18-Year Pulsar Study Hints at a Planet That Survived a Supernova

After an extensive 18-year observation campaign, an international team of astronomers has presented a detailed analysis of the double pulsar PSR J1906+0746, revealing not only refined measurements of the stellar masses but also intriguing evidence of a potential third, planet-like object in the system. This discovery, if confirmed, would place a planet in an extreme environment shaped by at least one supernova, challenging current theories of planetary formation and survival.

An 18-Year Cosmic Vigil

Discovered in 2004, PSR J1906+0746 is a young and energetic system, estimated to be just 112,000 years old. It features a pulsar, a rapidly rotating neutron star, spinning every 144 milliseconds, which orbits a compact companion every 3.98 hours. Due to the immense gravitational forces at play, the system is a perfect natural laboratory for testing Albert Einstein’s general theory of relativity. The research, led by Laila Vleeschower from the University of Manchester, combined data from six major radio telescopes: the now-decommissioned Arecibo, China’s FAST, the Green Bank Telescope, the Lovell Telescope, South Africa’s MeerKAT, and the Nancay Radio Telescope. This long-term monitoring allowed for unprecedented precision in measuring the system’s properties.

Weighing the Stars and a Potential Twist

The analysis has pinned down the masses of the pulsar and its companion to 1.316 and 1.297 times the mass of the Sun, respectively. With a total system mass of about 2.613 solar masses, these findings are consistent with the hypothesis that the system consists of two neutron stars. However, the authors do not rule out an alternative scenario where the companion is a massive white dwarf that formed before the pulsar. Further observations are needed to definitively identify the companion.

The Unexpected Guest: A Planet in the System?

The most surprising finding comes from the detection of a quasi-periodic behavior in the signal data, specifically in the spectral power density of the residuals and variations in the pulsar’s spin-down rate. This regular fluctuation, with a period of about two years, suggests the gravitational influence of a third body. The data points to a planet-like object with a mass of about four times that of Earth, orbiting the binary pair in approximately 736 days.

“If the planet-companion really exists, then PSR J1906+0746 would be part of a triple system, and the planet would have had to survive two supernova explosions if the companion is another neutron star, or one explosion in the less likely scenario that the companion is a massive white dwarf,” the authors conclude.

Implications for the Future

The existence of a planet in such a violent system would be a landmark discovery. Planets orbiting pulsars are exceptionally rare, with the first ones being the very first exoplanets ever discovered in 1992. Their formation is a topic of intense debate, as any original planets would likely be destroyed in the supernova explosion that creates the pulsar. This potential new world would be a “second-generation” planet, formed from the debris of the stellar explosion. Confirming its existence will require continued, dedicated observations to untangle the complex gravitational dance of this remarkable system and provide new insights into how planets can form and endure in the universe’s most extreme environments.