A strange winking star in the constellation Monoceros may signal the birth of a new planetary system, where clumps of dust, rocks, and possibly even asteroids circle about and intermittently obscure the light from a young sun.
William Herbst, an astronomer at Wesleyan University in Middletown, Connecticut, and his graduate student Kristin Kearns first noticed unusual light variations coming from the faint star, designated KH 15D, while observing the surrounding stellar cluster in 1997.
Unsure of the significance of the blinking, Herbst and several students kept an eye on KH 15D over the following years. "We couldn't predict what it was going to do next, but we knew that it could be something very interesting, so we kept watching," says Catrina Hamilton, an astronomer at nearby Connecticut College who is working on her Ph.D. with Herbst.
The star KH 15D (top) periodically dims by a factor of 25. Are unborn planets blocking the view?
Photographs courtesy of William Herbst.
By 1999 the researchers had collected enough data to determine a curious periodicity to the starlight: It shines brightly for 26 days, then fades and remains dim for 18 days before returning to full strength. An intervening star or planet would produce a brief eclipse, no longer than a day or so long. Herbst concluded that the extended disappearances could be explained only by a strung-out collection of smaller objects, similar to those in a still-forming planetary system. KH 15D is 2,400 light-years away, but its message hits home, showing what our solar system probably looked like 4.5 billion years ago. "This is the discovery that every astronomer hopes to find," Hamilton says.