Tour: X-ray Signal Points to Destroyed Planet, Chandra Finds

After tracking a puzzling X-ray signal from a dying star for decades, astronomers may have finally explained its source: the old star might have destroyed a nearby planet.

Dating back to 1980, X-ray missions have picked up an unusual reading from the center of the Helix Nebula. Using today’s most powerful X-ray missions, NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton, they now have a much clearer picture of this decades-long enigma.

The Helix Nebula is a so-called planetary nebula, which is the late-game stage of a star that has ejected its outer layers of gas and left behind a dimmer and smaller ember of a star known as a white dwarf.

In previous decades, the Einstein X-ray Observatory and ROSAT telescopes detected highly energetic X-rays coming from the white dwarf at the center of the Helix Nebula named WD 2226-210, located only 650 light-years from Earth. White dwarfs like WD 2226-210 do not typically give off strong X-rays.

A new study featuring the data from Chandra and XMM-Newton may finally have settled the question of what is causing these X-rays from WD 2226-210. A team of astronomers thinks 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.

Previously scientists determined that a Neptune-sized planet is in a very close orbit around the white dwarf — completing one revolution in less than 3 days. The researchers in this latest study conclude that there could have been a planet like Jupiter even closer to the star.

The besieged planet could have initially been a considerable distance from the white dwarf but then migrated inwards by interacting with the gravity of other planets in the system. Once it approached close enough to the white dwarf the gravity of the star would have partially or completely torn the planet apart.

The mysterious signal astronomers have been seeing could be caused by the debris from the shattered planet falling onto the white dwarf’s surface that is being heated to glow in X-rays. If this result is confirmed, it would be the first case of a planet seen to be destroyed by the central star in a planetary nebula.