- 4630 - HOW PLANETS FORM? - Every second in the Universe, more than 3,000 new stars form as clouds of dust and gas undergo gravitational collapse. Afterward, the remaining dust and gas settle into a swirling disk that feeds the star’s growth and eventually accretes to form planets known as a protoplanetary disk.
----------------------------------------- 4630 - HOW PLANETS FORM?
- This model, known as the “Nebular
Hypothesis”, is the most widely accepted theory, the exact processes that give
rise to stars and planetary systems are not yet fully understood. Shedding
light on these processes is one of the many objectives of the James Webb Space
Telescope (JWST).
-
- Astronomers used the JWST’s advanced
infrared optics to examine protoplanetary disks around new stars. These
observations provided the most detailed insights into the gas flows that sculpt
and shape protoplanetary disks over time.
-
- In order for young stars to grow, they must
draw in gas from the protoplanetary disk surrounding them. For that to happen,
the gas must lose angular momentum (inertia); otherwise, it would consistently
orbit the star and never accrete onto it.
-
- Magnetically driven disk winds have
emerged as a possible mechanism. Primarily powered by magnetic fields, these
“winds” funnel streams of gas away from the planet-forming disk into space at
dozens of kilometers per second.
-
- This causes it to lose angular momentum,
allowing the leftover gas to fall inward toward the star. Researchers selected four protoplanetary
disk systems that appear edge-on when viewed from Earth. Using Webb’s Near
Infrared Spectrograph (NIRSpec), the team could trace various wind layers by
tuning the instrument to detect distinct atoms and molecules in certain
transition states.
-
- The team also obtained spatially resolved
spectral information across the entire field of view using the spectrograph’s
Integral Field Unit (IFU).
-
- This allowed the team to trace the disk
winds in unprecedented detail and revealed an intricate, three-dimensional
layered structure: a central jet nested inside a cone-shaped envelope of winds
at increasing distances. There was a pronounced central hole inside the cones
in all four protoplanetary disks. This
is one of the most important processes at work is how the star accretes matter
from its surrounding disk.
-
- How a star accretes mass has a big influence
on how the surrounding disk evolves over time, including the way planets form
later on. Winds driven by magnetic
fields across most of the disk surface could play a very important role.
-
- However, other processes are also
responsible for shaping protoplanetary disks. These include “X-wind,” where the
star’s magnetic field pushes material outward at the inner edge of the disk.
-
- There are also “thermal winds,” which blow
at much slower velocities and are caused by intense starlight eroding its outer
edge. The high sensitivity and resolution of the JWST were ideally suited to
distinguish between the magnetic field-driven wind, the X-wind, and the thermal
wind. These observations revealed a nested structure of the various wind
components that had never been seen before.
-
- A crucial distinction between the
magnetically driven and the X-winds is how they are located farther out and
cover broader regions. These winds cover regions that correspond to the inner
rocky planets of our solar system, roughly between Earth and Mars. They also
extend farther above the disk than thermal winds, reaching hundreds of times
the distance between Earth and the Sun.
-
- The new JWST observations revealed a nested
structure and morphology that matched what astronomers anticipated for
magnetically driven disk wind. These
observations strongly suggest that we have obtained the first detailed images
of the winds that can remove angular momentum and solve the longstanding
problem of how stars and planetary systems form.
-
- Astronomers want to get a larger sample
with JWST and then also see if we can detect changes in these winds as stars
assemble and planets form.
-
-
November 30, 2024 HOW
PLANETS FORM? 4630
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--------------------- --- Tuesday, December 3,
2024
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