Black+holes,+Supernova

There should be on average one supernova every 50 to 100 years..



This cloud of gas,called the crab nebula,is all that remains of the supernova that exploded in 1054, which appeared bright enough to be seen in daylight.

//What is a black hole?//
A black hole is a region of spacetime from which nothing can escape, even light. To see why this happens, imagine throwing a tennis ball into the air. The harder you throw the tennis ball, the faster it is traveling when it leaves your hand and the higher the ball will go before turning back. If you throw it hard enough it will never return, the gravitational attraction will not be able to pull it back down. The velocity the ball must have to escape is known as the **escape velocity** and for the earth is about 7 miles a second.

150 times the size of the Sun has exploded in what is the brightest supernova ever seen.
The extraordinary discovery, announced yesterday by NASA, prompted astronomers to suggest a similar fate could be imminent for a star in Earth's galactic area. If that nearer star, named Eta Carinae, blows up like the one just discovered, they said, it could possibly spew dangerous radiation in Earth's direction. But The Washington Post reported it was more likely to erupt into the most luminous star in our sky - visible during the day and bright enough to let people read unaided at night, perhaps for months.