Understanding-the-univerese

Univerese

      People used to think of the univerese as giant sphere,but  we now know that things are not so simple . The univerese probably has no centre or outer edge. Only a fraction of it  the observable   univerese is visible to us. The whole univerese may be vastly bigger then this, perhaps infinitely so

The shape of space

      The three dimensions of space are bent by the force of gravity from matter in the we can't see .this is hard to visulize,so scientist use the metaphor of a two dimensional rubber sheet to explain the idea. The ass of the universe could bend this rubber sheet in one of  three ways , depending on how densely packed with matter the universe is . Most scientist now think the shape of univerese is flat

Looking back in time

      Because light takes time to travel,when we look into space we are looking back in time . The most distant objects visible are galaxies photographed by the Hubble telescope. We see them as  they were 13 billion years ago. The universe extends far beyond these, but it's impossible to see object much further because their light hasn't had Tim to reach us

What's the matter

      The elements hydrogen and helium make up 98per cent of the Matter​ we can see in the . Universe. But there doesn't seem to be enough matter to account for the way stars and galaxies contain dark matter which we cannot see. There is also an unknown force marking the univerese expand, known as dark energy

Star birth

    Star have been forming thuoughout the Universe for most its life.They take shape in vast clouds where thousands of stare are born atn a time.The clounds 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 reactions release energy in the form of heat and light.

Star death

     All stars eventually run out of fuel and die. Most fade away quietly, but the most massive stars self-destruct in a huge explosion that can outshine an entire galaxy.Like Earth, stars generate the  force of gravity, which squeezes theri hot cores.The more matter a star has,the greater the force of gravity and the hotter and denser the core becomes.The way a star dies depends on how much matter it contains (its mass) and how powerfully its core is squeezed by gravity.

    Stars make heat and light by the process of nuclear fusion:hydrogen atoms in the core crash together to form helum,releasing energy.In small stars,when hydrogen in the core runs out,the star's light slowly faded.But in more massive stars, the core is so hot and dense that fusion can spread beyond it, changing the star's appearance.The most massive stars are eventully overwhelmed by their own gravity, which crushes them so violently that they collapse into a pinprick to create a black hole.