"Neither Black Hole nor Neutron Star"... Korean Researchers Suggest Possibility of a 'Third Ultra-Dense Celestial Body' [Reading Science]

Breaking Down the Boundary Between Black Holes and Neutron Stars with a New Theory of Gravity

"Could Offer Clues to the Mysteries of Dark Matter and Gravitational Waves"

A team of Korean researchers has presented findings suggesting that the boundary between black holes and neutron stars could disappear under a new theory of gravity that goes beyond Einstein's general theory of relativity. The study is being recognized as opening new possibilities for understanding ultra-dense celestial objects and the nature of dark matter, both of which were difficult to explain with existing theories.

On May 15, a joint research team from the National Institute for Mathematical Sciences and the Korea Astronomy and Space Science Institute announced that their analysis, based on the "Hořava–Lifshitz (HL) gravity theory," confirmed the potential existence of a new type of ultra-dense celestial body between black holes and neutron stars.

Reference photo to assist understanding of the article. A black hole swallows surrounding dust, gas, and even entire stars. Photo by NASA

The findings were published online in the international academic journals Physics Letters B and Physical Review D on March 2, 2026, respectively.

The current standard theory of physics, general relativity, has been criticized for its limitations in explaining environments with extremely high energy, such as the inside of black holes or the early universe. To address these shortcomings, the research team utilized the HL gravity theory, which assumes that time and space can transform differently from one another.

"Possibility of Objects Existing Just Before Becoming Black Holes"

The results indicate that, under HL gravity, ultra-dense celestial bodies such as neutron stars can become much more massive than predicted by existing theories. In particular, the "compactness"—the ratio of mass to radius—of these bodies can increase to extreme levels. This suggests that the so-called "compactness gap," previously thought to exist between neutron stars and black holes in astronomy, could disappear.

The researchers explained that this could provide clues to the recently observed "objects difficult to classify as either black holes or neutron stars" in the international gravitational wave observation project LIGO-Virgo-KAGRA.

The team suggested that these celestial bodies, which are hard to explain within the framework of general relativity, could be new, ultra-dense objects predicted by HL gravity theory.

Possibility Raised for Dark Matter Candidates

The team also proposed, on a theoretical basis, that ultra-dense objects of extremely small size could serve as dark matter candidates.

They explained that certain particles, under the influence of HL gravity, could form objects that are very small yet possess strong gravitational forces, and that these could constitute a significant portion of the universe's mass as "cold dark matter."

Paper 1. Provided by the National Institute for Mathematical Sciences

However, the researchers noted that this is still at the theoretical research stage and that further observation and verification are needed to confirm their existence in the actual universe.

Dr. Son Jaeju stated, "This research is significant in that it is the first to propose a mass limit for neutron stars under HL gravity theory and suggests the possibility of new ultra-dense objects with higher densities than those observed so far."

Dr. Oh Junggeun commented, "This study shows the possibility of new types of celestial bodies existing between black holes and neutron stars, and future gravitational wave and pulsar timing observations may provide critical clues to verify HL gravity theory."

The researchers expect that these results could be utilized in a wide range of areas, including the study of ultra-dense celestial objects, gravitational wave astronomy, cosmology, and dark matter research.

This content was produced with the assistance of AI translation services.