Astronomers have revealed the true colour of the Universe 鈥� it is somewhere between 鈥減ale turquoise and medium aquamarine鈥�.
The discovery may appear to be as useless as the 鈥渁nswer鈥� to life, the Universe and everything given in the Hitchhikers Guide to the Galaxy 鈥� 42 鈥� but the colour is helping the astronomers trace the history of star formation.
Ivan Baldry and Karl Glazebrook at John Hopkins University in Baltimore, Maryland, found the cosmic colour by combining light from over 200,000 galaxies within two billion light years of Earth. They worked with data from the Australian 2dF Galaxy Redshift Survey at the Anglo-Australian Observatory in New South Wales, Australia.
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Combining the light gave a spectrum with a peak in the blue part of the optical spectrum 鈥� due to the large number of young stars burning hydrogen 鈥� and another in the red part of the spectrum -due to the glow of older red giants burning heavier elements.
Researchers can analyse such spectrums like fossils, to reveal the history of star formation in a given galaxy. But this is the first time anyone has calculated a spectrum for enough galaxies to be representative of the whole Universe.
鈥淣ot my favourite colour鈥�
When Baldry and Glazebrook worked out how their spectrum would appear to the human eye, which is not equally sensitive to all wavelengths of light, they came up with a pale green.
鈥淚t鈥檚 not my favourite colour,鈥� says Glazebrook. 鈥淚t鈥檚 on the greenish side of white, a subtle colour.鈥� For any computer buffs wishing to put the colour on their desktops, the red-green-blue values you will need are 0.269, 0.388 and 0.342.
Glazebrook and Baldry have already used their result to rule out some models of star formation. In 1994, astronomers working with images of the early Universe from the Hubble Space Telescope claimed that star formation in the Universe was slow to start with, peaked around six billion years ago, and has tailed off towards the present day.
But Glazebrook says such a scenario would produce a redder colour than is seen, because more old red stars from the early Universe would still be around. 鈥淲e take account of star death in our model as well,鈥� he says.
Instead Glazebrook believes star formation peaked one to two million years after the Big Bang. This is consistent with results announced by NASA on Tuesday. At that time, the Universe was mainly blue, due to the large number of young stars, but it鈥檚 now greening out and will turn red as stars age over the next five billion years.
The new research was presented at the American Astronomical Society meeting in Washington DC.