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SYFY WIRE Bad Astronomy

The Beautiful Death of the Sun’s Big Brother

By Phil Plait

The Ring Nebula is one of every amateur astronomerâs favorite objects. From the northern hemisphere it gets up high in the sky in the summer, is ridiculously easy to find, and when you look at it through a small telescope it looks like a ghostly, pale smoke ring.

Of course, when you look at it with Hubble, the picture is significantly more wow-inducing. New observations of the Ring show some amazing details, and have revealed even more information about the dying star that created it.

Itâll also melt your brain.

Trust me; you really want to click that picture to embiggen it. Youâre welcome.

This gigantic gas cloud, ten trillion kilometers across, is the dying gasp of an old star. It probably started out roughly twice the mass of the Sun, and after a few billion years began to run out of hydrogen fuel in its core. The star responded by expanding, cooling (and turning red), and blowing a slow, dense wind of subatomic particlesâa stellar wind, like the Sunâs solar wind. Over time, the core of the star underwent various other changes, and the star responded to that by shrinking, heating up, and blowing off a less dense but much faster wind. It lost much of its outer layers to this wind, eventually exposing the hot, dense core (which flooded the gas with ultraviolet light, causing it to glow; thatâs why we can see the nebula in the first place).

In rare cases these winds expand as a sphere, but most stars, weâve learned, possess planets. As the star expands, it can swallow these planets, which act like egg beaters as they orbit inside the star, whipping up the interior and increasing the starâs spin. That in turn changes the shape of the wind, creating fantastic shapes we call planetary nebulae.

In the case of the Ring, it was thought for a long time to be a sphere, but Hubble observations in the late 1990s showed it was actually shaped more like a barrel, and itâs pointed right at us; weâre looking straight down into it. The trick was to look at the blobs of dark material inside the ring; those are where the fast and slow winds meet. If you look carefully, youâll see they form in a circle at the inside rim. If the Ring were actually a spherical shell, weâd see those blobs scattered across the whole ring, even inside the rim. Since we only see them along that circle, itâs clear weâre looking down the top of a cylinder.

These new observations are even deeper and high-resolution than those older ones, and reveal new structure. You can see radial spokes heading away from the center, just outside the main ring. Those are actually due to shadowing, the light from the central star blocked by the darker, denser blobs. Theyâre cosmic crepuscular rays!

The nebula is filled with a blue glow due to helium gas, and itâs now thought that this hot gas fills the entire interior and sticks out the ends, a bit like a hot dog in a wrap-around bun. The Ring is a pig-in-the-blanket! Of course, itâs one thatâs a light year across, to give you a sense of scale. Thatâs a lot of hot dog.

The Ring is a fantastic and beautiful example of what happens when a star dies, and it happens to be close enoughâroughly 2000 light yearsâthat we get a pretty good view of it. And yet, after all this time, it also shows us thereâs still much to learn about what happens when a star shuffles off this mortal coil.

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