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Starts With A Bang

The ‘Eye of Creation’ holds the secret to cosmic life and death

The famed planetary nebula NGC 7293, the Helix Nebula, and its central white dwarf, as imaged by Hubble. Image credit: NASA, ESA, and C.R. O’Dell (Vanderbilt University).

Every star dies, but not every would-be star really lives.


“The origin and evolution of life are connected in the most intimate way with the origin and evolution of the stars.” –Carl Sagan

Supernovae may be the most spectacular cosmic explosions, but planetary nebulae are hundreds of times as numerous.

The color-coded layers correspond to different temperatures and elements, with the red hydrogen on the outskirts and heavier elements like carbon, oxygen, and silicon found on the interior layers. Image credit: NASA, ESA, and C.R. O’Dell (Vanderbilt University).

When they run out of nuclear fuel, Sun-like stars blow off their outer layers and contract into a central white dwarf.

Neutral gas is seen in globules where the blue bubble meets the gaseous disk, which the white dwarf works to evaporate. Image credit: NASA, ESA, and C.R. O’Dell (Vanderbilt University).

The outer nebula consists of hydrogen, blown off first, while the white dwarf is mostly carbon and oxygen.

In this contrast-enhanced view, the structure of the evaporating gas globules at the interior edge of the Helix Nebula is put on display. Each globule is only around the mass of the Moon, and evaporates too quickly to form anything of substance. Image credit: NASA, ESA, and C.R. O’Dell (Vanderbilt University); Processing by E. Siegel.

The white dwarf is small, but hot enough to evaporate the cold, neutral gas clumps surrounding it.

This close-up of the Helix Nebula showcases the details of the evaporating gas that are in the process of being returned to the interstellar medium, where it will participate in future generations of star formation. Image credit: NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner (STScI), and T.A. Rector (NRAO).

These evaporating gas globules are too small to form new stars, and instead return their material to the interstellar medium.

The Helix nebula has a disk-like and bubble-like structure to it, formed by the dying central star.

In this infrared image, the red, central glow is the final layer(s) of gas blown off by the dying star, while the colder, green details were blown off many thousands of years earlier. Image credit: NASA/JPL-Caltech/Univ. of Ariz.

An infrared view highlights the neutral, cold gas.

The ESO’s VISTA telescope took this image of the Helix Nebula, highlighting the gaseous, neutral structures that lie on its outskirts. The heated gas that obscures this view in the visible is simply transparent in the infrared, allowing further details to be seen. Image credit: ESO/VISTA/J. Emerson. Acknowledgment: Cambridge Astronomical Survey Unit.

All of it will evaporate over time, while the central star is so hot it barely shows up at these cold wavelengths.

Meanwhile, an ultraviolet view from GALEX highlights not only the bright, hot, central white dwarf, but the reflected ultraviolet light off of the surrounding material, as well as the emission lines from ionized hydrogen. Image credit: NASA/JPL-Caltech/SSC.

In the ultraviolet, however, the hot, reflected starlight is visible everywhere.

This combined image from NASA’s Spitzer Space Telescope and the Galaxy Evolution Explorer (GALEX). In death, the star’s dusty outer layers are unraveling into space, glowing from the intense ultraviolet radiation being pumped out by the hot stellar core. Image credit: NASA/JPL-Caltech.

The infrared and ultraviolet together showcase the tenuous, gaseous details that are lost in the optical.

The stark, stunning differences between the infrared views (top) and the visible light views (bottom) of this nebula showcase vastly different, but equally important, details about this astronomical object. Image credit: ESO/VISTA/J. Emerson. Acknowledgment: Cambridge Astronomical Survey Unit.

A multiwavelength view is required to reveal the full suite of structure here.

In a combined image that doesn’t include visible-light data, the gas globules truly stand out. However, they are temporary, and will be fully evaporated only a few thousand years into the future. Image credit: NASA/JPL-Caltech.

Eventually, all the external material will return to the galaxy, enabling new generations of stars to form.


Mostly Mute Monday tells the story of an astronomical entity, event, or phenomenon in visuals and no more than 200 words.

Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.

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