Helix Nebula / NGC 7293

The Helix Nebula (NGC 7293), often referred to as the “Eye of God” due to its distinctive shape, is one of the nearest and best-studied planetary nebulae, located about 650 light-years away in the constellation Aquarius. With a diameter of approximately 2.5 light-years, the Helix Nebula is a vast, complex cloud of ionized gas and dust created by the death of a Sun-like star. Its unique structure, intricate details, and close proximity make it a critical object for understanding the final stages of stellar evolution.

The Helix Nebula formed when its central star, a red giant, exhausted the hydrogen fuel in its core. As it neared the end of its life, the star shed its outer layers, ejecting them into space over several thousand years. This ejected material now forms the nebula’s outer shell, while the hot, exposed core of the former star remains at the center, emitting intense ultraviolet radiation that illuminates the surrounding gases and causes them to glow in vibrant colours. The Helix Nebula has a distinct layered, double-ring structure, with an inner and outer shell of glowing gases that give it a characteristic “eye” appearance. The inner ring, which contains dense knots of gas and dust, is surrounded by a fainter, more diffuse outer ring that extends several light-years from the center.

One of the Helix Nebula’s most intriguing features is its hundreds of small, comet-shaped knots known as “cometary globules.” Each of these knots, which resemble tiny “comets” pointing away from the nebula’s central star, consists of dense, dusty cores with long, glowing tails. These structures are likely formed by the interaction between the nebula’s ionized gas and the strong radiation and stellar winds from the hot central star, which push away the less-dense material and leave behind these knots.

At the heart of the Helix Nebula is a small, extremely hot white dwarf, the remnant core of the original star. With a surface temperature exceeding 100,000 K, this white dwarf emits high-energy ultraviolet light, causing the surrounding hydrogen and oxygen gases to fluoresce in visible light. As one of the closest white dwarfs to Earth, this core provides valuable insight into the fate awaiting our Sun.

The nebula’s gases are expanding outward at an average speed of around 31 kilometers per second, dispersing into the surrounding interstellar space. This expansion will continue until the gas and dust thin out to the point of becoming undetectable over the next 10,000 to 25,000 years.

The central white dwarf’s high-energy radiation drives much of the nebula’s current activity. Its powerful ultraviolet light ionizes the surrounding gases, while its stellar wind—streams of charged particles—pushes against the inner regions, contributing to the nebula’s layered structure and shaping its detailed features. Observing the Helix Nebula helps astronomers understand how stars evolve and lose mass as they enter the planetary nebula phase. These insights are crucial for predicting the future of solar-type stars, including our Sun, which is expected to enter a similar phase in about five billion years.

Over the next several thousand years, the Helix Nebula will continue to expand and disperse into space, gradually becoming more diffuse and eventually fading from view. The central white dwarf, too, will slowly cool, eventually becoming a cold, dim black dwarf—a hypothetical stellar remnant that emits virtually no light. Though this process takes billions of years, it represents the ultimate fate awaiting most of the stars in our galaxy.

The full colour data from the TS94EDPH has been augmented by Ha and OIII data from the RASA.