The riddle of the HYPERGIANTS

New research is uncovering the weird workings of the largest stars in the Universe

- Colin Stuart

You feel the vibrations as the rocket lifts off from the launch pad. This cramped spaceship is your home for two years as you journey all the way out to Jupiter, the Solar System's largest planet. It's so far away that when you get there the Sun's light is a mere 1/25th as bright as on Earth.

And yet, if you were to make a journey of the same distance in some planetary systems, you'd still be inside the star. These celestial beasts - known as hypergiant stars - are colossal. The biggest can fit 10 billion Suns inside, or 14 quadrillion Earths.

Such monsters are rare, but they play a crucial role in seeding the Universe with the rich array of chemistry required to sustain life. Their scarcity means they've been poorly understood in the past, but a run of recent research is giving astronomers unprecedented insights into their unique behaviour. Soon we may know their secrets.

Bizarre behemoths

Hypergiants are so massive, typically dozens of times the mass of the Sun or more, that they are highly unstable. They regularly cough huge quantities of their material back into space. "They are throwing out the mass of Jupiter or more in a single event," says Roberta Humphreys, an astrophysicist at the University of Minnesota.

A similar event on a smaller scale unfolded on the supergiant star Betelgeuse in 2019, when it dimmed noticeably in the night sky before brightening again. Painstaking analysis concluded that it spat out material weighing several times the mass of the Moon from its southern hemisphere. That material blocked out some of Betelgeuse's light, causing the temporary dimming. It was the first time astronomers had seen such a huge ejection from the surface of a star in real time.