A Class-B pulsar
A Class-B pulsar is a classification of pulsar used by Starfleet.
The USS Voyager passed an itinerant class B pulsar with a rotation cycle that peaked for 17 hours every 32 days, in the Delta Quadrant in late 2376. Pathfinder Project used the opportunity to use the MIDAS array to amplify the signal of a communication through the pulsar so it could reach Voyager some 30,000 lightyears away, in the form of a compressed datastream. This allowed for them to send each other quick bursts of information (such as letters and tactical updates) every 32 days, giving Voyager 17 hours to respond. (VOY: "Life Line")
After Voyager had passed the pulsar, Starfleet still used it to amplify the signal of a datastream every 32 days until late 2377 when Operation Watson bounced the signal off a quantum singularity instead. (VOY: "Inside Man", "Lineage", "Author, Author")