Roughly 11.5 million years ago in a galaxy not too far away, a starquake cracked the surface of a small and violent stellar corpse. This rupture caused an enormous flare that sent X-rays and gamma rays racing across the universe. After traveling for millions of years, the flood of high-energy radiation finally washed over our inner solar system just before 5 A.M. EST on April 15, 2020, lighting up the sensors of spacecraft orbiting the Sun, Earth, and Mars. The signal lasted just a fraction of a second, but it still offered telltale clues about where it came from.
And last week, a team of scientists studying the event announced they've deduced the bizarre origins of this cosmic flood of radiation. The signal came from a strange star called a magnetar —
short for magnetic star — an extreme object that packs the mass of our Sun into a city-sized sphere.
Magnetars should be commonplace in the universe. Yet, they’ve proven hard to track down and study. That’s why astronomers are so excited by this magnetar flare: It could teach us a lot about these elusive stars. Their findings were described in a handful of papers published January 13 in
Nature and
Nature Astronomy.
How to make a magnetar
When a massive star dies, it often explodes as a supernova. This blasts the star's outer layers into space, but its core instead collapses into an extremely dense object called a neutron star. These stellar corpses are so dense that just a teaspoonful would weigh about a billion tons.
But neutron stars come in a variety of flavors. Many are considered pulsars because they rapidly spin like cosmic lighthouses, broadcasting intense beams of radiation at perfect angles to be seen from Earth.
But about one in 10 neutron stars will become a magnetar, with magnetic fields up to 1,000 times more intense than those of the average neutron star, or hundreds of trillions of times the strength of Earth's magnetic field.
“If you had a magnetar really close, say between the Earth and the Moon, it would wipe all the information on your credit cards,” says astronomer and study author Oliver Roberts of the Universities Space Research Association. “It’s just that strong.”
And while astronomers have measured some of these magnetars’ extreme properties before, their daily lives and what drives their activity remains a mystery. That's because magnetars are somewhat difficult to find. “Not a lot is known about them,” Roberts says. “We know they exist, and we’ve cataloged about 29 within our galaxy.”