Category Archives: star death

archaeoastronomy, star death, supernova

A Star Set in Stone

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The supernova depiction at Chaco Canyon Copyright 2002, Mark and Carolyn Collins Petersen
The supernova depiction at Chaco Canyon © 2002, Mark and Carolyn Collins Petersen

A year ago we vacationed in Chaco Canyon in New Mexico for a couple of days. One of our goals was to hike out to the site of a pictograph drawn on a rock overhang that is said to depict the appearance of a supernova that occurred in 1054 A.D. The artist was part of the Anasazi group of people who populated this canyon during that time, and much archaeoastronomical debate centers on just what it meant for the artist to paint the scene.

It must have been an eerie sight when the explosion flared into view over the eastern horizon early on July 4, 1054 A.D. Perhaps it had some ritual meaning to the Anasazi. Or maybe it was just their way of recording a strange thing in the sky. We’ll never know, but that doesn’t stop learned astronomers and ethnographic types from tussling over what the rock record means. One thing’s for sure, the presence of a bright “guest” star must have been a surprise to ancient stargazers who knew the skies quite well. Certainly the Chinese and Japanese thought it so remarkable that they recorded it in their writings, and there’s even evidence that people living on Guam noticed this outburst and drew pictures of it on cave walls. But, apparently, few in Europe saw fit to record this apparition, although it would have been quite bright in their skies.

A Crab Nebula finder chart
A Crab Nebula finder chart (right-click to download a fullsize version)

Can we see the supernova today? Well, yes, sort of. It has faded quite a bit from the glory days of 1054 A.D. when it rivaled the full moon for brightness. To see it with any detail you need a medium-to-large backyard-type telescope and maybe even a filter or two. It’s definitely not a binocular object but if you want to just see where the Crab lies, look toward the horns of Taurus the Bull after they rise up out of the horizon clutter on these November nights. The southern horn of the Bull extends out to a star called Zeta Tauri. The Crab lies just above that star.

VLT view of the Crab Nebula
VLT view of the Crab Nebula

Of course, observatory scopes are really good at digging into the heart of the Crab and showing us the spectacular details of this explosion. Here are two of my favorites: the first is from the European Southern Observatory and the second is a combined Hubble Space Telescope and Chandra X-Ray Observatory image:

HST and Chandra view the heart of the Crab Nebula
HST and Chandra view the heart of the Crab Nebula

I often wonder what the ancient Chinese, Japanese, and Anasazi peoples would think if they only knew just what it was they were recording on their parchments and sandstone? For them, this sight was a mysterious one — another symbol of something in the sky that they didn’t understand. But they surely appreciated the beauty of the apparition — just as today we look at it and try to comprehend the stellar forces at play in the death of a supermassive star.

planetary nebulae, star death

Cat’s Eye!

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A different look at the Cats Eye Nebula by the Nordic Optical Telescope at La Palma (Canary Islands)
A different look at the Cat's Eye Nebula by the Nordic Optical Telescope at La Palma (Canary Islands)

Back in 2002 an astronomer using the Nordic Optical Telescope was studying a planetary nebula called the “Cat’s Eye.” To backyard scopes it appears like a complex-looking little puff of light and in fact, is a difficult object to find unless you have a pretty decent scope. Scientists like to study these nebulae for a number of reasons — for one thing, they give us a good idea of how our own Sun might die in a few billion years. For another, these ancient stars are putting out tremendous amounts of material into the interstellar medium — stuff which eventually will end up in the birthplaces of future stars and maybe even a few planets.

As these stars age, they puff off their outer atmospheres, forming a bubble of gas and dust in surrounding space. Eventually the radiation from the star lights up the outrushing debris, and sometimes the influence of a companion star, or a magnetic field, or a fast, hot jet of gases from the dying star, will sculpt the cloud into fantastic shapes. The Cat’s Eye is a cavern of gas and dust surrounding an ancient star and possibly a nearby companion. The interactions have shaped the surrounding materials and the star’s emissions have turned the whole sight into a glowing “cave” structure.

This fantastic picture shows various gases lit up by the star. Here’s how the scientist who did the observation — Romano Corradi — explains the colors:

“I put in green and blue for the ionized oxygen emission; I used two colours for a single emission line because of the large dynamical range of the nebula+halo (there is a contrast of 1 million between the faintest and brightest structures detected), and I wanted to display the three different components of the nebula, i.e. inner nebula, first halo with the (in blue) rings, and outer filamentary halo. Red is instead [NII]6583. The image is the deepest ever obtained of NGC 6543.”

A few years ago the Hubble Space Telescope studied the inner portion of the Cat’s Eye — the “marble” surrounded by loopy looking structures at the center of this image. They, too, color-coded the image to map the different kinds of emissions put out by the clouds. This “astro-chemical” analysis tells astronomers a great deal about the age of the star, the layers of its atmosphere it has lost, and what kinds of elements are being returned to space for the next generation of stars and planets.