Intermediate-Mass Black Hole May Be Hiding in Sagittarius Constellation

Intermediate-mass black holes are a void in black hole research, a mysterious missing-link between stellar-mass and supermassive black holes that have, until recently, managed to avoid detection. Yet, an international team of astronomers, led by the University of Manchester, might now have uncovered one in the Sagittarius constellation.

The team observed a pulsar at the centre of a globular cluster known as NGC 6624, and found it appeared to be orbiting an intermediate-mass black hole. “Millisecond pulsars, like the one we observed, are very stable rotators” study lead Dr Benetge Perera told I,Science, “They’re as precise as atomic clocks. Because of this, you can measure the gravitational effects on pulsar timing.”

The team monitored the beats of radiation emitted from the pulsar PSR B1820-30A, a collapsed star so dense that a grain of sand made of the same material would weigh approximately 60 million tonnes, and spinning so rapidly on its axis that it makes hundreds of rotations per second. By analysing variation in the timing of the emitted radiation, the researchers were able to calculate the distance and mass of nearby objects exerting gravitational forces on the pulsar. Their evidence appeared to show that the pulsar was orbiting an object 7,500 times the mass of the Sun, corresponding to an IMBH.

“This is an important discovery as it is the first time a pulsar so close to the centre of a globular cluster has been measured in this way” Dr Perera added.

Globular clusters, millions of tightly packed old stars, are good candidates for harbouring IMBHs as they have high stellar densities and so provide a favourable environment for forging these enigmatic objects. Although it is not well understood how IMBHs form, it is currently thought that they could be produced by the collapse of extremely massive primordial stars or through the merging of stellar mass black holes and runaway collisions in dense young star clusters. However, this discovery could aid understanding of how IMBHs form and evolve.

The team behind this discovery plan on observing more pulsars to collect further evidence for intermediate-mass black holes, although as Dr. Perera pointed out “You have to collect very large datasets. My colleagues have been taking the data since 1990, more than 25 years now.” So, it might be a little while till they detect the next one…

The globular cluster NGC 6624, which contains the pulsar PSR B1820-30A. Observations from this pulsar are consistent with the presence of a central intermediate-mass black hole.

Madeleine Finlay is studying for an MSc in Science Communication

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One thought on “Intermediate-Mass Black Hole May Be Hiding in Sagittarius Constellation

  1. Why a black star is the alternative to a black hole.
    How does the Chandrasekhar limit prevent the creation of intermediate black stars?

    Very little is known about the formation of black holes. An article, recently published in the Journal of High Energy Physics, Gravitation and Cosmology, in which I discuss a computer model that poses an alternative process to the accepted theory of the formation. It can be found at .

    Due to a unique requirement of creating black holes by freezing time and space from the inside out, the conventional method of deriving results from general relativity could not be used. Instead I used the Newtonian model, while factoring in relativistic corrections derived from general relativity which includes relative contraction of both space and time. This mathematical model, written in Excel and Visual Basic, takes about a day to run. It calculates time dilation profiles, density cross sections and red shift factors as it forms a “black star”. I use the term black star because the calculations show that during the collapse no singularity is formed and there is no event horizon as in the accepted theory of black holes.

    When a white dwarf or the remnant core of a supernova gets to a size that is just above the Chandrasekhar limit (1.44 solar masses), the pressure will overcome the electron degeneracy pressure. This happens at a density of 1×10^9 kg/m^3. It will then collapse down to a neutron star resulting in densities starting at 3.5 x 10^15 kg/m^3. The associated pressure at this density is just high enough to support neutron matter. During this contraction, the decreasing gravitational potential caused time to relatively slow.

    For a remnant greater than 2.2 solar masses, while it is still contracting, this gravitational potential causes time at the center to relatively freeze and stop the contraction before the pressure gets high enough to stop it, as it would in a neutron star. Then, above this frozen matter, as the contraction continues, the time freeze moves toward the surface, stopping the contraction of the rest of the remnant, creating a black star.

    The creation of black stars, using this model, lead to the discovery of why we do not have intermediate black stars. During the collapse of a white dwarf, it transitions from degenerate white dwarf matter, at a density of 1×10^9 kg/m^3, to neutron matter which starts at a density of 3.5x 10^15 kg/m^3. This matter has just crossed a span of densities that cannot be supported. The gap between these two densities relate to the answers of questions like:

    1. Why is there such a large size gap between stellar black stars and super massive black stars?
    2. Why are there no stellar black stars below 2 solar masses?
    3. Why are there no supernova created stellar black stars above 15 solar masses?
    4. Why does the smallest super massive black star start at 50,000 solar masses?
    5. Are super massive black stars made before or after the existence of first-generation stars in a galaxy?

    These questions cannot be answered using a model of black holes that have a singularity. They are answered by this model of the formation of black stars. The information produced by this model agrees with observation when available.

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