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Large disks are routinely observed in many star-forming regions such as the Orion nebula. [18] Artist's impression of the disc and gas streams around young star HD 142527. [53] The lifespan of the accretion disks is about 10 million years. [17] By the time the star reaches the classical T-Tauri stage, the disk becomes thinner and cools. [45]
A protostar is a very young star that is still gathering mass from its parent molecular cloud.It is the earliest phase in the process of stellar evolution. [1] For a low-mass star (i.e. that of the Sun or lower), it lasts about 500,000 years. [2]
Over about 100,000 years, [10] the competing forces of gravity, gas pressure, magnetic fields, and rotation caused the contracting nebula to flatten into a spinning protoplanetary disc with a diameter of about 200 AU [12] and form a hot, dense protostar (a star in which hydrogen fusion has not yet begun) at the centre. [26]
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] However, lower mass star formation is occurring about 400–450 light-years distant in the ρ Ophiuchi cloud complex. [12]
A protoplanetary nebula or preplanetary nebula [1] (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) phase and the subsequent planetary nebula (PN) phase. A PPN emits strongly in infrared radiation, and is a kind of reflection nebula.
These objects represent the final stage before a planetary nebula. During this stage, the red giant star begins to slowly expel its outermost layers of material. A protoplanetary nebula usually glows by reflecting the light from its parent star. This stage is usually brief, typically lasting no more than a few thousand years.
NGC 7538, near the more famous Bubble Nebula, is located in the constellation Cepheus. It is located about 9,100 light-years from Earth. It is home to the biggest yet discovered protostar which is about 300 times the size of the Solar System. [4] It is located in the Perseus Arm of the Milky Way and is probably part of the Cassiopeia OB2 ...
NGC 6357 is a diffuse nebula near NGC 6334 in the constellation Scorpius. The nebula contains many proto-stars shielded by dark discs of gas, and young stars wrapped in expanding "cocoons" or expanding gases surrounding these small stars. It is also known as the Lobster Nebula.