova". Transient Name Server Astronote.
  18. "SN 2025ahqr". [[International Astronomical Union.
  19. (2025). "Discovery and classification of SN 2025ahqr, a highly reddened low luminosity Type Iax in M108 (9 Mpc)". Transient Name Server Astronote.

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