Far out in space, there is a star that spins incredibly fast: 318 revolutions per second. That's faster than the blades of a kitchen blender. On the star's surface, there are hot spots. When a spot turns toward us, the star appears brighter; when it turns away, dimmer. So the star blinks like a lighthouse.

The NICER telescope on the International Space Station collected these flashes for over a year. Scientists tried different models: two round spots, two oval ones, three round ones. Three round spots fit best. From the exact pattern of the star's blinking, they deduced its size: between 9.88 and 12.77 kilometers. That's like the distance from downtown to the outskirts.

Previously, the star's size was poorly known. Now it's clear that the star is a bit smaller than thought. This helps understand what it's made of inside. If the star is smaller, its matter compresses more softly. Such stars are the only place in the universe where we can test what happens to matter when squeezed harder than in an atomic nucleus. Future observations of other such stars will refine this further.