The Owl Nebula
The Owl Nebula or Messier 97 (NGC 3587) is a planetary nebula located approximately 2,600 light-years away toward the bottom of the Big Dipper’s bowl in the constellation Ursa Major. It lies about 2.3 degrees to the east-southeast of the star Merak, Beta Ursae Majoris, just south of the line from Merak to Phecda, Gamma Ursae Majoris, the other star marking the bottom of the Dipper’s bowl. It was discovered by French astronomer Pierre Méchain on February 16, 1781. When William Parsons, 3rd Earl of Rosse, observed the nebula in 1848, his hand-drawn illustration resembled an owl’s head with two large dark eyes. It has been known as the Owl Nebula ever since
The nebula is arranged in three concentric shells, with the outermost shell being about 20–30% larger than the inner shell. 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. The nebula holds about 0.13 solar masses of matter, including hydrogen, helium, nitrogen, oxygen, and sulfur. Its outer radius is around 0.91 light years and it is expanding with velocities in the range of 27–39 km/s into the surrounding interstellar medium. The 14th magnitude central star (+9.9) has since reached the turning point of its evolution where it condenses to form a white dwarf. It has 55–60% of the Sun’s mass, 41–148 times the brightness of the Sun, and an effective temperature of 123,000 K.
Most stars that expel material to form planetary nebulae – about 80 percent of them – expel a large amount of it in two opposing directions. The jets blown off by the progenitor star of the Owl Nebula are almost aligned with our line of sight. The dust within the jets blocks enough light from the expanding nebula to create the appearance of owl-like eyes. One of the nebula’s eyes appears darker than the other. This is the jet that is emitted in our direction, while the fainter eye marks the jet expelled in the opposite direction, away from us. The nebula will gradually disperse over the next several thousand years, while the central white dwarf will cool and fade away. In about 5 billion years, our Sun will end its life in similar fashion.
Credits: NASA, Wikipedia.