|Designation|| Messier 97|
|Right ascension||11h 14m 47.734s|
|Declination||+55° 01′ 08.50″|
|Type of object||Planetary nebula|
|Magnitude||Apparent Mag: +9.9 Absolute Mag: +0.9|
|Distance from Earth||2,030 ly|
|Radial velocity||0±3 km/s|
|Proper motion|| RA: -3 mas/yr|
Dec.: 11 mas/yr
The Owl nebula (M97, NGC 3867) is a planetary nebula in the constellation of Ursa Major, the Great bear. Discovered in 1781 by Pierre Méchain, it is one of the four planetary nebulae in the Messier catalogue. The Owl nebula is located a couple of degrees from the brightest star in the Big Dipper, Merak. It was named the "Owl nebula" due to its resemblance of a circular face with two large eyes. A similar looking nebula can be seen in the Southern Hemisphere and is known as the Southern Owl nebula. It is one of the faintest Messier objects and regarded as one of the most complex planetary nebulae known.
The nebula was discovered by a French astronomer, Pierre Méchain, on February 16, 1781. Méchain later informed Charles Messier of his discovery, who then added it to his catalogue. Messier's description of M97 includes descriptions of two other deep sky objects. These two galaxies were retroactively added to Messier's catalogue after his death as Messier 108 and Messier 109 by Owen Gingerich in 1953. Admiral William Henry Smyth was the first person to identify the Owl nebula as a planetary nebula in 1837. William Parsons the 3rd Earl of Rosse (sometimes referred to as Lord Rosse) gave the nebula its common name, the "Owl nebula". The gaseous envelope surrounding central star was first noticed by William Huggins in his study of the nebula's spectrum.
Properties and Structure
The nebula distance of some 2,030 light years means its apparent size of 3.4x3.3 arc minutes corresponds to a physical radius of 0.91 ly. There is great uncertainty in the exact distance to the nebula, with distances varying from 1,300 to 12,000 light years. The gaseous component of the nebula has a mass estimated to be around 0.13-0.15 solar masses, though estimates vary, and is currently expanding at a rate somewhere between 27–39 km/s The nebula is notably brighter than other planetary nebula, such as the Ring nebula of the Little dumbbell nebula.
Spectrums of the nebula have shown it contains a variety of different elements, including: hydrogen, helium, nitrogen, oxygen and sulfur. The density of particles within the nebula is believed to be around 100 particles per cubic centimetre.
The structure of the nebula is thought to be a torus (doughnut). The nebula is enclosed by another nebula with a lower ionization and so fainter. The "eyes" of the nebula are believed to be due to two jets of matter that point in opposing directions, one towards and one away. Their axis is nearly aligned with us, but not quite. The extra matter in these jets results in less light reaching us from these regions meaning they appear darker. The jets are symmetrical around their axis, so it results in two dark circular patches on the nebula and hence the "eyes."
Like most planetary nebulae, there is a white dwarf star situated at its centre. Thought to have a mass of 0.7 solar masses, it has an estimated temperature of around 123,000 k and a radius 4% that of the Sun. The star is 41-148 brighter than the Sun, but the nebula's great distance from Earth means it appears as a star of the 16th magnitude.