Astronomers at NASA’s Space Telescope Science Institute (STScI) believe that a shadow spotted by the Hubble Space telescope could be evidence of a large planet orbiting inside the dust disk around a young star.
The team first noticed the shadow — also known as “brightness asymmetry” — in 2005, but at the time they did not have the proper data to explore the feature. This is because dim planets are very hard to see next to their bright host stars. While astronomers have special methods to view such systems, the new planet — located in the TW Hydrae stellar system some 192 light-years from Earth — acts in a unique way.
TW Hydra is surrounded by a disk of dust and gas known as a protoplanetary disk. These structures usually circle young stars and then eventually come together to form planets. However, while that process is well known, Hubble is not powerful enough to see what is going on inside a galaxy as far away as TW Hydra, The Christian Science Monitor reports.
To overcome this, the team analyzed over 16 years worth of data collected on the shadow. This revealed that, in the decade and a half researchers were studying it, the phenomenon had made one complete revolution around the host star. Protoplanetary disks commonly move at an extremely slow rate. If the dark spot was simply a feature on the disk, it would have taken centuries to go complete one rotation. The quick speed meant it had to be a celestial body.
“The fact that I saw the same motion over 10 billion miles from the star was pretty significant, and told me that I was seeing something that was imprinted on the outer disk rather than something that was happening directly in the disk itself,” said team leader John Debes of the Space Telescope Science Institute in Baltimore, Maryland, in a statement. “The best explanation is that the feature is a shadow moving across the surface of the disk.”
As the team investigated the shadow, they found that it is created by something that sits deep within the disk and is so close to the star that it cannot be viewed by any modern telescope. That led them to postulate that the shadow is the result of an unseen planet pulling dust and gas up and out of the disk. It is that matter which blocks the star’s light.
The team believes that further studies on the dark spot will lead to new ways to observe sites of planet formation indirectly. This could help expand future research on distant galaxies and allow astronomers to uncover hidden planets in other star systems.
“This is the very first disk where we have so many images over such a long period of time, therefore allowing us to see this interesting effect,” Debes added. “That gives us hope that this shadow phenomenon may be fairly common in young stellar systems.”