A doctoral student scrolling through old telescope data stumbled upon one of the most rare, dramatic events in the universe. He saw two planets colliding in real time.
Anastasios Tzanidakis, a doctoral candidate in astronomy at the University of Washington (UW), was going through archival telescope data from 2020 when he spotted a stable, sun-like star called Gaia20ehk, located about 11,000 light-years from Earth, behaving very strangely.
Instead of emitting the steady, predictable light expected of such a star, it had begun to flicker wildly.
“The star’s light output was nice and flat, but starting in 2016 it had these three dips in brightness. And then, right around 2021, it went completely bonkers,” said Tzanidakis.
The findings were published in The Astrophysical Journal Letters.
WHY WAS THE STAR BLINKING?
The flickering had nothing to do with the star itself.
Huge quantities of rocks and dust were passing in front of it, dimming the light reaching Earth as the debris orbited the system. The likely source of all that material was a catastrophic collision between two planets.
The conclusion came when the researchers switched from visible light to infrared data.
“As the visible light began to flicker and dim, the infrared light spiked — which could mean that the material blocking the star is hot, so hot that it’s glowing in the infrared,” Tzanidakis explained.
A planet-smashing collision would generate precisely that kind of extreme heat. The earlier, smaller dips in brightness, the researchers believe, were caused by the two planets spiralling closer together through a series of grazing impacts before their final, catastrophic crash.
IS IT SIMILAR TO EARTH AND MOON?
The collision bears a striking resemblance to the one thought to have created the Earth and Moon about 4.5 billion years ago.
The debris cloud is orbiting Gaia20ehk at roughly one astronomical unit, which is the same distance as the Earth from the Sun. This means that the material could one day cool and solidify into something similar to our own Earth-Moon system.
“How rare is the event that created the Earth and moon? That question is fundamental to astrobiology,” said James Davenport, the study’s senior author and a UW assistant research professor of astronomy.
The Moon, he noted, may be one of the key ingredients that makes Earth habitable, shielding it from some asteroids, driving ocean tides, and potentially even fuelling tectonic activity.
