- 4627 - HOW GALAXIES FORM? - The James Webb Space Telescope (JWST) reveals new things about how planetary systems 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.
--------------------------------------- 4627 - HOW GALAXIES FORM?
- JWST’s advanced infrared optics was used
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. They also confirm what scientists have
theorized for a long time and offer clues about what our Solar System looked
like roughly 4.6 billion years ago.
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- 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.
-
- The mechanism that allows this to happen
has remained the subject of debate among astronomers. In recent years,
“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. Using Webb’s Near Infrared Spectrograph
(NIRSpec), the astronomers 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 envelop of winds
at increasing distances. The team also noted a pronounced central hole inside
the cones in all four protoplanetary disks.
-
- How a star accretes mass has a big
influence on how the surrounding disk evolves over time, including the way
planets form later on. The specific ways in which this happens have not been
understood, but we think that 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 JWST observations revealed a nested
structure 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.
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November 29, 2024 HOW GALAXIES
FORM? 4627
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