First observed event: A white dwarf star at the center of a planetary nebula may have destroyed a nearby planet - something astronomers have never seen. Strange X-ray signals from the Helix Nebula's white dwarf stars have puzzled astronomers for more than 40 years. Now, they may have the answer - the star's gravity may have torn the entire planet apart.

A white dwarf star in the Helix Nebula may have destroyed a planet, explaining decades of unexplained X-rays. Astronomers believe the planet drifted too close and was torn apart, with its fragments now fueling the star's radiation. Source: X-ray: NASA/CXC/SAO/UnivMexico/S.Estrada-Dorado et al.; Ultraviolet: NASA/JPL; Optics: NASA/ESA/STScI(M.Meixner)/NRAO(TARector); Infrared: ESO/VISTA/J.Emerson; Image processing: NASA/CXC/SAO/K.Arcand

New evidence from Chandra: Data from NASA's Chandra X-ray Observatory suggests that a previously unknown planet orbiting a white dwarf star was torn apart.

A new class of X-ray sources: This discovery suggests that white dwarfs may produce a new type of variable X-ray emission associated with planetary destruction.

A white dwarf star at the center of the Helix Nebula may have destroyed a nearby planet, an event astronomers have never observed. The discovery could explain more than 40 years of mysterious X-ray signals detected in the nebula. The Helix Nebula is the remnant of a dying star, similar to our Sun, that shed its outer layers, leaving a small, dense white dwarf in its core.

This composite image of the Helix Nebula combines X-ray data from Chandra (magenta), visible light data from Hubble (orange, light blue), infrared data from ESO (gold, dark blue), and ultraviolet data from GALEX (purple). Chandra's observations showed that the white dwarf star had torn apart a planet orbiting near it.

The artist's illustration below depicts the scene: a planet (left) is pulled too close to a white dwarf and is torn apart by the star's powerful gravity. A white dwarf is surrounded by the luminous remnants of a planetary nebula and lies at the center of a complex planetary system. The doomed planet may have initially been much farther away from the white dwarf, but it drifted inward over time due to gravitational interactions with other planets.

This artist's impression shows a planet (left) passing too close to a white dwarf star (right) and being torn apart by the star's tidal forces. The white dwarf is at the center of the planetary nebula, which is outlined by blue gas in the background. The planet is part of a planetary system that includes one planet on the upper left and another on the lower right. The besieged planet may have initially been quite far away from the white dwarf, but later migrated inward through gravitational interactions with other planets in the system. Image source: CXC/SAO/M.Weiss

As the planet's broken remnants spiral inward, they will eventually form a disk around the white dwarf. When this debris falls onto the star's surface, it produces a persistent X-ray signal that astronomers have been detecting for decades.

As early as 1980, X-ray missions such as the Einstein Observatory and the ROSAT telescope took unusual readings from the center of the Helix Nebula. They detected high-energy X-rays from the white dwarf star WD2226-210 at the center of the Helix Nebula, which is only 650 light-years away from Earth. White dwarfs like WD2226-210 typically do not emit strong X-rays.

A new study using data from Chandra and XMM-Newton may finally resolve why WD2226-210 emits these X-rays: The X-ray signal could be fragments of a destroyed planet being pulled toward the white dwarf. If confirmed, this would be the first time a planet has been found destroyed by the star at the center of a planetary nebula.

In about 5 billion years, our sun will run out of fuel and expand, possibly engulfing the Earth. The final stages of a star's life can be incredibly beautiful, like this planetary nebula called the Helix Nebula. Image source: X-ray: NASA/CXC/SAO/UnivMexico/S.Estrada-Dorado et al.; Ultraviolet: NASA/JPL; Optics: NASA/ESA/STScI(M.Meixner)/NRAO(TARector); Infrared: ESO/VISTA/J.Emerson; Image processing: NASA/CXC/SAO/K.Arcand

Observations by ROSAT, Chandra and XMM-Newton between 1992 and 2002 showed that the brightness of the X-ray signal emitted by the white dwarf remained essentially unchanged during this period. However, the data suggest that the X-ray signal may change with subtle regularity every 2.9 hours, providing evidence for the presence of a planetary remnant very close to the white dwarf.

Previously, scientists determined that a Neptune-sized planet is orbiting the white dwarf in a very close orbit - completing one revolution in less than three days. In this latest study, researchers concluded that there may be a planet closer to the star, such as Jupiter. The trapped planet may have initially been quite far away from the white dwarf, but then migrated inward through gravitational interactions with other planets in the system. Once it gets close enough to the white dwarf, the star's gravity can tear the planet apart, partially or completely.

The X-ray behavior of WD2226-210 has some similarities to two other white dwarfs that are not inside planetary nebulae. One of them may be sucking material away from the companion planet, but in a more gentle way so that the planet is not destroyed as quickly. Another white dwarf is likely dragging the planet's remnants of material to its surface. These three white dwarfs may constitute a new class of variable or changing objects.

A paper describing the results was published in Monthly Notices of the Royal Astronomical Society.


Compiled from /ScitechDaily