The black hole is "black"?The truth is amazing
The black hole, it must be the "black"?In fact black holes can't direct observation, but can borrow by indirect way to know its existence with quality, and to observe its effects on other things.About black holes "black" or not, "knowledge is power" magazine gave us a popular science, take a look at together.
More than 200 years ago, michelle in the UK and France, Laplace's proposed: a quality big enough but the volume is small enough, dense stars will produce strong gravitational field, so much so that even light can escape from its surface, so it is completely "black" for us.
But the corollary then forgotten, because it used Newton's theory doesn't solve the problem of light gravity.
Soon Einstein published the general theory of relativity in 1915, the German mathematics history tile west under the hypothesis of static and spherically symmetric solution of Einstein's field equations are obtained, the solution in a special radius (later called the schwarzschild radius) exist singularity.
In 1939, American physicist Oppenheimer further with the theory of relativity, is indeed a "time - space" area, light can't escape from this area in order to the distant observer.
This is known as the event horizon, the edge of the area under the condition of the static spherically symmetric, horizon radius is the schwarzschild radius.If an object of the radius is less than the schwarzschild radius, then the object should be "black", itself cannot be we see.
Physicists have these very dense, gravity and "see" the object is called "black hole".
Ever found in the smallest hole, 3.8 times the mass of the sun
We in the universe can truly find these mysterious elves "black hole"?Astronomers have found many of the black hole is not dense objects, such as a White Dwarf and neutron stars, they are the product of stellar evolution to the late, and there is a quality ceiling, respectively 1.4 times and 3.2 times the mass of the sun.
If in the late evolution of stars, can form more than a neutron star quality dense objects, then it is likely to be a black hole.
More than half of the stars in our Milky Way galaxy has a companion star, is located in the binary system.When the binary system evolution, in which a massive star after supernova explosions can form dense objects, it can strong gravity accretion from another star through the material, the material to spiral into the orbit of fast movement, and became very hot and X-ray light around the dense objects.
Astronomers by analyzing the observation data of these X-ray binaries, among them the quality of the compact objects may be calculated.Scientists within the Milky Way galaxy on a compact X-ray source Cygnus X - 1 calculation shows that the dense not visible to the quality of the celestial bodies is about 10 times the mass of the sun, so it can't be a White Dwarf or a neutron star, can only be a black hole.
Now in the Milky Way has been found more than 20 similar such hole Cygnus X - 1 X-ray binaries, their black hole mass is about 4 ~ 20 times the mass of the sun.
Ps: while it is true that a black hole itself is "black", but a black hole is not no trace can be found in the universe, black holes can be powerful gravity near the accretion of material around it.That astronomers can be found through observation matter around the black hole hole, and to measure its most important physical parameters, quality.