HYDROGEN CLOUD:-
Hydrogen cloud also known as Hi region. In our universe hydrogen exist in neutral form rather than molecular ionised. Most of the matter in our universe exist in this form, even if you see between the stars or in our galaxy. These cloud are easily detectable at radio wavelength and wavelength exist some where at 20cm.
Neutral hydrogen is found so much in clouds. Even have tendency to form. hydrogen atom but due to lack of photons, it form a hot star. The hydrogen can be easily predictable at the upper edge of molecular cloud. The hydrogen gas exist in cold in our milky galaxy or any other spiral galaxy. The gas cloud is also known by the nebulae.
HOW A STAR IS BORN?
STAR BIRTHS are started when the interstellar matter in gas clouds, such as the Nebula shown here, compresses and fuses.
irregularities in the density of the gas causes a net gravitational force that pulls the gas molecules closer together.
As the gases collect, they lose potential energy, which results in an increase in temperature.
As the collapse continues, the temperature increases. The collapsing cloud separates into many smaller clouds, each of which may eventually become a star. The core of the cloud collapses faster than the outer parts, and the cloud begins to rotate faster and faster to conserve angular momentum. When the core reaches a temperature of about 2,000 degrees Kelvin, the molecules of hydrogen gas break apart into hydrogen atoms. Eventually the core reaches a temperature of 10,000 degrees Kelvin, and it begins to look like a star. Also known as proto star. The size become 25 times that of sun.
When the pressure and temperature in the core become great enough to sustain nuclear fusion, the outward pressure acts against the gravitational force. At this stage the core is about the size of our sun. The remaining dust envelope surrounding the star heats up and glows brightly. 
A star looks like our sun has a lifetime of about 10 billion years and is just middle-aged, with another five billion years or so left.
HOW THE FORMATION OF BLACK HOLE TAKE PLACE?
Black holes are made when the center of a very big star falls in upon itself, or collapses. When this happens, it causes a supernova. A supernova is an exploding star that blasts part of the star into space.
A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying.
Because no light can get out, people can't see black holes. They are invisible. Space telescopes with special tools can help find black holes. The special tools can see how stars that are very close to black holes act differently than other stars.
HOW BLACK HOLES IS DETECTED?
A black hole can not be seen because strong gravity pulls all of the light into the middle of the black hole. But scientists can see how the strong gravity affects the stars and gas around the black hole. Scientists can study stars to find out if they are flying around,orbiting, a black hole.
When a black hole and a star are close together, high-energy light is made. This kind of light can not be seen with human eyes. Scientists use satellites and telescopes in space to see the high-energy light.
THAT'S ALL ABOUT BLACK HOLE.