A team of Brazilian astronomers observed a rare sight in the Milky Way. They saw a brown dwarf killing its brother star, turning it into a white dwarf.

Researchers from Brazil saw a really weird event occurring in an eclipsing binary. This binary system is composed of a white dwarf and a low-mass brown dwarf.

Brazilian astronomers determined that the brown dwarf may have caused a “premature death” and transition of its stellar companion into a white dwarf.

Scientists published the work on September 21 in the Monthly Notices of the Royal Astronomical Society.

Leonardo Andrade de Almeida, a postdoctoral fellow from the University of São Paolo’s Institute of Astronomy, Geophysics, and Atmospheric Sciences (IAG-USP), led the team of astronomers along with members from the National Institute for Space Research (MCTIC), and the State University of Feira de Santana.

How did the brown star kill its brother?

This binary lies in the constellation Perseus. It once held a normal, Sun-like star and a brown dwarf (depending on its initial mass). The normal star began to swell, as stars do when they enter the last hydrogen-burning stage of their life cycles and become red giants, thus, engulfing the smaller object. But instead of destroying it, it triggered a massive ejection of material from the red giant that killed it instead.

The primary star’s outer layers began to be stripped away. Thus, exposing its helium core and sending massive amounts of matter to the brown dwarf.

However, the tiny object remained, orbiting its companion from within the envelope.

Because of this loss of mass, the remnant effectively died, becoming a white dwarf.

Our own Sun will expand too. It will swell to at least the circumference of Earth’s orbit.

The Study.

The team conducted observations of a binary star system between 2005 and 2013 using the Pico dos Dias Observatory in Brazil. Researchers, then, combined this data with information from the William Herschel Telescope, which is located in the Observatorio del Roque de los Muchachos on the island of La Palma.

Leonardo Andrade de Almeida explained in a FAPESP press release, “This type of low-mass binary is relatively rare. Only a few dozen have been observed to date.”

Such a “death” is unusual and, the astronomers say, “premature,” because it’s not usually how white dwarfs form. And all the while, the companion remained, though it never gained enough mass to begin burning hydrogen on its own (hence the reason it is a brown dwarf). The two now orbit each other closely with a period of just 3 hours.

Thumbnail Image: A brown dwarf (left) and its stellar companion, a white dwarf. Credit: FAPESP