Unseen Newborn Planets Are Stirring Up Dust Around a Young Star
Our universe is so capricious it sometimes likes to play a game of hide and seek. In 2017, astronomers were surprised to see a huge shadow sweeping across a disk of dust and gas encircling the nearby young star TW Hydrae. The shadow is cast by an inner disk of dust and gas that is slightly tilted to the plane of the outer disk. The shadow can only be clearly seen because the system is tilted face-on to Earth, giving astronomers a bird’s-eye view of the disk as the shadow sweeps around the disk like a hand moving around a clock.
But a clock has two hands (hours and minutes) sweeping around at different rates. And, it turns out, so does TW Hydrae. Astronomers used Hubble to find a second shadow emerging from yet another inner disk, that is tilted to the two outer disks. So, the system looks increasingly complicated with at least three nested disks slightly tilted relative to each other. The disks are proxies for unseen planets around the star. Each planet is gravitationally pulling on material near the star and warping what would have been a perfectly flat, pancake-shaped disk if no planets were present. This is not a surprise because the planets in our solar system have orbital planes that vary in tilt by a few degrees from each other. TW Hydrae gives astronomers a ringside seat to how our solar system may have looked during its formative years.
Hubble Space Telescope Follows Shadow Play Around Planet-Forming Disk
The young star TW Hydrae is playing “shadow puppets” with scientists observing it with
Now, a second shadow – playing a game of peek-a-boo – has emerged in just a few years between observations stored in Hubble’s MAST archive. This could be from yet another disk nestled inside the system. The two disks are likely evidence of a pair of planets under construction.
TW Hydrae is less than 10 million years old and resides about 200 light-years away. In its infancy, our solar system may have resembled the TW Hydrae system, some 4.6 billion years ago. Because the TW Hydrae system is tilted nearly face-on to our view from Earth, it is an optimum target for getting a bull’s-eye-view of a planetary construction yard.
The second shadow was discovered in observations obtained on June 6, 2021, as part of a multi-year program designed to track the shadows in circumstellar disks. John Debes of AURA/STScI for the
The best solution the team came up with is that there are two misaligned disks casting shadows. They were so close to each other in the earlier observation they were missed. Over time they’ve now separated and split into two shadows. “We’ve never really seen this before on a protoplanetary disk. It makes the system much more complex than we originally thought,” he said.
The simplest explanation is that the misaligned disks are likely caused by the gravitational pull of two planets in slightly different orbital planes. Hubble is piecing together a holistic view of the architecture of the system.
The disks may be proxies for planets that are lapping each other as they whirl around the star. It’s sort of like spinning two vinyl phonograph records at slightly different speeds. Sometimes labels will match up but then one gets ahead of the other.
“It does suggest that the two planets have to be fairly close to each other. If one was moving much faster than the other, this would have been noticed in earlier observations. It’s like two race cars that are close to each other, but one slowly overtakes and laps the other,” said Debes.
The suspected planets are located in a region roughly the distance of
The TW Hydrae data are from Hubble’s Space Telescope Imaging Spectrograph. The DOI: 10.3847/1538-4357/acbdf1
The Hubble Space Telescope is a project of international cooperation between NASA and ESA. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.