The Star That Blinks on Schedule express
The binary star KL Dra works like a neon clock: every two months it lights up for a few days, and between these outbursts it blinks with short but bright pulses. For eleven straight years, telescopes have kept their eyes on it, and now the whole mechanism is visible.
In this pair, one star is a dense white dwarf, and the other is an ordinary star that loses matter. The matter doesn't fall directly but first accumulates in a disk around the white dwarf, like water behind a dam. When enough accumulates, the disk becomes unstable and breaks through: that's the outburst. Large outbursts last on average 5.7 days. After them, the star "winks" several times: these are short rebrightenings. Then, a few weeks later, a series of three or four normal outbursts begins, each lasting just over a day.
The cycle repeats every 60.4 days. The longer the star "rests" after a large outburst, the shorter the subsequent series of rebrightenings, but the brighter the large outburst itself. Such precision allows us to test models: why the disk loses stability, how exactly matter falls onto the white dwarf, and why sometimes outbursts are skipped.
The recurrence period of large outbursts in KL Dra is 60.4 days with an uncertainty of only 0.1 days. That's more precise than some train schedules.