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The Westbrook Nebula, a protoplanetary nebula. A protoplanetary nebula or preplanetary nebula [ 27 ] (PPN, plural PPNe) is an astronomical object which is at the short-lived episode during a star 's rapid evolution between the late asymptotic giant branch (LAGB) [a] phase and the subsequent planetary nebula (PN) phase.
The nebula consists of material ejected from the central star during the asymptotic giant branch stage, beginning about 8,500 years ago. The main nebula was formed at about half that age. [ 7 ] The central star of this planetary nebula is a 17.7- magnitude white dwarf , [ 3 ] with a surface temperature of about 75,000 K (74,700 °C).
The nebula is rich in carbon, and is a very interesting object for the study of carbon chemistry in dense molecular material exposed to strong ultraviolet radiation. [18] The spectrum of NGC 7027 contains fewer spectral lines from neutral molecules than is usual for planetary nebulae.
The Rosette Nebula (also known as Caldwell 49) is an H II region located near one end of a giant molecular cloud in the Monoceros region of the Milky Way Galaxy. The open cluster NGC 2244 (Caldwell 50) is closely associated with the nebulosity, the stars of the cluster having been formed from the nebula's matter.
A molecular cloud, sometimes called a stellar nursery (if star formation is occurring within), is a type of interstellar cloud, the density and size of which permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen, H 2), and the formation of H II regions.
The nebula's color depends on its chemical composition and degree of ionization. Due to the prevalence of hydrogen in interstellar gas, and its relatively low energy of ionization, many emission nebulae appear red due to strong emissions of the Balmer series. If more energy is available, other elements will be ionized, and green and blue ...
A protoplanetary disk forming in the Orion Nebula. The main problem in the physics of accretion disks is the generation of turbulence and the mechanism responsible for the high effective viscosity. [2] The turbulent viscosity is thought to be responsible for the transport of the mass to the central protostar and momentum to the periphery of the ...
The nebula contains a prominent northwest lobe which extends up to 3.0′ away from the central star and is estimated to have formed from an eruptive event around 1,900 years ago. It has a circular part whose walls are expanding such that each part has a speed proportional to its distance from the central star.