Speaker
Silvia Traversi
(INFN Ferrara)
Description
Binaries Neutron Stars (NSs) mergers can provide many constraints about
stellar composition because the evolution and features of these processes
strongly depends on the Equation Of State (EOS) of NSs. Indeed, the time
of the collapse after the merger, for given masses, is determined by the
softness of the EOS. Moreover, the process results in the ejection of
matter, both during the merger due to tidal torques and/or shocks and
after the merger from the disk formed around the remnant. This suggests
NSs mergers to host r-processes. The decay of the produced nuclei has been
directly detected as an EM signal (AT2017gfo kilonova), after the merger
event observed on the 17th August 2017. The luminosity, frequency, time
evolution and angle of the signal has been directly related to the
features of the ejecta. We have performed hydrodynamical simulations of
the NS merger in the general relativistic framework of the Einstein
Toolkit code. We have compared two EOSs for different total masses of
symmetric binaries; the first is the SFHo EOS which contains just ordinary
matter while the second is an EOS which is characterized by the appearence
in the high density regime of hyperons and delta particles. This feature
leads to a softening, preventing this EOS to reach the two solar mass
limit (in this scenario the more massive compact stars would be quark
stars). The features of the two EOSs translate into different outcomes of
the simulations: we have calculated the treshold mass for the hyperonic
EOS, meaning the maximum mass for which the remnant does not make a promtp
collapse to black hole. While the remnant in the case of SFHo survives for
dozens of ms for a 1.3-1.3 solar masses binary, we found that already
the 1.23-1.23 solar masses binary collapses promptly. In this scenario the
event of August 2017 is interpreted as the merger of a quark star with a
NS. We have also calculated the amount, the mean velocity and the angular
distribution of the dynamical ejecta for a NS-NS merger. We found that, if
a prompt collapse does not take place, the amount of matter ejected is
from 4 times to an order of magnitude larger for the hyperonic with
respect to the SFHo EOS case. This can be explained in terms of a greater
contribution of the shock component for softer EOS.
Selected session
Nuclear Astrophysics
Primary author
Silvia Traversi
(INFN Ferrara)
Co-authors
Alessandro Drago
(INFN Ferrara)
Giuseppe Pagliara
(INFN Ferrara)
Roberto De Pietri
(Università di Parma)
