Etudes des proprietes des neutrinos dans les contextes ...

tel-00450051, version 1 - 25 Jan 2010
1.4 to 2 solar mass forms a neutron star. 4 The rest of the mass of the star gets
ejected into the intergalactic space. A star going through this mechanism of
explosion is called a core-collapse supernova.
The energetic balance of the explosion
As the core collapses, it gets more tightly bound gravitationally, so it releases the
extra energy. The energy release ∆E is given by a Newtonian description of the
gravitational energy potential:
2 GNm
∆E = −
R
star
2 GNm
− −
R
NS
(3.5)
where GN is the gravitational constant, M the mass of the astrophysical object
studied, and R the distance from the center to the outside. If one takes into
account the fact that the star is a few 10 10 cm while a neutron star has only a
radius of about 10 6 cm. Since Mstar is at most about 10 times the mass of the
neutron star, the first term in Eq.(3.5) can be neglected and Eq.(3.5) becomes:
∆E = 5.2 × 10 53
10km MNS
erg ·
RNS 1.4 M⊙
2
(3.6)
Besides the variation of the potential energy, there is the binding nuclear energy
and the kinetic energy taken away by expelled matter. The nuclear binding
energy ENB is about 3.2 MeV. Therefore, the total energy used to bind nuclei is:
EB = NN ∗ ENB
= MNS
∗ Na ∗ ENB
MN
6MNS
≃
× 10
1.4M⊙
51 erg (3.7)
The kinetic energy in the explosion is
1
2 Mv2 = 2.5 × 10 51
M
v
10M⊙ 5000km.s−1 2
(3.8)
which is small even under extreme assumptions about the mass and the velocity.
The liberated gravitational energy corresponds to a few 10 53 erg, of which
only about 0.01% is transformed into electromagnetic radiation and about 1%
is transformed into kinetic energy of the ejecta. Therefore 99% of the binding
gravitational energy released must be carried away by the neutrinos.
Let us now study the features of the neutrino flux that result from this process.
4 or a black hole if the mass is larger. Nevertheless, we focus in this thesis on supernova
giving rise to a neutron star.
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