On February 28, 2006,NASA and theEuropean Space Agency released a very detailed image of the Pinwheel Galaxy, which was the largest and most detailed image of a galaxy byHubble 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 illuminates the [grating] wires."[11]
William Herschel wrote in 1784 that the galaxy was one of several which "...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."[11]
Lord Rosse observed the galaxy in his 72-inch-diameterNewtonian 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 withbinoculars 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]
M101 – combined infrared, visible, and X-ray imagesDark sky image with some objects around Pinwheel Galaxy (M 101). The quarter in the lower right shows the tail ofUrsa Major with the starsMizar,Alcor andAlkaid.
M101 is a large galaxy, with a diameter of 252,000 light-years. By comparison, theMilky Way has a diameter of 87,400 light-years.[13] It has around a trillion stars.[4] 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.[14] Its characteristics can be compared to those ofAndromeda Galaxy.
M101 has a high population ofH 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 wherestars form. H II regions are ionized by large numbers of extremely bright and hot young stars; those in M101 are capable of creating hotsuperbubbles.[15] In a 1990 study, 1,264 H II regions were cataloged in the galaxy.[16] Three are prominent enough to receiveNew General Catalogue numbers—NGC 5461, NGC 5462, and NGC 5471.[17]
M101 is asymmetrical due to the tidal forces from interactions with its companion galaxies. These gravitational interactions compressinterstellar hydrogen gas, which then triggers strongstar formation activity in M101's spiral arms that can be detected in ultraviolet images.[18]
In 2001, the X-ray source P98, located in M101, was identified as anultra-luminous X-ray source—a source more powerful than any single star but less powerful than a whole galaxy—using theChandra X-ray Observatory. It received the designation M101 ULX-1. In 2005,Hubble andXMM-Newton observations showed the presence of an optical counterpart, strongly indicating that M101 ULX-1 is anX-ray binary.[19] Further observations showed that the system deviated from expected models—the black hole is just 20 to 30solar masses, and consumes material (including captured stellar wind) at a higher rate than theory suggests.[20]
It is estimated that M101 has about 150globular clusters,[21] the same as the number of theMilky Way's globular clusters.
M101 has six prominent companion galaxies:NGC 5204,NGC 5474,NGC 5477,NGC 5585,UGC 8837 andUGC 9405.[22] 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.[22] The list comprises most or all of theM101 Group.[23][24][25][26]
SN 1909A (type unknown, mag. 10) was discovered byMax Wolf on 21 February 1909.[27][28]
SN 1951H (type unknown, mag. 17.5) was discovered byMilton Humason on a photographic plate taken on 3 February 1951.[29][30] Analysis of the light curve suggested that the supernova was probably of Type II, with maximum magnitude of 11 to 12 occurring around October 1950.[29]
^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.ISBN978-0-933346-51-2.
^abcHartmut Frommert."Messier 101".SEDS Messier Database. Retrieved4 March 2018.
^"M 101".Messier Objects Mobile — Charts, Maps & Photos. 2016-10-11. Archived fromthe original on 2016-11-01. Retrieved4 March 2018.
^Goodwin, S. P.; Gribbin, J.; Hendry, M. A. (August 1998). "The relative size of the Milky Way".The Observatory.118:201–208.Bibcode:1998Obs...118..201G.
^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.
^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.
^"SN1909A".Transient Name Server.IAU. Retrieved25 November 2024.
^abSandage, A.; Tammann, G. A. (1974). "Steps toward the Hubble constant. III. The distance and stellar content of the M101 group of galaxies".The Astrophysical Journal.194: 223.Bibcode:1974ApJ...194..223S.doi:10.1086/153238.
^Stienon, Francis; Wdowiak, Thomas (1971). "The Spectrum of the July 1970 Supernova in M101".Information Bulletin on Variable Stars.505: 1.Bibcode:1971IBVS..505....1S.
