November 9, 2012
Excess Of Carbon Monoxide Around Ancient Star Caused By Comet Collisions
Brett Smith for redOrbit.com - Your Universe Online
Using a radio telescope in the mountainous area of southern Spain back in 1995, astronomer Benjamin Zuckerman and two colleagues found an unusually high amount of carbon monoxide gas orbiting a star in the constellation Cetus, 49 CETI.
"We now believe that 49 CETI is 40 million years old, and the mystery is how in the world can there be this much gas around an otherwise ordinary star that is this old," said Zuckerman, currently a UCLA professor of physics and astronomy. "This is the oldest star we know of with so much gas."
The origin of this gas was a mystery to these astronomers until recently, when Zuckerman and his colleague Inseok Song, an astronomy professor from the University of Georgia, determined that millions of comets colliding every six seconds in an orbit around the star were the source of the carbon monoxide, according to their report in the Astrophysical Journal.
While many younger stars have gaseous clouds orbiting them for millions of years after their formation, 49 CETI was singled out by the astronomers because it was thought to be older and they had determined that any gas orbiting it should have dissipated long ago.
Zuckerman and Song propose that the mysterious gas comes from comets found in a disk-shaped region around the star that is analogous to our solar system's Kuiper Belt, located just outside the orbit of Neptune.
Kuiper Belt, including Pluto, has about one-tenth the mass of the Earth, but as the solar system was forming, about 4.5 billion years ago, experts say the Kuiper Belt likely weighed approximately 40 times more than our planet. That continuing loss of mass is the result of collisions in the belt that pulverize the planetoids and comets into dust and gas.
By comparison, the belt of planetoids, comets and other objects that orbit around 49 CETI has a mass of about 400 Earths, 4,000 times the current mass of the Kuiper Belt.
"Hundreds of trillions of comets orbit around 49 CETI and one other star whose age is about 30 million years. Imagine so many trillions of comets, each the size of the UCLA campus – approximately 1 mile in diameter – orbiting around 49 CETI and bashing into one another," Zuckerman said. "These young comets likely contain more carbon monoxide than typical comets in our solar system. When they collide, the carbon monoxide escapes as a gas. The gas seen around these two stars is the result of the incredible number of collisions among these comets.”
"We calculate that comets collide around these two stars about every six seconds," he said. "I was absolutely amazed when we calculated this rapid rate. I would not have dreamt it in a million years. We think these collisions have been occurring for 10 million years or so."
Cetus, the constellation that contains 49 CETI, is located just 220 light years away from Earth and can be seen with the naked eye on a clear night. Named after a mythic Greek sea creature, Cetus can be found in the sky alongside other water-related constellations like Aquarius and Pisces.