August 7, 2008
A Dutch schoolteacher has discovered a mysterious and unique astronomical object through the Galaxy Zoo project, which enables members of the public to take part in astronomy research on-line.
Hanny van Arkel, a primary schoolteacher from the Netherlands, came across the image of a strange gaseous object with a hole in the center that has been described as a "cosmic ghost" while using the galaxyzoo.org
web site to classify images of galaxies.
She posted about the image — which quickly became known as Hanny's "Voorwerp" after the Dutch word for "object" — on the Galaxy Zoo forum and the astronomers who run the site began to investigate. They soon realized the potential significance of what they think is a new class of astronomical object and will now use the Hubble Space Telescope to get a closer look at "Hanny's Voorwerp."
"At first we thought it was a distant galaxy," said Dr. Chris Lintott of Oxford University, a galaxyzoo.org team member, "but we realized there were no stars in it so that it must be a cloud of gas." What was particularly puzzling to astronomers was that the gas was so hot — more than 18,000° Fahrenheit (10,000° Celsius) — when there were no stars in the vicinity to heat it up.
"We now think that what we're looking at is light from a quasar — the bright, stormy center of a distant galaxy powered by a supermassive black hole," said Dr. Lintott. "The quasar itself is no longer visible to us, but its light continues to travel through space and the Voorwerp is a massive 'light echo' produced as this light strikes the gas."
The black hole at the center of the galaxy, IC 2497, is now "turned off" — which is why the quasar has gone dim — but around 100,000 years ago the quasar was bright enough to have been visible from Earth through a small, inexpensive telescope.
Dr. Lintott added: "From the point of view of the Voorwerp, the galaxy looks as bright as it would have done before the black hole turned off — it's this light echo that has been 'frozen in time' for us to observe. It's rather like examining the scene of a crime where, although we can't see them, we know the culprit must be lurking somewhere nearby in the shadows."