New Method Helps Astronomers Directly Image Exoplanets Around Distant Stars

Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

Published

Arist's impression of an exoplanet. NASA/JPL-Caltech/Ames

An international team of astronomers has managed to directly image several objects orbiting stars larger than our Sun. The objects orbit far away from their host stars and may be either planets or small stars, but that they have been seen directly suggests a new approach to finding long-orbit exoplanets.

In a paper, published in the Astrophysical Journal, the team looked for far-away companions of six intermediate mass stars. They discovered that three stars, Gamma Hya, HD 5608, and HD 109272, have stellar companions, which were imaged directly. The companions have 61 percent, 10 percent, and 28 percent of the mass of the Sun, respectively. These objects are located further than Neptune is from our star.

The other three stars also have companions but they are too faint to be seen with current technology. Estimates by the researchers suggest that iota Dra, 18 Del, and HD 14067 have potential exoplanets with a mass between 30 and 60 times the mass of Jupiter.

^{Above, direct images of three of the objects, circled. The host stars are shown in white. NAOJ}

To look for the objects around the stars, the researchers started by using a well-known method called the radial velocity method. They looked at the wobbles in the stars generated by the gravitational effect planets have. The shape and intensity of the wobbles change depending on how close and how big the companion is.

Nearby objects generate a wave-like wobble, but if the companion is further out than 1.5 billion kilometers (930 million miles) from its star, the wobble looks more like a linear increase. The team had to prove that this linear trend was due to a distant object, so they observed the candidate objects with the Subaru telescope in Hawaii.

The astronomers hope that this method will be used to discover many more distant objects that we might be missing from current surveys. So far we have confirmed the existence of more than 3,500 exoplanets, and every new finding allows us to refine our planetary formation theories, getting a better idea as to how Earth got here.