- The Helix nebula is a planetary nebula. It is the remaining outer layers of gas that the original star shed when it became a white dwarf.
- Astronomers have detected puzzling X-ray signals coming from the nebula since 1980. But the specific source remained unknown.
- A destroyed planet near the white dwarf is the most likely explanation, a new study says.
Remains of destroyed planet found lurking in Helix nebula
Since 1980, astronomers have detected unusual X-ray signals coming from the center of the Helix nebula. The nebula is a colorful gas and dust shroud: the remains of a dying star that became a white dwarf. But, until now, the scientists have been unable to determine a specific source for those X-rays. On March 4, 2025, astronomers using NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton, said the X-ray signals might be coming from debris from a destroyed planet falling onto the white dwarf star.
The researchers, in Mexico, Spain and Taiwan, published their peer-reviewed findings in the Monthly Notices of the Royal Astronomical Society on December 12, 2024.
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Puzzling X-ray signals from Helix nebula
Astronomers first began detecting the Helix nebula’s X-ray signals in 1980. Although they knew the signals came from the center of the nebula, they didn’t know the specific source. The Helix nebula is a planetary nebula, 650 light-years away. It’s the remaining layers of gas leftover from when the original star became a white dwarf.
So, at the end of its life, the star shed its outer layers of gas, forming the nebula. The white dwarf – named WD 2226-210 – is the remaining smaller hot core of the star and lies in the middle of the nebula.
A destroyed planet?
The X-ray signals were intriguing, since planetary nebulae like the Helix don’t usually emit strong X-rays. So what was causing them in the Helix nebula? The researchers think it was likely a destroyed planet. Lead author Sandino Estrada-Dorado at the National Autonomous University of Mexico said:
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. We might have finally found the cause of a mystery that’s lasted over 40 years.
1 planet, or 2?
In addition, astronomers already knew about one planet, about the size of Neptune, that still orbits the white dwarf. If there used to be a second planet – the one that was destroyed – it was probably closer in size to Jupiter. The scientists say it likely migrated inward, closer to the white dwarf. Once it got too close, however, the white dwarf tore it to shreds. That destroyed planet, the researchers say, is probably the source of the X-ray signals. As co-author Martin Guerrero at The Institute of Astrophysics of Andalusia, in Spain, said:
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. If confirmed, this would be the first case of a planet seen to be destroyed by the central star in a planetary nebula.
Another possibility is that the destroyed object was a lower-mass star instead of a planet. But stars that size are too massive to get ripped apart easily by the white dwarf’s gravity.
Subtle changes in the signals
Overall, the X-ray signals have remained pretty constant in brightness. This is based on observations in 1992 (ROSAT), 1999 (Chandra) and 2002 (XMM-Newton). On closer inspection, however, the researchers found a subtle, regular change occurring every 2.9 hours. According to the researchers, this points to a planet – well, the remains of one – very close to the white dwarf.
While the planet itself is no more, its remains are still orbiting the white dwarf.
Astronomers have detected unusual X-ray emissions from the white dwarf star at the center of the Helix Nebula, known as WD 2226-210. 1/#Science #News #Astronomy #Astrophysics ? chandra.harvard.edu/press/25_rel…
— Erika (@explorecosmos.bsky.social) 2025-03-04T19:47:07.492Z
Similar white dwarfs
If confirmed, this would be the first time astronomers have found a destroyed planet orbiting a white dwarf inside a planetary nebula. But this white dwarf is also similar to at least two other known white dwarfs, ones that are not inside planetary nebulae.
Both have planets that are either destroyed or are in the process of being annihilated. For the first one, the white dwarf is ripping material off the planet, but not as violently as would have happened with the Helix nebula planet. In the second case, the white dwarf is also pulling material from the planet, but that material is accumulating on the white dwarf’s surface. All three of these white dwarfs can provide important clues about how planets might survive around white dwarfs … or not. As co-author Jesús Toala at the National Autonomous University of Mexico noted:
It’s important to find more of these systems because they can teach us about the survival or destruction of planets around stars like the sun as they enter old age.
Also, as reported just a few days ago, astronomers found that rocky planets like Earth that still orbit white dwarfs can still be potentially habitable if they orbit fast enough. The faster, smaller orbits can keep those planets warmer than astronomers first thought.
Bottom line: Mysterious X-ray signals coming from the Helix nebula most likely originate from the debris of a destroyed planet near a white dwarf star, a new study suggests.
Source: Accretion onto WD 2226-210, the central star of the Helix nebula
Via Chandra X-ray Observatory
Read more: New infrared view of Helix nebula looks like golden eye in the sky
Read more: Speedy white dwarf planets are more likely to be habitable