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Black holes are certainly one of the most enigmatic objects in our Universe. There are four types, including supermassive black holes, sometimes weighing several million times the mass of the Sun. Recently, a team of researchers led by astrophysicist Dheeraj Pasham from the Massachusetts Institute of Technology (MIT) managed to calculate the rotation speed of a very distant black hole, located a billion & #8217;light years from Earth. To do this, they used a new technique based on the observation of the oscillations of its accretion disk.
These are the periodic variations in density, temperature, or other physical parameters in the material that swirls around the black hole before exiting. #8217;sink into it. The results of their research were published on May 22 in the journal Nature.
A method that gives dizziness
By analyzing the subtle variations of light emitted during the awakening of a low-activity black hole, scientists have determined its rotation speed, a world first! Result: it rotates on itself at a speed estimated at less than 25% of the speed of light, or approximately 74 948 km/s. As Pasham, one of the researchers involved in the study, explains: “By studying several systems in the coming years with this method, astronomers will be able to estimate the global distribution of black hole rotation speeds and understand how they evolve over time “.
These cosmic giants, lurking at the heart of galaxies, can go from a state of tranquility to intense activity, producing bursts of light among the brightest in the Universe. In 2020, astronomers observed the spectacular awakening of a quiescent black hole in a distant galaxy, causing a gigantic flare of light that&# 8217;they named AT2020ocn. The data revealed that the emission of this intense light occurred due to an event dubbed the “tidal rupture event< /em> ”. This is the moment when a star is devoured by the gravity of the black hole, forming a luminous disk around it.
A careful observation
To measure the rotation of the black hole, it was essential to observe this event from its beginnings. Pasham explains: “To be successful, one must immediately point a telescope at the object as soon as a tidal dislocation event occurs, and observe it continuously for an extended period of time, so that one can analyze varied time scales, from a few minutes to several months “.
With instruments constantly scanning the sky , the researchers were able to capture AT2020ocn just in time. They thus observed that the galaxy emitted X-rays approximately every 15 days, a phenomenon that they linked to the oscillation of the accretion disk of the neighboring black hole. By combining these observations with the estimated mass of the black hole (approximately 2.5 million times that of the Sun), they were able to precisely calculate its rotation speed.
This new measurement technique could radically transform our understanding of black holes. Indeed, it is much more precise and direct than the techniques previously used, often based on indirect observations. Thanks to the analysis of variations in luminosity of the accretion disk, it is now possible to obtain much more reliable and usable data in a greater number of situations: evolution of the disk, interactions between the black hole and nearby stars or periods of low activity. Thanks to this discovery, it will one day be possible to map the different rotation speeds of black holes, which will allow us to better understand the evolution of these cosmic objects through the ages.
- MIT researchers have succeeded in calculating the rotation speed of a black hole using a new method.
- Rather than observing it indirectly, they analyzed the analysis of the variations in luminosity of its accretion disk.
- A technique that will allow us to collect more reliable data on black holes and better understand them.
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