Null result: Scientists have failed to detect one of the leading theoretical candidates for dark matter.
Never mind! Scientists who published a study last month that said they could find no evidence of dark matter in nearby interstellar space have re-analyzed their data and found that the dark matter is apparently there.
A new study by astronomers has found a vast structure of satellite galaxies and star clusters aligned perpendicular to the Milky Way and extending outward above and below the galaxy’s nucleus by as much as a million light years.
In their effort to understand exactly what surrounds our Galaxy, the scientists used a range of sources from twentieth century photographic plates to images from the robotic telescope of the Sloan Deep Sky Survey. Using all these data they assembled a picture that includes bright ‘classical’ satellite galaxies, more recently detected fainter satellites and the younger globular clusters.
“Once we had completed our analysis, a new picture of our cosmic neighbourhood emerged”, says Pawlowski. The astronomers found that all the different objects are distributed in a plane at right angles to the galactic disk. The newly-discovered structure is huge, extending from as close as 33,000 light years to as far away as one million light years from the centre of the Galaxy.
An animation illustrating this galactic distribution is posted below the fold. You can read the actual preprint paper here.
The problem with this polar alignment with the Milky Way’s core is that the theories for explaining the distribution of dark matter do not predict it.
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The uncertainty of science: A new study has found no evidence of dark matter within 13,000 light years of the Sun, something that had not been expected.
According to widely accepted theories, the solar neighborhood was expected to be filled with dark matter, a mysterious invisible substance that can only be detected indirectly by the gravitational force it exerts. But a new study by a team of astronomers in Chile has found that these theories just do not fit the observational facts. This may mean that attempts to directly detect dark matter particles on Earth are unlikely to be successful.
These findings will be as controversial as the now abandoned faster-than-light neutrino results last fall. Here, however, the new data is likely going to be more robust, which will cause the entire astrophysical community some real conniptions.
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A look at the universe’s dark side.
CERN will be making an announcement on the status of its search for the Higgs particle on December 13. From this interview of one of its scientists:
The thing I know for sure is that [CERN Director General] Rolf-Dieter Heuer, who must know the results of both experiments, says that on December 13 we will not have a discovery and we will not have an exclusion.
The inteview is fascinating, as he notes how the Higgs research might also have a bearing on the search for dark matter.
The uncertainty of science: Recent results from the Fermi Gamma-ray Space Telescope have found no evidence of dark matter, a result in some conflict with data obtained from several underground research detectors.
The mystery here is that there is no doubt that something causes the outer objects in galaxies to move faster than expected. Scientists have labeled this something as dark matter, guessing that some undetected and unknown mass exists in the outer reaches of galaxies, thereby increasing the gravity potential and hence the velocity in which objects move.
The problem is that they have yet to identify what that dark matter is.
The uncertainty of science: Multiple dark matter experiments produce multiple results.
From a paper published today on the Los Alamos astro-ph preprint website, scientists suggest that three different physics experiments might have identified dark matter. From the abstract:
Three dark matter direct detection experiments (DAMA/LIBRA, CoGeNT, and CRESST-II) have each reported signals which are not consistent with known backgrounds, but resemble that predicted for a dark matter particle with a mass of roughly ~10 GeV. . . . In this article, we compare the signals of these experiments and discuss whether they can be explained by a single species of dark matter particle, without conflicting with the constraints of other experiments. We find that the spectrum of events reported by CoGeNT and CRESST-II are consistent with each other and with the constraints from CDMS-II, although some tension with xenon-based experiments remains. Similarly, the modulation signals reported by DAMA/LIBRA and CoGeNT appear to be compatible, although the corresponding amplitude of the observed modulations are a factor of at least a few higher than would be naively expected, based on the event spectra reported by CoGeNT and CRESST-II. This apparent discrepancy could potentially be resolved if tidal streams or other non-Maxwellian structures are present in the local distribution of dark matter.
The last sentence above suggests that the differences between the various experiments might be explained by the motion of dark matter itself as it flows through the solar system.
This conclusion is very tentative. The scientists admit that there remain conflicts between the results of the three experiments, and that there also could be explanations other than dark matter for the results. Furthermore, the results of other experiments raise questions about this conclusion.
Nonetheless, it appears that physicists might be closing in on this most ghostlike of all particles in the universe.
The uncertainty of science: “After completing this study, we know less about dark matter than we did before.”
Every year, as part of its educational and research mission, the Space Telescope and Science Institute in Baltimore, Maryland holds a science symposium that focuses one of the big questions of astronomy, inviting over a hundred scientists to come and give their individual perspectives on the state of the field.
This year’s symposium ended yesterday, and the subject was the mysteries of dark matter. Though I wasn’t able to attend the symposium itself, they held a workshop for journalists yesterday, which I did attend. (You can watch the webcast here.)
So, what is dark matter?
First of all, it isn’t dark energy. Dark energy is that mysterious unknown phenomenon that is causing — on vast scales of many billions of light years — the expansion of the universe to accelerate rather than decelerate. It has nothing to do with the question of dark matter.
Second, no one knows. All that scientists do know is that objects in the outer regions of galaxies as well as the galaxies themselves don’t move at the speeds and directions expected if their known mass and gravity were the only forces influencing them. In order to successfully plot their orbits and motions, astronomers have to add a gigantic halo of extra mass, which they have dubbed “dark matter” because it is unseen, undetected, and completely invisible.
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Dark matter: light or heavy?
Later today I will be attending press conference at a symposium on dark matter that is being held this week at the Space Telescope Science Institute in Baltimore. I will post more on this subject then.
The uncertainty of science: An underground experiment in Italy has failed to detect dark matter, as theorized by scientists.
In a paper published online last night, the XENON100 researchers report three events detected during a 100-day run of the experiment last year that might have been due to dark matter1. However, as they expected to see between 1.2 and 2.4 background events — interactions mostly caused by a radioactive contaminant in the xenon — their result is statistically negative and therefore rules out the existence of many of the more strongly interacting and heavier WIMPs.
