In a giant cloud of gas and dust 1,400 light-years away, twin shadows extend through space from a star, like the vast wings of a colossal cosmic bat. Now astronomers have surprised the hit of these shadows, and are not sure what is causing it.
The winged shadow, photographed using Hubble in 2018 and nicknamed Bat Shadow, is caused by a disk of dust and gas surrounding a young star. And it’s possible the wing wobble is caused by a baby planet.
“The shadow moves. It flaps like the wings of a bird!” said astronomer Klaus Pontoppidan of the Space Telescope Science Institute.
The star is called HBC 672, and it is only one or two million years old.
Because he is so young, he is still sitting in the middle of the disk of dust and gas that fed the star as it grew. We believe that these disks then clump together, forming asteroids and planets like the Solar System, but that process is far from complete for HBC 672.
The star and its disk are in a much larger cloud of gas and dust called the reflection nebula. It is so named because it is illuminated by stars, which reflect their light (unlike emission nebulae, which emit their own light). Think of HBC 672 as a light bulb that lights up the walls of the room around you.
In this metaphor, the protoplanetary disk is like a cylindrical screen. The star’s light shines freely from the top and bottom of the disk, but the disk blocks light around the center, casting a long shadow: at least 17,000 astronomical units, or 0.24 light years, in each direction. (By context, the average distance from Pluto to the Sun is 39 astronomical units).
Hubble studied the region twice: first on July 22, 2017, and then 404 days later, on August 30, 2018. And when Pontoppidan and his team compared these observations, they noticed that the shadow had changed position. Something was staggering him.
The culprit may be a low-mass, low-light companion star that orbits outside the plane of the disk. But the team believes this is unlikely.
Although the disk is too small and too far away to be seen directly, light analysis suggests that the inner part of the disk is still there, which would not be the case if HBC 672 had a binary partner. And a binary partner would probably have sucked up more material from the disk than has been observed.
The other option is a double warp on the disk, as seen in the video above, presented by a young planet in an orbit of at least 180 days, within a few astronomical units of the star, and which is highly tilted from the map of the Dto.
With just two sets of observations it is difficult to pinpoint an exact cause, but if it is a deformed disk caused by an orbiting planet then the ‘wings’ should flap at regular intervals. This periodicity could be detected with future observations.
“We suggest that further monitoring of disk shadow from a stable platform like Hubble, or the upcoming James Webb Space Telescope, offers a unique opportunity to constrain, in real time, the hydrodynamics of terrestrial regions that form planets,” wrote the investigators in their role
The research has been published in The astrophysical journal.