By David Graff, AAU Communication and Public Affairs. Photo: Daniëlle Futselaar

When Professor Thomas Tauris in the autumn of 2022 began to analyze the observations his colleagues at the Max Planck Institute in Bonn had obtained via the MeerKAT radio telescope, he was thrilled like a child on Christmas Eve:

"Research in the Universe continues to surprise, but this finding is something out of the ordinary – the combination of a millisecond pulsar and a mysterious compact object that is likely a black hole is probably what my pulsar colleagues have been looking most for in the last 40 to 50 years," he says.

The discovery was made in our galaxy, specifically in a star cluster (globular cluster) called NGC 1851, where the stars swarm closely and constantly influence each other.

Chance of fundamental breakthrough

The researchers' excitement stems from the fact that the combination of a millisecond pulsar and a black hole in a binary system may provide an opportunity to test Einstein's general theory of relativity at points where the theory is not entirely clear. Hence, the door may open to clarifying one of the most important scientific theories of the 20th century.

- Our ultimate hope is that we can get one step closer to unifying Einstein's general theory of relativity and quantum mechanics in our understanding of gravity, explains Thomas Tauris. However, he stresses that it is far too early to say whether it will succeed.

In order for it to be even possible in principle to further develop the theory of relativity, the object around which the millisecond pulsar orbits in the newfound system must be a black hole. But it is not yet clarified whether this is the case.

Never seen before

The study of the binary system takes place through calculations of mass, orbital motion, rotation, gravity and radiation, and it has not yet been possible to determine what the object around which the millisecond pulsar orbits is. It can be either a black hole or a record high-mass neutron star.

Both types of compact objects are characterized by dense mass and the influence on its surroundings through gravity.

Furthermore, calculations have revealed that if it is a black hole, it is the lightest version of such a hole ever measured. In the case of a neutron star, it is the heaviest version ever measured.

In the coming years, researchers will try to determine which of the two phenomena they have discovered – or whether it may be something third - a hitherto unknown exotic object with a mass between that of a black hole and a neutron star.

However, one thing is certain: With this discovery, scientists have found a unique laboratory to study fundamental physics in the form of gravity and the properties of matter under the most extreme conditions in the Universe.