Searching for planets around other stars is a tricky business. They’re so small and faint that it’s hard to spot them. But a possible planet in a nearby stellar system may be betraying its presence in a unique way: by a shadow that is sweeping across the face of a vast pancake-shaped gas-and-dust disk surrounding a young star.
The planet itself is not casting the shadow. But it is doing some heavy lifting by gravitationally pulling on material near the star and warping the inner part of the disk. The twisted, misaligned inner disk is casting its shadow across the surface of the outer disk.
A team of astronomers led by John Debes of the Space Telescope Science Institute in Baltimore, Maryland say this scenario is the most plausible explanation for the shadow they spotted in the stellar system TW Hydrae, located 192 light-years away in the constellation Hydra, also known as the Female Water Snake. The star is roughly 8 million years old and slightly less massive than our sun. Debes’ team uncovered the phenomenon while analyzing 18 years’ worth of archival observations taken by NASA’s Hubble Space Telescope.
“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 said. “That gives us hope that this shadow phenomenon may be fairly common in young stellar systems.”
Debes will present his team’s results Jan. 7 at the winter meeting of the American Astronomical Society in Grapevine, Texas.
Debes’ first clue to the phenomenon was a brightness in the disk that changed with position. Astronomers using Hubble’s Space Telescope Imaging Spectrograph (STIS) first noted this brightness asymmetry in 2005. But they had only one set of observations, and could not make a definitive determination about the nature of the mystery feature.
Searching the archive, Debes’ team put together six images from several different epochs. The observations were made by STIS and by the Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS).
STIS is equipped with a coronagraph that blocks starlight to within about 1 billion miles from the star, allowing Hubble to look as close to the star as Saturn is to our sun. Over time, the structure appeared to move in counter-clockwise fashion around the disk, until, in 2016, it was in the same position as it was in images taken in 2000.
Read More:
http://www.isn-news.net/2017/01/hubble-captures-shadow-play-caused-by.html
