Use the following inputs to estimate whether neutron-star mergers can supply the…

PHYSICS · Multi-part · Fermi University Physics · Nuclear Physics · Astrophysics & Cosmology · Stellar death and compact objects

Stars from the Inside, Ch Neutron stars and pulsars: the densest matter, the maximum mass and the spinning magnet

Problem

Use the following inputs to estimate whether neutron-star mergers can supply the Galaxy's europium. ((a)) Each merger like GW170817 ejects a heavy-element-rich mass of Mej=0.05 M⊙M_{\rm ej} = 0.05\,M_\odot, of which the europium mass fraction is XEu=1×10−5X_{\rm Eu} = 1\times10^{-5}. Estimate the europium mass ejected per merger. ((b)) The Milky Way's disc holds a stellar mass of Mdisc=5×1010 M⊙M_{\rm disc} = 5\times10^{10}\,M_\odot with a mean europium mass fraction (set by stellar surface abundances) of XEu,⊙=4×10−10X_{\rm Eu,\odot} = 4\times10^{-10}. Estimate the total europium mass locked in the disc's stars. ((c)) Given that the disc has formed stars for t=10 Gyrt = 10\,\mathrm{Gyr}, estimate the number of mergers needed over that time and the average Galactic merger rate this requires.

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