In a cosmic first, scientists have witnessed the moment that a white dwarf – the remnant of a star that has shed its outer layers – ripped apart a comet in its vicinity. The findings were published in The Astrophysical Journal Letters.
The discovery was made using the Keck Observatory in Hawaii and NASA’s Hubble Space Telescope. Observing the distant white dwarf 170 light-years from Earth, called WD 1425+540, they saw evidence that a massive comet had fallen towards the star and been “tidally disrupted” – or torn apart.
Found in the constellation of Bootes, this white dwarf was first recorded in 1974. It is part of a binary system with another star, which orbits about 2,000 astronomical units (AU, 1 AU is the distance from Earth to the Sun) away.
As for the comet, well, it was rather huge, about 100,000 times as massive as the famous Halley’s Comet in our own Solar System and with a much higher amount of water. It is also thought to be rich in the elements essential for life such as nitrogen, carbon, oxygen, and sulfur.
“Nitrogen is a very important element for life as we know it,” said lead author Siyi Xu of the European Southern Observatory, Germany, in a statement. “This particular object is quite rich in nitrogen, more so than any object observed in our Solar System.”
The finding is important because it lends evidence to the idea that other planetary systems have some of the same icy material as our own, which may have been transported via comets to various worlds.
Up to half of all white dwarfs are thought to be polluted with infalling debris from asteroids into their atmospheres, although this is the first time comet-like material has been seen. It also hints at a region like our own Kupier Belt – made up of ancient icy material – around the white dwarf.
The discovery shows that icy material like this can survive the entire evolution of a star. This white dwarf would have once been a red giant, before it discarded its outer layers and left behind just the dense core of the old star.
How this comet moved from a distant orbit towards the white dwarf isn’t clear, though. The researchers suggest it may have been pushed inwards by unseen planets in the system. Alternatively, this white dwarf’s companion may have disturbed the distant belt of comets, or perhaps a combination of the two ideas took place.
But on the plus side, it proves we’re not alone in having icy material in our Solar System. And if comets delivered water and life here, where else did they do it?