Pinwheel Galaxy

The Pinwheel Galaxy (also known as Messier 101, M101 or NGC 5457) is a face-on spiral galaxy distanced 21 million light-years (six megaparsecs)[3] away from Earth in the constellation Ursa Major. It was discovered by Pierre Méchain on March 27, 1781 and was communicated to Charles Messier, who verified its position for inclusion in the Messier Catalogue as one of its final entries.

For other uses, see Pinwheel Galaxy (disambiguation).
Pinwheel Galaxy
The Pinwheel Galaxy, as taken by Hubble Space Telescope
Observation data (J2000 epoch)
ConstellationUrsa Major
Right ascension 14h 03m 12.6s
Declination+54° 20′ 57″
Redshift0.000804
Helio radial velocity241 ± 2 km/s
Distance20.9 ± 1.8 Mly (6.4 ± 0.5 Mpc)
Apparent magnitude (V)7.86
Characteristics
TypeSAB(rs)cd
Number of stars1 trillion (1012)
Size~170,000 ly in diameter[1]
Apparent size (V)28′.8 × 26′.9
Other designations
Messier 101, M101, NGC 5457, UGC 8981, PGC 50063, Arp 26
References: [2][3][4][5][6][7]

On February 28, 2006, NASA and the European Space Agency released a very detailed image of the Pinwheel Galaxy, which was the largest and most detailed image of a galaxy by Hubble Space Telescope at the time.[8] The image was composed of 51 individual exposures, plus some extra ground-based photos.

On August 24, 2011, a Type Ia supernova, SN 2011fe, was discovered in M101.

Discovery

Pierre Méchain, the discoverer of Messier 101, described it as a "nebula without star, very obscure and pretty large, 6' to 7' in diameter, between the left hand of Bootes and the tail of the great Bear. It is difficult to distinguish when one lits the [grating] wires."[9]

William Herschel noted in 1784 that "...in my 7, 10, and 20-feet [focal length] reflectors shewed a mottled kind of nebulosity, which I shall call resolvable; so that I expect my present telescope will, perhaps, render the stars visible of which I suppose them to be composed."[9]

Lord Rosse observed M101 in his 72-inch diameter Newtonian reflector during the second half of the 19th century. He was the first to make extensive note of the spiral structure and made several sketches.[9]

To observe the spiral structure in modern instruments requires a fairly large instrument, very dark skies, and a low power eyepiece.[10]

Structure and composition
M101 - combined infrared, visible, and x-ray images.

M101 is a large galaxy, with a diameter of 170,000 light-years. By comparison, the Milky Way has a diameter of 100,000[11] light years. It has around a trillion stars, twice the number in the Milky Way.[12] It has a disk mass on the order of 100 billion solar masses, along with a small central bulge of about 3 billion solar masses.[13]

M101 has a high population of H II regions, many of which are very large and bright. H II regions usually accompany the enormous clouds of high density molecular hydrogen gas contracting under their own gravitational force where stars form. H II regions are ionized by large numbers of extremely bright and hot young stars; those in M101 are capable of creating hot superbubbles.[14] In a 1990 study, 1264 H II regions were cataloged in the galaxy.[15] Three are prominent enough to receive New General Catalogue numbers - NGC 5461, NGC 5462, and NGC 5471.[16]

M101 is asymmetrical due to the tidal forces from interactions with its companion galaxies. These gravitational interactions compress interstellar hydrogen gas, which then triggers strong star formation activity in M101's spiral arms that can be detected in ultraviolet images.[17]

In 2001, the x-ray source P98, located in M101, was identified as an ultra-luminous X-ray source - a source more powerful than any single star but less powerful than a whole galaxy - using the Chandra X-ray Observatory. It received the designation M101 ULX-1. In 2005, Hubble and XMM-Newton observations showed the presence of an optical counterpart, strongly indicating that M101 ULX-1 is an x-ray binary.[18] Further observations showed that the system deviated from expected models - the black hole is just 20 to 30 solar masses, and consumes material (including captured stellar wind) at a higher rate than theory suggests.[19]

It is estimated that M101 has about 150 globular clusters[20], the same as the number of the Milky Way's globular clusters.

