The research team includes the renowned British cosmologist Joseph Silk, professor of physics and astronomy at Johns Hopkins University and researcher at Sorbonne University\u2019s Institute of Astrophysics. Silk and his colleagues used fresh data from the Gaia mission and powerful supercomputer simulations to reinterpret results from NASA\u2019s Fermi Gamma-ray Space Telescope.<\/p>\n
Why dark matter still matters<\/p>\n
Without dark matter, galaxies simply wouldn\u2019t have formed as quickly as they did. The invisible material acts as a cosmic scaffolding, forming vast filaments that pull ordinary matter together through gravity. Observations of the cosmic microwave background from the Planck satellite also can\u2019t be explained without it.<\/p>\n
But because dark matter doesn\u2019t emit light\u2014or interacts only faintly with it\u2014it remains invisible. Scientists know it can\u2019t be made of known Standard Model particles, since that would contradict predictions from Big Bang nucleosynthesis, which describes the early production of hydrogen, helium, and other light elements.<\/p>\n
So far, dark matter has revealed itself only through its gravitational effects, outweighing the visible matter in galaxies and clusters. Yet, some theories predict that dark matter particles might occasionally annihilate, releasing detectable bursts of gamma rays in the process.<\/p>\n<\/p>\n
This video begins with a plunge toward the center of the Milky Way using visible-light images. It ends with a superimposition of these images with gamma-ray images taken with Fermi instruments. They show a region approximately 5,000 light-years across that is particularly bright in false color. Red indicates the maximum brightness. \u00a9 NASA, YouTube<\/p>\n
The mysterious gamma-ray glow<\/p>\n
Since the late 1970s, researchers have suspected that such annihilations could leave behind a telltale gamma-ray signature. Over the years, Fermi\u2019s telescope has observed an unexplained excess of these high-energy photons coming from the Milky Way\u2019s center\u2014and even from Andromeda.<\/p>\n
Most dark matter models predict that these particles should be densest near galactic cores, where collisions are more likely. More collisions mean more annihilations\u2014and potentially more radiation. But in 2015, researchers from MIT and Princeton offered another explanation: pulsars.<\/p>\n<\/p>\n
Fermi, supernovae, and gamma-ray pulsars. For a fairly accurate French translation, click on the white rectangle in the bottom right corner. The English subtitles should then appear. Next, click on the gear icon to the right of the rectangle, then on \u201cSubtitles,\u201d and finally on \u201cAuto-translate.\u201d Choose \u201cFrench.\u201d \u00a9 NASA Goddard<\/p>\n
Pulsars or dark matter?<\/p>\n
Pulsars\u2014rotating neutron stars that emit powerful beams of radiation\u2014are well-known gamma-ray sources. Because thick clouds of gas and dust obscure our view of the Milky Way\u2019s core, it\u2019s possible that a large population of faint, unresolved pulsars could be creating the same glow once attributed to dark matter.<\/p>\n
To test this, scientists modeled the Fermi data. If the signal came from dark matter, the gamma-ray map should look smooth and even. If pulsars were responsible, it should appear patchy and \u201cclumpy.\u201d In 2015, the results seemed to favor the pulsar explanation.<\/p>\n
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