Bright sources of X-rays are apparently black holes of a new type - more massive than those created by the collapse of a single star, but smaller than those found in the centers of galaxies, and probably created by the collision of stars
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In the galaxy M82, a relatively close galaxy located at a distance of about 12 million light years from the Milky Way galaxy, there is a body that emits X-rays with great intensity. Similar bodies, called ULX - ultra luminous X-ray bodies, have also been discovered in other galaxies. A normal star cannot evolve over time with such intensity: the pressure exerted by the radiation is stronger than the gravitational force that captures the star, and therefore the star will completely disintegrate.
The emission of such large amounts of energy suggests that this is a black hole, which absorbs matter from its surroundings. In the process of absorption, the material attracted to the black hole becomes hot and very compressed, and before falling into the black hole, it emits a lot of energy as radiation. Today it is common to think that in the centers of many galaxies there are black holes with huge masses, but the ULX is not in the center of the galaxy. This fact provides us with an upper limit to the mass of the body: its mass is no more than 10,000 solar masses, since if it were greater, the deceleration due to the friction with the rest of the material in its environment would have caused it to sink into the center of the galaxy.
Philip Kaaret and his colleagues, from the University of Iowa in the United States, followed the brightness of the radiation emitted by this body. The radiation is not uniform, and it is possible to identify changes, some of which are cyclical. Tracking the rate of changes can provide a lot of information about the body. Thus, for example, the radius of the radiating body can be estimated: the faster the changes in the brightness of the radiation, the smaller the body.
Since the rate of information progress is limited to the speed of light, the information about the change will not be enough to spread over a very large body in a very short time, and thus it is possible to have another upper limit to the size of the body. From measuring the rate of changes in the brightness of the radiation, the researchers concluded that the mass of the ULX is between 100 and 1,000 solar masses. This mass corresponds to bodies called intermediate black holes, which are more massive than those created by the collapse of a single star, but smaller than those found in the centers of galaxies. A medium-sized black hole was created, apparently, as a result of stellar collisions, which are possible in a sufficiently dense environment. The study of this category of black holes, medium-sized black holes, is still in its infancy.
The X-rays of the radiating body in the galaxy M82 are characterized by a cycle of about 60 days, which is apparently related to the existence of another star nearby. The two bodies are gravitationally bound and move around a common center of mass, and the extra star transfers mass to the black hole. This mass transfer is the source of the energy that allows the body to emit X-radiation at such a high intensity. Based on the rotation rate and geometry of the paired system, the researchers calculated the density of the companion star, and came to the conclusion that it is a giant star, which is in an advanced and short-lived stage of its development. This phase lasts about 10,000 years, which are only a hundredth of the star's lifetime so far.
Astrophysics experts - black holes
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