Gravitational waves from binary supermassive black holes missing in pulsar observations

Understand

Gravitational waves are expected to be radiated by supermassive black hole binaries formed during galaxy mergers.

• A stochastic superposition of gravitational waves from all such binary systems will modulate the arrival times of pulses from radio pulsars.
• Using observations of millisecond pulsars obtained with the Parkes radio telescope, we constrain the characteristic amplitude of this background, $A_{\rm c,yr}$, to be < $1.0\times10^{-15}$ with 95% confidence.
• This limit excludes predicted ranges for $A_{\rm c,yr}$ from current models with 91-99.7% probability.