Tuesday, December 06, 2022

How disc winds refuel an airplane

How disc winds refuel an airplane
editorial board
/ Press release from the Max Planck Institute for Astronomy
16 August 2022

Now, for the first time, a flow of gas from an accretion disk has been traced directly into a jet that spews material into space. The study now presented confirms the scenario described in the hydrodynamics of disk winds emanating from accretion disks around objects such as black holes or newly formed stars.

Protobintang IRAS 21078+5211.
NASA/JPL-Caltech/2MASS/B. Whitney (SSI/University of Wisconsin)

Many celestial bodies, such as supermassive black holes, stars and gas giant planets, are surrounded by accretion disks as they form and emit intense jets. This jet consists of ionized gas that is concentrated along the axis of rotation of the disc. The relationship between accretion, the process by which gases are directed toward celestial bodies, and their removal is important for their formation. They collapse during the accretion process, resulting in very high angular velocities due to conservation of angular momentum. The beam removes angular momentum from this system, creating a continuous build-up on the central body.

In a study now presented, astronomers from Italy and Germany have observed for the first time a gas beam along the path of gas flow from the accretion disk to the jet. The reconstructed current lines match a working prediction that scientists developed 40 years ago: hydrodynamic magnetic disk winds. Magnetic hydrodynamics describes the motion of an ionized gas, also called a plasma, that is affected by a magnetic field. Magnetohydrodynamic disc winds are the predicted mechanism that partially deflects the accretion current and accelerates it along the axis of rotation of the disc during the formation of the dipole jet.

Luca Moscadelli and Alberto Sanna, both from the National Institute for Astrophysics (INAF) in Florence and Cagliari, Heinrich Bother from the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Ander Oliva from the University of Tübingen, and one from Rolf Kuiper at the University of Duisburg-Essen Discover the core of the newly formed giant star. It bears the designation IRAS 21078 + 5211. Using radio interferometry, they observed the typical emission of radio waves with a frequency of about 22 GHz, or a wavelength of 1.4 cm. This emission indicates the surprising presence of water vapor, which is seen as naturally bright masers in star-forming regions – the equivalent of a microwave laser. Like lasers, lasers are fast, highly focused radio frequency beams. The hydrometer tracked the motion of the gas, allowing the team to quickly monitor two motion patterns typical of magnetodynamic disc winds: helical motion near the axis of rotation and combined spin currents at greater distances.

Use global team Dasr Ultra-Pwang Interferometer (VLBI) a group of 26 radio telescopes spread across Europe, Asia and the United States. These stations simultaneously monitor the emission of water masers towards the newborn star for 24 hours. This technology makes it possible to simulate a giant telescope with the same diameter as Earth. It achieves a high-angle resolution, comparable to seeing a meter-sized object on the Moon from Earth. This property is important for studying the spatial distribution of water masses near rising stars.

“Our work shows that the very long fundamental interferometry disks of water pumps near star formation may be an effective tool for studying wind physics in unprecedented detail,” explains Muscadelli, lead author of the new study. “We have made a new observation of water maser emission by integrating all available telescopes into the VLBI network to simulate a next-generation radio interferometer that will increase the current sensitivity by more than an order of magnitude.”

So far, the best experimental evidence for magnetohydrodynamic disk winds is determining what astronomers call a velocity gradient perpendicular to the jet’s axis. However, this method is inferior to the newly applied technology because it cannot differentiate between different gas paths. Instead, all the movements seem to overlap. Therefore, it provides only circumstantial evidence and there is a potential for misinterpretation and systematic error. The detection of the specific flow line of a magnetodynamic disc air through the spatial position and velocity of the wave device, i.e. gas packets along the flow path, is more convincing evidence. “Although scientists have long been able to describe jets well in theory, we can use these data for the first time to observe and analyze the distribution of gases with magnetic fields,” Boster emphasizes. “It’s great to see how well modeling and observation work together.”

The team wrote about their observations in a special article published in the journal natural astronomy he came.

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