After the carbon burning stage comes the neon burning, oxygen burning and silicon burning stages, each lasting a shorter period of time than the previous one. The end result of the silicon burning stage is the production of iron, and it is this process which spells the end for the star.
Just before core-collapse, the interior of a massive star looks a little like an onion, with shells of successively lighter elements burning around an iron core.
These burning stages become shorter and shorter as lighter elements are fused into heavier elements. Up until this stage, the enormous mass of the star has been supported against gravity by the energy released in fusing lighter elements into heavier ones. Iron, however, is the most stable element and must actually absorb energy in order to fuse into heavier elements. The formation of iron in the core therefore effectively concludes fusion processes and, with no energy to support it against gravity, the star begins to collapse in on itself.
The star has less than 1 second of life remaining. During this final second, the collapse causes temperatures in the core to skyrocket, which releases very high-energy gamma rays. These photons undo hundreds of thousands of years of nuclear fusion by breaking the iron nuclei up into helium nuclei in a process called photodisintegration.
At this stage the core has already contracted beyond the point of electron degeneracy , and as it continues contracting, protons and electrons are forced to combine to form neutrons. This process releases vast quantities of neutrinos carrying substantial amounts of energy, again causing the core to cool and contract even further. The contraction is finally halted once the density of the core exceeds the density at which neutrons and protons are packed together inside atomic nuclei. It is extremely difficult to compress matter beyond this point of nuclear density as the strong nuclear force becomes repulsive.
Therefore, as the innermost parts of the collapsing core overshoot this mark, they slow in their contraction and ultimately rebound. This type of SNe, called Type Ia supernovae SNe Ia , exhibit such a uniform appearance, thus being used as distance indicators on extragalactic scales. They have been attracting much interests since the recent discovery of the accelerating expansion of the Universe Perlmutter et al.
Although much dimmer than core-collapse SNe, SNe Ia produce a burst of neutrinos because of electron captures on free protons and nuclei in the hot, dense matter in an exploding white dwarf. In this paper, we report on a detailed prediction of the energy spectrum of neutrinos from a SN Ia, and discuss their detectability in the current and future neutrino experiments. We adopt the W7 model Nomoto et al. The explosion is triggered at the center when energy generation by thermonuclear burning overcomes the neutrino cooling.
It is assumed that the burning spreads outwardly as a convective deflagration. The hydrodynamic evolution has been followed by one-dimensional numerical simulations assuming spherical symmetry.
The W7 model has been quite successful in reproducing the light curves and spectra of standard SNe Ia Branch et al. The physics of nuclear burning propagation is not yet fully understood because of its highly turbulent nature. However, since observations show that SNe Ia are quite homogeneous, the uncertainty in the SN Ia explosion model is much smaller compared with core-collapse SNe. Thus, we focus on a single model in this study. Neutrinos are chiefly produced by electron captures on free protons and nuclei. The detailed abundances at each time instant of an explosion are needed to calculate the neutrino emissivities.
However, they are not fully available from the W7 paper. We then reproduced the abundances with the densities and temperatures given by the W7 model to make our calculations consistent with the original model.
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We adopted partition functions tabulated in Rauscher and Thielemann We consulted the nucleosynthesis results of the original W7 model to pick out the isotopes to be included in our NSE calculations table 1. The temperature and the density distributions, as well as their evolutions, in an exploding white dwarf were given numerically as functions of time and the enclosed mass of the shells in the W7 model. Figure 1 shows the total all-flavor neutrino solid line and anti-neutrino dashed line luminosities as a function of time since the explosion.
Type Ia Supernovae: Nucleosynthesis and Constraints on Progenitors
We found the neutrino light curve to be similar to that of Nomoto et al. Fuller et al.
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Total neutrino and anti-neutrino light curves. The solid and dotted lines indicate the neutrino and anti-neutrino luminosities, respectively, as a function of time since the explosion.
Figure 2 shows the total neutrino energy spectra for several epochs after the explosion. The peak energy of the neutrinos slightly decreases with time as the density falls off due to expansion. Total neutrino energy spectra at 0.http://1stclass-ltd.com/wp-content/gps/2366-handy-hacken.php
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Then, there is a non-zero probability that the neutrinos generated as neutrinos are observed as other flavor neutrinos, such as and neutrinos. To estimate the conversion probability from electron to other flavor neutrinos, we solved equation 7 using the electron number densities of the W7 model. Figure 3 shows the time-integrated neutrino energy spectrum.
The dotted line denotes the sum of all-flavor neutrinos. Time-integrated neutrino energy spectrum. The dotted line designates the total energy spectrum including all-flavor neutrinos. For an illustrative case, we took kpc as the distance to SN Ia. In reality, the value of depends on the experiments and methods of data analyses.
Based on analyses for solar neutrino experiments at SK Hosaka et al. Then, we studied the backgrounds and now point out the importance of early optical observations for establishing the statistical significance of a possible detection.
The direction of incident neutrinos can be determined for electron-scattering events. Such a nearby SN Ia should be observed optically, and the direction of the SN can be determined accurately. Then, we might be able to reduce the number of background events by a factor of Nakahata With optical observations of SN Ia from very early phases and afterwards, we can constrain the time of the explosion to within a time interval of 0. Whether can be reduced further is an open question, depending on the qualities of the optical data and theoretical light-curve modeling.
Thus, it is necessary to determine the time of the explosion within 0. If we happen to detect multiple events events with a time lag as short as s, which is the duration of the neutrino burst, we would obtain a high statistical significance. The probability of detecting neutrinos from multiple SNe in such a short time interval is negligibly small, considering the current SN rate. Therefore, at least one of the events is very likely to be a signal from the relevant SN Ia if the events are included in the interval T. Supernova surveys and early follow-up observations are also encouraged.
The progenitors of SNe Ia have not been identified so far Parthasarathy et al. A closer look at optical light curves for a sample of SNe Ia reveals that there is a small dispersion in the peak absolute luminosity, and that the luminosity is correlated with the light curve width, i. There are uncertainties in the binary evolution of the progenitor system and the history of mass accretion Badenes et al.