Fermi Observations of Dwarf Galaxies Provide New Insights on Dark Matter

Master VersionHorizontal version. This is for use on any YouTube or non-YouTube platform where you want to display the video horizontally. Vertical VersionThis vertical version of the episode is for IGTV or Snapchat. The IGTV episode can be pulled into Instagram Stories and the regular Instagram feed. When astronomers using NASA’s Hubble Space Telescope uncovered an oddball galaxy that looks like it doesn’t have much dark matter, some thought the finding was hard to believe and looked for a simpler explanation. Dark matter, after all, is the invisible glue that makes up the bulk of the universe’s contents. All galaxies are dominated by it; in fact, galaxies are thought to form inside immense halos of dark matter. So, finding a galaxy lacking the invisible stuff is an extraordinary claim that challenges conventional wisdom. It would have the potential to upset theories of galaxy formation and evolution.For more information, visit https://nasa.gov/hubble. Additional Visualizations:Galaxy Motion Simulation: Credit: ESO/L. Calçada.Dark Matter Simulation: Credit: Additional Visualizations:Galaxy Motion Simulation: Credit: ESO/L. Calçada.Dark Matter Simulation: Credit: Wu, Hahn, Wechsler, Abel(KIPAC), Visualization: Kaehler (KIPAC)Music Credits: "Aphelion Horizon" by Alistair Hetherington [PRS] via Atmosphere Music Ltd. [PRS], and Universal Production Music. Related pages

Watch this video on the NASA Goddard YouTube channel.Music credit: "Reborn" by Maksim Tyutmanov [PRS] and Victoria Beits [PRS]; Atmosphere Music Ltd PRS; Score Addiction; Killer Tracks Production Music Instagram videoMusic credit: "Reborn" by Maksim Tyutmanov [PRS] and Victoria Beits [PRS]; Atmosphere Music Ltd PRS; Score Addiction; Killer Tracks Production Music NASA's Hubble Space Telescope took an image of a bizarre, ghostly looking galaxy called NGC 1052-DF2 that astronomers calculate to have little to no dark matter. This is the first galaxy astronomers have discovered to be so lacking in dark matter, which is thought to comprise 85% of our universe's mass.Read the full story at nasa.gov.Download the release images at HubbleSite.org.Find the science paper at nature.com. Related pages

