TheOwl Nebula (also known asMessier 97,M97 orNGC 3587) is aplanetary nebula approximately 2,030light years away in theconstellationUrsa Major.[2] Estimated to be about 8,000 years old,[6] it is approximately circular in cross-section with a faint internal structure. It was formed from the outflow of material from thestellar wind of the centralstar as it evolved along theasymptotic giant branch.[5] The nebula is arranged in three concentric shells, with the outermost shell being about 20–30% larger than the inner shell.[7] The owl-like appearance of the nebula is the result of an inner shell that is not circularly symmetric, but instead forms a barrel-like structure aligned at an angle of 45° to the line of sight.[5]
The nebula holds about 0.13solar masses (M☉) of matter, including hydrogen, helium, nitrogen, oxygen, and sulfur;[5] all with a density of less than 100 particles per cubic centimeter.[7] Its outer radius is around 0.91 ly (0.28 pc) and it is expanding with velocities in the range of 27–39km/s into the surroundinginterstellar medium.[5]
The Owl Nebula was discovered byFrenchastronomerPierre Méchain on February 16, 1781.[8] Pierre Méchain wasCharles Messier's observing colleague, and the nebula was observed by Messier himself a few weeks following the initial sighting.[11] Thus, the object was named Messier 97, and included in hiscatalog on March 24, 1781.[12] Of the object, he noted:[13][14][15][16]
Nebula in thegreat Bear, near Beta: It is difficult to see, reportsM. Méchain, especially when one illuminates the micrometer wires: its light is faint, without a star. M. Méchain saw it the first time on Feb 16, 1781, & the position is that given by him. Near this nebula he has seen another one, [the position of] which has not yet been determined[Messier 108], and also a third which is nearGamma of the Great Bear[Messier 109]. (diam. 2′).
In 1844,Admiral William H. Smyth classified the object as aplanetary nebula.[12][17] WhenWilliam Parsons, 3rd Earl of Rosse, observed the nebula inIreland in 1848, his hand-drawn illustration resembled anowl's head. In his notes, the object was described as "Twostars considerably apart in the central region, darkpenumbra round each spiral arrangement, with stars as apparent centres of attraction. Stars sparkling in it; resolvable."[18][19] It has been known as the Owl Nebula ever since.[20] More recent developments in the late 1900s include the discovery of a giant red halo of wind extended around its inner shells,[21] and the mapping of the nebula's structure.[17][22][23]
Although the Owl Nebula can not be seen with the naked eye, a faint image of it can be observed under remarkably good conditions with a small telescope or 20×80 binoculars. To make out the nebula's more distinctive owl like eye features, a telescope with an aperture 10" or better is required. To locate the nebula in the night sky, look to the southwest corner of theBig Dipper's bowl, marked by the starBeta Ursae Majoris. From there, M97 lies just over 2.5 degrees in the southeast direction towards the star positioned opposite Beta Ursae Majoris in the other bottom corner of theBig Dippers Bowl,Gamma Ursae Majoris; which marks the constellations southwest corner. M97, together withAlpha Ursae Majoris, point the way toPolaris.[24]
^abKerber, F.; et al. (September 2003), "Galactic Planetary Nebulae and their central stars. I. An accurate and homogeneous set of coordinates",Astronomy and Astrophysics,408 (3):1029–1035,Bibcode:2003A&A...408.1029K,doi:10.1051/0004-6361:20031046.
^Per Guerrero et al. (2003), the age is 12,900 ×d years, whered is the distance in kpc. According to Stanghellini et al. (2008),d is 0.621 kpc. Hence, the age is 12,900 × 0.621 ≈ 8,000 years.
^Capriotti, Eugene R.; Kovach, William S. (March 1968), "Effective Temperatures of the Central Stars of Planetary Nebulae",Astrophysical Journal,151 (5):991–995,Bibcode:1968ApJ...151..991C,doi:10.1086/149498.
^Manchado, A.; Guerrero, M.; Kwitter, K. B.; Chu, Y.-H. (December 1992). "A Halo of Red Giant Wind around the Owl Nebula".AAS.181: 67.04.Bibcode:1992AAS...181.6704M.
^O'Meara, Stephen James, 1956- (2007).Steve O'Meara's Herschel 400 observing guide : how to find and explore 400 star clusters, nebulae, and galaxies discovered by William and Caroline Herschel. Cambridge: Cambridge University Press.ISBN978-0-521-85893-9.OCLC85829276.{{cite book}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
^Nasim, Omar W., 1976- (6 January 2014).Observing by hand : sketching the nebulae in the nineteenth century. Chicago: University of Chicago Press.ISBN978-0-226-08440-4.OCLC868276095.{{cite book}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
^García-Díaz, Ma. T. Steffen, W. Henney, W. J. López, J. A. García-López, F. González-Buitrago, D. Aviles, A. (2018-06-12).The Owl and other strigiform nebulae: multipolar cavities within a filled shell.OCLC1098137978.{{cite book}}: CS1 maint: multiple names: authors list (link)
