Neutrino cooling

Sometimes referred to as neutrino cooling , although it does not in general lead to lower temperatures. 

Diquarks gained popularity in astrophysics about a decade ago, when they were suggested to influence the supernova collapse and bounce-off [8-12], and to enhance the neutrino cooling of quark-stars. The latter effect is now subject to much research within improved scenarios Refs. [7, 9, 8]. 

If the phase transition is somewhat stronger than we have discussed in the previous subsection, the initial temperature is higher, To 10 MeV. Neutrinos are trapped for a while in the interior of the newly formed quark star. For lower densities, where the quark matter contains trapped neutrinos the direct Urea process is operative and neutrino cooling is a surface effect. 

Cooling delay due to neutrino trapping. Estimates of the time interval after which an explosive effect of energy release like a GRB could be observed, depend on the possible structure of a compact object after the... 

In the previous Section we noted that the typical temperature, above which the star becomes opaque to neutrinos is Topac 0.4 4- 3 MeV, where we ignore here the differences in the absorption/production properties of different neutrino flavors [45], Saying neutrino we actually will not distinguish neutrino and antineutrino, although their absorption/production could be different. If we assume an initial temperature of To < T%pac, the star radiates neutrinos directly from the interior region. For To > T"po/P the neutrino transport to the surface is operative and leads to a delay of the cooling evolution. 

The following stage is core collapse caused by electron capture or photodisintegration of iron. According to the traditional view, collapse leads to formation of a neutron star which cools by neutrino emission and decompression of matter when it reaches nuclear density (10 g cm ). The rebound that follows generates a shock wave which is capable of reigniting a good few nuclear reactions as it moves back out across the stellar envelope. 

Fig. 5.4. Schematic evolution of the internal structure of a star with 25 times the mass of the Sun. The figure shows the various combustion phases (shaded) and their main products. Between two combustion phases, the stellar core contracts and the central temperature rises. Combustion phases grow ever shorter. Before the explosion, the star has assumed a shell-like structure. The centre is occupied by iron and the outer layer by hydrogen, whilst intermediate elements are located between them. CoUapse followed by rebound from the core generates a shock wave that reignites nuclear reactions in the depths and propels the layers it traverses out into space. The collapsed core cools by neutrino emission to become a neutron star or even a black hole. Most of the gravitational energy liberated by implosion of the core (some 10 erg) is released in about 10 seconds in the form of neutrinos. (Courtesy of Marcel Amould, Universite Libre, Brussels.)...

As the weak interaction is the slowest of all, it was the first to find itself unable to keep up with the rapid expansion of the Universe. The neutrinos it produces, which serve as an indicator of the weak interaction, were the first to experience decoupling, the particle equivalent of social exclusion. By the first second, expansion-cooled neutrinos ceased to interact with other matter in the form of protons and neutrons. This left the latter free to organise themselves into nuclei. Indeed, fertile reactions soon got under way between protons and neutrons. However, the instability of species with atomic masses between 5 and 8 quickly put paid to this first attempt at nuclear architecture. The two species of nucleon, protons and neutrons, were distributed over a narrow range of nuclei from hydrogen to lithium-7, but in a quite unequal way. 

In this report the results of old calculations (Mayle 1985 Woosley, Wilson, Mayle 1986 Mayle, Wilson, Schramm 1987) of collapse driven explosions and new calculations of the Kelvin-Helmholtz proto-neutron star cooling will be compared with the neutrino observations of supernova 1987a. The calculations are performed by a modern version of the computer model of Bowers and Wilson 1982. (See Mayle 1985 for more recent improvements). 

Perhaps the most novel aspect of SNl987a is the detection [6,7] of neutrinos from the production and cooling of a compact remnant. One hopes this is only the beginning of a new field of astronomy. The analysis I present here [5], parallel to the analysis of many other authors [23-28], finds remnant binding energy 2.0 0.5 X 1053 ergs and remnant mass 1.2 to 1.7 Mq consistent with what one expects for neutron star generation. An upper limit of 10-15 eV may also be inferred for the electron neutrino mass. 

There are a number of other interesting limits to be drawn on neutrino properties by somewhat more sophisticated use of the supernova dynamics. Putting another neutrino-antineutrino pair [30], i.e., another two species, into any calculation of the neutron star cooling would probably accelerate this process unacceptably. Further, one can place an upper limit [5] of 45 eV on the mass of any species mixing with the electron neutrino, else no supernova mechanism would succeed, delayed or prompt. 

The supernova 1987A in the Large Magellanic Cloud has provided a new opportunity to study the evolution of a young neutron star right after its birth. A proto-neutron star first cools down by emitting neutrinos that diffuse out of the interior within a minutes. After the neutron star becomes transparent to neutrinos, the neutron star core with > 1014 g cm-3 cools predominantly by Urea neutrino emission. However, the surface layers remain hot because it takes at least 100 years before the cooling waves from the central core reach the surface layers (Nomoto and Tsuruta 1981, 1986, 1987). 

As the universe expands and cools below the electron rest mass energy, the e pairs annihilate, heating the CMB photons, but not the neutrinos which have already decoupled. The decoupled neutrinos continue to cool by the expansion of the universe (T oc a-1), as do the photons which now have a higher temperature T1 = (11 /4)4/3T (n7/n = 11/3). During these epochs... 

At temperatures above a few MeV, when the universe is tens of milliseconds old, interactions among photons, neutrinos, electrons, and positrons establish and maintain equilibrium (T7 = TV = Te). When the temperature drops below a few MeV the weakly interacting neutrinos decouple, continuing to cool and dilute along with the expansion of the universe (T oc a-1, nv oc 7j), and pv oc 7))). 

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