A powerful display of glowing gases around a dead star is fueled by a mysterious source that scientists can’t explain, in an unprecedented way.
As stars move through space, they push objects and create what is called a bow shock in front of them similar to a curved river of water that forms in front of a moving boat. Using the European Southern Observatory’s Very Large Telescope, a team of astronomers discovered a shock that shouldn’t be there.
The star RXJ0528+2838 is a white dwarf, the remnant of a dead star that no longer produces energy through nuclear fusion. However, the white dwarf is surrounded by a bright heat wave that glows red, green, and blue—and its origin is unknown. The discovery, published Monday in Nature Astronomy, cannot be explained by any known universal method.
A cosmic mystery
The dwarf white star is located at a distance of 730 light-years from Earth, which is very close in cosmological terms. The rest of the low-mass star has a companion star, a Sun-like star orbiting it. In these types of binary systems, the companion star’s material is often transferred to its dead neighbor, forming a disk around a small white object. The disk ignites the white dwarf, while other material is ejected from space to form the outflow.
The newly discovered star, however, shows no sign of a disk. “We found something unprecedented and, more importantly, unexpected,” said Simone Scaringi, associate professor at Durham University, England, and lead author of the study, in a statement. “The wonder that a supposedly silent, invisible system could drive such an amazing nebula was one of those rare ‘wow’ moments.”
As a small white object orbits the center of the Milky Way, it mixes with the surrounding gas to create a powerful shock wave in front of it. These bow tremors are often created by interstellar matter, but the white dwarf shows no such evidence of producing any kind of matter.
“Our observations reveal a powerful outflow that, according to our current understanding, should not exist,” said Krystian Ilkiewicz, a postdoctoral researcher at the Nicolaus Copernicus Astronomical Center in Warsaw, Poland, and the leader of the study, in a statement.
The origin is unknown
The scientists behind the discovery mapped the bow shock in detail and analyzed its composition, confirming that it originated in a binary star system. They found that the shape and size of the bow shock suggest that the white dwarf has been emitting this material for at least a thousand years, furthering the mystery of how a lifeless star without a disk produces such persistent outflows.
Although this is the first cosmic mystery of its kind, a team of scientists has a clue as to how it might have come into existence. The results point to a hidden energy source that may be magnetic. The magnetic field of a white dwarf could be a route of material stolen from its companion star directly to its dead remnants without forming a surrounding disk.
The theory, however, still needs some work. The magnetic field may be strong enough to power the bow shock for several hundred years, solving only part of the cosmic mystery.
“These findings challenge the conventional picture of how things move and interact in these extreme binary systems,” Ilkiewicz said. “Our findings show that even in the absence of a disc, these systems can drive strong outflows, revealing a mechanism we do not yet understand.”
