Hubble Catches Young Star Flapping Its “Bat Shadow” Wings

HBC 672 and the bat shadow. NASA, ESA, and STScI

The Serpens Nebula has a peculiar feature – a dark shadow produced by a protoplanetary disk that surrounds a young star. When it was first discovered a few years ago, it was nicknamed the Bat Shadow due to its shape. Now we know this name is more apt than originally thought. The shadowy features of this bat-like phenomenon "flap" like real wing beats.

The feature has two possible explanations. The one favored by researchers is that an exoplanet is orbiting the star at an angle, warping the disk as it moves. The star is known as HBC 672 and is located 1,400 light-years away. As reported in a paper to be published in The Astrophysical Journal, researchers tracked the “flapping” for 404 days. 

The shadow of the protoplanetary disk moves over 404 days. ESA/Hubble, K. Pontoppidan, L. Calçada, M. Kornmesser

"The shadow moves. It's flapping like the wings of a bird!" lead author Klaus Pontoppidan, an astronomer at the Space Telescope Science Institute (STScI) in Baltimore, said in a statement. "You have a star that is surrounded by a disk, and the disk is not like Saturn's rings – it's not flat. It's puffed up. And so that means that if the light from the star goes straight up, it can continue straight up – it's not blocked by anything. But if it tries to go along the plane of the disk, it doesn't get out, and it casts a shadow."

The shadow is 200 times the solar system across and the light of the star takes up to 45 days to reach its edges. If the planet exists, it is probably at a similar distance from its star as Earth is from the Sun. The alternative is that another star outside the disk is creating the wobble, but no evidence of such a companion has yet been found.

The team did not go out looking for such a phenomenon. The original image of the system was taken by another team in a single light filter. When the image was selected to be used in NASA's Universe of Learning, Pontoppidan collected more observations of the shadow. When they compared them to the original one, they noticed that the shadow had moved.

This animation depicts how the “flapping” motion of the shadow of the star HBC 672 has been observed by the NASA/ESA Hubble Space Telescope. ESA/Hubble, L. Calçada



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