Neutron Stars: Formed, Spun and Kicked

TL;DR

This paper reviews recent developments in understanding neutron star formation, spins, and kicks, highlighting new pathways and challenging previous assumptions based on recent observations and theoretical interpretations.

Contribution

It broadens the existing understanding by incorporating additional formation pathways and nuanced interpretations of neutron star properties.

Findings

Neutron stars form via both core collapse and electron-capture supernovae.

Birth kicks vary significantly, being high for some and low for others.

Spin-up mechanisms include Roche-lobe overflow, wind accretion, and hypercritical accretion.

Abstract

One of the primary goals when studying stellar systems with neutron stars has been to reveal the physical properties of progenitors and understand how neutron star spins and birth kicks are determined. Over the years a consensus understanding had been developed, but recently some of the basic elements of this understanding are being challenged by current observations of some binary systems and their theoretical interpretation. In what follows we review such recent developments and highlight how they are interconnected; we particularly emphasize some of the assumptions and caveats of theoretical interpretations and examine their validity (e.g., in connection to the unknown radial velocities of pulsars or the nuances of multi-dimensional statistical analysis). The emerging picture does not erase our earlier understanding; instead it broadens it as it reveals additional pathways for neutron star formation and evolution: neutron stars probably form at the end of both core collapse of Fe cores of massive stars and electron-capture supernovae of ONeMg cores of lower-mass stars; birth kicks are required to be high (well in excess of 100 km/s) for some neutron stars and low (< 100 km/s) for others depending on the formation process; and spin up may occur not just through Roche-lobe overflow but also through wind accretion or phases of hypercritical accretion during common envelope evolution.