What does "Post-common-envelope Binaries" mean?
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Post-common-envelope binaries are pairs of stars where one star has gone through a special phase called the common envelope stage. During this phase, the outer layers of one star spill over and surround both stars, allowing them to interact closely.
What Are They Made Of?
Typically, in these systems, one star is a white dwarf, which is the remnant of a star that has run out of fuel. The other star is usually a main-sequence star, which is still actively burning fuel. These pairs can have varying distances between them, with some being quite far apart.
How Do They Form?
The formation of these binary systems happens when the outer layers of the more massive star expand as it ages. When this expansion occurs, the two stars end up sharing a common envelope. After this phase, if the two stars are still bound together, they become a post-common-envelope binary. They can end up at different distances from each other based on how the envelope was ejected.
New Findings
Recent studies show that many of these post-common-envelope binaries have been observed at wide distances, much farther than expected. This discovery indicates that the process of how some stars evolve and interact can be different from what scientists previously thought.
Implications
These findings can help scientists better understand how stars evolve over time and how different types of stars can be related to each other. It also suggests that some pairs can form without needing additional energy sources, relying only on their natural processes.