Since Albert Einstein first proposed it, then withdrew his idea because it was just too weird to believe, physicists have puzzled about ‘dark matter.’

Two recent discoveries suggest that hard evidence of dark matter has been detected. The first of these startling discoveries is that the universe has recently started speeding up (by ?recently,? they mean between 4 and 8 billion years ago). And now the Hubble Space Telescope has spotted an ancient exploding star that provides evidence that a mysterious form of ?dark energy? is causing the expansion of the universe to accelerate.

Scientists expected to find that gravity slowed down the expansion of the universe after the Big Bang, but the repulsive force of dark energy is winning out over gravity?s grip. The idea that the universe is expanding faster and faster, instead of slowing down, is the opposite of what scientists have long believed.

Image courtesy of NASA.

?This is absolutely extraordinary,? says Michael Turner, an astronomer from the University of Chicago. ?For 70 years astronomers believed that the universe would be slowing down and tried to measure it. When they finally succeeded in doing it, the darn thing was speeding up.?

The Hubble has spied the most distant supernova ever, an 11 billion-year-old exploding star which is the furthest and therefore the oldest of its kind ever observed. ?This supernova appears to be one of a special class of explosions that allows astronomers to understand how the universe?s expansion has changed over time, much as the way a parent follows a child?s growth spurts by marking a doorway,? says Adam Riess of the Space Telescope Science Institute. ?It shows us the universe is behaving like a driver who slows down approaching a red stoplight and then hits the accelerator when the light turns green.?

The exact definition of ?dark energy? remains elusive, but it behaves more like energy than matter. It cannot be stopped, and it is unseen. It pervades the cosmos. Whatever it is, there?s lots of it: scientists think it makes up 65 percent of the universe.

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