Companion galaxies

M101 has six prominent companion galaxies: NGC 5204, NGC 5474, NGC 5477, NGC 5585, UGC 8837 and UGC 9405.[21] As stated above, the gravitational interaction between M101 and its satellites may have triggered the formation of the grand design pattern in M101. M101 has also probably distorted the companion galaxy NGC 5474.[21] M101 and its companion galaxies comprise most or possibly all of the M101 Group.[22][23][24][25]

Supernovae
M101 - noting Type Ia supernova SN 2011fe.

On August 24, 2011, a Type Ia supernova, SN 2011fe, initially designated PTF 11kly, was discovered in M101. The supernova was visual magnitude 17.2 at discovery and reached magnitude 9.9 at its peak.[26][27][28] This was the fourth supernova recorded in M101. The first, SN 1909A, was discovered by Max Wolf in January 1909 and reached magnitude 12.1. SN 1951H reached magnitude 17.5 in September 1951 and SN 1970G reached magnitude 11.5 in January 1970.[29]

On February 10, 2015, a luminous red nova, known as M101 OT2015-1 was discovered in the Pinwheel Galaxy.[30]

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See also
  • Messier 74 – a similar face-on spiral galaxy
  • Messier 83 – a similar face-on spiral galaxy that is sometimes called the Southern Pinwheel Galaxy
  • Messier 99 – a similar face-on spiral galaxy
  • Triangulum Galaxy – another galaxy sometimes called the Pinwheel Galaxy

