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Dark matter may not be interactive after all

Hubble Space Telescope image of the four giant galaxies in the heart of the Abell 3827 cluster. An exposure of nearly three hours shows the view at wavelengths visible to the human eye, and near infrared, as used in the original study of 2015. The distorted image of a more distant galaxy behind the cluster is faintly visible, wrapped around the four galaxies. Credit: NASA / ESA / Richard Massey (University of Durham)

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. [19659005] 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.

A view of the four central galaxies in the Abell 3827 cluster nucleus over a wider range of wavelengths, including images from the Hubble Space Telescope in the ultraviolet (shown as blue) and Atacama Large Milimeter Array at very long wavelengths (sub-mm) (shown as red contour lines.) At these wavelengths, the foreground becomes almost transparent, allowing the background galaxy be clearer Now it is easier to identify how that background galaxy has been distorted Credit: NASA / ESA / ESO / Richard Massey (University of Durham)

"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 "[19659005] 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.

A supercomputer simulation of a collision between two galaxy clusters, similar to the real object known as the "Bullet Cluster", and showing the same proven effects r in Abell 3827. All galaxy clusters contain stars (orange), hydrogen gas (shown in red) and invisible dark matter (shown in blue). Individual stars and individual galaxies are so separated from one another that they pass quickly over each other. Diffuse gas slows down and separates from galaxies, due to the forces between ordinary particles that act as friction. If the dark matter only feels the force of gravity, it should stay in the same place as the stars, but if it feels other forces, its trajectory through this collider of giant particles would be modified. Credit: Andrew Robertson / Institute of Computational Cosmology / University of Durham

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.

A simulation of the same collision if the dark matter consisted of extremely strong "autointeractive" particles that feel great forces in addition to gravity. The resulting distribution of dark matter and gas does not match what is observed in the real Universe; In fact, the interaction is so strong in this case that the dark matter stopped near the point of impact. As this is not seen in the real Universe, this allows us to discard this particular model of dark matter. Credit: Andrew Robertson / Institute of Computational Cosmology / University of Durham

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" [19659028] 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 .

Explore more:
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More information:
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. [19659005] 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.

Journal reference:
Monthly notices from the Royal Astronomical Society

Provided by:
Royal Astronomical Society

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