A giant telescope dish does not look like the small tube you might point at the night sky. FAST, the Five-hundred-metre Aperture Spherical Radio Telescope in Guizhou province, collects radio signals. It helps astronomers study objects such as pulsars, which can send regular signals across enormous distances.
In 2025, the Chinese Academy of Sciences reported a rare eclipsing pulsar discovered using FAST. The story is technical, but the first question is easy: if you cannot see an object clearly with your eyes, what other kind of signal can help you know it is there?
A sky full of information we cannot see
Radio waves are part of the electromagnetic spectrum. The telescope detects them; scientists then analyse patterns. Calling that “listening” is a useful metaphor, but FAST is not recording the sound of an astronaut talking in space.
A pulsar is a rotating neutron star whose signal can seem to pulse when a beam crosses our line of sight. In an eclipsing system, another object can block or change what we detect at certain times. Researchers use those changes as clues rather than treating a missing signal as a broken telescope.
Two clocks in the same signal
The reported discovery contains two very different rhythms. The pulsar spins on a timescale of milliseconds, while the two stars take about 3.6 hours to orbit each other. One belongs to the rapid pulses; the other helps explain when those pulses are obscured.
The researchers reported that the radio signal was blocked for roughly a sixth of the orbit. A recurring interruption is more informative than a signal that vanishes at a completely unpredictable moment. It gives the team a pattern to investigate.
Picture a rotating torch seen from a distance. Its beam may reach you once per turn, although the torch itself hasn’t been switched on and off. That helps explain the pulsar’s apparent pulses. Now imagine something interrupting the route at regular intervals; you have another pattern layered over the first.
The comparison is only a guide to the geometry. A neutron star isn’t a torch, and the real observations require more careful analysis. What matters is separating the source of the fast rhythm from the cause of the longer interruption.
The team used these observations to investigate how a pair of stars could have reached its present arrangement. The academy’s report describes a likely helium-star companion, not a photograph with a label already attached to it. The explanation comes from interpreting the evidence.
This is why a missing signal can be part of a discovery. If you expected information at a particular time and it repeatedly disappeared in a pattern, the absence itself could tell you something about the system. It would still need checking against other possibilities.
The telescope supplies observations rather than an instant finished picture. Researchers turn timings and changes into questions about objects too distant to inspect close up. A rhythm in the data can become the outline of a relationship in space.
Why build something so large?
Very faint signals are difficult to detect. A large collecting area helps the telescope receive them, although size alone does not guarantee a discovery. Careful observation and interpretation are still the work.
If you could ask the sky one question, perhaps it would be “What is hidden there?” FAST cannot answer everything, but it reminds us that looking is only one way to investigate a place. Sometimes the most interesting picture begins as a pattern in a signal.
Explore another instrument for observing from space and a place for looking at the sky: Can a satellite see through clouds? and Inside Beijing Planetarium’s artificial sky.
Sources
- Chinese Academy of Sciences: Chinese Scientists Discover Rare Eclipsing Pulsar