Artist’s impression of the common-envelope evolution in a binary system J 1920. Credit: Jingchuan Yu
Chinese and Australian Astronomers Find Direct Evidence for Binary Common Envelope Evolution
A staff of astronomers has collectively found a binary system ejecting a typical envelope at a pace of about 200 kilometers per second (450,000 miles per hour). The researchers had been led by Prof. Zhanwen Han from the Yunnan Observatories (YAO) of the Chinese Academy of Sciences and Prof. Chris Wolf from the Australian National University.
This is the primary time astronomers have noticed direct proof of widespread envelope evolution, which is a key means of binary star evolution. This important discovery offers a strategy to precisely characterize the widespread envelope evolution of binary stars by way of remark.
The examine was revealed on July 7, 2022, in Monthly Notices of the Royal Astronomical Society.
Stars make up the vast majority of the luminous objects within the universe. It is believed that greater than half of all stars are a part of binary methods. Two stars in a binary system orbit round one another as a result of their gravitational attraction.
The destiny of stellar objects is considerably influenced by the evolution of binary methods. It has usually been cited as the reason for many mysteries in astronomy and astrophysics such because the formation of bizarre stellar objects together with Type Ia supernovae, double black holes, and double neutron stars, and so on.
An illustration of widespread envelope evolution in binary star evolution. Credit: YAO
Common envelope evolution is without doubt one of the key processes of binary evolution. In this course of, the donor star of a binary system expands dramatically because of the mass loss, thus resulting in the 2 stars spiraling in direction of one another and the formation of a typical envelope. This course of determines the following evolution of the binary system. A binary system with a shorter orbital interval could be anticipated to kind if the widespread envelope is ejected efficiently. Otherwise, the 2 stars inside the widespread envelope would merge right into a single object.
Common envelopes had been first postulated by B. Paczynski in 1976. However, a typical envelope had by no means been seen prior to now. As a consequence, scientists had been fairly unclear about what precisely occurs throughout the widespread envelope part of binary star evolution.
Based on the observations from the two.3-meter wide-field telescope at Australian National University and the Kepler Space Telescope, Chinese and Australian scientists have jointly found a binary system consisting of a hot subdwarf and a white dwarf, named J 1920. In this binary system, the two stars orbit around each other with an orbital period of about 3.5 hours, and are getting closer and closer.
In addition, scientists have seen that this binary system is surrounded by an expanding shell moving at a speed of about 200 kilometers per second (450,000 miles per hour). This expanding shell is further confirmed to be a common envelope that was ejected from the binary system about 10,000 years ago. Continuous orbital contraction observed in the J 1920 binary system indicates that friction caused by the orbital motion of the two stars in the envelope can severely dissipate orbital angular momentum. This is a new mechanism for angular momentum loss in addition to the mechanisms of magnetic braking and gravitational radiation.
The significance of this important discovery is that it turns a theoretical idea into reality. Scientists have not only seen the first evidence of common envelope evolution, but have also been able to accurately characterize the common envelope evolution of binary stars through observation.
Reference: “A Roche Lobe-filling hot Subdwarf and White Dwarf Binary: Possible detection of an ejected common envelope?” by Jiangdan Li, Christopher A Onken, Christian Wolf, Péter Németh, Mike Bessell, Zhenwei Li, Xiaobin Zhang, Jiao Li, Luqian Wang, Lifang Li, Yangping Luo, Hailiang Chen, Kaifan Ji, Xuefei Chen and Zhanwen Han, 7 July 2022, Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stac1768
