THE most distant supernova ever observed appears to have blown its top when the expansion of the Universe was slowing down. Ironically, this observation boosts the idea that the Universe is filled with "dark energy" that stretches space and is now making it expand faster. Adam Riess of the Space Telescope Science Institute in Baltimore and Peter Nugent of the Lawrence Berkeley National Laboratory in California spotted the explosion in Hubble Space Telescope data.
Because the Universe is expanding, distant stars and galaxies recede from Earth and their light is stretched out, pushing it towards the red end of the spectrum. Hence, assuming the Universe expands predictably, you can judge how far away a star is by the size of its red shift.
Two years ago, two teams of astronomers reported that distant stellar explosions known as type Ia supernovae, which always have the same brightness, appeared about 25 per ...
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