Astronomy (USA): what are the sizes of the black hole? | Science | Foreign media

Somewhere in the center of the Milky Way lies a giant black hole, the mass of which is several million times greater than the mass of the Sun. Like all black holes, this supermassive giant called “Sagittarius A *” (abbreviated Sgr A *, pronounced “Sagittarius A with an asterisk” – approx. Transl.) Absorbs everything that falls within the scope of its gravitational field – this giant devours absolutely everything, including light. Nevertheless, the absorption of matter is only one of the ways by which these cosmic monsters truly grow to astronomical sizes, gaining an amazing mass. Note that when characterizing a black hole as a gigantic space object, astronomers usually have in mind its gigantic mass, not its size.

And here a logical question arises: what are the sizes of different black holes?

Classification of black holes by mass

An ordinary black hole (known as the “stellar mass black hole”) is formed when the evolutionary cycle of a massive star, whose weight exceeds almost 8 solar masses, comes to an end. After the remnants of nuclear fuel are burned out, the phase of rapid gravitational compression (or gravitational collapse) of the star begins, after which a giant explosion occurs – this is how a supernova appears. And what remains will turn into either a neutron star or a black hole – it all depends on the mass of the star. The mass of such black holes can vary from a couple to several tens of solar masses.

Nevertheless, the question of the origin of superheavy black holes, such as Sagittarius A *, which may be millions or even billions of times the mass of the Sun, remains unresolved. Astronomers know that the gigantic size and mass of such black holes seems to be related to galaxies by a kinship, with the largest of the superheavy black holes found in the centers of the largest galaxies.

These arguments, as well as recent evidence of the existence of one theoretically predicted class of medium-sized black holes (they are called medium-sized black holes, which vary from hundreds to a million solar masses), apparently indicate that black holes can become supermassive after of how countless black holes of stellar mass and intermediate mass will merge together in billions of years.

It is clear that different types of black holes can vary significantly in mass, and yet, it is not entirely clear how much they vary in size.

But what if the Earth and the Sun were once black holes?

To study the size of black holes, let’s first look at the two most studied objects – the Earth and the Sun.

Earth mass is about 6 × 10²⁴ kg And although from the point of view of the layman this is a gigantic figure, it is still insignificant in comparison with the mass of the black hole.

For a black hole to appear, a sufficiently large mass must be concentrated, and its gravitational attraction must be so strong that no other force can prevent the gravitational collapse of this mass. That is why scientists could not find black holes as light as the Earth – these space objects simply would not have enough mass for gravitational compression. (But some scientists believe that in the first few moments after the Big Bang a class of so-called ancient primary black holes could appear. The mass of these hypothetical objects could vary from very small to gigantic, tens of thousands of times the mass of the Sun.)

It is believed that in the center of the black hole is a bottomless gravitational pit of space-time, called the gravitational singularity. The density of this singularity is infinite, and everything that gets there stays there forever. The outer edge of the black hole is called the event horizon; it represents the boundary beyond which no particle of matter that has fallen into the gravitational field of a black hole, including light quanta, can escape. The radius of the event horizon depends on the mass of the black hole; this radius was first calculated by the German astronomer Karl Schwarzschild in 1916.

For a black hole with a mass comparable to that of the Earth, the Schwarzschild radius is less than one inch (2.54 cm) —that is, the size of a ball for table tennis. For the Sun, the Schwarzschild radius is a little less than two miles (3.2 km).

What are the smallest known black holes?

As we know, black holes are very difficult to detect. And all because, unlike stars, they do not glow, because photons of light will never escape beyond the horizon of events. Nevertheless, sometimes an accretion disk appears in a black hole – an aura of matter moving around a black hole; in this case, due to friction between the layers of this substance, a glow occurs. Scientists are only able to observe a black hole thanks to the light emitted from the accretion disk; otherwise the black hole is invisible. In addition, a black hole can be detected by the effect that it has on other space objects. For example, scientists discovered the object “Sagittarius A *” only after the strangeness in the behavior of seven stars rotating around it was recorded.

Using these methods, scientists in recent years have found many candidates for the role of the black hole, including the smallest black hole known to us, located in the binary system GRO J1655-40. Gas from a visible star located in this system flows to a black hole, generating a sufficient flow of energy to power the microquasar.

