An Introduction to Modern Astrophysics · Problem 18.21

Physical Processes in the Solar System — Carroll & Ostlie

Physics — Astrophysics · xray-pulsar-4u0115-mass-transfer-spinup

Problem

The X-ray pulsar 4U0115+63 has a period of 3.61 s and an X-ray luminosity of about

L_x = 3.8 \times 10^{29}

W. Assuming that it is a

1.4\,\mathrm{M}_\odot

neutron star with a radius of 10 km and a surface magnetic field of

10^8

T, find its mass transfer rate,

\dot{M}

, and the value of

\dot{P}/P

. Repeat these calculations assuming that this object is a

0.85\,\mathrm{M}_\odot

white dwarf with a radius of

6.6 \times 10^6

m and a surface magnetic field of 1000 T. For which of these models do you obtain better agreement with the measured value of

\dot{P}/P = -3.2 \times 10^{-5}\text{ yr}^{-1}