SPACE MYSTERIES
What are Black Holes?
Massive black holes are now thought to be located at the centers of galaxies found throughout the universe. These objects, millions or billions of times more massive than the Sun, have gravity so strong that not even light can escape them. They are the "monsters" that power the most energetic objects known in the universe.
Black holes are thought to form from stars or other massive objects if and when they collapse from their own gravity to form an object whose density is infinite: in other words, a singularity. 
During most of a star's lifetime, nuclear fusion in the core generates electromagnetic radiation, including photons, the particles of light. This radiation exerts an outward pressure that exactly balances the inward pull of gravity caused by the star's mass.
As the nuclear fuel is exhausted, the outward forces of radiation diminish, allowing the gravitation to compress the star inward. The contraction of the core causes its temperature to rise and allows remaining nuclear material to be used as fuel. The star is saved from further collapse -- but only for a while.
Eventually, all possible nuclear fuel is used up and the core collapses. How far it collapses, into what kind of object, and at what rate, is determined by the star's final mass and the remaining outward pressure that the burnt-up nuclear residue (largely iron) can muster. If the star is sufficiently massive or compressible, it may collapse to a black hole. If it is less massive or made of stiffer material, its fate is different: it may become a white dwarf or a neutron star.
Are there really aliens? And have they ever visited our planet?
This is quite a controversial problem and some of the discussions often bring fear into our hearts. But it is possible that there are as much as 60 percent (or more) of the population who believe that the government is hiding what they know about worldly visitors. Whether for our own protection or their own abuse of power, the reason for this secrecy is unclear. But one thing we can be sure is the large number of reports on the sightings of UFOs. 
Sure, there is a large percentage of claims that can be explained away, often as a simple misidentification. But unfortunately there are also a lot of claims that can't be explained away and remain true unknowns. Much of the evidence that can't be explained is in photographic and video evidence Even when there are multiple witnesses of an event it is sometimes explained as no more than mass hallucination.
From the subjects of early cave paintings to ancient art and scriptures, history would seem to indicate that we may have had visitors from other worlds or dimensions. In fact, some ancient scriptures from many different cultures, give the impression that it was common knowledge that we've had visitors from the stars. How do you explain ancient tales of chariots from the sky? And what of flying ships appearing in art far before the first plane was ever thought about. Even the Bible has been suggested as possible evidence of alien contact, for its numerous accounts of objects in the sky, wondrous miracles and other strange events. What secrets lie with the Stonehenge, and even Atlantis? How about ancient Egypt and their pyramids? The ancient Egyptians could not have made the exact calculations for the building of the pyramids and even if they did then how could they have built the structure with such heavy stones that could only be cut with a laser beam even today? Have there indeed been more advanced civilizations of man that have somehow been lost?