James Webb Space Telescope studies dusty ‘pancakes’ that feed baby stars and natal planets

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Using the James Webb Space Telescope (JWST), astronomers have gained a more detailed view of the turbulent ‘pancakes’ of gas and dust that surround young stars, feeding them and facilitating their growth before planets form.

JWST gathered new details about the ‘winds of change’ gas currents blowing through these protoplanetary disks and carving their shapes. As it did this, the powerful space telescope saw evidence of a mechanism that allows a young star to collect the disk material it needs to grow.

A team led by astronomers from the University of Arizona collected observations of four protoplanetary disk systems, all of which appear sideways from Earth. They are the most comprehensive look at the forces that shape protoplanetary disks and provide a snapshot of what our Solar System and our young Sun looked like about 4.6 billion years ago, before the formation of Earth and the other planets.

“Our observations strongly suggest that we have obtained the first detailed images of the wind that could remove angular momentum and solve the long-standing problem of star and planet formation,” said team leader Ilaria Pascucci of the Lunar and Planetary Laboratory of the University of Arizona. said in a statement.

“How a star builds up mass has a major impact on how the surrounding disk evolves over time, including how planets form later,” Pascucci says. “The specific ways in which this happens are not yet understood, but we think that winds driven by magnetic fields over most of the disk surface may play a very important role.”

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The team’s research was published Friday (Oct. 4) in the journal Nature Astronomy.

Tracking the winds of change around young stars

It is estimated that within the part of the cosmos that humanity can see, as many as 3,000 stars are born every second. In their infancy, these stellar bodies are called ‘protostars’ and are surrounded by a prenatal cocoon of gas and dust from which they formed.

Over time, this cloud flattens as it orbits the protostar, which feeds from it to gather enough mass to initiate the fusion of hydrogen into helium in the core. This process defines what a main sequence or “mature” star is.

However, in order for the protostar to nourish and grow, the gas swirling around it must lose its angular momentum. If it didn’t, it would just keep spinning around the protostar forever, hanging and never falling to the surface.

But despite how ubiquitous this process must be in the cosmos, scientists have struggled to understand the mechanism behind the loss of inertia. One suggestion that has recently gained support is that winds driven by magnetism rushing through the protoplanetary disk may carry gas away from the surface, carrying away angular momentum.

Team member Tracy Beck, a researcher at NASA’s Space Telescope Science Institute, pointed out that because there are other mechanisms at work that generate winds in protoplanetary disks, it was critical for the team to distinguish between these processes.

For example, a protostar’s magnetic field creates an “X-wind” that pushes out material on the inner edge of the protoplanetary disk. Meanwhile, the baby star’s intense radiation blows away material in the outer parts of the disk, eroding it and creating “thermal winds.” These latter winds blow at lower speeds than X-winds, which can travel tens of kilometers per second.

X-winds are not only faster, but also originate further from the central protostar than thermal winds. They can also extend further above the disk than thermal winds, reaching distances hundreds of times greater than the distance between Earth and the Sun.

Fortunately, the incredible sensitivity and high resolution of JWST’s infrared vision are ideally suited to distinguish between magnetic field-driven winds, thermal winds, and X-winds blowing around protostars.

The $10 billion space telescope was aided in its research by selecting protostar systems that are on the edge as seen from Earth. That orientation means that the dust and gas in the protoplanetary disk acted as a natural shield, blocking starlight from the protostars, keeping JWST from being blinded and allowing it to distinguish between the winds.

Without this hindrance, the team was able to use JWST’s Near Infrared Spectrograph (NIRSpec) to trace various atoms and molecules as they traveled through these protoplanetary disks. Using NIRSpec’s Integral Field Unit (IFU), they were then able to build a complex 3D image of the structure of a central jet within a conical envelope of disk winds. This shell was structured like an onion, made of layers that originated at increasingly larger radii in the disk.

The team discovered clear central holes in these cones, formed by the wind in each of the four protoplanetary disks.

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The researchers now want to study other protoplanetary disks in an attempt to discover whether these holes are common. They can then try to determine what role they can play in nurturing young stars.

“We think they are common, but with four objects it’s a bit hard to say,” Pascucci concluded. “We want to get a larger sample with JWST and then also see if we can detect changes in these winds as stars gather and planets form.”