As if it were a huge “donut” (or torus) that grows as the days go by . This is how Jesús Corra, a researcher at the Instituto de Astrofísica de Canarias (IAC), describes the peculiar structure of the binary system Swift J1357.2-0933, composed of a ‘normal’ star and a stellar-mass black hole, that is, that feeds of the companion star, and which is situated on edge . A study of which Corral is the first author and that appears published in the latest issue of Science has followed the steps of the eruption phase of the system, a fact that only occurs once every tens or hundreds of years.
In this way, the team of astrophysicists observed strange eclipses in the system that lasted and repeated every few minutes. This finding led them to two conclusions: the black hole should be placed practically “edge” (an inclination of at least 75 degrees) and presents a peculiar vertical structure located in the accretion disk of the system, that is, the whole of the matter that the hole is stealing from the star and that forms a disk-shaped stream, similar to that generated by water when uncovering a sink.
This is the first time that a black hole has been observed with this inclination . Astrophysicists suspect that the structure described by the study could be present in many other systems, making Swift J1357.2-0933 the prototype for a hitherto hidden population of very high-tilt systems in which the black hole is located. found obscured.
Black holes are formed from the death of very massive stars and, from the outset, it is difficult to find them. By not emitting light, it is almost impossible to detect them if they are alone. In the case that they form a system with a star, the probability of observation is higher, since what is seen is the process of ‘cannibalization’ of the star by the hole . In this way it is understood that, since the first one was detected in 1964, only another 18 black holes have been confirmed in our galaxy.
Swift J1357.2-0933, discovered by the Swift X-ray satellite in 2011 and studied by the IAC team, was the latest to be added to the list. It is located about 5,000 light years away, and the star completes an orbit around the black hole every 2.8 hours. The hole’s mass is at least 3 times that of the Sun.
The most unusual finding of the system has been its eclipses , which occur every few minutes , reduce the brightness of the system by up to 30%, last only seven seconds and are repeated at longer intervals after a few days. “It is the first time that a phenomenon of these characteristics has been observed. None of the 50 known transient X-ray binaries (18 with confirmed black holes and 32 candidates) show eclipses produced by the star ”, explained Corral.
