Astronomers use the James Webb Space Telescope (JWST) to look for planets in the process of forming around baby stars. The powerful space telescope delivered the goods quickly, albeit unexpectedly.
These baby planets are forming into swirling clumps of gas and dust called protoplanetary disks, accumulating more mass as they do so. Humanity has imaged many of these protoplanetary disks, but to date astronomers have only seen the planets forming within them a handful of times.
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 wide 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 hopes of detecting a planet formation.
The research also revealed hitherto unseen interactions between protoplanetary disks and envelopes of gas closer to the stars at the heart of these disks.
Relating to: Baby star’s planet-forming disk contains 3 times more water than all of Earth’s oceans
“Basically, in every disk we observed with sufficiently high resolution and sensitivity, we saw large structures such as gaps, rings, and, in the case of SAO 206462, spirals,” team member and University of Michigan astronomer Gabriele Cugno said in a statement. . “Most, if not all, of these structures can be explained by the formation of planets interacting with disk material, but there are other explanations that do not involve the presence of giant planets.
“If we eventually manage to see these planets, we can connect some of the structures together by forming companions and relate their formation processes to the properties of other systems at much later stages. We can eventually connect the dots and understand how planets and planetary systems evolve as a whole.”
Finding an unexpected planet
Cugno led a JWST survey of the protoplanetary disk around the protostar SAO 206462. A protostar is a stellar body that does not have sufficient mass in its core to trigger the fusion of hydrogen into helium; this process defines a full-fledged main sequence. star like the sun.
The team detected signals of a forming planet in the protoplanetary disk around SAO 206462, but with a twist: It wasn’t the planet they expected to see.
“Many simulations suggest that the planet should be huge, large, hot and bright inside the disk. But we couldn’t find it. This means either the planet is much colder than we thought, or it may be obscured by some material that prevents us from seeing it,” he said. continued Cugno. “What we found is a distinct planet candidate, but we can’t say with 100% certainty whether it’s a planet, a faint background star, or a galaxy that’s polluting our image.
“Future observations will help us understand exactly what we are looking at.”
This isn’t the first time the SAO 206462 disk has been in focus. Hubble, Alma, and the Very Large Telescope (VLT) examined this protoplanetary disk, and these observations revealed that the disk consists of two powerful spirals.
These spirals are probably created by a planet forming. But before searching for this planet with JWST, the team expected to see a gas giant planet composed mostly of helium, like Saturn or Jupiter.
“The problem is that everything we’re trying to detect is hundreds of thousands, if not millions of times fainter than the star,” Cugno said. said. “It’s like spotting a small light bulb next to a lighthouse.”
JWST’s Near Infrared Camera (NIRCam) allowed Cugno and his colleagues to examine the disk of SAO 206462 more deeply and detect thermal energy from the planet; Some of this energy is released when material falls on it at high speeds.
“When the material falls on the planet, it hits the surface and emits an emission line at certain wavelengths,” Cugno said. “We use a series of narrow-band filters to detect this accumulation. This has been done before at optical wavelengths from the ground, but with JWST this is the first time it has been done in the infrared.”
This showed a planet separated from the central protostar by about 300 times the distance between Earth and the sun. Gas giants usually form much closer to their stars than this; Some migrate outwards after the protoplanetary disk breaks up.
NIRCam results ruled out the presence of an object in the disk with a mass greater than 2.2 times the mass of Jupiter; Cugno and his colleagues concluded that if there was a gas giant forming the smooth spirals of SAO 206462’s protoplanetary disk, this must be it. Be very cold.
Relating to: Exoplanets: Everything you need to know about worlds beyond our solar system
Youngest star has the right ingredients for planet formation
While Cugno and colleagues looked at the disk around SAO 206462, Victoria University researcher Camryn Mullin used JWST to study the star HL Tauri (HL Tau). This is a baby located about 450 light-years from Earth and also studied with numerous telescopes.
With an estimated age of no more than 1 million years (compared to our middle-aged sun of 4.6 billion years), HL Tau is the youngest star in the JWST protoplanetary disk survey.
“HL Tau is the youngest system in our study and is still surrounded by a dense stream of dust and gas falling onto the disk,” said Mullin. “We were amazed at the level of detail we could see in this surrounding material with JWST, but unfortunately it blocks signals from potential planets.”
It is well known that the HL Tau disk has numerous cavities and solar system-sized rings that could host planets. But because the disk is full of dust and the system is young, even JWST is unlikely to directly see planets around HL Tau.
With JWST, the team was able to distinguish a feature called the proto-stellar envelope. This represents a dense flow of dust and gas beginning to coalesce around HL Tau. This raw material flows from the interstellar medium, the gas and dust found between stars, into the star and its disk, and will eventually serve as raw material for the birth of planets.
The planet-building quest continues!
NASA Hubble/Sagan Fellow Kevin Wagner of the University of Arizona Steward Observatory examined the proto-planetary disk of MWC 758 with JWST. This is another protoplanetary disk with spiral arms that could indicate the existence of a massive planet.
This possible planet and others failed to show up in the team’s study, but the sensitivity and power of JWST allowed them to place constraints on possible planet formation within this protoplanetary disk. This included ruling out the possibility of planets being found in the outskirts of the disk, away from the star MWC 758.
“The lack of detection of planets in all three systems suggests that the planets causing gaps and spiral arms are either too close to their host stars or too faint to be seen with JWST,” Wagner said. “If the latter is true, this tells us that they were relatively low-mass, low-temperature, dust-covered, or a combination of the three, as was likely the case with MWC 758.”
RELATED STORIES:
— James Webb Space Telescope finds water and methane in atmosphere of ‘hot Jupiter’
— James Webb Space Telescope digs through the dust to find an ancient ghost galaxy
— James Webb Space Telescope peering into a galactic garden of budding stars (image)
Such studies of the formation of planets around young stars are vital to understanding how material is distributed in young systems and how mature assemblies such as solar systems emerge, the researchers said.
“Only 15% of stars like the Sun have planets like Jupiter. Understanding how they form and evolve and improving our theories is really important,” said team member and University of Michigan astronomer Michael Meyer. said. “Some astronomers think that these gas giant planets regulate the distribution of water to rocky planets that form in the interiors of the disks.”
Therefore, this research could be crucial to understanding how the Earth was formed and how it can support life.
The team’s research was discussed in three papers published last week in The Astronomical Journal.