How a Supernova Shoots Out a Lone Spinning Star ⚡ экспресс
Be stars are rapidly rotating and usually arise in binary systems. But single Be stars are a mystery. A new scenario: a companion (a helium star) explodes as a Type Ia supernova. Material flows onto the neighboring star, spinning it up, and the explosion ejects the lone star. About 0.4% of binary systems with a helium star and a normal star evolve into this scenario. Moreover, 22% of the resulting Be stars become runaways (speed >24 km/s), which explains their origin.
Be stars are rapidly rotating luminaries with bright gas disks. Usually, a companion star spins them up: mass flowing from the neighbor whirls the star like a bullet in a rifled barrel. But there are also lone Be stars without a partner—their origin long remained a mystery.
New research shows that solitaries can be born from a supernova explosion. In a binary system, a massive helium star "feeds" its neighbor hydrogen fuel, spinning it up. Upon reaching the Chandrasekhar limit (about 1.4 solar masses), the helium star detonates as a type Ia supernova. The blast acts like a gunpowder charge and launches the already-spun-up star into free flight—exactly like a bullet from a barrel.
Such runaway stars carry the "memory" of the explosion: their high speed betrays a turbulent past. Astronomers can track them down by measuring the motion of helium witnesses to bygone cataclysms.
🎯 The 'e' in Be stars stands for 'emission'—radiation. It occurs because rapid rotation tears gas from the star's equator, forming a bright disk.