Formation of the planet orbiting the millisecond pulsar J1719-1438

TL;DR

This paper explores modified evolutionary scenarios for the binary system PSR J1719-1438, suggesting that pulsar irradiation and donor wind can explain its short orbital period within the universe's age.

Contribution

It introduces two modifications to standard UCXB evolution—pulsar irradiation and donor wind—that can produce the observed system within cosmic timescales.

Findings

Donor heating and bloating by pulsar irradiation can accelerate orbital expansion.

Donor wind enhances angular momentum loss, speeding up orbital period growth.

Modified models can explain the 131-minute orbit within the age of the Universe.

Abstract

In 2011, Bailes et al. reported on the discovery of a detached companion in a 131 minute orbit around PSR J1719-1438, a 173 Hz millisecond pulsar. The combination of the very low mass function and such a short orbital period is unique. The discoverers suggested that the progenitor system could be an ultracompact X-ray binary (UCXB), which is a binary with a sub-hour orbital period in which a (semi-)degenerate donor fills its Roche lobe and transfers mass to a neutron star. The standard gravitational-wave driven UCXB scenario, however, cannot produce a system like PSR J1719-1438 as it would take longer than the age of the Universe to reach an orbital period of 131 min. We investigate two modifications to the standard UCXB evolution that may resolve this discrepancy. The first involves significant heating and bloating of the donor by pulsar irradiation, and in the second modification the system loses orbital angular momentum via a fast stellar wind from the irradiated donor, additional to the losses via the usual gravitational wave radiation. In particular a donor wind is effective in accelerating orbital expansion, and even a mild wind could produce the 131 minute period within the age of the Universe. We note that UCXBs could be an important class of progenitors of solitary millisecond radio pulsars.