Pinwheel Galaxy

Coordinates: Sky map 14h 03m 12.6s, +54° 20′ 57″
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Pinwheel Galaxy
The Pinwheel Galaxy, as taken by Hubble Space Telescope
Observation data (J2000 epoch)
ConstellationUrsa Major
Right ascension14h 03m 12.6s
Declination+54° 20′ 57″
Heliocentric radial velocity241 ± 2 km/s
Distance20.9 ± 1.8 Mly (6.4 ± 0.5 Mpc)
Apparent magnitude (V)7.9[1]
Number of stars1 trillion (1012)
Size51.91 kpc (169,300 ly)
(diameter; 25.0 mag/arcsec2 B-band isophote)[2][3]
Apparent size (V)28′.8 × 26′.9
Other designations
Messier 101, M101, NGC 5457, UGC 8981, PGC 50063, Arp 26
References: [4][5][6][7][8][9]
Dark sky image with some objects around Pinwheel Galaxy (M 101). The quarter in the lower right shows the tail of Ursa Major with the stars Mizar, Alcor and Alkaid.

The Pinwheel Galaxy (also known as Messier 101, M101 or NGC 5457) is a face-on spiral galaxy located 21 million light-years (6.4 megaparsecs)[5] from Earth in the constellation Ursa Major. It was discovered by Pierre Méchain in 1781[a] and was communicated that year to Charles Messier, who verified its position for inclusion in the Messier Catalogue as one of its final entries.

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.[10] The image was composed of 51 individual exposures, plus some extra ground-based photos.


Pierre Méchain, the discoverer of the galaxy, 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."[11]

William Herschel wrote in 1784 that the galaxy was one of several which " 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."[11]

Lord Rosse observed the galaxy 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.[11]

Though the galaxy can be detected with binoculars or a small telescope, to observe the spiral structure in a telescope without a camera requires a fairly large instrument, very dark skies, and a low-power eyepiece.[12]

Structure and composition[edit]

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 87,400 light-years.[13] It has around a trillion stars.[14] 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.[15] Its characteristics can be compared to those of Andromeda Galaxy.

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.[16] In a 1990 study, 1,264 H II regions were cataloged in the galaxy.[17] Three are prominent enough to receive New General Catalogue numbers—NGC 5461, NGC 5462, and NGC 5471.[18]

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.[19]

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.[20] 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.[21]

It is estimated that M101 has about 150 globular clusters,[22] the same as the number of the Milky Way's globular clusters.

Companion galaxies[edit]

M101 has six prominent companion galaxies: NGC 5204, NGC 5474, NGC 5477, NGC 5585, UGC 8837 and UGC 9405.[23] As stated above, the gravitational interaction between it and its satellites may have spawned its grand design pattern. The galaxy has probably distorted the second-listed companion.[23] The list comprises most or all of the M101 Group.[24][25][26][27]

Supernovae and luminous red nova[edit]

Six internal supernovae have been recorded:

See also[edit]

  • List of Messier objects
  • Messier 74 – Face-on spiral galaxy in the constellation Pisces – a similar face-on spiral galaxy
  • Messier 83 – Barred spiral galaxy in the constellation Hydra – a similar face-on spiral galaxy that is sometimes called the Southern Pinwheel Galaxy
  • Messier 99 – Spiral galaxy in the constellation Coma Berenices – a similar face-on spiral galaxy
  • Triangulum Galaxy – Spiral galaxy in the constellation Triangulum – another galaxy sometimes called the Pinwheel Galaxy


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  2. ^ De Vaucouleurs, Gerard; De Vaucouleurs, Antoinette; Corwin, Herold G.; Buta, Ronald J.; Paturel, Georges; Fouque, Pascal (1991). Third Reference Catalogue of Bright Galaxies.
  3. ^ NASA Content Administrator, ed. (31 May 2012). "The Pinwheel Galaxy". NASA. Retrieved 4 March 2017.
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  19. ^ 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. S2CID 15360023.
  20. ^ 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.
  21. ^ 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. S2CID 4447299.
  22. ^ 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. arXiv:astro-ph/0407460. Bibcode:2004ApJ...611..220C. doi:10.1086/421934. ISSN 0004-637X.
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  1. ^ on March 27

External links[edit]