Partially accreted crusts of neutron stars

Vol. 662
2. Astrophysical processes

Partially accreted crusts of neutron stars

by L. Suleiman, J. L. Zdunik, P. Haensel, M. Fortin, 2022, A&A, 662, A63

Accretion of matter onto a neutron star heats its surface. Transient X-ray binaries experience sporadic outbursts, lasting weeks to months, during which matter falls at a high rate onto the neutron star surface. A puzzle arises when studying the following cooling of the neutron star: the surface is too hot for the amount of material that has fallen onto it during the outburst. A new, unknown source of heat is usually postulated so as to make observations agree with theory. In this study, Suleiman and collaborators investigate, for the first time, the impact of a crust made by freshly accreted matter, as well as the original crust compressed by the new material (known as hybrid crust). From this preliminary study, the authors show that the amount of heat due to compression of the original crust is of the same order of the one due to the accreted crust, paving the way for a solution to this long-standing problem.