This stellar fight caused a beautiful cosmic rainbow

February 7, 2020, 12:47 p.m.
This ALMA image shows the outcome of a stellar fight: a complex and stunning gas environment surrounding the binary HD101584.
Photo: ALMA (ESO/NAOJ/NRAO), Olofsson et al. Acknowledgement: Robert Cumming

A few hundred years ago, two stars were involved in a winner-take-all confrontation. One star grew so big that it engulfed the other, resulting in a dramatic rainbow cloud of gas.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers observed the star system HD101584 and a "peculiar gas cloud" they believe came from a fight between two stars, according to a statement from the European Southern Observatory.

As one star grew, it began to swallow the other. That caused the smaller star to spiral toward its growing stellar partner, but it didn't collide with it. Instead, it triggered it into an outburst, shedding its outer layer. This resulted in the clouds of gas captured in the ALMA image above.

As a star ages, it typically goes through a phase when it burns through all the hydrogen in its core. Then it swells up into a bright red-giant star. When it dies, it loses its outer layers and leaves behind a hot, dense core called a white dwarf.

But it didn't work that way for this system.

"The star system HD101584 is special in the sense that this 'death process' was terminated prematurely and dramatically as a nearby low-mass companion star was engulfed by the giant," said Hans Olofsson of the Chalmers University of Technology, Sweden, who led a recent study published in Astronomy & Astrophysics on the system.

In the photo, the colors represent speed. The blue clouds are the gas moving the fastest towards us while the red are the gas clouds moving the fastest away. The stars are located at the single bright dot in the center of the image.

"Currently, we can describe the death processes common to many Sun-like stars, but we cannot explain why or exactly how they happen," said co-author Sofia Ramstedt from Uppsala University in Sweden. "HD101584 gives us important clues to solve this puzzle since it is currently in a short transitional phase between better studied evolutionary stages. With detailed images of the environment of HD101584 we can make the connection between the giant star it was before, and the stellar remnant it will soon become."