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Astronomy and Space Exploration Reporting

Hubble discovers a black hole that should not exist

The origin and growth of supermassive black holes are not well understood by astrophysicists, but it is a key to the evolution of galaxies. In seeking to better explain these riddles, researchers came across one of these black holes which should not be surrounded by an accretion disk, contrary to what the Hubble Space Telescope shows.

Nearly a century ago, shortly after the final formulation by Einstein in his relativistic theory of gravitation, the simplest way to describe the framework of general relativity theory on a star had been found by astrophysicist Karl Schwarzschild, a few months before his death on the Russian front in 1916. It took decades for us to understand its hidden physical content and especially that we take it seriously: nothing less than what we call today the physics of black holes.

We now know, as it was suspected about 50 years ago, that supermassive black holes, or compact stars appearing as such, are at the heart of most major galaxies. They are even the origin of the active nuclei of galaxies whose most spectacular manifestation is that of quasars. The study of these objects is rich in promises of all kinds for fundamental physics as well as for astrophysics and cosmology because everything indicates that supermassive black holes coevolve with galaxies.

Physics and astrophysics laboratories

These are great laboratories for testing alternatives to the theory of general relativity, especially when it comes to the supermassive black hole of the Milky Way, Sgr A * but also M87 *. This is what was done with the Gravity instrument on the VLT, the Event Horizon Telescope and, in the near future, what eLisa will do with the detection of gravitational waves in space.

With respect to their role in the growth and history of galaxies, it is necessary to understand how supermassive black holes are formed and how they grow and the processes that accompany their manifestation as active nuclei of galaxies. One of the elements of all these processes that astrophysicists want to understand is the way they accredit and absorb matter by constructing theoretical models that are fed and tested by observations.

It is by following this research program that an international team of astrophysicists studying the galaxy NGC 3147 using the Hubble telescope came across a surprise as it explains in an article published in the journal Monthly Notices of the Royal Astronomical Society. Their research is posted on Arxiv.

NGC 3147 is a Seyfert galaxy located in the constellation Dragon about 130 million light years from the Milky Way. It was discovered by the German-British astronomer William Herschel, in 1785. Recall that the Seyfert galaxies are spiral galaxies characterized by an extremely bright and compact nucleus forming one of two important groups of active galaxies. The second is quasars, which are even more active and bright galactic nuclei.

In both cases, the energy producing the brightness of the nuclei is derived from the accretion of the material by a black hole of Kerr in rotation but whereas this one must be very substantial to generate a quasar, it is much more important in the case of a Seyfert galaxy. With respect to NGC 3147, which is ultimately low light for a Seyfert galaxy, theorists expected that its central supermassive black hole would be dietary, so to speak, and not therefore not surrounded by an accretion disk because it is not fed regularly enough quantities of materials (cold gas currents , stars etc).

A challenge to supermassive black hole accretion models

Stefano Bianchi, from the Università degli Studi Roma Tre in Italy, one of the main researchers involved in the discovery clearly gives says “the type of disc we see is that of a quasar in reduction that we did not think we could exist. This is the same type of disc that we see in 1,000 objects, or even 100,000 times brighter. Predictions of current models for very weak active galaxies have clearly failed.”

As a bonus, the disc seems to offer an excellent laboratory to test not only the theory of general relativity but also the theory of special relativity as explained by another astrophysicist involved in the work on NGC 3147, Marco Chiaberge of Johns University Hopkins (USA):  “We have never seen the effects of general relativity and restricted in visible light with so much clarity.

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