Dark energy stunting growth of galaxies

The mysterious force causing the universe to expand at an accelerated pace is also stifling the growth of the matter inside it, astronomers revealed Tuesday.
This illustration shows snapshots from a simulation representing the growth of cosmic structure when the universe was 0.9 billion, 3.2 billion and 13.7 billion years old, which it is now, evolving from a smooth state to one containing a vast amount of structure. ((MPE/V.Springel))

The mysterious force causing the universe to expand at an accelerated pace is also stifling the growth of the matter inside it, astronomers revealed Tuesday.

Astronomers used NASA's Chandra X-ray Observatory to measure the size of distant and massive galaxy clusters and found that they either grew marginally or not at all in the last five billion years.

"This result could be described as 'arrested development of the universe'," said lead researcher Alexey Vikhlinin of the Smithsonian Astrophysical Observatory in Cambridge, Mass., in a statement. "Whatever is forcing the expansion of the universe to speed up is also forcing its development to slow down."


The explanation, say the astronomers, lies in the mysterious force known as dark energy, which acts as a kind of counter to gravity at large scales, pulling galaxies and galaxy clusters further away from each other as they draw material in.

Dark energy's existence was first inferred from measuring the rate at which far-off supernovas were speeding away from Earth. While astronomers believe it makes up about three quarters of the known universe — with dark matter making up about 23 per cent and visible matter making up just four per cent — they have had little to go on in identifying it.

Galaxy clusters, composed of hot gas, are the largest collapsed objects in the universe, with masses of 100 trillion suns and larger, and provided Vikhlinin and his colleagues with an opportunity to look at the interplay between gravity and dark energy at huge scales.

A composite image of the galaxy cluster Abell 85, about 740 million light years from Earth. The purple emission is multimillion-degree gas detected in X-rays by NASA's Chandra X-ray Observatory. The galaxy cluster is one of 86 observed by Chandra to trace how dark energy has stifled the growth of these massive structures. ((X-ray: NASA/CXC/SAO/A.Vikhlinin et al. Optical: SDSS))

They observed 86 galaxy clusters at a variety of distances to gauge the relative growth of clusters over time, and compared those findings with how they might have been expected to grow using different theories, including those without dark energy.

He said the findings of Chandra support the theory of dark energy, and suggested it is connected to Albert Einstein's "cosmological constant."

Einstein coined the term to describe an energy or force needed to counter the effect of gravity. But when he did so it was with the intention of keeping his model of the universe static in size, neither expanding nor contracting.

He later abandoned the idea in 1929 after astronomer Edwin Hubble found evidence that the universe was expanding, calling it a "blunder."

Astronomers dusted off the theory after evidence was found that the universe's expansion was speeding up and were looking for a possible culprit.

"Putting all of this data together gives us the strongest evidence yet that dark energy is the cosmological constant, or in other words, that 'nothing weighs something'," said Vikhlinin. "A lot more testing is needed, but so far Einstein's theory is looking as good as ever."

The results will have consequences for the universe, eventually pushing all of the other matter clusters away from each other. From our view here in the Milky Way, such an event would push all of the other galaxies out of sight in 100 billion years and the local supercluster of galaxies would disintegrate.