Life of a Star: 12 Billion Years in 6 Minutes

Because I haven’t posted this here yet — a little video I spliced together a while ago.

Taken from a “Volume Visualisation” of the Orion Nebula, created by the American Museum of Natural History.
Note that not all of the objects depicted here are fully fledged stars. Some teardrop shaped objects are stellar cocoons, containing stars which are still forming. Their shape is due to the strong stellar wind from the central hot stars in the nebula — this same stellar wind is responsible for the ‘pocket’ blown in the nebula, which the video is exploring.
A T Tauri star is a newly formed star. These objects are still condensing (not yet fusing hydrogen in their cores) and typically have a circumstellar accretion disk and two polar jets.
Planetary accretion video, originally “Birth of a Comet” created by NASA JPL. Which unfortunately, got cut slightly short when I exported the video for uploading…
Footage of the Sun, taken by NASA SOHO. This clip shows a couple of solar prominences.
NASA JPL visualisation of the Sun’s Heliosphere.
Hubble Space Telescope image of LL Orionis. Note the “bow shock” created by the star as it travels through the Orion Nebula. This is from the interaction between the star’s wind and the interstellar medium.
The expansion into a red giant typically takes around a billion years — ample time for evolution. You have to wonder how life might try to adapt in this time, and how successful it might be. Could life survive somehow?
This is an actual timelapse film, created from stills taken by the Hubble Space Telescope. The star is V838 Monocerotis, which let out a bright flash of light in 2002. It might look like an expanding shockwave, but the film actually shows a “light echo” — the brief pulse of light emitted by the star is travelling outwards and illuminating the surrounding clouds of interstellar dust. It’s still unknown what caused the outburst, but a “Helium Flash” (as I labelled it in the video) is one possibility. A helium flash is a sudden thermal pulse caused by the ignition of a helium shell surrounding a star’s core, when the temperature and pressure become high enough to initiate fusion. This is, in theory, one sign of a star’s imminent demise.

Incidentally, a Helium flash only occurs in middleweight stars. Low mass stars will never be hot enough to fuse helium, while in massive stars it occurs readily, so there’s no sudden burst of fusion.

Once helium has been consumed, a star follows the “Asymptotic Giant Branch” becoming an “AGB star”. Slightly different to a “Red Giant Branch” star, AGB stars are running low on Helium to burn and amass a lot of Carbon and Oxygen. AGB stars generate more energy than red giants, but are more sporadic. They’re virtually always variable and have huge mass loss rates, typically losing vast swathes of stellar material in pulses. Being rich in all manner of interesting elements which condense into dust and molecules, these stars are fascinating to us astrochemists.

A final huge pulse expels the star’s outer layers. This is caused as the star’s core runs out of fuel and collapses, forming a hot white dwarf. Because newly collapsed white dwarfs are so hot, they have an intense stellar wind, which sweeps away the star’s outer layers (Sun Kwok’s Interacting Stellar Winds model). The star’s outer layers form a planetary nebula.

All planetary nebula images and visualisations are based on the Helix Nebula.

A close-up of the “cometary knots” seen in many planetary nebulae. Highly symmetric and with varying sizes, if you exlude the tails these are roughly the size a solar system would be. Draw your own conclusions.
Actual Hubble Space Telescope images of the Helix Nebula. It’s estimated to contain around 20,000 of those cometary knots.
Close up of the white dwarf at the core of the Helix Nebula.

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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