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TW Hydrae

Hubble captures shadow play on a planet-forming disk!

Hubble captures “shadow puppets” as scientists observe the young star TW Hydrae with NASA’s iconic space telescope.”

Prior Observation of the Shadows:

In 2017, scientists reported finding a shadow moving across the surface of the red dwarf star’s encircling gas and dust disk, which has the appearance of a large pancake. The inner disk, which is slightly tilted about the much larger outer disk and casts the shadow, not a planet, is to blame. One hypothesis is that the gravity of an undiscovered planet is drawing gas and dust into its inclination orbit.

Recent Observation of the Shadows:

Now, a second shadow has appeared in just a few years between observations kept in Hubble’s MAST archive, playing peek-a-boo. This might come from a hidden disk inside the system. The existence of the two disks suggests that there are currently two planets being built.

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Hubble Space Telescope photos show shadows sweeping across the disks encircling the system. The interpretation is these shadows are from slightly inclined inner disks that block starlight from reaching the outer disk, and therefore are casting a shadow. NASA, AURA/STScI for ESA, Leah Hustak (STScI)

What is TW Hydrae and what is its significance?

TW Hydrae is a star that is 200 light-years away and less than 10 million years old. 4.6 billion years ago, when our solar system was still young, it might have resembled the TW Hydrae system. The TW Hydrae system is an ideal target for gaining a bull’s-eye view of a planetary construction yard since it is turned nearly face-on to our view from Earth.

Observations made on June 6, 2021, as part of a multi-year mission to track the shadows in circumstellar disks, revealed the second shadow. In Baltimore, Maryland, at the Space Telescope Science Institute, John Debes of AURA/STScI for the European Space Agency compared the TW Hydrae disk to earlier Hubble observations.

Explanation of the chief investigator about the Hubbles’ image:

Debes, who served as the study’s chief investigator and lead author, said, “We found out that the shadow had done something completely different,” She explains, “When I first looked at the data, I thought something had gone wrong with the observation because it wasn’t what I was expecting. I was flummoxed at first, and all my collaborators were like: what is going on? We really had to scratch our heads and it took us a while to actually figure out an explanation.”

Best Explanation:

The best explanation the team could come up with is that two shadows are being cast by mismatched disks. They were overlooked in the earlier inspection because they were so close to one another. They eventually split apart and became two separate shadows. This is something we’ve never truly seen on a protoplanetary disk before. The system becomes considerably more intricate than we first believed, he said.

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Credits: NASA, ESA, STScI, and John Debes (AURA/STScI for ESA); Image Processing: Joseph DePasquale (STScI)

What is the cause of the misaligned disks in the TW Hydrae system?

The gravitational force of two planets in slightly different orbital planes is most likely what is causing the misaligned disks, according to the simplest explanation. Hubble is assembling a comprehensive picture of the system’s architecture.

The disks could be substitutes for planets that are circling the star and lapping one another. It resembles slightly varying the speeds of two vinyl phonograph records. Labels may coincide occasionally, but eventually one overtakes the other.

The two planets must be rather close to one another, according to the evidence. If one was traveling considerably more quickly than the other, earlier observations would have shown this. It’s similar to two race cars that are parallel to one another, but one gradually passes and laps the other, Debes added.

Where the presumed planets are situated?

The presumed planets are situated in an area roughly where Jupiter is from our Sun. Additionally, the shadows orbit the star once every 15 years, which is the expected orbital period given their proximity to the star.

What is the evidence for an outer planet in the TW Hydrae system, and why are inner planets challenging to detect?

Additionally, the angle between these two inner disks and the plane of the outer disk is between five and seven degrees. The variety of orbital inclinations within our solar system is equivalent to this. This architecture fits the typical solar system style, according to Debes.

Outer Planet:

The outer disk on which the shadows are cast could be several times as large as the Kuiper belt of our solar system. At a distance twice as far from the Sun as Pluto’s typical distance, this bigger disk contains an odd gap. This could be proof that the system contains a third planet.

Inner Planet:

Any inner planets would be challenging to find since their light would be obscured by the star’s brightness. Their reflected light would also be diminished by dust in the system. If Jupiter-mass planets are pulling on the star, ESA’s Gaia space observatory might be able to detect a wobble, although this would take years due to the planets’ lengthy orbital periods.

The Hubble Space Telescope Imaging Spectrograph provided the TW Hydrae data. The infrared vision of the James Webb Space Telescope might also be able to reveal the shadows in greater detail.

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