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Hubble sights a starry necklace

This beautiful Necklace Nebula, situated 15,000 light-years away in the constellation Sagitta and sighted by the Hubble Space Telescope, is the result of a stellar smash-up that happened long ago.

When stars the size of our sun near the ends of their lives, they're prone to puff away their outer layers, creating glowing shells of gas and dust. These shells can take on the appearance of rings, or globes, or even complex butterfly shapes. Centuries ago, when astronomers looked at these phenomena through their telescopes, they looked like fuzzy, blobby planets — and they've been known as "planetary nebulae" ever since.

In today's image advisory, the Hubble team says this particular planetary nebula came about when an agingi giant star whirled too close to its sun-sized companion, setting off a huge explosion. Because the stars were spinning around each other, most of the blast debris was ejected in a ringlike pattern, like water shooting out from a sprinkler. The jewels in the "necklace" are dense knots of hydrogen and oxygen gas thrown out by the blast. Scientists speculate that the gas clumped up because it was following magnetic field lines, or because of density fluctuations in the stars themselves.

Hubble took this picture of the scene on July 2, using the Wide Field Camera 3. The image is color-coded to reflect emissions in wavelengths associated with different elements: hydrogen (blue), oxygen (green) and nitrogen (red).

We're seeing the nebula today as it was 15,000 years ago, and astronomers surmise that the necklace ring was created about 5,000 years before that — which is just the blink of an eye in cosmic terms. The clumps are glowing in this picture because the gas is lit up by the ultraviolet radiation coming from the shattered stars. You can see the stars as a single bright dot at the ring's center. They're too close to each other to be made out separately, but based on repeated observations, astronomers surmise that the beat-up stars are still spinning around each other every 1.2 Earth days.

From this far away, the nebula looks like a wearable piece of jewelry — but the ring is actually 12 trillion miles wide, which is wider than our own planetary system. You couldn't wear this necklace, even if your head was as big as Pluto's orbit.

More about planetary nebulae:

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