Black Holes in Space 
WHAT ARE THEY?
Black holes are places in the universe where gravity is so dense that everything is attracted to its core (including light), it is important notion of this phenomenon in the u Nivers. Below I will put the information and some pictures of this phenomenon (I hope you like it).
foman HOW?
A black hole is created when an object becomes unable to maintain the strength of its own gravity, objects (including the earth and our sun) will never become black holes. Its gravity is not sufficient to overcome the force of atomic and nuclear interiors.
black holes form from dying stars which after a natural process begins to accumulate an enormous concentration of mass in a minimum radius so that the escape velocity of this star is larger than speed light. From this, the former star allows nothing to escape its gravitational field, even light can not escape it. To understand more clearly what is written above should we study the phases in the formation of a star: Star Formation - The Chandrasekhar limit
First, not all stars can become black holes, for it must meet certain requirements such as size, lifespan, among other features.
Stars form from large concentrations of gas, mainly hydrogen atoms by gravitational effects that make these gases start to collapse against each other to contract and generate a gas heating, heat gradually increase reaching generate significant reactions between atoms (molecules transformation of hydrogen into helium). These reactions lead to soaring energy emanations that give the stars the brightness feature. All this occurs to a time when the atoms reach a balance from which longer contract. The Sun is now in the balance, in which there is no type of contraction by its components.
Ahora bien, durante el período de tiempo que toma el proceso de contracción de los átomos la estrella sigue acumulando más gases y crece en tamaño, este tamaño fue estudiado por Subrahmanyan Chandrasekhar, quien indicó el tamaño máximo que una estrella puede alcanzar antes de llegar a consumir todo su combustible natural. Chandrasekhar descubrió el límite al cual una estrella puede crecer de manera que su masa pueda llegar a ser tal que la estrella llegue al límite de soporte de su gravedad. (Esto puede resultar un poco complicado de explicar así que tómalo con calma). ¿Qué significa lo anterior? que si la estrella es muy grande su gravedad podría cause this "collapse on itself" (to understand think of an egg dropping to 400 meters deep under the sea, what would happen is that the egg will break the effect of water pressure which is exerted perpendicular on the egg surface before falling to the bottom of the sea).
Well, this gentleman happens then mathematically calculated Chandrasekhar critical mass of a star would be equal to 1.5 times the mass of the sun at this mass is called the Chandrasekhar limit, below this limit find white dwarfs and neutron stars, while above that limit ... no good was not until 1939 that it failed to explain what would happen to a star with a mass greater than the Chandrasekhar limit, this star would possess a gravitational field so strong that light rays emanating from the star begins to radiate to the surface (like a boomerang ), little by little the light rays are more strongly inclined towards the same star from which they emanate. In the distance an observer as the star loses contemplate turning bright red (an effect similar to when a lamp batteries are running out of a few), when the star comes to reaching a critical radius the gravitational field will grow exponentially, eventually reaching to catch the same light in it. At this moment the black hole has been created and their presence can only be noticed by X-ray emission caused.
Finally, in recent years lus theory has handled in the center of our galaxy, there is a supermassive hole, which causes the movement and shape of it, I think this is true and I tell them because if you look, when we fill a bathtub and we remove the cap, the water movement is making a spiral (the same of our galaxy), because if we assume that the bath water is space that includes our galaxy, and the plug hole, the black hole, we would have at the event. I hope you have been Interesting this information, if you want to know more can visit the Hubble Space Telescope: http://hubblesite.org/explore_astronomy/black_holes/ , or http://es.wikipedia.org/wiki/Agujero_negro
Pedro Vivas.
The first, and the nearest, called 2002 NT7, which is estimated will make impact with the ground on 1 February 2019 in Europe, the which has a volume of 4,400 million cubic meters, a diameter of 2.03 km, a mass of 11,000 tons, reached a speed of 26.24 km / s, on impact generera an energy of 1 million megatons (something like 59,000 Hiroshima bombs at the same time), q is estimated provoke tsunamis, earthquakes and hurricanes to 1,000 km radius, a drop of 8 ° C week in temperature, loss of crops and severe damage to the atmosphere, so do not go to Europe by that time hehe. 
The second most dangerous observed by NASA Apophis is 999,942, the exact date is April 13, 2029, at 4:36 a.m. Greenwich meridian time, 250 meters wide and 25 million tons, passed through the orbit of the moon and walked in our planet at a speed of 45,000 km / h, unleashed the energy of 65,000 Hiroshima bombs. Asimple view may be observed (the first in human history), imagine it will be more catastrophic than 2019, but of course NASA is already in the development of strategies to deflect or destroy these and the 850 asteroids that threaten our planet. 
