Secretofphysics

Star birth:                                                                                                                 stars have been forming throughout the universe for most of its life. They  take shape in vast clouds where thousands of stars are born at a time . The clouds that give birth to the stars are cold and dense and consist mainly of hydrogen gas . the newly formed stars are huge spinning globes of hot , glowing gas  mainly hydrogen , with helium and small amounts  of other elements . much of this material is packed tightly into the stars cores ,and it is here that nuclear reaction release energy in the form of heat and light .              ...

The universe is the whole of existence ,all of space , matter , energy and time . The universe is so vast as to be unimaginable , but we do know that it is steadily  expanding following its beginning 13.8 million years ago in an explosive event called big bang .  people used to think of the universe as a giant sphere , but we know that things are not simple . the universe probably has no centre or outer edge . only a fraction of it  the observable universe is visible to us the whole universe may be vastly bigger than this .  The three dimensions of space are " bent " by the force of gravity from matter  in the universe into four dimension that we can't see. this is hard to visualize , so scientists use the metaphor of a  two dimensional rubber sheet to explain the idea . the mass of the universe could bend this rubber sheet in one of three ways , depending on how densely packed with matter the universe is most scientists now think the shape of the universe ...