Australian, Chinese researchers observe critical star phase in world first

CANBERRA, July 8 (Xinhua) -- Australian and Chinese astronomers have made a breakthrough in understanding a mysterious stage in the life of stars.

In research published on Thursday, the team from Australian National University (ANU) and the Yunnan Observatories of the Chinese Academy of Sciences (CAS) revealed they had observed the common envelope (CE) phase of binary stars for the first time.

Half of the stars in the known universe come in pairs, known as binary stars.

Christian Wolf, co-author of the study from ANU, said the phase is believed to be particularly important for binary stars but had never been observed until the research team discovered a tight binary star with the leftover of a CE.

"The common envelope phase is a missing link in the very long and complex chain of events making up the life of stars. Now we are starting to fix that link," Wolf said in a media release, "It could even help us better reconstruct gravitational wave events, such as black hole mergers."

The CE phase starts when two stars begin to circle each other. But when one of the stars grows into a red giant, it does not just claim more empty space the way a single star will do, according to Wolf.

"Instead, it 'embraces' or engulfs its companion, and they appear as one star under an opaque envelope," he said.

The friction of their motion inside the envelope profoundly alters what happens next for the stars. It not only causes heat but slows down the stars, so they spiral into an ever-tighter orbit, the envelope finally overheats and gets blown away, said Wolf.

The blow-out of this particular binary star observed by the researchers happened approximately 10,000 years ago.

Researchers are hopeful the discovery will help them find more stars in the CE phase and better understand the phenomenon.