Using Pulsar Parameter Drifts to Detect Subnanohertz Gravitational Waves.

Area of Science:

• Astrophysics
• Cosmology
• Gravitational Wave Astronomy

Background:

• Gravitational waves (GWs) below 1 nHz are challenging to detect due to their long periods.
• These ultralow-frequency GWs cause slow drifts in observables, unlike typical periodic signals.
• Pulsar timing arrays offer a potential avenue for probing this low-frequency GW regime.

Purpose of the Study:

• To demonstrate the viability of using pulsar timing parameters to detect ultralow-frequency gravitational waves.
• To establish a new search method for continuous-wave signals in the ultralow-frequency band.
• To probe the astrophysical implications of supermassive black hole inspirals.

Main Methods:

• Utilized two complementary pulsar timing observables sensitive to systematic shifts from ultralow-frequency GWs.
• Searched existing pulsar timing data for continuous-wave signals in the ultralow-frequency regime.
• Established sensitivity near predictions for supermassive black hole binary inspirals.

Main Results:

• Achieved sensitivity in the ultralow-frequency GW band, approaching predictions from supermassive black hole inspirals.
• Set an upper limit on the GW strain of 1.3×10⁻¹² at 450 pHz.
• Demonstrated a decreasing sensitivity with frequency down to 10 pHz.

Conclusions:

• The pulsar timing method successfully opens a new frequency range for gravitational wave detection.
• The findings have significant implications for understanding supermassive black hole populations, cosmology, and fundamental physics.
• The absence of detected signals allows for stringent constraints on astrophysical and cosmological models.