Planetary collision: researchers capture first-ever afterglow of two ice giants colliding

Two icy giant planets collided in a blaze of light emitting plumes of dust - which was spotted on social media by an amateur astronomer.

Two exoplanets 1,800 light years away from Earth crashed around a sun-like star and the bright afterglow of the explosive collision moved in front of the sun which dimmed it over time.

The star has been named ASASSN-21qj after the network of telescopes that first detected the fading of the star at visible wavelengths.

The amateur astronomer saw the star brightening over 1,000 days which was then explored by a team of international astronomers.

The star's light curve showed the system doubled in brightness at infrared wavelengths three years before the star started to fade in visible light.

“It would be very spectacular,” said Dr Matthew Kenworthy, a co-lead author on the study at the Leiden Observatory in the Netherlands. “The energy of the collision would turn the remnant into something resembling a star, fainter than the main star in the system but about seven times larger in size, visible all through the rest of the stellar system.”

“I was looking for something completely different,” Dr Kenworthy said. “The infrared brightening told us something unusual had happened in the neighbourhood of this star, and so it took us down this new path.”

He said he knew it was an "unusual event".

For two years a network of professional and amateur astronomers studied the star looking for changes in its brightness.

Dr Simon Lock, co-lead author from the University of Bristol, said: "Our calculations and computer models indicate the temperature and size of the glowing material, as well as the amount of time the glow has lasted, is consistent with the collision of two ice giant exoplanets."

It is expected the cloud of dust will begin to spread out along the orbit of the remnant created in the collision. The remnant becomes a new planet with the mass of material around it likely to condense and form a collection of moons that will orbit it, Dr Zoe Leinhardt, another co-lead author from the University of Bristol said.

Light from this dust cloud could be detected from both ground-based telescopes and Nasa's largest telescope in space, known as James Webb Space Telescope and the next developments will be monitored closely by astronomers.

The paper, 'A planetary collision afterglow and transit of the resultant debris cloud', is published in the journal Nature.