Top: Gamma rays (magenta lines) coming from a bright source like NGC 1275 in the Perseus galaxy cluster should form a particular type of spectrum (right). Bottom: Gamma rays convert into hypothetical axion-like particles (green dashes) and back again when they encounter magnetic fields (gray curves). The resulting gamma-ray spectrum (lower curve at right) would show unusual steps and gaps not seen in Fermi data, which means a range of these particles cannot make up a portion of dark matter.Credit: SLAC National Accelerator Laboratory/Chris Smith Top half of two-panel animation: Gamma rays (magenta lines) coming from a bright source like NGC 1275 in the Perseus galaxy cluster should form a particular type of spectrum (right). Credit: SLAC National Accelerator Laboratory/Chris Smith Bottom half of two-panel animation. Gamma rays convert into hypothetical axion-like particles (green dashes) and back again when they encounter magnetic fields (gray curves). The resulting gamma-ray spectrum (lower curve at right) would show unusual steps and gaps not seen in Fermi data, which means a range of these particles cannot make up a portion of dark matter.Credit: SLAC National Accelerator Laboratory/Chris Smith The Small Magellanic Cloud (SMC), at center, is the second-largest satellite galaxy orbiting our own. This image superimposes a photograph of the SMC with one half of a model of its dark matter (right of center). Lighter colors indicate greater density and show a strong concentration toward the galaxy's center. Ninety-five percent of the dark matter is contained within a circle tracing the outer edge of the model shown. In six years of data, Fermi finds no indication of gamma rays from the SMC's dark matter.Credits: Dark matter, R. Caputo et al. 2016; background, Axel Mellinger, Central Michigan University Visible light image of the Small Magellanic Cloud (SMC, at center), which is located about 200,000 light-years away and is the second-largest of the small satellite galaxies orbiting our Milky Way galaxy. The bright globular cluster 47 Tucanae (NGC 104) is visible at left and lies about 17,000 light-years away. Credit: Axel Mellinger, Central Michigan University This animation switches between two images of the gamma-ray sky as seen by Fermi's Large Area Telescope (LAT), one using the first three months of LAT data, the other showing a cumulative exposure of seven years. The blue color, representing the fewest gamma rays, includes the extragalactic gamma-ray background. Blazars make up most of the bright sources shown (colored red to white). With increasing exposure, Fermi reveals more of them. A new study shows blazars are almost completely responsible for the background glow.Credits: NASA/DOE/Fermi LAT Collaboration Higher-quality version of the above animation. This animation switches between two images of the gamma-ray sky as seen by Fermi's Large Area Telescope (LAT), one using the first three months of LAT data, the other showing a cumulative exposure of seven years. The blue color, representing the fewest gamma rays, includes the extragalactic gamma-ray background. Blazars make up most of the bright sources shown (colored red to white). With increasing exposure, Fermi reveals more of them. A new study shows blazars are almost completely responsible for the background glow.Credits: NASA/DOE/Fermi LAT Collaboration Dark matter, the mysterious substance that constitutes most of the material universe, remains as elusive as ever. Although experiments on the ground and in space have yet to find a trace of dark matter, the results are helping scientists rule out some of the many theoretical possibilities. Three studies published earlier this year, using six or more years of data from NASA's Fermi Gamma-ray Space Telescope, have extended the mission's dark matter hunt using some novel approaches.Dark matter neither emits nor absorbs light, primarily interacts with the rest of the universe through gravity, yet accounts for about 80 percent of the matter in the universe. Astronomers see its effects throughout the cosmos -- in the rotation of galaxies, in the distortion of light passing through galaxy clusters, and in simulations of the early universe, which require the presence of dark matter to form galaxies at all.Among the new studies, the most exotic scenario investigated was the possibility that dark matter might consist of hypothetical particles called axions or other particles with similar properties. An intriguing aspect of axion-like particles is their ability to convert into gamma rays and back again when they interact with strong magnetic fields. These conversions would leave behind characteristic traces, like gaps or steps, in the spectrum of a bright gamma-ray source. But a study to search for these effects in gamma rays from NGC 1275, the central galaxy of the Perseus galaxy cluster, excluded a small range of axion-like particles that could have comprised about 4 percent of dark matter. Another broad class of dark matter candidates are called Weakly Interacting Massive Particles (WIMPs). In some versions, colliding WIMPs either mutually annihilate or produce an intermediate, quickly decaying particle. Both scenarios result in gamma rays that can be detected by the LAT.In another study, scientists determined that the distribution of dark matter in the Small Magellanic Cloud (SMC), the second-largest of the small satellite galaxies orbiting our Milky Way galaxy, was enough to produce detectable signals for two WIMP types. But no signal from dark matter annihilation was found to be statistically significant.Lastly, another team used more than 6.5 years of LAT data to analyze the background glow of gamma rays seen all over the sky. Fermi has shown that much of this light arises from unresolved gamma-ray sources, particularly galaxies called blazars, which are powered by material falling toward gigantic black holes. But some models predict that EGB gamma rays could arise from distant interactions of dark matter particles, such as the annihilation or decay of WIMPs. Instead, the new study shows that blazars and other discrete sources can account for nearly all of this emission. Although these latest studies have come up empty-handed, the quest to find dark matter continues both in space and in ground-based experiments. For More InformationSee [NASA's Fermi Mission Expands its Search for Dark Matter](http://www.nasa.gov/feature/goddard/2016/nasas-fermi-mission-expands-its-search-for-dark-matter) Related pages

