Deuterium fusion

Deuterium (H) is the most easily fused nucleus available to accreting protostars, and such fusion in the center of protostars can proceed when temperatures exceed 10 K. The reaction rate is so sensitive to temperature that the temperature does not rise very much above this. When the energy transport mechanism switches from convective to radiative, energy transport slows, allowing the temperature to rise and hydrogen fusion to take over in a stable and sustained way. Hydrogen fusion will begin at . The rate of energy generation is proportional to the product of deuterium concentration, density and temperature. If the core is in a stable state, the energy generation will be constant. If one variable in the equation increases, the other two must decrease to keep energy generation constant. As the temperature is raised to the power of 11.8, it would require very large changes in either the deuterium concentration or its density to result in even a small change in temperature. ==In substellar objects==

Hydrogen fusion requires much higher temperatures and pressures than does deuterium fusion, hence, there are objects massive enough to burn H but not massive enough to burn normal hydrogen. These objects are called brown dwarfs, and have masses between about 13 and 80 times the mass of Jupiter. Brown dwarfs may shine for a hundred million years before their deuterium supply is burned out. Objects above the deuterium-fusion minimum mass (deuterium burning minimum mass, DBMM) will fuse all their deuterium in a very short time (~4–50 Myr), whereas objects below that will burn little, and hence, preserve their original H abundance. "The apparent identification of free-floating objects, or rogue planets below the DBMM would suggest that the formation of star-like objects extends below the DBMM." The onset of deuterium burning is called deuterium flash. Deuterium burning induced instability after this initial deuterium flash was proposed for very low-mass stars in 1964 by M. Gabriel. In this scenario a low-mass star or brown dwarf that is fully convective will become pulsationally unstable due to the nuclear reaction being sensitive to temperature. Observations of very low-mass stars failed to detect variability that could be connected to deuterium-burning instability, despite these predictions. Ruíz-Rodríguez et al. proposed that the elliptical carbon monoxide shell around the young brown dwarf SSTc2d J163134.1-24006 is due to a violent deuterium flash, reminiscent of a helium shell flash in old stars. ==In planets==

It has been shown that deuterium fusion should also be possible in planets. The mass threshold for the onset of deuterium fusion atop the solid cores is also at roughly 13 Jupiter masses (1 = ). ==Other reactions==

Though fusion with a proton is the dominant way to consume deuterium, other reactions are possible. These include fusion with another deuteron to form helium-3, tritium, or more rarely helium-4, or with helium to form various isotopes of lithium. Pathways include: : ==References==