The James Webb Space Telescope joins the hunt for newborn exoplanets

Astronomers are looking for planets forming around baby stars using the James Webb Space Telescope (JWST). The powerful space telescope delivered the goods quickly, albeit in an unexpected way.

These infant planets take shape in swirling clumps of gas and dust called protoplanetary disks, gathering more mass as they do. Humanity has images of many of these protoplanetary disks, but astronomers have only seen the planets forming within them a few times so far.

Now, a team led by scientists from the University of Michigan, the University of Arizona, and the University of Victoria has added the power of JWST’s sensitive infrared instruments to this quest. The team used the large scope to observe the protoplanetary disks HL Tau, SAO 206462, and MWC 758, adding observations to data collected by the Hubble Space Telescope and the Atacama Large Millimeter Array (ALMA) in the hope of seeing a planet at formation.

The investigation also revealed hitherto unseen interactions between protoplanetary disks and the gas envelopes closer to the stars at the core of these disks.

Related: The formation disk of a child planet has 3 times more water than all of Earth’s oceans

“Essentially, in every disk we have observed with high enough resolution and sensitivity, we have seen large structures like gaps, rings and, in the case of SAO 206462, spirals,” said team member and University of Michigan astronomer Gabriele Cugno in statement. . “Most, if not all, of these structures can be explained by the formation of planets interacting with the disc material, but there are other explanations that do not involve the presence of giant planets.

“If we finally get to see these planets, we can link some of the structures to formation companions and link formation processes to other system properties at much later stages. Total.”

Unexpected planet arrival

Cugno led the JWST investigation of the protoplanetary disk around the protostar SAO 206462. A protostar is a stellar body that has not yet accumulated enough mass to trigger hydrogen-to-helium fusion at its core, the process that defines an entire main sequence. a star like the sun.

In the protoplanetary disk around SAO 206462, the team saw the signs of a planet forming, but with a twist: It wasn’t the planet they expected to see.

“Some simulations suggest that the planet should be inside the disk, huge, big, hot and bright. But we didn’t find it. This means that the planet is much colder than we think, or for “It could be obscured by some material that prevents us from seeing it,” Cugno continued. “What we have found is another planet candidate, but we cannot say with 100% certainty whether it is a planet or a star or a galaxy or a faint galaxy that contaminates our image.

“Future observations will help us understand exactly what we are observing.”

photograph of a protoplanetary disk around an infant star, showing a blue-white spiral against the darkness of space

photograph of a protoplanetary disk around an infant star, showing a blue-white spiral against the darkness of space

This is not the first time that attention has been drawn to the disk of SAO 206462. Hubble, Alma, and the Very Large Telescope (VLT) have all studied this protoplanetary disk, and these observations have shown that it is composed of two strong spirals .

These spirals are probably being created by a forming planet. Before searching for this planet with JWST, however, the team expected to see a gas giant planet composed mostly of helium, like Saturn or Jupiter.

“The problem is, whatever we are trying to detect is hundreds of thousands, if not millions of times smaller than the star,” said Cugno. “That’s like trying to detect a small light bulb near a lighthouse.”

JWST’s Near Infrared Camera (NIRCam) allowed Cugno and his colleagues to penetrate deeper into the disk of SAO 206462 and detect thermal energy from the planet, some of which is released as material falls onto it at high speeds.

“When material falls into the planet, it shocks the surface and sets off an emission line at specific wavelengths,” said Cugno. “We use a series of narrowband filters to try to detect this accretion. This has already been done from the ground at optical wavelengths, but this is the first time it has been done in the infrared with JWST.”

This showed a planet separated from the central protostar by about 300 times the distance between Earth and the sun. Gas giants tend to be much closer to their stars than this, and some escape there after the protoplanetary disk has dispersed.

The NIRCam results ruled out an object in the disk with a mass greater than 2.2 times the mass of Jupiter, and Cugno and his colleagues concluded that if a gas giant is carving the neat spirals of the protoplanetary disk of SAO 206462, it must. be very cold.

Related: Exoplanets: Everything you need to know about life outside our solar system

The youngest star has the right material for planet formation

As Cugno and his colleagues looked at the disk around SAO 206462, University of Victoria researcher Camryn Mullin used the JWST to study the star HL Tauri (HL Tau). This is an infant located about 450 light years from Earth that has also been explored by many telescopes.

With an estimated age of no more than 1 million years (compared to our sun’s 4.6-billion-year-old average age), HL Tau is the youngest star in the JWST protoplanetary disk investigation.

“HL Tau is the youngest system in our survey and is still surrounded by a dense inflow of dust and gas falling onto the disk,” Mullin said. “We were surprised at the level of detail with which we could see the surrounding material with JWST, but unfortunately, it obscures any signals from the potential planets.”

The disk of HL Tau is well known to contain several solar system-sized voids and rings that could host planets. However, due to the dust-packed nature of the disk and the youth of the system, it is unlikely that even the JWST will see planets around HL Tau directly.

photo of fuzzy yellow and orange concentric rings in deep spacephoto of fuzzy yellow and orange concentric rings in deep space

photo of fuzzy yellow and orange concentric rings in deep space

The team was able to distinguish a feature known as a proto-stellar envelope with the JWST. This indicates the dense inflow of dust and gas that is beginning to coalesce around HL Tau. This raw material is flowing to the star and its disk from the interstellar medium, the gas and dust that exists between the stars, and will eventually become the raw material for the birth planets.

The hunt for planet formation continues!

Kevin Wagner, a NASA Hubble/Sagan Fellow at the University of Arizona’s Steward Observatory, examined the protoplanetary disk MWC 758 with the JWST. This is another protoplanetary disc with spiral arms that could indicate the presence of a giant planet.

This and any other possible planet failed to show up in the team’s study, but the sensitivity and power of the JWST allowed them to place constraints on any planets that may have formed within this protoplanetary disk. This included ruling out the possibility of planets at the edge of the disc, far from the MWC 758 star.

“The lack of planets detected in all three systems tells us that the planets causing the gaps and spiral arms are either too close to their host stars or too faint to see with JWST,” said Wagner. “If the latter is true, it tells us that they have relatively low mass, are at low temperature, shrouded in dust, or have some combination of all three – as is likely the case in MWC 758.”

Composite image of a planet forming disk in deep space with blue and yellow hues of different wavelengths.Composite image of a planet forming disk in deep space with blue and yellow hues of different wavelengths.

Composite image of a planet forming disk in deep space with blue and yellow hues of different wavelengths.


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Such investigations of planet formation around young stars are critical to understanding how materials are distributed in young systems and how mature assemblies such as the solar system came to be, the researchers said.

“There are only about 15% of stars like the sun at planets like Jupiter. It is very important to understand how they form and evolve and refine our theories,” said a team member and the University of Michigan astrologer Michael Meyer. “Some astronomers think that these gas giant planets control the delivery of water to rocky planets that form in the inner parts of the disks.”

Therefore, this investigation could ultimately be the key to understanding how the Earth was formed and how it managed to support life.

The team’s research is discussed in three papers published last week in The Astronomical Journal.

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