Quasars develop in the extremely bright active nuclei of galaxies (these are the centers of galaxies), in which there is a supermassive black hole surrounded by a bright and powerful accretion disk. According to some estimates, the black hole in GRO J1655-40 weighs about 5.4 times the size of the Sun, and its radius is about 10 miles (16 km). By studying such microquasars, astronomers hope to better understand the possible connection between giants hidden in the nuclei of galaxies and small accreting black holes scattered across galaxies.

In 2008, scientists initially came to the conclusion that they discovered a black hole of even smaller size, but later the same researchers corrected the mass of this space object. Any smaller black hole could appear, most likely, as a result of the merger of two neutron stars, and not as a result of the gravitational collapse of a dying star. The Laser Interferometric Gravitational Wave Observatory (LIGO) detected gravitational waves from a possible merger of neutron stars in 2017, just two years after gravitational waves were first discovered. Gravitational waves emitted during mergers give scientists a new way to identify black holes within a radius of 100 million light-years from Earth.

On the other hand, the size of a black hole of stellar mass depends on how massive the star that preceded it was. The heaviest star of all known, which has been found to date, is designated by the abbreviation R136a1, it weighs 315 times more than the sun. A black hole with the same mass resulting from it as a result of gravitational collapse would have a radius of about 578 miles (930.2 km). Despite its large size (compared to the smallest known black holes), even this huge black hole of stellar mass cannot be compared to its supermassive relatives.

How big are black holes of intermediate mass?

Between stellar mass black holes and supermassive black holes are the so-called intermediate mass black holes – that is, the long-awaited “missing link” in the evolution of a black hole. To date, only a few candidates for the role of this link have been found, including the space object found by the Hubble telescope at the beginning of this year. Such objects are even more difficult to find, since they are less active in the absence of closely spaced space objects, which serve as a kind of “fuel” for them.

The mass of the black hole recently discovered by Hubble is 50,000 times the mass of the Sun. It is located in a distant dense star cluster located on the outskirts of a larger galaxy, where astronomers expected to find evidence of these “missing links”. Such a candidate for the role of a black hole of intermediate mass will be tens of thousands of times heavier than the Sun, and its radius will be one fifth of the radius of the Sun, or about twice the radius of Jupiter.

And although black holes of intermediate mass have significant sizes, their weight ranges from 100 to 100 thousand solar masses. Meanwhile, the mass of superheavy black holes can be billions of times greater than the sun.

Determine the dimensions of superheavy black holes

The central black hole of our galaxy, “Sagittarius A *”, located 26 thousand light-years from the Sun, has a radius of about 17 times that of the sun, which means that the dimensions of this black hole are limited, for example, by the orbit of Mercury. Although the black hole we mentioned in the Milky Way weighs about 4 million solar masses, its size is small compared to the size of some other supermassive black holes that are hidden in the center of other galaxies.

The largest of the supermassive black holes discovered to date is in the cluster of galaxies Abell 85. In the center of this cluster is the galaxy Holm 15A, where the total mass of the substance concentrated there is about 2 trillion solar masses. The center of this galaxy is almost as large as the Large Magellanic Cloud, whose radius is 7000 light years.

This cluster of stars is located at a distance of 700 million light years from Earth, its size is twice the size of any of the previous black holes. This was established after information began to come from the observatory on Mount Wendelstein at the University. Ludwig and Maximilian and from the VLT (Very Large Telescope) European Southern Observatory. Scientists have discovered that the black hole in the center of the Holm 15A galaxy has a colossal mass of 40 billion solar masses, or about two-thirds of the mass of all the stars of the Milky Way. With such a gigantic mass, it has a diameter comparable to the diameter of the solar system – in general, this is an unprecedented size for any single object.

But the size of the observable Universe is 46.5 billion light years in all directions, which means that astronomers take only the first steps to understand the nature of black holes. Only a year ago, with the help of the Event Horizon Telescope, which consists of eight telescopes located in different parts of the Earth, for the first time it was possible to obtain an image of a black hole. In addition, it is expected that the LIGO and Virgo observatories studying gravitational waves will be able to annually detect about 40 fusions of binary stars thanks to new technologies, as well as discover black holes and neutron stars adjacent to such stars. In addition, thanks to more advanced telescopes, such as the NASA James Webb Space Telescope (JWST) and the European Space Agency’s Extremely Large Telescope (ELT), which will receive the first images over the next decade, it’s hard to predict how many black holes in general – these space monsters – will be discovered in the future in the dark depths of space.