The Millennia-Old Mystery of the Faded Star ✛ ✦
Two figure skaters spin on the ice. First in wide circles, then they close in, and one passes a shimmering fabric to the other — a spray of sparks flies from the friction. Then the motion settles into a smooth circling. This dance explains the fate of the star θ Eridani (Acamar).
In antiquity, Acamar was among the brightest stars in the sky, but now its brightness has dropped dozens of times. Spectroscopy and brightness measurements revealed: the system is triple, and the central pair are stars on very close orbits. One of them, a larger star, burned up its hydrogen fuel and swelled, filling its helium shell. At the same time, its proportion of heavy elements is close to solar — a sign that the violent outburst was the only upheaval in its life.
Computer modeling reconstructed the events: the mass transfer circularized the orbit, the outburst faded, and the star dimmed.
The name Acamar comes from Arabic for 'end of the river.' When Achernar, an even brighter star, was discovered further south, Acamar lost its status as the last star in the constellation Eridanus.