Three University of Toronto astronomers may have made history this past summer by simply taking a picture. Dr. David Lafrenière, Professor Ray Jayawardhana, and Professor Marten van Kerkwijk claim to have taken the first direct image of an extra-solar planet orbiting a sun-like star.
After searching approximately 80 stars in the Upper Scorpius association using the Gemini North telescope, the team noticed the star 1RXS J160929.1-210524 seemed to have a planet orbiting it. Unlike anything in our solar system, the planet is eight times the mass of Jupiter, has an estimated temperature of 1500°C, and orbits 330 times further from its star than Earth does from the sun. Due to its distance from the star, a complete orbit takes around 6,000 years.
A direct image of an orbit is extremely rare, as stars are so bright they outshine anything in their vicinity. It can take years to completely verify that an image is showing a planet-star companion. Using other methods, astronomers have tracked down more than 300 planets that suggest they might be orbiting a star. One method involves looking for light alterations made by a planet passing in front of a star. Another looks for Doppler shift, a back and forth movement in the star.
The U of T astronomers’ surprising planetary find was made possible by the Gemini telescope’s high resolution adaptive optics capabilities. The sophisticated technology allowed the researchers to distinguish between the many things that orbit a star: namely other stars, brown dwarfs, and planets. Being able to differentiate between these objects became critical when the team first detected two stars with what seemed like objects orbiting them.
Jayawardhana explains that the first star’s object turned out to be a background star that appeared to be a close companion, but was actually much further away. To make a distinction between planets and stars, the team took infra-red and near infra-red images through filters to determine the object’s “colour.” The redder the object, the cooler it is. “We targeted young stars so that any planetary mass object they hosted would not have had time to cool, and thus would still be relatively bright,” says van Kerkwijk. Special filters allow astronomers to determine the composition of the planet’s atmosphere, which is usually water vapor and carbon dioxide. This eventually showed the star’s companion to be a planet, not another star.
While it may seem odd that a heat emitting ball of fire could possibly be a planet, Jayawardhana explains that temperatures of this magnitude are very low in stellar standards. It might be a hot planet, but is by no means even close to a cool star. The fact that it is hot and bright but remains at such a distance from its star means the planet is producing its own heat. In several hundred million years, the planet is expected to cool down and shrink to a size equal to Jupiter.
