The star in question appears to harbor an immense exoplanet. It is one of the few exoplanets directly observed to date. But that may now be about to change.
In the meantime, astronomers have already tracked down more than 5000 exoplanets. Most of them, however, are not directly depicted. Researchers usually rely on indirect methods, inferring the presence of an exoplanet by peering at the parent star, hoping to witness the star’s brightness dip momentarily. Space telescope Gaia may change this. Because thanks to this satellite, researchers encountered a ‘wobbly’ star, after which researchers saw a truly gigantic exoplanet appear before their eyes.
As mentioned, there are two ways astronomers hunt for exoplanets: directly and indirectly. Historically, most exoplanets have been found using indirect methods. Direct means that a telescope actually sees the planet. Currently, of the thousands of exoplanets known to us, only twenty have been directly imaged. It is not surprising that there are so few of them. Exoplanets are extremely difficult to see with existing telescopes. To get a good image of them, the exoplanet must be far from its parent star and also much more massive than Jupiter, the largest planet in our solar system. And the universe unfortunately doesn’t make many such planets.
But maybe Gaia will make the direct observation of exoplanets a bit easier now. Using this telescope, astronomers scanned the night sky, looking for stars that literally wobbled in the sky. When a planet revolves around a star, the star wobbles back and forth, increasing or decreasing its relative speed relative to the Earth. So a wobbling star can betray the presence of a planet.
After thoroughly studying the collected data, the researchers did indeed discover a number of promising wobbling stars, which may well be home to a giant planet. Then they turned to the Subaru telescope, located on the island of Hawaii. And not much later they spotted an immense exoplanet orbiting the star HIP 99770.
The newly discovered exoplanet has been named HIP 99770 b and is about sixteen times the mass of Jupiter, the researchers write in the journal Science. The exoplanet orbits a star that is almost twice as massive as our sun. Although the planet’s orbit is more than three times that of Jupiter’s orbit around the sun, it receives nearly the same amount of light as Jupiter because its parent star is much brighter than ours.
With the discovery, the researchers show that with the help of Gaia it is possible to directly image exoplanets in a much easier way. And that is an important step forward. In addition, the discovery of HIP 99770 b also has broader implications. “Not only does it show how we can detect more exoplanets, it also shows how we can better characterize them,” said study co-author Thayne Currie. That’s because direct and indirect detection methods yield different information about a planet. Using direct methods, astronomers can accurately determine the temperature and composition of a planet. Meanwhile, indirect methods provide accurate measurements of mass and orbit, especially if they are then combined with measurements of the planet’s position through direct observations.
In short, the combination of the Gaia data with observations from the Subaru telescope gives astronomers the best of both worlds. And this is just the beginning. Now that astronomers know that the planet exists and is also visible, other telescopes can take on the task of further analyzing the light. “The discovery of this planet will lead to dozens of follow-up studies,” Currie believes.
Moreover, many more discoveries are likely to come. HIP 99770 was one of the first stars to be studied. Currie and his team are currently analyzing data from about 50 other stars. And what they’ve seen so far suggests that more discoveries of as-yet-unknown exoplanets are in the pipeline.