This animation zooms into an image of the Milky Way, shown in visible light, and superimposes a gamma-ray map of the galactic center from NASA's Fermi. Raw data transitions to a view with all known sources removed, revealing a gamma-ray excess hinting at the presence of dark matter. The final file below—labeled MPEG—is an animated GIF.Visible light imagery provided by Axel Mellinger, Central Michigan Univ.Credit: NASA Goddard/A. Mellinger (Central Michigan Univ.) and T. Linden (Univ. of Chicago) Side-by-side maps, with labels. At left is a map of gamma rays with energies between 1 and 3.16 GeV detected in the galactic center by Fermi's LAT; red indicates the greatest number. Prominent pulsars are labeled. Removing all known gamma-ray sources (right) reveals excess emission that may arise from dark matter annihilations. Credit: T. Linden (Univ. of Chicago) Side-by-side maps, without labels. At left is a map of gamma rays with energies between 1 and 3.16 GeV detected in the galactic center by Fermi's LAT; red indicates the greatest number. Prominent pulsars are labeled. Removing all known gamma-ray sources (right) reveals excess emission that may arise from dark matter annihilations. Credit: T. Linden (Univ. of Chicago) Movie, no labels, dissolving from the unprocessed map to one with sources removed and back to unprocessed. Details as above. The first file—labeled MPEG—is an animated GIF.Credit: T. Linden (Univ. of Chicago) Movie, with labels, dissolving from the unprocessed map to one with sources removed and back to unprocessed; details as above. The first file—labeled MPEG—is an animated GIF.Credit: T. Linden (Univ. of Chicago) Frames and video of dissolve sequence from unprocessed to background removed. Credit: T. Linden (Univ. of Chicago) A view of the entire gamma-ray sky from Fermi's LAT instrument, shaded to emphasize the central galaxy. The inset is a map of the galactic center with known sources removed, which reveals the gamma-ray excess (red, green and blue) found there. This excess emission is consistent with annihilations from some hypothesized forms of dark matter. Credit: NASA/DOE/Fermi LAT Collaboration and T. Linden (Univ. of Chicago) Using public data from NASA's Fermi Gamma-ray Space Telescope, independent scientists at the Fermi National Accelerator Laboratory, Harvard University, MIT and the University of Chicago have developed new maps showing that the galactic center produces more high-energy gamma rays than can be explained by known sources and that this excess emission is consistent with some forms of dark matter. No one knows the true nature of dark matter, but WIMPs, or Weakly Interacting Massive Particles, represent a leading class of candidates. Theorists have envisioned a wide range of WIMP types, some of which may either mutually annihilate or produce an intermediate, quickly decaying particle when they collide. Both of these pathways end with the production of gamma rays — the most energetic form of light — at energies within the detection range of Fermi's Large Area Telescope (LAT).The galactic center teems with gamma-ray sources, from interacting binary systems and isolated pulsars to supernova remnants and particles colliding with interstellar gas. It's also where astronomers expect to find the galaxy's highest density of dark matter, which only affects normal matter and radiation through its gravity. Large amounts of dark matter attract normal matter, forming a foundation upon which visible structures, like galaxies, are built. When the astronomers carefully subtract all known gamma-ray sources from LAT observations of the galactic center, a patch of leftover emission remains. This excess appears most prominent at energies between 1 and 3 billion electron volts (GeV) — roughly a billion times greater than that of visible light — and extends outward at least 5,000 light-years from the galactic center. The researchers find these features difficult to reconcile with other explanations proposed, such as undiscovered pulsars. The gamma-ray spectrum of the excess, its symmetry around the galactic center and its overall brightness, is, however, consistent with annihilations of dark matter particles in the mass range of 31 and 40 GeV. The scientists note that discoveries in other astronomical objects, such as dwarf galaxies, and experiments on Earth designed to directly detect dark matter particles will be needed to confirm this interpretation. For more information: Fermi Data Tantalize With New Clues To Dark Matter Related pages

Animation showing some characteristics of WIMPs Weakly Interacting Massive Particles, or WIMPs, represent one hypothesized class of particles to explain dark matter.They neither absorb nor emit light and don't interact strongly with other particles. But when they encounter each other, they annihilate and make gamma rays. For More InformationSee [http://www.nasa.gov/mission_pages/GLAST/news/dark-matter-insights.html](http://www.nasa.gov/mission_pages/GLAST/news/dark-matter-insights.html) Related pages