How to Spin a Disk Around Young Protostars
by Staff Writers
Garching, Germany (SPX) Sep 09, 2019
The main steps of star and planet formation are well understood: a dense, interstellar cloud will collapse under its own gravity; a central core forms as well as a protostellar disk due to the conservation of angular momentum; finally, after about 100,000 years or so, the star will become dense enough to ignite nuclear fusion at its centre and so will start to shine, while in the disk, planets will form.
But there are still many open questions about the details of this process, e.g., what is the role of angular momentum in disk formation or how does the circum-stellar disk gather most of its mass?
An international team of scientists led by the Max Planck Institute for Extraterrestrial Physics (MPE) has now observed three of the youngest protostellar sources in the Perseus molecular cloud. These sources are close to edge-on in the plane of the sky, allowing a study of the velocity distribution of the dense cloud.
"This is the first time that we were able to analyze the gas kinematics around three circum-stellar disks in early stages of their formation," states Jaime Pineda, who led the study at MPE. "All systems can be fit with the same model, which gave us the first hint that the dense clouds do not rotate as a solid body."
A solid body rotation is the simplest assumption, which describes the gas in the dense cloud with a fixed angular speed at any given radius. The model best describing all three systems is in between those expected for solid body rotation and pure turbulence.
Furthermore, when comparing these observations to previous numerical models, it is clear that magnetic fields play a role in the formation of these disks: "If a magnetic field is included it makes sure that the collapse is not too fast and the gas rotation matches the observed one," explains Pineda. "Our latest observations give us an upper limit on the disk sizes, which are in great agreement with previous studies."
In particular, the specific angular momentum of the in-falling material is directly related to the possible maximum Keplerian radius of the protostellar disk. Assuming a stellar mass of about 5% of the mass of our Sun, the scientists estimate that the upper limit of the Keplerian disk is about 60 astronomical units (AU), or about the double the size of our planetary system, in agreement with previous estimates. This suggests that big disks (greater than 80 AU) cannot be formed early in the life of a star, and therefore affects the starting point for planet forming scenarios.
The next step for the astronomers will be to observe such systems at various stages in their evolution and in different environments to check if these influence the specific angular momentum profile. These findings can then be incorporated in or compared with numerical simulations to better understand the co-evolution of the dense core forming a star and the circumstellar disk forming planets.
|The content herein, unless otherwise known to be public domain, are Copyright 1995-2024 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us.|