A new image captured by the European Southern Observatory’s Very Large Telescope (ESO’s VLT) reveals a beautiful cosmic shockwave, produced as gas and dust flowing out of a star unexpectedly crash into their surroundings.
Beyond creating a striking astronomical image, the observed structure is anomalous, as the small dead star RXJ0528+2838 should not possess such extensive surrounding material.
The international team of researchers who discovered this expectation-defying shockwave reported their findings in a recent paper published in Nature Astronomy.
An Impossible Star
“We found something never seen before and, more importantly, entirely unexpected,” said Simone Scaringi, associate professor at Durham University in the UK and the recent study’s co-lead author.
“Our observations reveal a powerful outflow that, according to our current understanding, shouldn’t be there,” added co-lead author Krystian Ilkiewicz, a postdoctoral researcher at the Nicolaus Copernicus Astronomical Center in Warsaw, Poland.
Located a mere 730 light-years from our Sun, RXJ0528+2838 also rotates around the center of the Milky Way. Similar to waves crashing against a ship, the star impacts the interstellar gas on its journey, creating a type of shockwave called a bow shock. Normally, a bow shock would result from the material outflow from the star itself, yet that shouldn’t be possible in this case.
The star is part of an anomalous binary system in which RXJ0528+2838 is a white dwarf star orbited by a Sun-like companion. Usually, the companion star in such a situation will transfer material to the white dwarf, resulting in a disk surrounding the star’s leftover core. Material from such disks typically moves in two directions: some accretes onto the white dwarf as fuel, and the rest is driven out into space.
Presently, astronomers have detected no disk around RXJ0528+2838, raising questions about the origin of the observed outflow and nebula.
Uncovering an Astronomical “wow” Moment
“The surprise that a supposedly quiet, discless system could drive such a spectacular nebula was one of those rare ‘wow’ moments,” Scaringi said.
The researchers first noticed RXJ0528+2838’s nebula in imagery obtained by the Isaac Newton Telescope. Intrigued by the odd splotch of color, the team followed up with subsequent observations using the MUSE instrument on ESO’s VLT.
“Observations with the ESO MUSE instrument allowed us to map the bow shock in detail and analyse its composition,” Ilkiewicz explained. “This was crucial to confirm that the structure really originates from the binary system and not from an unrelated nebula or interstellar cloud.”
After analyzing measurements from MUSE observations, the team determined that the shape and size of the bow shock indicate that the white dwarf outflow has been accumulating for at least a millennium. Astronomers cannot conclusively determine how a dead star could continue to push out material for such an extended period.
A Dead Star Hypothesis
One data-driven hypothesis could explain the observed phenomenon, as MUSE observations indicate that RXJ0528+2838 hosts a strong magnetic field, which brings material from its binary companion directly into the dead star without accreting a disk.
“Our finding shows that even without a disc, these systems can drive powerful outflows, revealing a mechanism we do not yet understand,” Ilkiewicz said. “This discovery challenges the standard picture of how matter moves and interacts in these extreme binary systems.”
The research suggests that the strong magnetic field may be powering this long-term outflow, although the magnetic field detected in the MUSE observations should be able to power such an outflow for more than a few hundred years. Overall, the team says that further observations will be required to conclusively determine the true source of this bizarre cosmic shockwave.
The team’s recent paper, “A Persistent Bow Shock in a Diskless Magnetised Accreting White Dwarf,” appeared in Nature Astronomy on January 12, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.