Universe shines twice as bright

The universe is shining twice as brightly as previously thought, astronomers have discovered. A team of British, Australian and German scientists found that half the light is being obscured by clouds of dust.

The spiral galaxy NGC891 seen edge on reveals a dark lane of dustAstronomers have long been aware that much of the universe is made up of dust. But they had not realised the extent to which it was masking what we see.

The team was led by Dr Simon Driver of the University of St Andrews, in Scotland. He said: “For nearly two decades we’ve argued about whether the light that we see from distant galaxies tells the whole story or not.

“It doesn’t. In fact only half the energy produced by stars actually reaches our telescopes directly. The rest is blocked by dust grains.”

The dust absorbs starlight, then re-emits it in a glow. Astronomers realised their old ideas about the universe were flawed because the dust seems to be emiting more energy than possible with the stars known to exist.

Dr Driver added: “You can’t get more energy out than you put in so we knew something was very wrong. Even so, the scale of the dust problem has come as a shock. It appears that galaxies generate twice as much starlight as previously thought.”

The team made their discovery using data from the Millennium Galaxy Catalogue, a high-resolution catalogue of 10,000 galaxies assembled by Driver and his team using the Isaac Newton Telescope in the Canary Islands and others.

They used this to test a new model for dust distribution in galaxies developed by scientists in the UK and Germany which allowed them to calculate precisely the fraction of starlight blocked by the dust. The key test that the new model passed was whether the energy of the absorbed starlight equated to that detected from the glowing dust.

“The equation balanced perfectly,” said Dr Cristina Popescu, of the University of Central Lancashire, who helped draw up the model. “For the first time we have a total understanding of the energy output of the Universe over a monumental wavelength range.”

The photo shows the spiral galaxy NGC891 edge on, revealing a dark lane of dust. Photo by Robert Gendler. You can see more great photos of galaxies here.