Dark matter 'smoother' than we thought: study

The finding may throw into question what little we know about the birth and growth of the cosmos, astronomers reported.

"All we can say for now is that something appears to be not quite right," study co-author Konrad Kuijken of the Leiden Observatory in the Netherlands told AFP. 

Studying the light of some 15 million distant galaxies with Europe's Very Large Telescope (VLT) in Chile, Kuijken and a team found dark matter to be significantly "less clumpy" than previously shown by the European Space Agency's Planck satellite.

Dark matter is a mysterious substance not visible to telescopes and perceived only through its gravitational pull on other objects in the Universe.

Planck, retired in 2013, studied radiation remnants from the "Big Bang" that created the Universe some 14 billion years ago.

The new study, in turn, examined how the light from distant galaxies is bent through the gravitational influence of matter.

"The surprise result... has implications for our understanding of the Universe, and how it has evolved during its almost 14-billion-year history," the Royal Astronomical Society (RAS) and the European Southern Observatory, which hosts the VLT, said in a statement.

"Such an apparent disagreement with previously established results from Planck means that astronomers may now have to reformulate their understanding of some fundamental aspects of the development of the Universe."

This could mean rethinking the very essence of dark energy -- an unexplained force thought responsible for accelerating the expansion of the Universe.

Instead of the single "cosmological constant" suggested by Albert Einstein, there could be several different forms of dark energy, said Kuijken.

"Another exciting possibility is that this is a sign that the laws of gravity on the scale of the Universe are different from general relativity" -- Einstein's gravity theory which underpins much of physics today.

The results were published in the Monthly Notices of the Royal Astronomical Society.

The Planck satellite in 2013 reshaped our understanding of the Universe's key ingredients.

It found that "normal matter" -- which makes up human beings, planets, stars and galaxies -- comprises 4.9 percent of the Universe, up from 4.5 percent previously measured.

Dark matter makes up significantly more than thought -- 26.8 percent of the Universe in total. Dark energy accounts for the rest at 68.3 percent.

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