Dark matter stars are believed to be behind these strange gravitational waves.

This new theory would unravel one of the most puzzling mysteries in cosmology.
While it was estimated that the gravitational waves detected last year were the result of the most significant black hole collision ever recorded. An international team of astrophysicists now proposes an exotic alternative, instead involving two boson stars, hypothetical objects. Invisible and particularly dense.


Gravitational waves are ripples in the sheer mesh of space-time, produced in some of the most energetic cataclysms in the cosmos (usual collisions between black holes and neutron stars). Incredibly sophisticated instruments, operated by the LIGO / Virgo (LVC) collaboration, pick up these waves as they pass above Earth. The signals can then be analyzed to determine the masses of the objects involved in the initial fusion.

About 50 gravitational wave signals have been detected since their initial discovery in 2015, with one exciting event known as GW190521, described by LVC in September 2020. Possessing masses 65 and 85 times that of the Sun, the two colliding objects were the most massive ever detected by this method. The object created afterward represented 142 solar masses, placing it in a rare class of intermediate-mass black holes (IMBH).

With such masses, the original objects were presumed to be black holes, albeit unusually large. But today, a team of astrophysicists has come up with a new explanation that may fit better: a collision between two exotic objects called boson stars.

As their name suggests, if they exist, these stars would be mainly composed of bosons, one of two classes of elementary particles (classical stars primarily being written of the other course, called fermions). These objects would theoretically function like black holes, sucking matter from their surroundings with their phenomenal gravitational pull, but with one significant difference.


While it is well known that light itself cannot escape from a black hole, boson stars do not possess such specificity, which means that these exotic objects would not be black but transparent and widely.

In work featured in the journal Physical Review Letters, researchers simulated star-to-boson fusions. They found that they would produce a signal consistent with the detection of the GW190521 event last year. The team claims that these stars provide an even stronger explanation than the one implicating black holes.

The main problem with the theory of colliding black holes remains that the mass of any of these objects would not fit into the accepted categories. There are black holes of stellar mass, formed from the collapse of stars and having groups between five and a few dozen suns and the black holes of intermediate-mass mentioned above (between 100 and 10,000 masses solar). With 85 solar masses, the objects involved in the GW190521 event, therefore, fall within a “forbidden” mass range.

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But although the boson star theory removes this obstacle, it does so by introducing another and knowing that the revised hypothesis would also change other collisions’ properties.

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“First, we would no longer be talking about black hole collisions, which would eliminate the question of how to treat a ‘forbidden’ black hole,” said Juan Calderón Bustillo, one of the study’s authors. “Second, since the star-to-boson mergers are much weaker. This thing would imply a much smaller distance than estimated by the LVC, leading to a much larger mass for the final black hole, of around 250 solar masses,” so the fact that we witnessed the formation of an intermediate-mass black hole would hold. “

Although the team says this may be the first evidence for boson stars’ existence, it is still very speculative. More in-depth studies and simulation improvements will be needed to explore this possibility.

If the study stands up to scrutiny, the implications will go far beyond confirming new celestial objects. They could help unravel one of the most puzzling mysteries in cosmology: dark matter. For boson stars to exist, they would need to be composed of a stable “self-repulsive” boson, and a hypothetical particle called an axion (considered a prominent candidate for dark matter particles) also to be involved.

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