“One of the rare ‘wow’ moments”: A rainbow shockwave that shouldn’t exist occurs on a zombie planet near Earth

Stunned astronomers discovered a zombie star relatively close to Earth. The zombie star inexplicably emits a persistent rainbow-like shockwave as it speeds through the Milky Way. The remains of this undead star are currently consuming its companion star, leaving researchers puzzled.

All the stars in the Milky Way are constantly rotating around a supermassive black hole called Sagittarius A* at the center of our galaxy. Most of these stars, including the Sun, experience bow shocks that push material around the star, similar to the waves that occur around the bow of a ship as it moves through water. These bow shocks are caused by gas and dust flowing out of the star hitting and pushing the interstellar medium (the residual matter and radiation that exists in the gaps between the stars).

Other, smaller, less active stars lack bow shock because they lack outflow material. This means there is little or no resistance to the interstellar medium. Some of the best examples of bowshock-free stars are white dwarfs, deflated shells left behind from the centers of massive stars that died in violent supernova explosions.

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But in a new study published January 12 in the journal Nature Astronomy, a group of astronomers discovered a white dwarf star named RXJ0528+2838 surrounded by a bow shock. The rule-breaking star is located about 730 light-years from Earth and is part of a binary star system alongside another sun-like star that is slowly being swallowed up by a cosmic zombie.

The researchers used observations from the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in Chile to map this surprising shock wave. This shock wave spread from the pair of stars about 4,000 meters away from Earth and the Sun, and is at least 1,000 years old. The images also show that the bow shock contains a dense cloud, or nebula, of colorful gas and dust, which only deepens the mystery.

“We’ve discovered something we’ve never seen before, and more importantly, something completely unexpected,” Simone Scaringi, another co-lead author of the study and an astronomer at Durham University in the UK, said in an ESO statement.

“Our observations revealed a strong outflow that, according to current understanding, should not exist,” added the study’s other co-lead author, Krystian Iłkiewicz, a postdoctoral researcher at the Nicolaus Copernicus Astronomical Center in Poland. “This discovery challenges the standard picture of how matter moves and interacts in these extreme binary systems.”

Given that RXJ0528+2838 is part of a binary star system, the obvious explanation for its bow shock is that its partner star is an outflow of material colliding with the interstellar medium. However, researchers strongly believe that this is not the case.

In such a binary system, the most massive star (in this case, an ultra-dense white dwarf) slowly engulfs its partner by pulling material from its surface. This means that RXJ0528+2838’s partner will not be outflowing like a similar star of the same size, as the white dwarf will also obscure the outflow material.

This process typically leaves behind a disk of extra stellar material around the more massive star, and a similar type of stellar outflow can also occur. However, there are no disks visible around RXJ0528+2838, which strongly suggests this is not happening.

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“The surprise that a supposedly quiet diskless system could drive such a spectacular nebula was one of those rare ‘wow’ moments,” Scaringi said.

Rather, researchers suspect that RXJ0528+2838’s mysterious “spill” is related to its extremely strong magnetic field. This invisible energy source is also the reason why white dwarfs do not have disks. Because white dwarfs, like black holes, suck in everything around them.

But researchers have been unable to identify the exact mechanism by which magnetic fields act to reproduce the effects of star outflow, calling it the “mystery engine.”

Researchers are now looking for a similar system that could provide clues about what’s going on with RXJ0528+2838. Fortunately, ESO’s upcoming Extremely Large Telescope (ELT), the VLT’s successor scheduled to be operational as early as 2028, could help with this.

ELT will allow astronomers to map “more of these systems, as well as fainter stars, and detect similar systems in greater detail, which will ultimately help us understand mysterious energy sources that remain unexplained,” Scaringi said.