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Still other nebulae form as planetary nebulae. This is the final stage of a low-mass star's life, like Earth's Sun. Stars with a mass up to 8–10 solar masses evolve into red giants and slowly lose their outer layers during pulsations in their atmospheres.
Planetary nebulae are generally faint objects, and none are visible to the naked eye. The first planetary nebula discovered was the Dumbbell Nebula in the constellation of Vulpecula, observed by Charles Messier in 1764 and listed as M27 in his catalogue of nebulous objects.
1912 — Vesto Slipher's spectrographic studies of spiral nebulae find high Doppler shifts indicating recessional velocity. 1917 — Heber Curtis finds novae in Andromeda Nebula M31 were ten magnitudes fainter than normal, giving a distance estimate of 150,000 parsecs supporting the "island universes" or independent galaxies hypothesis for spiral nebulae.
[2] [35] Every nebula begins with a certain amount of angular momentum. Gas in the central part of the nebula, with relatively low angular momentum, undergoes fast compression and forms a hot hydrostatic (not contracting) core containing a small fraction of the mass of the original nebula. [38] This core forms the seed of what will become a star.
Pre-solar nebula forms and begins to collapse. Sun begins to form. [38] 100,000 – 50 million years 4.6 bya: Sun is a T Tauri protostar. [9] 100,000 – 10 million years 4.6 bya: By 10 million years, gas in the protoplanetary disc has been blown away, and outer planet formation is likely complete. [38] 10 million – 100 million years 4.5–4. ...
Globular Cluster Messier 15, known to have an intermediate black hole and the only globular cluster observed to include a planetary nebula, Pease 1, forms; 2.02 billion years (11.78 Gya): Messier 62 forms – contains high number of variable stars (89) many of which are RR Lyrae stars.
About half the total mass of the Milky Way's galactic ISM is found in molecular clouds [9] and the galaxy includes an estimated 6,000 molecular clouds, each with more than 100,000 M ☉. [10] The nebula nearest to the Sun where massive stars are being formed is the Orion Nebula, 1,300 light-years (1.2 × 10 16 km) away. [11]
The Hubble Space Telescope, the first large optical telescope in orbit, is launched using the Space Shuttle, but astronomers soon discovered that it is crippled by a problem with its mirror. A complex repair mission in 1993 allows the telescope to start producing spectacular images of distant stars, nebulae, and galaxies.