Lense-Thirring frame dragging induced by a fast-rotating white dwarf in a binary pulsar system

Abstract: Radio pulsars in short-period eccentric binary orbits can be used to study both gravitational dynamics and binary evolution. The binary system containing PSR J1141$-$6545 includes a massive white dwarf (WD) companion that formed before the gravitationally bound young radio pulsar. We observe a temporal evolution of the orbital inclination of this pulsar that we infer is caused by a combination of a Newtonian quadrupole moment and Lense-Thirring precession of the orbit resulting from rapid rotation of the WD. Lense-Thirring precession, an effect of relativistic frame-dragging, is a prediction of general relativity. This detection is consistent with the evolutionary scenario in which the WD accreted matter from the pulsar progenitor, spinning up the WD to a period $< 200$ seconds.

Lense-Thirring Frame Dragging Induced by a Fast-Rotating White Dwarf in a Binary Pulsar System

The paper by V. Venkatraman Krishnan et al. explores the dynamics of a binary system comprising PSR J1141-6545, a radio pulsar with a white dwarf (WD) companion. This study focuses on the Lense-Thirring (LT) frame dragging effect predicted by General Relativity (GR), related to the spin of the fast-rotating WD. In this system, the WD exerting relativistic frame dragging influences the precession of the orbital plane of the pulsar, which is observable as a change in the orbital inclination.

Radio pulsars in binary systems serve as important laboratories for testing predictions of GR, particularly in systems with short-period eccentric orbits. PSR J1141-6545 is of interest because the WD formed before the pulsar, offering a unique opportunity to observe evolutionary dynamics. Observations have shown a temporal evolution in the orbital inclination of the pulsar, attributing the changes to Newtonian quadrupole effects from the WD's mass distribution and relativistic spin-orbit coupling, specifically LT precession.

The LT precession arises as a relativistic effect where the spin of a massive rotating body causes nearby inertial frames to drag. The spin of the WD, accelerated due to mass accretion from the pulsar's progenitor, leads to frame dragging measured within pulsar timing. The pulsar timing methodology allows for precision measurements of spin and orbital parameters over extended periods, facilitating insights into relativistic corrections in observed phenomena.

Through pulsar timing analysis using DDGR models, the team measured the temporal evolution of the projected semimajor axis of PSR J1141-6545's orbit ($\dot{x}_{\mathrm{obs}}$). Results indicate changes are predominantly driven by contributions from LT precession by the WD, with a smaller portion due to geodetic precession of the pulsar itself. The inferred spin period for the WD is constrained to less than 200 seconds, demonstrating the detection of LT drag.

The implications of these findings are significant for both astrophysical theory and GR's applicability in complex stellar environments. Practically, they support the hypothesis of WD spin-up through mass transfer, adding constraints on WD dynamical models. Theoretically, this detection of LT frame dragging in a binary system complements similar terrestrial and other astrophysical measurements, reinforcing GR's predictions under varying conditions.

Future research directions involve pinpointing precise contributions to orbital dynamics in similar systems, potentially providing further tests of GR against alternative gravity theories. Additionally, understanding accretion effects and angular momentum exchange in compact binary systems could refine models predicting stellar evolution outcomes, especially in NS-WD binaries. Overall, these insights enrich astrophysical knowledge domains and enhance the toolkit for probing fundamental physics across cosmic scales.