NEWS & PRESS
Scientists believe they have found a way to explain why there are not as many galaxies orbiting the Milky Way as expected. Computer simulations of the formation of our galaxy suggest that there should be many more small galaxies around the Milky Way than are observed through telescopes.
This has thrown doubt on the generally accepted theory of cold dark matter, an invisible and mysterious substance that scientists predict should allow for more galaxy formation around the Milky Way than is seen.
Institute for Computational Cosmology and the Institute for Particle Physics Phenomenology, at Durham University, working with colleagues at LAPTh College & University in France, think they have found a potential solution to the problem.Now cosmologists and particle physicists at the
Writing in the journal Monthly Notices of the Royal Astronomical Society, the scientists suggest that dark matter particles, as well as feeling the force of gravity, could have interacted with photons and neutrinos in the young Universe, causing the dark matter to scatter.
Scientists think clumps of dark matter – or haloes – that emerged from the early Universe, trapped the intergalactic gas needed to form stars and galaxies. Scattering the dark matter particles wipes out the structures that can trap gas, stopping more galaxies from forming around the Milky Way and reducing the number that should exist.
Lead author Dr Celine Boehm, in the Institute for Particle Physics Phenomenology at Durham University, said: "We don’t know how strong these interactions should be, so this is where our simulations come in."
"By tuning the strength of the scattering of particles, we change the number of small galaxies, which lets us learn more about the physics of dark matter and how it might interact with other particles in the Universe."
"This is an example of how a cosmological measurement, in this case the number of galaxies orbiting the Milky Way, is affected by the microscopic scales of particle physics."
There are several theories about why there are not more galaxies orbiting the Milky Way, which include the idea that heat from the Universe’s first stars sterilised the gas needed to form stars. The researchers say their current findings offer an alternative theory and could provide a novel technique to probe interactions between other particles and cold dark matter.
Co-author Professor Carlton Baugh said: "Astronomers have long since reached the conclusion that most of the matter in the Universe consists of elementary particles known as dark matter."
"This model can explain how most of the Universe looks, except in our own backyard where it fails miserably."
"The model predicts that there should be many more small satellite galaxies around our Milky Way than we can observe."
"However, by using computer simulations to allow the dark matter to become a little more interactive with the rest of the material in the Universe, such as photons, we can give our cosmic neighbourhood a makeover and we see a remarkable reduction in the number of galaxies around us compared with what we originally thought."
The calculations were carried out using the COSMA supercomputer at Durham University, which is part of the UK-wide DiRAC super-computing framework.
Durham University Media Relations Team
Dr Robert Massey
The science contacts are available for interview via down-the-line broadcast quality TV facilities from the Durham City campus, via broadcast provider Globelynx.
To access the fixed camera and circuit directly, broadcasters can log into Globelynx. The IFB number is +44 (0)191 384 2019. If you have not booked a Globelynx feed before please call +44 (0)20 7963 7060 for assistance.
A broadcast quality ISDN radio line is also available at Durham University and bookings can be arranged via the Media Relations Team on the contact details above. The ISDN number is +44 (0)191 386 2749.
A landline number is available in the Media Suite which houses the television and radio facilities: +44 (0)191 334 6472.
All the contacts are available for interview on Monday 8 and Tuesday 9 September.
Professor Carlton Baugh
Images and captions
Images are available for download from the RAS website and from the Durham media relations team.
The simulated distribution of dark matter in a Milky Way-like galaxy for standard, non-interacting dark matter (top left), warm dark matter (top right) and the new dark matter model that interacts with the photon background (bottom). Smaller structures are erased up to the point where, in the most extreme model (bottom right), the galaxy is completely sterilised. Credit: Durham University
Two models of the dark matter distribution in the halo of a galaxy like the Milky Way, separated by the white line. The colours represent the density of dark matter, with red indicating high-density and blue indicating low-density. On the left is a simulation of how non-interacting cold dark matter produces an abundance of smaller satellite galaxies. On the right the simulation shows the situation when the interaction of dark matter with other particles reduces the number of satellite galaxies we expect to observe around the Milky Way. Credit: Durham University
This research has been published in Boehm C. el al., 2014, "Using the Milky Way satellites to study interactions between cold dark matter and radiation", Monthly Notices of the Royal Astronomical Society, vol. 445, p. L31-L35, published by Oxford University Press. A preprint version is available on the arXiv.
Useful Web Links
Notes for editors
The DiRAC Data Centric system at Durham University is operated by the Institute for Computational Cosmology on behalf of the STFC DiRAC HPC Facility. The DiRAC system is funded by BIS National E-infrastructure capital grant ST/K00042X/1, STFC capital grant ST/H008519/1, STFC DiRAC Operations grant ST/K003267/1, and Durham University. DiRAC is part of the National E-Infrastructure.
The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3800 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
Follow the RAS on Twitter