April 2, 2001: Gazing to the far reaches of space and time, NASA's Hubble Space Telescope identified the farthest stellar explosion ever seen, a supernova that erupted 10 billion years ago. By examining the glow from this dying star, astronomers have amassed more evidence that a mysterious, repulsive force is at work in the cosmos, making galaxies rush ever faster away from each other.See the rest:
This faraway supernova provides convincing evidence that the expansion of the cosmos is actually accelerating. In 1998 information from a passel of other distant supernovas hinted at an increasing expansion rate. Some astronomers, however, had proposed alternative theories to explain why the universe's expansion is accelerating. This discovery refutes those theories.
This invisible force, also called "dark energy," comprises the bulk of the cosmos. Albert Einstein originally suggested its existence about 80 years ago. Even today astronomers and physicists are still debating the nature of this mysterious force. Many scientists do, however, think this force is responsible for prying galaxies apart at an accelerating rate. The rapidly widening gaps between galaxies mean that the universe is expanding at a faster rate than in the past. Galaxies have been migrating apart since the Big Bang 15 billion years ago.
A supernova is the explosive death of a star, which unleashes a burst of light through the cosmos. These violent deaths occur once every 100 years in a typical spiral galaxy like our Milky Way. Some astronomers call some types of supernovas nature’s “60-watt light bulbs” because they burn at nearly the same brightness. By measuring their predictable light output, astronomers can estimate how far they are from Earth. Many of them are billions of years away. But supernovas blaze so brightly that they can be seen far across space. That’s why some astronomers also call them “cosmic mile markers”: their light provides important information about the universe’s behavior. Supernovas illuminate the dark corners of space, allowing astronomers to map the history of the universe’s expansion.