Ken Croswell talks about The Lives of Stars

"The stars that speckle the sky have long fascinated humanity, but only in the past century have astronomers figured out how stars are born, live, and die," said author and astronomer Ken Croswell at the start of a talk Wednesday with the Seattle Astronomical Society. "Now we can attempt to use that knowledge to try to figure out which stars near the sun might be supporting life-bearing planets."

Croswell, a frequent visitor to Seattle and author of eight books, is in town to talk about the latest, The Lives of Stars. The talk, like the book, was an easily accessible primer on various star types, from main sequence stars to red dwarfs, red giants, red supergiants, neutron stars, and pulsars.

Croswell noted that the notion that the sun is an "average" star is a misconception. In fact, the sun emits far more light than the average star, more than 95 percent of all stars in the universe. While the sun is a main-sequence star, which means it uses nuclear reactions to convert hydrogen to helium at its center, the most common main-sequence stars are red dwarfs. Seventy-five percent of the stars in the universe are red dwarfs.

Croswell said, however, that while only one in 25 stars is like the sun, it would be best to focus our search for extraterrestrial life on such stars, and that there's an intriguing possibility very close by, that being Alpha Centauri, which is actually a three-star system. Alpha Centauri A is very much like the sun, though a little older. Alpha Centauri B is an orange dwarf. Proxima Centauri is a much smaller main sequence star somewhat further away from the other two. Alpha Centauri A and B could each have disrupted the gas and dust disk around the other, impeding the formation of planets. And indeed, no planets have yet been discovered around either. Croswell added, though, that there's plenty of room in the system and both A and B could have four planets close to them and in stable orbits, just as our sun has Mercury, Venus, Earth, and Mars.

"Who knows, maybe by good luck one of those planets is the right distance from its star to have mild temperatures, oceans of liquid water, and some form of life," said Croswell. "So as we search the galaxy for another Earth we may end up finding what we're looking for surprisingly close to home in the Alpha Centauri star system."

Asked his take on the odds of finding extraterrestrial life there or anywhere else, Croswell said he has no idea.

"Earth-like conditions surely exist on lots of other planets, I have little doubt about that," he said. "But how readily you go from that to biology? We have no idea because we have just one example. So I've always said we should keep an open mind on this."

Croswell will give a similar talk Saturday at the Pacific Science Center in Seattle.

For more information: http://kencroswell.com/