References
  1. NASA Content Administrator, ed. (31 May 2012). "The Pinwheel Galaxy". NASA. Retrieved 4 March 2017.
  2. "NED results for object MESSIER 101". NASA/IPAC Extragalactic Database. Retrieved 2006-12-06.
  3. Shappee, Benjamin; Stanek, Kris (June 2011). "A New Cepheid Distance to the Giant Spiral M101 Based on Image Subtraction of Hubble Space Telescope/Advanced Camera for Surveys Observations". Astrophysical Journal. 733 (2): 124. arXiv:1012.3747. Bibcode:2011ApJ...733..124S. doi:10.1088/0004-637X/733/2/124.
  4. 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.
  5. "Distance Results for Messier 101". NASA/IPAC Extragalactic Database. Retrieved 2010-05-01.
  6. "M 101". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2009-11-29.
  7. Armando, Gil de Paz; Boissier; Madore; Seibert; et al. (2007). "The GALEX Ultraviolet Atlas of Nearby Galaxies". Astrophysical Journal Supplement. 173 (2): 185–255. arXiv:astro-ph/0606440. Bibcode:2007ApJS..173..185G. doi:10.1086/516636.
  8. "Hubble's Largest Galaxy Portrait Offers a New High-Definition View". NASA. 28 February 2006. Retrieved 4 February 2018.
  9. Hartmut Frommert. "Messier 101". SEDS Messier Database. Retrieved 4 March 2018.
  10. "M 101". Messier Objects Mobile — Charts, Maps & Photos. 2016-10-11. Retrieved 4 March 2018.
  11. Shappee, Benjamin J.; Stanek, K. Z. (2018). "Evidence for an Intermediate-Mass Milky Way from Gaia DR2 Halo Globular Cluster Motions". The Astrophysical Journal. 873 (2): 118. arXiv:1804.11348. doi:10.3847/1538-4357/ab089f.
  12. Plait, Phil (2006-02-28). "Hubble delivers again: M101". Slate. ISSN 1091-2339. Retrieved 2018-05-04.
  13. Comte, G.; Monnet, G. & Rosado, M. (1979). "An optical study of the galaxy M 101 - Derivation of a mass model from the kinematic of the gas". Astronomy and Astrophysics. 72: 73–81. Bibcode:1979A&A....72...73C.
  14. Immler, Stefan & Wang, Q. Daniel (2001). "ROSAT X-Ray Observations of the Spiral Galaxy M81". The Astrophysical Journal. 554 (1): 202. arXiv:astro-ph/0102021. Bibcode:2001ApJ...554..202I. doi:10.1086/321335.
  15. Hodge, Paul W.; Gurwell, Mark; Goldader, Jeffrey D.; Kennicutt, Robert C., Jr. (August 1990). "The H II regions of M101. I - an atlas of 1264 emission regions". Astrophysical Journal Supplement Series. 73: 661–670. Bibcode:1990ApJS...73..661H. doi:10.1086/191483.
  16. Giannakopoulou-Creighton, J.; Fich, M.; Wilson, C. D. (1999). "Star formation in the giant HII regions of M101". The Astrophysical Journal. 522 (1): 238–249. arXiv:astro-ph/9903334. Bibcode:1999ApJ...522..238G. doi:10.1086/307619.
  17. Waller, William H.; Bohlin, Ralph C.; Cornett, Robert H.; Fanelli, Michael N.; et al. (20 May 1997). "Ultraviolet Signatures of Tidal Interaction in the Giant Spiral Galaxy M101". The Astrophysical Journal. 481 (1): 169. arXiv:astro-ph/9612165. Bibcode:1997ApJ...481..169W. doi:10.1086/304057.
  18. Kuntz, K.D.; et al. (10 February 2005). "The Optical Counterpart of M101 ULX-1". The Astrophysical Journal. 620 (1): L31–L34. Bibcode:2005ApJ...620L..31K. doi:10.1086/428571. hdl:2060/20050123916.
  19. Liu, Jifeng; Bregman, Joel N.; Bai, Yu; Justham, Stephen; et al. (2013). "Puzzling accretion onto a black hole in the ultraluminous X-ray source M101 ULX-1". Nature. 503 (7477): 500–3. arXiv:1312.0337. Bibcode:2013Natur.503..500L. doi:10.1038/nature12762. PMID 24284727.
  20. Chandar, Rupali; Whitmore, Bradley; Lee, Myung Gyoon (2004-08-10). "The Globular Cluster Systems of Five Nearby Spiral Galaxies: New Insights fromHubble Space TelescopeImaging". The Astrophysical Journal. 611 (1): 220–244. doi:10.1086/421934. ISSN 0004-637X.
  21. A. Sandage; J. Bedke (1994). Carnegie Atlas of Galaxies. Carnegie Institution of Washington. ISBN 978-0-87279-667-6.
  22. R. B. Tully (1988). Nearby Galaxies Catalog. Cambridge University Press. ISBN 978-0-521-35299-4.
  23. P. Fouque; E. Gourgoulhon; P. Chamaraux; G. Paturel (1992). "Groups of galaxies within 80 Mpc. II – The catalogue of groups and group members". Astronomy and Astrophysics Supplement (2nd ed.). 93: 211–233. Bibcode:1992A&AS...93..211F.
  24. A. Garcia (1993). "General study of group membership. II – Determination of nearby groups". Astronomy and Astrophysics Supplement. 100: 47–90. Bibcode:1993A&AS..100...47G.
  25. Giuricin, G.; Marinoni, C.; Ceriani, L.; Pisani, A. (2000). "Nearby Optical Galaxies: Selection of the Sample and Identification of Groups". Astrophysical Journal. 543 (1): 178–194. arXiv:astro-ph/0001140. Bibcode:2000ApJ...543..178G. doi:10.1086/317070.
  26. Nugent, Peter; et al. (24 August 2011). "Young Type Ia Supernova PTF11kly in M101". The Astronomer's Telegram. 3581: 1. Bibcode:2011ATel.3581....1N. Retrieved 25 August 2011.
  27. Nugent, Peter; et al. "Supernova Caught in the Act". Retrieved 7 September 2011.
  28. Hartmut Frommert & Christine Kronberg (15 Sep 2011). "Supernova 2011fe in M101". Retrieved 17 Sep 2011.
  29. Stoyan, Ronald Atlas of the Messier Objects, Cambridge University Press 2008 page 329
  30. "Transient object followup reports". Central Bureau for Astronomical Telegrams.

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