Helix Nebula

NASA, ESA, C.R. O'Dell (Vanderbilt University), and M. Meixner, P. McCullough, and G. Bacon ( Space Telescope Science Institute).

Overview

This is a visible light image of the Helix Nebula captured by the Hubble Space Telescope. It is the closest representation of how the human eye would perceive this object in space.

Known as NGC 7293 or popularly as the "Eye of God", the nebula is located about 700 light-years away in the constellation of Aquarius. Formed approximately 10,600 years ago, it is one of the closest planetary nebulae to Earth. Its characteristic spiral shape was created when a Sun-like star, reaching the end of its life, expelled its outer layers. At its center shines a white dwarf, the hot core of what remains of the star, which uses its energy to make the surrounding gases glow.

This nebula is essential for understanding the fate of our solar system, showing us what will happen when the Sun dies in about billion years.

What is a Planetary Nebula?

Despite its name, a planetary nebula has nothing to do with planets. The term was coined by 18th-century astronomers because, through the telescopes of that era, these objects appeared as round discs similar to giant planets. In reality, it is an expanding shell of ionized gas expelled by a low-to-medium mass star during the final stages of its evolution. It is a relatively brief cosmic phenomenon, lasting about 10,000 years before the gas disperses into the interstellar medium. Our own Sun is also destined to create a planetary nebula in about 5 billion years.

The Spitzer Near-Infrared

Near-infrared frequencies are those closest to visible light, with the difference that they can see through cosmic dust. In the case of the Helix Nebula with this band, Spitzer captures the light emitted by stars and the glow of the outer layers of molecular hydrogen and the cometary knots, which form the iconic eye shape, expelled by the star at the moment of its death.

Frequency

Blue infrared (3.6 microns): mainly captures the glow of the outer gaseous layers composed of hydrogen. Through this frequency, it is possible to observe the stars located behind the nebula and the white dwarf, the central star.

Green infrared (4.5 microns): this frequency is used to observe the cometary knots, as it is particularly sensitive to molecular hydrogen emissions.

Red infrared (8.0 microns): this frequency identifies the warm dust and complex molecules present within the nebula.

The Spitzer mid-infrared

Le frequenze del medio infrarosso riescono a vedere il calore; nel caso della Nebulosa Elica, individuano la polvere cosmica e le molecole organiche complesse che formano la struttura. Inoltre, grazie al medio infrarosso, è possibile osservare il calore emanato dal disco di detriti polverosi situato al centro della nebulosa, proprio attorno alla nana bianca.

Frequency

Blue infrared (3.6 microns): this frequency mainly captures the light emitted by the outer layers of hydrogen gas and the surrounding stars.

Green infrared (5.8 microns): it also shows light from the outermost gaseous envelopes, contributing to the greenish hue seen in composite images.

Red infrared (24.0 microns): this frequency identifies the densest gas and warm dust. This wavelength reveals the red glow in the center of the "eye," indicating the debris dust expelled by the dying star.