New image may reveal embryonic world
David Shiga
A bright spot (red) within a clearing in the dusty disc around the star AB Aurigae may mark the site of a developing planet. The planet would be too dim to see directly, but its gravity may have captured a dense cloud of gas and dust around it that could create the bright patch (Image: Lyot Project)
An intriguing bright spot detected next to a star 470 light years from Earth may indicate the presence of a developing planet in the young star system. The discovery suggests astronomers could soon directly image planets around ordinary stars.
Astronomers have detected more than 270 planets around stars to date, but the vast majority have been discovered indirectly by the way the planet's gravity makes the star wobble.
No one has ever obtained an undisputed image of a planet around an ordinary star. One confirmed planet called 2M1207b has previously been photographed in orbit around a brown dwarf. A brown dwarf is more massive than a planet but too puny to shine the way ordinary stars do, by sustaining the nuclear fusion of hydrogen in their cores.
Although the new observations are not sensitive enough to see the suspected planet directly, they show a small bright patch that may be a cloud of gas and dust falling onto a developing planet.
The bright spot is next to a star called AB Aurigae, which is 2.4 times the mass of the Sun and about 3 million years old. That is about the age when planets are thought to form, so further observations could reveal unprecedented details about the early stages of the process.
Blocked light
Normally the glare of the star would make it impossible to see things in its vicinity. But astronomers led by Ben Oppenheimer of the American Museum of Natural History in New York City, US, obtained their image using an instrument called a coronagraph, which blocks the light from the central star but lets light from the surroundings shine through.
Their instrument, part of an effort called the Lyot Project to survey the vicinity of stars, was used in conjunction with the US Air Force's 3.6-metre telescope, called the Advanced Electro-Optical System (AEOS) in Hawaii, US. AEOS uses adaptive optics, which compensates for atmospheric blurring to produce very sharp images.
The image shows a swirling disc of gas and dust around the star. The disc appears to have a notch in it – a relatively empty area that may have been cleared out by the gravity of a planet. Inside the empty patch sits the intriguing bright spot.
Powerful imager
The patch is so faint that it is barely detectable. The astronomers cannot completely rule out the possibility that it is simply noise in their detector, caused for example, by starlight bouncing around inside the instrument. But the instrument has never produced such a reflection in the four years it has been observing stars.
Regardless of the nature of the bright patch, the notch in the disc suggests the presence of an object that is clearing away material.
"The deficit of material could be due to a planet forming and sucking material onto it, coalescing into a small point in the image and clearing material in the immediate surroundings," Oppenheimer says. "It seems to be indicative of the formation of a small body, either a planet or a brown dwarf."
The image gives a taste of the potential of an even more powerful instrument called the Gemini Planet Imager, which could take pictures of planets around other stars. It is scheduled to start observing in 2010 using the Gemini South 8-metre telescope in Chile.
Journal reference: Astrophysical Journal (in press)