|
Deuterium burning is a nuclear fusion reaction that occurs in stars and some substellar objects, in which a deuterium nucleus and a proton combine to form a helium-3 nucleus. It occurs as the second stage of the proton–proton chain reaction, in which a deuterium nucleus formed from two protons fuses with a further proton, but can also proceed from primordial deuterium. ==In protostars== Deuterium is the most easily fused nucleus available to accreting protostars, and burning in the center of protostars can proceed when temperatures exceed 106 K. The reaction rate is so sensitive to temperature that the temperature does not rise very much above this.〔 Deuterium burning drives convection, which carries the heat generated to the surface.〔 If there were no deuterium burning, then there should be no stars with masses more than about two or three times the mass of the Sun in the pre-main-sequence phase because hydrogen burning would occur while the object was still accreting matter.〔 Deuterium burning prevents this by acting as a thermostat that stops the central temperature rising above about one million degrees, which is not hot enough for hydrogen burning. Only after energy transport switches from convective to radiative, forming a radiative barrier around a deuterium exhausted core, does central deuterium burning stop. Then the central temperature of the protostar can increase. While there is Deuterium in the star the temperature is kept at 10^6K because the Deuterium prevents the star from any further collapsing or contracting therefore the star's temperature will stay at 10^6K until the Deuterium has been completely consumed, once the star is void of Deuterium it will begin to contract and collapse, the temperature increasing with contraction, and at 10^7K Hydrogen burning will begin. The energy generation rate is proportional to (deuterium concentration)x(density)x(temperature)^11.8, the core is in a stable state therefore the energy generation should be constant. If one variable in the equation increases, the other two must decrease to keep energy generation constant. Due to the variable of temperature being to the power of 11.8, there would need to be very large changes to either the deuterium concentration, and density to make any small change in temperature. 〔〔 The matter surrounding the radiative zone is still rich in deuterium and burning proceeds in a shell that gradually moves outwards as the star becomes more and more radiative. The generation of nuclear energy in these low-density outer regions causes the protostar to swell, delaying the gravitational contraction of the object and postponing its arrival onto the main sequence.〔 The total energy available by deuterium burning is comparable to that released by gravitational contraction.〔 Due to the scarcity of deuterium in the universe, a protostar's supply of it is limited. After a few million years it will have effectively been completely consumed. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Deuterium burning」の詳細全文を読む スポンサード リンク
|