The Helix Nebula, otherwise known as NGC7293, is a favourite among amateur astronomers. It was one of the first objects that I imaged with my own telescope using the tri-colour tecniquing. As I recall I ended up with hundreds of individual frames that, when combined created a stunning image. It’s also known as NGC7293 and is a planetary nebula located 650 light years away in the constellation Aquarius.
The nebula is the result of a dying star of similar mass to our Sun. Throught the life of sun-like stars, the fusion process deep in the core exerts an outward pressure known as the thermonuclear force. During the majority of the life of the star, this force balances the inward force of gravity and the star remains stable. Eventually, through numerous processes, the thermonuclear force wins, causing ther outer layers of the star to be shed, leaving behind a dense, hot core known as a white dwarf. The outer layers of the star that have been expelled glow as they are illuminated by ultraviolet radiation from the central star.
The X-ray emissions from the Helix Nebula aren’t new news though since they were first detected in 1980, have finally been identified through observations with NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton. The two space observatories have confirmed that the emissions are coming from the white dwarf at the centre, designated WD 2226-210. What makes this discovery particularly intriguing is that white dwarfs typically don’t emit strong X-rays.
Artist illustration of the Chandra X-ray Observatory (Credit : NASA/CXC/NGST)
The lead researcher on the study, Sandino Estrada-Dorado explains “We think this X-ray signal could be from planetary debris pulled onto the white dwarf, revealing the death of a planet destroyed by the central star of the Helix Nebula.” Scientists had previously identified a Neptune-sized planet orbiting WD 2226-210 with a period under three days,
The latest research suggests an even closer Jupiter-like planet might have once existed. The research proposes this planet initially formed far from its star but gradually migrated inward through gravitational interactions with other planets. Eventually, the propose, it came close enough to be torn apart by the white dwarf’s intense gravitational forces and it is this that is thought to have created the unusual X-ray signatures.
The study reveals that the X-ray emissions have maintained consistent brightness across observations in 1992, 1999, and 2002 using ROSAT, Chandra, and XMM-Newton respectively. Observations revealed a subtle 2.9-hour periodicity in the X-ray signal, suggesting the presence of planetary remnants in an extremely close orbit around the white dwarf. The team did consider whether a low-mass star might have been destroyed instead of a planet but they determined this less likely since such stars, despite being similar in size to Jupiter-like planets, have greater mass and would better resist the white dwarf’s destructive gravitational forces.
Source : X-ray Signal Points to Destroyed Planet, Chandra Finds
