Astronomers have returned to the dark about what dark matter might be, after new observations showed that the mysterious substance may not be interacting with forces other than gravity after all. Dr. Andrew Robertson of the University of Durham will present today (Friday, April 6) the new results in the European Week of Astronomy and Space Science in Liverpool.
Three years ago, an international team of researchers led by Durham thought they had made a breakthrough in finally identifying what dark matter is.
Observations using the Hubble Space Telescope seemed to show that a galaxy in the Abell group 3827 – approximately 1.3 billion light years from Earth – separated from the surrounding dark matter.
Such a deviation is predicted during collisions if dark matter interacts with forces other than gravity, providing clues as to what the substance might be.  The random orientation of the Abell 3827 cluster from Earth allows highly sensitive measurements of its dark matter.
However, the same group of astronomers now says that new data from more recent observations show that dark matter in the Abell 3827 cluster has not separated from its galaxy after all. The measurement is consistent with dark matter that only feels the force of gravity.
Lead author, Dr. Richard Massey, at the Center for Extragalactic Astronomy at the University of Durham, said: "The search for dark matter is frustrating, but that is science, data improves, conclusions can change.
"Meanwhile, hunting continues for dark matter to reveal its nature.
" As long as dark matter does not interact with the Universe around it, we are having difficulty determining what it is " The universe is composed of approximately 27 percent dark matter, and the rest consists largely of the mysterious dark energy, normal matter, such as planets and stars, contributes a relatively small five percent of the Universe.
believes that it is about five times more dark matter than all the other particles understood by science, but nobody knows what it is.
However, dark matter is an essential factor in how the Universe looks today, since without the restrictive effect of its extra gravity, galaxies like our Milky Way would be thrown to pieces as they turned.
In this latest study, the researchers used Atacama Large Millimeter Array (ALMA) in Chile, South America, to view the Abell 3827 cluster.
ALMA collected in the distorted infrared light of an unrelated background galaxy, revealing the location of dark matter that would otherwise be invisible in its previous study.
Research co-author, Professor Liliya Williams of the University of Minnesota, said: We obtained a higher resolution view of the distant galaxy using ALMA than even the Hubble Space Telescope.
"The true position of dark matter became clearer than in our previous observations".
While the new results show dark matter remaining with its galaxy, the researchers said it does not necessarily mean that dark matter does not interact. Dark matter could interact very little, or this galaxy in particular could be moving directly towards "S us, then we would not expect to see its dark matter displaced sideways," the team added.
Several new theories of non-standard dark matter have been invented in the last two years and many have been simulated at Durham University using high-powered supercomputers.
Robertson, who is a co-author of the work, and based at the Computational Cosmology Institute of the University of Durham, added: "The different properties of dark matter leave telltale signs.
" We will continue to seek that nature has done what experiment we need, and so we can see it from the right angle.
"An especially interesting test is that the dark matter interactions make the aggregates of dark matter more spherical, that's the next thing we're going to look for"  A simulation of the same collision if dark matter does not existed The resulting distribution of stars and gas does not agree with what is observed in the real Universe, which provides convincing evidence that dark matter is present in the real Universe. Credit: Andrew Robertson / Institute of Computational Cosmology / University of Durham
To measure dark matter in hundreds of galaxy clusters and continue this research, Durham University has just helped build the new SuperBIT telescope, which gets a view clear when rising above the Earth's atmosphere under a giant helium balloon.
The research was funded by the Royal Society and the Council for Science and Technology Facilities in the United Kingdom and NASA. The findings will appear in a new document in the journal Monthly Notices of the Royal Astronomical Society .
Hubble weighs more than three million million suns
The new research will appear in "Dark Matter Dynamics in Abell 3827: New Data Consistent with Standard Dark Cold Matter", R. Massey et al., Monthly Notices from the Royal Astronomical Society in press.  Continues the 2015 research paper, "The behavior of dark matter associated with four bright cluster galaxies in the 10 kpc core of Abell 3827", R. Massey et al. Monthly Notices of the Royal Astronomical Society ] Volume 449, Number 4, June 1, 2015, pages 3393-3406.