In the dense family of old stars that astronomers call the cluster NGC 6791, a lonely radio beacon has been spotted — the pulsar PSR J1922+3745. Such objects are born when a massive star explodes and its core collapses into a tiny sphere the size of a city, which spins and emits radio waves like a rotating lighthouse beam. If the pulsar truly belongs to the cluster, it would be the first known case for open clusters — old stellar groups that gradually disperse across the galaxy. But is it so?
The scientists used the large radio telescope FAST in China to monitor the pulsar for several months. They precisely measured its position, how quickly its spin is slowing down, and how its radio waves are polarized: that is, in which plane the signal oscillates. It turns out the pulsar is old: about 7.8 million years, similar to a small group of slow pulsars in globular clusters — dense, very old stellar clumps. But age alone doesn't prove kinship with NGC 6791.
To check whether it's just a random neighbor, the astronomers re-examined observational data of this sky region with higher sensitivity, but found no other pulsars. They also assessed whether the distance to the pulsar could be measured via the absorption of radio waves by interstellar hydrogen (like gauging fog thickness by how much it dims headlights). It turned out that current instruments aren't sensitive enough for such a measurement. So for now, we can't say for sure whether the pulsar is a cluster member or just passing by in the background.
The most direct path to solving this is to look for other pulsars nearby with similar characteristics. If found, that would be strong evidence that PSR J1922+3745 was indeed born in this cluster alongside its stellar neighbors. For now, it remains a lonely beacon, its connection to NGC 6791 hanging in the air like an unconfirmed kinship.
Pulsar PSR J1922+3745 completes a full rotation in about 20 milliseconds — faster than a hummingbird's wingbeat, but for pulsars, that's considered slow spinning.
In Carl Sagan's novel "Contact," pulsars are used as natural beacons for navigation, and the protagonist hears their signals turned into sound.