This Can’t Be Real, But It Is

One of the most amazing geometrical forms in outer space, the nebula IRAS 23166+1655 is centered on a hidden star in the early stages of becoming a planetary nebula. Photo taken by the Hubble Space Telescope. Credit: NASA/ESA

I saw this photo on another online post and wanted to share it with you. It belongs in the same category as the planet Saturn when seen for the first time through a telescope – you can’t believe it’s real. What you’re looking at is a spiral-shaped nebula around the star AFGL 3068 in the constellation Pegasus the Winged Horse. Star you say? Where is it? The star is hidden in the center of the spiral within a dense cloud of gas and dust. We see only the cloud’s dark silhouette. Material in the spiral is moving outward at about 31,000 mph. If you combine this speed with the distance between the shells, it turns out that once every 800 years a new shell is spun out from the center, where there lurks not one but a pair of closely orbiting stars called a binary.

In the distant future, the sun will begin burning helium in its core and consequently balloon out as a red giant. Red giants expel their outer atmospheres into space. The remaining stellar core emits ultraviolet light causing the expanding gases to glow as planetary nebulas, so-called because many are round like the planets.

Their period of revolution about one another closely matches the age of each shell in the pinwheel. One of the stars is a red giant called a carbon star because its atmosphere is rich in carbon formed through the fusion of helium in the star’s core. Numerous sun-like stars pass through a giant phase in their evolution when they lose mass from their atmospheres into space. In this case, the star sloughs off material at the rate of 1/100,000 of the sun’s mass each year or an entire sun’s worth over 100,000 years. The companion star is hotter and bluer and revolves around the giant. The gravitational interaction of the giant and its companion during their 800-year revolution channels some of the giant’s gas and dust into an expanding shell. Over many millennia, a series of concentric layers are spun out. I count five separate shells which adds up to 800 x 5 or 4000 years this gem’s been in the making.

You may be wondering why we should see the spiral nebula at all if the stars that form it are hidden behind dust. Astronomers propose that the nebula is being illuminated by galactic starlight. The dense plane of the galaxy, where stars are concentrated, is off to the right. That also happens to be the brightest part of the spiral. It all makes sense in a wonderfully natural way.

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