Has ESA's XMM-Newton cast doubt over dark energy?

December 15, 2003

Observations of eight distant clusters of galaxies, the furthest of which is around 10 thousand million light years away, were studied by an international group of astronomers led by David Lumb of ESA's Space Research and Technology Centre (ESTEC) in the Netherlands. They compared these clusters to those found in the nearby Universe. This study was conducted as part of the larger XMM-Newton Omega Project, which investigates the density of matter in the Universe under the lead of Jim Bartlett of the College de France. Clusters of galaxies are prodigious emitters of X-rays because they contain a large quantity of high-temperature gas. This gas surrounds galaxies in the same way as steam surrounds people in a sauna. By measuring the quantity and energy of X-rays from a cluster, astronomers can work out both the temperature of the cluster gas and also the mass of the cluster.

Theoretically, in a Universe where the density of matter is high, clusters of galaxies would continue to grow with time and so, on average, should contain more mass now than in the past.

Most astronomers believe that we live in a low-density Universe in which a mysterious substance known as 'dark energy' accounts for 70% of the content of the cosmos and, therefore, pervades everything. In this scenario, clusters of galaxies should stop growing early in the history of the Universe and look virtually indistinguishable from those of today.

In a paper soon to be published by the European journal Astronomy and Astrophysics, astronomers from the XMM-Newton Omega Project present results showing that clusters of galaxies in the distant Universe are not like those of today. They seem to give out more X-rays than today. So clearly, clusters of galaxies have changed their appearance with time.

In an accompanying paper, Alain Blanchard of the Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées and his team use the results to calculate how the abundance of galaxy clusters changes with time. Blanchard says, "There were fewer galaxy clusters in the past."

Such a result indicates that the Universe must be a high-density environment, in clear contradiction to the 'concordance model,' which postulates a Universe with up to 70% dark energy and a very low density of matter. Blanchard knows that this conclusion will be highly controversial, saying, "To account for these results you have to have a lot of matter in the Universe and that leaves little room for dark energy."

To reconcile the new XMM-Newton observations with the concordance models, astronomers would have to admit a fundamental gap in their knowledge about the behaviour of the clusters and, possibly, of the galaxies within them. For instance, galaxies in the faraway clusters would have to be injecting more energy into their surrounding gas than is currently understood. That process should then gradually taper off as the cluster and the galaxies within it grow older.

No matter which way the results are interpreted, XMM-Newton has given astronomers a new insight into the Universe and a new mystery to puzzle over. As for the possibility that the XMM-Newton results are simply wrong, they are in the process of being confirmed by other X-ray observations. Should these return the same answer, we might have to rethink our understanding of the Universe.
-end-


European Space Agency

Related Dark Energy Articles from Brightsurf:

UH Mānoa researchers predict location of novel candidate for mysterious dark energy
UH researchers explain what may be the cause of the universe's accelerating growth.

New test of dark energy and expansion from cosmic structures
A new paper has shown how large structures in the distribution of galaxies in the Universe provide the most precise tests of dark energy and cosmic expansion yet.

IKBFU astrophysicists have developed a theory explaining the 'Dark Energy' phenomenon
The article refers to the issue of the 'Dark Enegry' and an assumption is made that the Universe has borders.

Are black holes made of dark energy?
Two University of Hawaii at Manoa researchers have identified and corrected a subtle error that was made when applying Einstein's equations to model the growth of the universe.

Lab-based dark energy experiment narrows search options for elusive force
An experiment to test a popular theory of dark energy has found no evidence of new forces, placing strong constraints on related theories.

A survey machine and a data trove: Dark Energy Survey's rich legacy
On the night of Jan. 9, 2019, the V. M.

String theory: Is dark energy even allowed?
In string theory, a paradigm shift could be imminent. In June, a team of string theorists from Harvard and Caltech published a conjecture which sounded revolutionary: String theory is said to be fundamentally incompatible with our current understanding of 'dark energy'.

Dark energy survey publicly releases first three years of data
At a special session held during the American Astronomical Society meeting in Washington, D.C., scientists on the Dark Energy Survey (DES) announced today the public release of their first three years of data.

Star mergers: A new test of gravity, dark energy theories
Observations and measurements of a neutron star merger have largely ruled out some theories relating to gravity and dark energy, and challenged a large class of theories.

Doing without dark energy
Three mathematicians have a different explanation for the accelerating expansion of the universe that does without theories of 'dark energy.' Einstein's original equations for General Relativity actually predict cosmic acceleration due to an 'instability,' they argue in paper published recently in Proceedings of the Royal Society A.

Read More: Dark Energy News and Dark Energy Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.