# Messier 108

Messier 108
A Sloan Digital Sky Survey image of M108.
Observation data (J2000 epoch)
ConstellationUrsa Major[1]
Right ascension11h 11m 31.0s[2]
Declination+55° 40′ 27″[2]
Redshift696.1 ± 0.6 km/s[2]
Distance8.8 Mpc (28.7 Mly) [3]
Apparent magnitude (V)10.0[4]
Characteristics
TypeSB(s)cd[5]
Apparent size (V)8′.7 × 2′.2[2]
Other designations
NGC 3556,[2] PGC 34030,[2] UGC 6225[2]

Messier 108 (also known as NGC 3556, nicknamed the Surfboard Galaxy[6]) is a barred spiral galaxy about 28 million light-years away from Earth[3] in the northern constellation Ursa Major. It was discovered by Pierre Méchain in 1781 or 1782.[7] From the Earth, this galaxy is seen almost edge-on.

This galaxy is an isolated[8] 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)[9][note 1] and bears about 290 ± 80 globular clusters.[9] 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.[10]

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.[8][note 2] 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 (M).[11]

In January 1969, a type II supernova designated as SN 1969B was discovered in Messier 108. It reached a brightness of 13.9 mag.[6]

SPIRITS 16tn, another supernova in Messier 108, 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.[12]

Location of M108

## Notes

1. ^ Using an assumed distance of 7.1 Megaparsec to Messier 108, based on a 1986 study.[1]
2. ^ 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),[8] 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 ${\displaystyle 2.6/60\cdot \pi /180\cdot 14100=10.7}$ kpc, or roughly 10 kiloparsec (kpc), which is the value given in the 2003 study. Using the more recent distance estimate, this would be ${\displaystyle 2.6/60\cdot \pi /180\cdot 8800=6.7}$ kpc. Compare the list of distance measurements in the NASA/IPAC Extragalactic Database.[2]

## References

1. ^ R. W. Sinnott, ed. (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. ISBN 978-0-933346-51-2.
2. "NASA/IPAC Extragalactic Database". Results for NGC 3556. Retrieved 30 March 2022.
3. ^ a b c Sorce, J. G.; et al. (2014). "From Spitzer Galaxy photometry to Tully–Fisher distances". Monthly Notices of the Royal Astronomical Society. 444 (1): 527–541. doi:10.1093/mnras/stu1450.
4. ^ "Messier 108". SEDS Messier Catalog. Retrieved 30 April 2022.
5. ^ a b Tully, R. B.; Fisher, J. R. (1977). "A new method of determining distances to galaxies". Astronomy and Astrophysics. 54 (3): 661–673. Bibcode:1977A&A....54..661T.
6. ^ a b "Messier 108: Surfboard Galaxy". Messier Objects: Guide to the Bright Galaxies, Nebulae and Clusters Listed in the Messier Catalogue. 26 September 2015.
7. ^ Kepple, George Robert; Glen W. Sanner (1998). The Night Sky Observer's Guide. Vol. 2. Willmann-Bell. p. 399. ISBN 978-0-943396-60-6.
8. ^ a b c Wang, Q. Daniel; et al. (2003). "Chandra Observation of the Edge-on Galaxy NGC 3556 (M 108): Violent Galactic Disk-halo Interaction Revealed". The Astrophysical Journal. 598 (2): 969–981. arXiv:astro-ph/0308150. Bibcode:2003ApJ...598..969W. doi:10.1086/379010. S2CID 49349099.
9. ^ a b Rhode, Katherine L.; et al. (2007). "Global Properties of the Globular Cluster Systems of Four Spiral Galaxies". Astronomical Journal. 134 (4): 1403–1418. arXiv:0708.1166. Bibcode:2007AJ....134.1403R. doi:10.1086/521397. S2CID 15834447.
10. ^ Gopal-Krishna; Irwin, Judith A. (2000). "Radio jet-blown neutral hydrogen supershells in spiral galaxies?". Astronomy and Astrophysics. 361: 888–894. arXiv:astro-ph/0008251. Bibcode:2000A&A...361..888G.
11. ^ Satyapal, S.; et al. (2008). "Spitzer Uncovers Active Galactic Nuclei Missed by Optical Surveys in Seven Late-Type Galaxies". Astrophysical Journal. 677 (2): 926–942. arXiv:0801.2759. Bibcode:2008ApJ...677..926S. doi:10.1086/529014. S2CID 16050838.
12. ^ Jencson, Jacob E.; et al. (2018). "SPIRITS 16tn in NGC 3556: A Heavily Obscured and Low-luminosity Supernova at 8.8 Mpc". The Astrophysical Journal. 863 (1): 20. arXiv:1803.00574. Bibcode:2018ApJ...863...20J. doi:10.3847/1538-4357/aacf8b. hdl:10150/631110. S2CID 56398022.