Every second, more than 3,000 stars are born in the visible Universe. Many are surrounded by what astronomers call a protoplanetary disk—a “pancake” of hot gas and dust from which planets form. However, the exact processes that give rise to stars and planetary systems are still poorly understood.
A team of astronomers led by researchers from the University of Arizona used NASA’s James Webb Space Telescope to obtain some of the most detailed information yet on the forces that shape protoplanetary disks. The observations provide an idea of what the solar system might have looked like 4.6 billion years ago.
Specifically, the team was able to track the disc’s so-called winds in unprecedented detail. These winds are streams of gas that blow into space from the planet-forming disk. Fueled largely by magnetic fields, these winds can travel tens of kilometers in a single second.
The researchers’ findings, published in Nature Astronomyhelps astronomers better understand how young planetary systems form and evolve.
According to the paper’s lead author, Ilaria Pascucci, a professor at the Lunar and Planetary Laboratory at the University of England, one of the most important processes that takes place in a protoplanetary disk is the consumption of matter by the star from the disk around it, a known process under the name of accretion.
“The way a star accumulates mass has a big influence on how the surrounding disk evolves over time, including how planets form later,” said Pascucci.
What might the Solar System have looked like 4.6 billion years ago?
“The specific ways in which this happens are not understood, but we think that winds driven by magnetic fields across most of the disk’s surface could play a very important role.”
Young stars grow by pulling in gas from the disk orbiting around them, but for this to happen, the gas must first lose some of its inertia. Otherwise, the gas would constantly orbit the star and never fall onto it. Astrophysicists call this process “loss of angular momentum,” but exactly how this happens has proven to be unclear.
For accretion to occur, the gas in the disk must lose momentum, but astrophysicists have difficulty agreeing on exactly how this happens.
In recent years, disc winds have emerged as important players in removing some of the gas from the disc’s surface—and with it, the angular momentum—which allows the remaining gas to drift inward and eventually fall onto the star, write EurekAlert.
The old problem of how stars form
According to the paper’s second author, Tracy Beck of NASA’s Space Telescope Science Institute, because there are other processes that shape protoplanetary disks, it is essential to be able to distinguish between the different phenomena.
While material at the inner edge of the disc is pushed apart by the star’s magnetic field in what is known as the X wind, the outer parts of the disc are eroded by intense starlight, resulting in so-called thermal winds, which blow at much lower speeds.
Unlike the narrowly focused X wind, the winds observed in the present study come from a wider region that would include the rocky inner planets of the solar system – roughly between Earth and Mars. These winds also extend further above the disc than thermal winds, reaching distances hundreds of times greater than the distance between the Earth and the Sun.
“Our observations strongly suggest that we have obtained the first images of winds that can remove angular momentum and solve the age-old problem of how stars and planetary systems form,” said Pascucci.
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Source: www.descopera.ro
