Bounty from a Planetary Nebula

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.