More evidence should follow from similar projects, like the Parkes Pulsar Timing Array (PPTA) in Australia, which began around the same time as NANOGrav. George Hobbs of the Commonwealth Scientific and Industrial Research Organisation (CSIRO), who leads the project, says that PPTA will present an analysis of its observations “sometime soon” with similar results.
“The NANOGrav result is much more convincing than many of the false alarms that we’ve had in the past,” he says. Still, Hobbs cautions against jumping to conclusions. “I’ve now had around 15 years of people saying, ‘Hey, we’ve found gravitational waves in our data,’ and so we need to be enthusiastic and cautious at the same time.”
Seeking confirmation
Luckily, NANOGrav already has roughly 2.5 years of additional data from both Green Bank and Arecibo — with the latter observing pulsars right up until Arecibo went offline after a cable failure in August 2020, which eventually led to the telescope’s total collapse in December.
The loss of Arecibo was a huge blow to NANOGrav, but the team’s simulations suggest that the data they already have should be enough to reveal the timing correlations between pulsars, if they exist. But now they need to analyze it, which the team hopes to complete within the next two years, says Scott Ransom, the project’s chair and a researcher at the National Radio Astronomy Observatory.
If they succeed in making a detection, it would open up an entirely new area of the gravitational wave spectrum for study. “NANOGrav and LIGO complement each other wonderfully,” says Weinstein. “If you compare with electromagnetic (light) observations, NANOGrav is like radio astronomy, while LIGO is like optical astronomy. They ‘see’ different sources.”
In the case of binary supermassive black holes, astronomers hope gravitational waves will clarify the physics of how they evolve, perhaps resolving the “final parsec problem” — the inability of theoretical models to get pairs of black holes to lose enough orbital energy to close the last few light-years of distance between them.