doi.org/10.48550/arXiv.2509.03216
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#White dwarf
Astronomers have just identified two extremely strange dead stars that are redefining what we know about stellar remnants
These objects, called white dwarf merger remnants, share such unusual characteristics that researchers propose the creation of a new class of stars.
Most fascinating is that both emit X-rays even though they are completely isolated, without any companion star nearby to explain this phenomenon.
White dwarfs are what remains after a star like our Sun exhausts its nuclear fuel.
They become extremely dense objects, approximately the size of Earth, but with a much greater mass.
Normally, when a white dwarf is part of a binary system, it can steal material from the neighboring star, a process called accretion that generates X-rays.
However, these two objects-named Gandalf and Moon-Sized-have no companions, making their X-ray emission a true enigma.
Gandalf was studied by a team from the Austrian Institute of Science and Technology (ISTA), led by Professor Ilaria Caiazzo.
Initially, scientists thought it was a binary system because they detected signs of material around it.
But more detailed observations revealed something surprising: the object rotates on its own axis every six minutes, a very fast rate.
Furthermore, the hydrogen emission spectrum shows double peaks that alternate with the rotation period, suggesting the presence of an incomplete ring of material around the star, as if it were half of a disk trapped by the object’s powerful, asymmetrical magnetic field.
This strong and irregular magnetic field is rare in white dwarfs of similar age, which are generally not magnetic.
Gandalf formed about 60 to 70 million years ago, after a violent collision between two stars.
The name was inspired by Tolkien’s character, known for his enigmas, precisely because of all the mysteries it presents.
The other star, Moon-Sized, previously discovered by the same team, is like a more evolved version of Gandalf.
It compresses the mass of the Sun into a volume comparable to that of the Moon, rotates rapidly, possesses an extremely intense magnetic field, and also emits X-rays, despite being alone in space.
Its merger occurred about 500 million years ago, making it older.
While Gandalf shines about 100 times brighter in X-rays, Moon-Sized appears to be gradually losing the energy that fuels this emission.
The two objects share five main characteristics: they are ultra-massive, highly magnetic, rotate very rapidly, have no companions, and emit X-rays.
For astronomers, finding two examples with so many similarities is enough to define a new category of stellar remnants.
As Professor Caiazzo explains, in such a vast universe, one strange object already motivates searches for similar ones, but two with so many coincidences indicate that we are facing something more common than previously thought.
Scientists propose several explanations for the X-rays.
One favorite suggests that strong magnetism and rapid rotation are able to strip material from the white dwarf’s surface itself, creating a flow similar to that which occurs in pulsars (very magnetic neutron stars).
Another possibility is that remnants of the original collision are still falling back onto the star in elongated orbits over hundreds of millions of years.
A third hypothesis considers external material, such as asteroids or destroyed planets, but this seems less likely because it doesn’t adequately explain the continuous emission in either case.
These discoveries open new doors to understanding stellar evolution and the fate of binary systems.
Researchers emphasize that there is still much to learn: how these objects affect possible planetary systems around them, for example, and whether all five characteristics are essential to belong to this new class.
Finding more similar examples will help confirm the theories and unravel the mechanisms behind these extraordinary behaviors.
In short, Gandalf and Moon-Sized are not just cosmic curiosities.
They show that the universe still holds fascinating surprises and that, even in objects that have already died, such as stars, physics can behave in ways that defy our expectations.
Future studies with more powerful telescopes will certainly bring new revelations about these exotic remnants and about the ultimate fate of stars like our Sun.
Published in 05/31/2026 11h28
Text adapted by AI (Grok) and translated via Google API in the English version. Images from public image libraries or credits in the caption. Information about DOI, author and institution can be found in the body of the article.
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