A new class of cosmic object observed by NASA’s Chandra X-ray Observatory could hold the key to unraveling two long-standing mysteries, astronomers say.
In a recent paper published in Nature Astronomy, researchers described these new cosmic objects as having high levels of ultraviolet radiation but low-intensity X-rays.
In the NASA Chandra data, the team identified 84 of these strange objects, which they dubbed “hypersoft X-ray sources,” across six galaxies. The unexpected discovery could finally help answer puzzling questions related to star formation and the expansion of the universe.
“We’ve never encountered a group of objects that act like this,” said lead author Mustafa Muhibullah of the University of Alabama. “Of course, the next step was to try to figure out what these things are.”
The new research used data from a publicly accessible Chandra archive provided by NASA, including the spiral Andromeda and Pinwheel galaxies and an additional four elliptical galaxies. Intriguingly, both older regions and active star-forming regions contained the new objects.
The team discovered the objects by comparing Chandra’s high- and low-energy X-ray images to identify sources that were disappearing. Their departure from high-energy X-ray images indicated the objects were producing only low-energy X-rays, which border ultraviolet light on the spectrum. This led the researchers to then identify the high-energy ultraviolet radiation coming from the objects.
Currently, the team cannot effectively determine what these objects are, but they do have some suspects, including black holes, neutron stars, or white dwarves pulling material from a companion. Such material would heat as it fell into one of the three suggested objects, theoretically producing the observed X-rays. While these types of binary systems have all been observed previously, this combination of ultraviolet radiation and low-energy X-rays hasn’t been associated with them.
Because the researchers found so many of these objects in just six galaxies, they suggest many more of these likely binary systems remain undiscovered across the universe.
These objects were not previously identified for two reasons. The more obvious is how faint their X-ray signature is, which requires extremely sensitive equipment to detect. The other is that helium and hydrogen gas between stars absorbs the stronger ultraviolet radiation, obscuring these otherwise brilliant signals.
“By combing through the Chandra archive, we were able to eliminate what used to be a blind spot for telescopes,” said co-author Rosanne Di Stefano, Senior Astrophysicist with the Center for Astrophysics, Harvard & Smithsonian. “That’s how we found what appears to be a new class of cosmic objects with remarkable qualities.”
“These clandestine X-ray sources are actually among the most energetic objects in galaxies, and they could be solving two cosmic mysteries at once,” said Muhibullah.
One of the mysteries this may solve ties to the rate of universal expansion itself. Type Ia supernova observations have provided astrophysicists with essential data indicating that the universal expansion is accelerating. Although they suggest these supernovae likely come from white dwarf binary systems, astronomers have never observed a star turning into one to confirm the hypothesis.
“If we could find a way to spot these Type Ia supernova explosions before they go off, that would be really important,” said co-author Jimmy Irwin, also of the University of Alabama. “Right now, we study them after they’ve exploded, and astronomers have struggled to understand what is actually ignited.”
The other mystery is what removes electrons from the free-floating gas between some stars, which could have major ramifications for star formation and galactic life cycles. Hot, massive stars were previously identified as likely partially responsible, but they couldn’t account for the full extent by themselves. The research team says hyper-soft X-rays and intense ultraviolet radiation could be the missing culprit.
Only continued observation and research can provide a definitive answer on the mystery objects that Chandra observed.
The paper, “Hypersoft X-Ray Sources as a Low-Energy Class of Luminous Cosmic Emitters,” appeared in Nature Astronomy on September 9, 2026.
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.
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