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The “death knell” of an entire world.
Since they were first detected over four decades ago, unusually powerful x-ray emissions originating from the site of a dying star called the Helix Nebula have proved an enigma to astronomers.
Now, we may finally have an explanation for what they are — and it’s pretty grisly. As detailed in a new study published in the journal Monthly Notices of the Royal Astronomical Society, a team of researchers make the case that the emissions are the last gasp of a planet being devoured by the star, a type of stellar remnant known as a white dwarf.
“We think this X-ray signal could be from planetary debris pulled onto the white dwarf, as the death knell from a planet that was destroyed by the white dwarf in the Helix Nebula,” study lead author Sandino Estrada-Dorado of the National Autonomous University of Mexico said in a statement. “We might have finally found the cause of a mystery that’s lasted over 40 years.”
White dwarfs like this one, WD 2226-210, form after a star similar in mass to our Sun exhausts all its fuel. Gradually, they begin to shed their outer layers, leaving behind a small but burning hot core. The energy radiated by the core ionizes the lingering gases expelled by the star, and over time forms a vast glowing cloud. This is known as a planetary nebula, which describes the Helix Nebula.
As luminous as these regions may be, the white dwarfs at their center are extremely dim, making them difficult to observe. Previous observations of WD 2226-210, which is approximately 650 light years from Earth, revealed the presence of a Neptune-sized planet in an extremely tight orbit around the white dwarf, completing a full revolution in less than three Earth days.
Analyzing the data collected by powerful x-ray telescopes including NASA’s Chandra observatory, the astronomers found evidence that there was once a Jupiter-sized planet at an even closer orbit — this tale’s murder victim. The giveaway was that amidst the x-ray emissions, which the astronomers found remained relatively constant between 1992 and 2002, there was a subtle blip occurring roughly every three hours, a near unmistakable sign of something orbiting the star — in this case, ludicrously close.
Tragically, the doomed world may have originally been significantly farther away, before being nudged into lethal proximity through gravitational interactions with other planets in the star system. Once there, it was only a matter of time before it got eviscerated by the white dwarf’s gravity.
As to what’s actually causing the x-ray “death knell”? What we’re witnessing may be more akin to the still-sizzling corpse of a planet burned at the stake.
“The mysterious signal we’ve been seeing could be caused by the debris from the shattered planet falling onto the white dwarf’s surface, and being heated to glow in x-rays,” co-author Martin Guerrero of the Institute of Astrophysics of Andalusia in Spain said in a statement. “If confirmed, this would be the first case of a planet seen to be destroyed by the central star in a planetary nebula.”
More on astronomy: James Webb Spots Mysterious Object Crossing Space Between Stars
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