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hubble space telescope, planetary nebulae

Where Star Stuff Comes From

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Bounty from a Planetary Nebula

The planetary nebula NGC 2818, courtesy Hubble Space Telescope.
The planetary nebula NGC 2818, courtesy Hubble Space Telescope.

I love me some planetary nebulae.

They provide many of the most evocative images in astronomy. This new image from the Hubble Space Telescope folks shows NGC 2818, a planetary nebula that lies about 10,000 light-years away from us and is nestled inside the open star cluster NGC 2818A.

It’s pretty rare to find such planetary nebulae inside open clusters because most clusters are pretty loosely bound and they tend to disperse (spread out over space) in the course of a few hundred million years. A star that forms a planetary is usually billions of years old, and so you wouldn’t expect to find one as part of an open cluster. Yet, here’s this cluster — which itself is about a billion years old (pretty ancient for an open cluster) — sporting a planetary nebula.  Pretty slick. And, astronomers will eventually figure out just how this is possible.

So, planetaries are made up of stars that are aging, or if you want to get poetic about it, thrashing about amid their death throes.  What’s a stellar death throe?  For stars like the Sun (which are the most likely to become planetary nebulae) death throes begin when the star begins losing more mass than usual as it gets older. That stuff blows off the star as a stellar wind, and it accumulates in a shell of gas and dust.  The star at the center continues to age by expanding and contracting and heating up the surrounding clouds of its former self. They glow in a kind of ghostly tribute to the slowly contracting white dwarf that remains behind.

Eventually that glowing cloud expands out to space and becomes part of the interstellar mix of “stuff” from other planetary nebulae and supernova explosions that will become — some millions or billions of years from now — the seeds of new stars, planets and — dare we say it? — life. Take a good look at NGC 2818 up there — some of the stuff in your body may well have come from a star that went through exactly what this one did more than 5 billion years ago.

astronomy news, astrovisualization, hubble space telescope, starbirth, stars

Hey, You! Yeah, Look at THOSE Bright Stars!

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Follow the Pointer

A wide-field image of WR-25 and Tr16-244 in the Carina Nebula. Courtesy NASA/ESA Hubble Space Telescope.
A wide-field image of WR-25 and Tr16-244 in the Carina Nebula. Courtesy NASA/ESA Hubble Space Telescope.

My friend Phil Plait has a thing about instances of pareidolia — the tendency of humans to see interesting patterns in things.  It’s a peculiar psychological thing that our primate brains do to us when we see things we don’t immediately understand or can’t place in context. So, for example, you look up at clouds in the sky and see spaceships or dogs playing or sheep sleeping or whatever it is that the cloud seems to resemble. And, of course, there are tendencies among some folks to see things like faces of deities in toast and tortillas, or peeling paint, or the bark on trees. It’s all very amusing and shows you how complex our brains are.

Astronomy images provide hours of merriment for pareidoliacs.  Take this picture, for example.  It’s a Hubble Space Telescope view of a gas and dust cloud where star formation is taking place. Notice in the very top of the picture that there’s a thick cloud of dust in the shape of a pointing finger. At least, that’s what it looks like to me.  And, it  might appear that way to you, too.

Well, you might ask — what’s it pointing to?  Good question, and the answer is what the subject of the image really is:  a pair of massive bright stars down in the lower third of the image that are shining out like a pair of headlights. (Or, if you’re a fan of LOLcats, they look like “cat lazors” charging up.)

This scene is smack in the middle of the Carina Nebula, a huge region where clouds of gas and dust are combining to form new stars. It is about 7,500 light-years away from us, and also contains the luminous blue variable Eta Carinae, which is expected to pop off as a supernova pretty much any time now (in cosmic terms).

It turns out those two bright stars have an interesting connection to the pointy-finger cloud. The bright star in the lower center is called WR-25, and its quite massive — more than 50 times the mass of our Sun.  In fact, it’s really two stars orbiting a common center of mass. They hot, bright, and interacting with each other.

The star to the left of WR-25 is called Tr16-244, and it’s actually three stars orbiting a common center of gravity — a triple-star system. Together, these two star systems are eating away at the clouds of gas and dust. That “cannibalization by radiation” is actually what sculpted the finger-shaped cloud. It’s amost as if the cloud is pointing the finger of blame back to the stars that shaped it — a nice case of cosmic pareidolia.