Two stars twirl in a cosmic waltz in the constellation Hercules. This is a binary star system consisting of two red giants — old suns swollen like balloons. They lie 15 thousand light-years away, yet their dance appears as a faint, pulsating point. Brightness measurements revealed that one full orbit takes 60 days.
The smaller star is overflowing, unable to hold onto its outer layers. Gas streams onto the more massive partner and swirls into an accretion disk — a hot maelstrom. Spectroscopy with the LAMOST telescope detected a blueshift in the hydrogen Hα line, meaning the material is moving away from us. It also showed that the stars’ metallicity (the fraction of heavy elements) is slightly lower than the Sun’s. Photometry (brightness measurements) revealed a smooth sine wave — no eclipses, just the deformation caused by mutual gravitational pull. numerical simulation rewound the history: initially the orbit was tight, with a period of just 2.24 days. Later, mass exchange pushed the stars apart to today’s 60 days. The calculations even included the faint gravitational radiation described by the formulas of Lev Landau and Lifshitz.
In 13 thousand years, the stars’ envelopes will merge into one, giving birth to a single luminary. The system J05+50 is the first discovered pair of red giants in the mass-transfer phase. Such objects are the missing link in stellar evolution. They help us understand how white dwarfs form and where future sources of gravitational waves are born.
As far back as the 17th century, astronomers noticed that the star Algol blinks. It took another hundred years to realize it is actually two stars, one spilling onto the other. The very same process as in J05+50, just in miniature.