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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 ]
A pre-main-sequence star (also known as a PMS star and PMS object) is a star in the stage when it has not yet reached the main sequence.Earlier in its life, the object is a protostar that grows by acquiring mass from its surrounding envelope of interstellar dust and gas.
Thirteen-year timelapse of material ejecting from a class I protostar, forming the Herbig–Haro object HH 34. The stars from which HH jets are emitted are all very young stars, a few tens of thousands to about a million years old. The youngest of these are still protostars in the process of collecting from their surrounding gases.
A star forms by accumulation of material that falls in to a protostar from a circumstellar disk or envelope. Material in the disk is cooler than the surface of the protostar, so it radiates at longer wavelengths of light producing excess infrared emission. As material in the disk is depleted, the infrared excess decreases.
The radiation from the protostar and early star has to be observed in infrared astronomy wavelengths, as the extinction caused by the rest of the cloud in which the star is forming is usually too big to allow us to observe it in the visual part of the spectrum. This presents considerable difficulties as the Earth's atmosphere is almost entirely ...
The Boomerang Nebula is an excellent example of a bipolar outflow. Image credit: NASA, STScI. A bipolar outflow comprises two continuous flows of gas from the poles of a star.
The collapse releases gravitational energy, which heats up the protostar. This process occurs on the free fall timescale, which is roughly 100,000 years for solar-mass protostars, and ends when the protostar reaches approximately 4000 K. This is known as the Hayashi boundary, and at this point, the protostar is on the Hayashi track.
The stellar birthline is a predicted line on the Hertzsprung–Russell diagram that relates the effective temperature and luminosity of pre-main-sequence stars at the start of their contraction. [1]