Astronomy (USA): what is the size of a black hole?

Somewhere in the center of the milky Way lurks a giant black hole, whose mass is several million times the mass of the Sun. Like all black holes, supermassive this giant called “Sagittarius a*” (abbreviated to Sgr A*, pronounced “Sagittarius a star” — approx. transl.) absorbs everything that comes within the scope of its gravitational field — this giant devours everything, including light. However, the absorption of matter is just one of the ways by which these cosmic monsters grow to truly astronomical proportions, gaining a mind-blowing mass. Note that describing a black hole as a giant space objects, astronomers usually have in mind its huge mass, not the size.

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

Distribution black holes is by class depending on weight

A normal black hole (known as the “black hole of stellar mass”) is formed when the evolutionary cycle of a massive star, the weight of which exceeds almost 8 solar masses, is about to end. After burning down the remains of nuclear fuel, the phase of rapid gravitational contraction (or gravitational collapse) of a star, then there is a giant explosion, — so there is a supernova. And what is left will become either a neutron star or a black hole depending on the mass of the star. The mass of such black holes can range from a couple to several tens of solar masses.

However, the question of the origin of superheavy black holes, such as “Sagittarius a*”, which are millions and even billions of times greater than the mass of the Sun remains unresolved. Astronomers know that a giant the size and mass of such black holes, seem to be associated with galaxies related communication, and the biggest of superheavy black holes was discovered in the centers of most large galaxies.

These arguments and recent evidence of the existence of a theoretically predicted class of black holes of medium size (they are called black holes the average weight that varies from hundred to one million solar masses), seem to indicate that black holes may be the supermassive after countless black holes of stellar mass and intermediate mass through billions of years will merge together.

It is clear that different types of black holes vary greatly in weight, and yet, not entirely clear how they differ in size.

What if the earth and the Sun were once black holes?

To examine the sizes of black holes, let us first consider the two most studied object — the Earth and the Sun.

The mass of the Earth is about 6×1024 kg And although from the standpoint of the layman is a huge figure, it is still negligible compared to the mass of the black hole.

Below appeared a black hole, it is necessary to concentrate a large enough mass, and its gravitational pull should be so strong that no other force will be able to prevent gravitational collapse of the mass. That’s why scientists have been unable to find black holes as light as the Earth, these space objects just did not have enough mass for gravitational compression. (But some scholars believe that in the first few moments after the Big Bang could appear ancient class of so-called primary black holes. The mass of these hypothetical objects might vary from very small to huge, in the tens of thousands of times the mass of the Sun.)

It is believed that in the center of a black hole is a bottomless gravitational pit of space-time, called gravitational singularity. The density of the singularity is infinite, and all that gets there stays there forever. The outer edge of a black hole is called the event horizon; it represents the boundary beyond which it can not escape, no particle of matter trapped in the gravitational field of a black hole, including light quanta. The radius of the event horizon depends on the mass of the black hole; the radius was first calculated by the German astronomer Karl Schwarzschild (Schwarzschild, Karl) in 1916.

For a black hole with a mass comparable to the mass 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 will be slightly 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 because, unlike stars, they don’t glow, because the light photons will never escape beyond the event horizon. However, sometimes appears a black hole accretion disk — halo of matter moving around a black hole; however, due to friction between the layers of this substance occurs glow. Scientists are able to observe a black hole only by the light emitted by the accretion disk; otherwise, a black hole is invisible. In addition, the black hole can be detected by the impact it has on other space objects. For example, the scientists found the object of “Sagittarius a*” only after it was fixed the weirdness in the behavior of seven stars revolving around it.

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

Quasars evolve in an extremely bright active galactic nuclei (the centers of galaxies), which 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 greater than the Sun, and its radius is about 10 miles (16 km). By studying microquasars such, astronomers hope to better understand the possible link between giants, hidden in the cores of galaxies, and a small excretiruemami black holes scattered throughout the galaxies.

In 2008, scientists at first concluded that they had discovered a black hole even smaller, but later the same researchers the mass of this space object has been adjusted. Any black hole smaller could appear, most likely, the merger of two neutron stars, and not the result of a gravitational collapse of a dying star. Laser interferometric gravitational-wave Observatory (LIGO) detects gravitational waves from mergers of neutron stars in 2017, just two years after the gravitational waves were actually discovered for the first time. Gravitational waves emitted during the mergers, give scientists a new way to identify black holes in 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 was, she was preceded. The heavy star, which has been found to date, denoted by the acronym R136a1, it weighs 315 times greater 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 is nothing in comparison with their supermassive cousins.

How big are black holes of intermediate mass?

Between black holes of stellar mass and supermassive black holes are the so-called black holes of intermediate mass — 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 level, including space object found by the Hubble telescope earlier this year. These objects are even harder to find because they are less active in the absence of close space objects, which serve as a kind of “fuel”.

The mass of the black hole, recently discovered by Hubble in 50 thousand times the mass of the Sun. It is in a remote and dense star cluster, located on the outskirts of the galaxy large size, this is where astronomers expected to find evidence of these “missing links”. A candidate for the role of black holes of intermediate masses will be in the tens of thousands of times heavier than the Sun, and its radius will be one-fifth of the Sun’s radius, or about twice the radius of Jupiter.

Although black holes of intermediate masses have considerable size, their weight ranges from 100 to 100 thousand solar masses. Meanwhile the mass of the super-heavy black holes may be billions of times greater than the sun.

Measure the dimensions of superheavy black holes

From the Central black hole of our galaxy, “Sagittarius A*”, located 26 thousand light years from the Sun, the radius is about 17 times solar, and this means that the size of this black hole is limited, for example, the orbit of mercury. Although we mentioned the black hole in the milky Way weighs about 4 million solar masses, its dimensions are small in comparison to some other supermassive black holes that lurk at the center of other galaxies.

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

This star cluster is located at a distance of 700 million light years from Earth, its dimensions are twice the dimensions of any of the previous black holes. It was installed after began to receive information from the Observatory on the mountain Wendelstein at the University. Ludwig and Maximilian and from the telescope VLT (Very Large Telescope “Very large telescope”) ESO. Scientists have discovered that the black hole at the center of the galaxy Holm 15A has an enormous mass of 40 billion solar masses, or about two-thirds of the mass of all stars in the milky Way. With such a huge mass it has a diameter comparable to the diameter of the Solar system — generally 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 make the first steps in understanding the nature of black holes. Only a year ago with a telescope Event Horizon Telescope (Telescope the event horizon), which consists of eight telescopes located in different parts of the Earth, for the first time managed to image the black hole. In addition, it is expected that the observatories LIGO and Virgo, gravitational waves learners will be able annually to detect thanks to new technologies, about 40 mergers of double stars, and open black holes and neutron stars, located in the neighborhood of such stars. In addition, due to the more advanced telescopes, such as Space telescope NASA’s James Webb (James Webb Space Telescope, JWST) and Extremely large telescope (Extremely Large Telescope, ELT) of the European space Agency that will receive the first images within the next decade, it is difficult to predict how all black holes — those space monsters will be discovered in the future in the dark depths of space.