All sky intensity map derived from 9 years of Fermi-LAT data shows the Entire Universe
This picture is an all sky intensity map derived from 9 years of Fermi-LAT data, (August 4, 2008 – August 4, 2017) time integrated all-sky image (based on Pass 8 Source class, PSF3 event type-internal collaboration notation). The map is also integrated above 1 GeV (that is 1 billion electron volt energy gamma rays and above up to about 1 trillion electron volt energy). The intensity scale is false color with low intensity black and high intensity white. The map shows the entire universe in standard astronomical Galactic coordinates (in what is called a Hammer-Aitoff projection – not simple), these coordinates and projection have the center of our galaxy at the center of the picture (very bright), and the anticenter of the galaxy at the edges of the picture centerline (the anticenter is in the direction out from the Galactic center along the Galactic center-sun axis) The images are smoothed with a 0.25 deg FWHM Gaussian. The maps are in intensity units. The images have a logarithmic scaling, from about 3 x 10-7 gamma rays per cm-2 s-1 sr-1 to 1 x 10-3 gamma rays per cm-2 s-1 sr-1. The actual maximum intensity in the map is 0.02 cm-2 s-1 sr-1. (cm-2 is per square centimeter of detector area, s-1 is per sec and sr-1 is per steradian). The images are 3600×1800 (0.1 degree pixels). The bright dots are point sources of gamma rays in the sky, and many of these are time variable that you don’t notice in this time lapse image. The band that you see horizontally across the picture is the Milky Way Galaxy (our galaxy). Above this plane and below this plane are gamma ray sources from the rest of the universe and typically many millions to billions of light years away from us. Not so obvious in this picture are the “Fermi Bubbles” the diffuse structures that protrude above and below the region of the Galactic center. These structures are thought to be remnants of energetic jet activity powered by the central black hole of our galaxy in times long past and were discovered using Fermi-LAT data.
Photo Credit: Fermi-LAT Collaboration
Picture Series Indicating How We Decompose the Gamma Ray Sky
Picture 1: All-Sky intensity in black and white
Picture 2: Diffuse – in a complex analysis we can isolate the Galactic diffuse signal and it looks as in this picture. This gamma ray signal mostly originates in the interaction of Galactic cosmic rays with the gas of the Galaxy.
Picture 3: Point sources – In different complex analysis we can extract the point and near point sources of gamma rays.
Picture 4: Extra Galactic diffuse – In yet a different complex analysis we can extract the diffuse gamma ray radiation coming from beyond our galaxy, likely from the furthest reaches of the universe. This diffuse is uniform from all directions.
Picture 5: Use Dwarf Galaxies to search for dark matter – This picture is similar to the point sources in which I try to demonstrate how we can set limits on gamma rays coming from dark matter particle decay or annihilation-with another DM particle. There are now about 60 dwarf satellite galaxies of the Milky Way that have been discovered and new ones are discovered every year via ground based optical telescope surveys of the sky. One can measure from the stellar motions in these galaxies using big optical telescopes that they are heavily dark matter dominated.
The future SuperCDMS SNOLAB experiment will hunt for weakly interacting massive particles (WIMPs), hypothetical components of dark matter. If a WIMP (white trace) strikes an atom inside the experiment’s detector crystals (gray), it will cause the crystal lattice to vibrate (blue). The collision will also send electrons (red) through the crystal that enhance the vibrations. (Greg Stewart/SLAC National Accelerator Laboratory)
Looking for Dark Matter by Observing Dwarf Galaxies
Dark matter makes up about 28% of the matter in the universe. Regular matter that we are used to makes up about 5% of the matter in the universe. The rest of the energy density of the universe is made up of dark energy. Thus about 80% of the matter in the universe is of a very different kind than the matter we know about-all of the elements of the periodic table, and does not shine so we can see it in any kind of EM radiation from radio to gamma rays. Theories of dark matter, mainly invented by Particle Physicists, propose that it is a new sector of matter very different than normal matter. What is it?
The Fermi-LAT community has be searching for emission of gamma -rays from dark matter that has been predicted by theoretical models of what might make up the dark matter (new types of elementary particles).
This last picture shows as a green dot a hypothetical dwarf galaxy located where there are no gamma ray point sources (this is typical in our data, though this sky location is hypothetical). Optical telescopes would measure the presence of a small galaxy with not too many stars, and also indicate that the dwarf galaxy was dark matter dominated.
Fermi knows where to look as the optical telescopes precisely establish the location of this dwarf galaxy. When the Fermi – LAT does its observations and analysis of this spot it finds no emission of gamma-rays, and then we can set limits on the gamma ray intensity from this dwarf. These limits challenge theories of particle dark matter that predict the Fermi-LAT should have observed gamma-rays from this source. There are a number of other ways that the Fermi – LAT can search for dark matter gamma ray signals, but using dwarf galaxies has proven so far to give the most stringent limits on dark matter gamma ray emission.
New Search Underway for the Dark Matter at SLAC
Scientists know that visible matter in the universe accounts for only about 15% of all matter and the rest is a mysterious substance, called dark matter. Due to its gravitational pull on regular matter, dark matter is a key driver for the evolution of the universe, affecting the formation of galaxies like the Milky Way. Still searching for what dark matter is made of, scientists at SLAC believe it could be composed of dark matter particles, and WIMPs are top contenders. If these particles exist, they would barely interact with their environment and fly right through regular matter untouched. However, every so often, they could collide with an atom of our visible world, and dark matter researchers are looking for these rare interactions.
Construction Begins on One of the World’s Most Sensitive Dark Matter Experiments
The SuperCDMS SNOLAB project, a multi-institutional effort led by SLAC, is expanding the hunt for dark matter to particles with properties not accessible to any other experiment.
U.S. Department of Energy funded the construction of SuperCDMS SNOLAB experiment, which will begin operations in the early 2020s to hunt for hypothetical dark matter particles called weakly interacting massive particles, or WIMPs. The DOE Office of Science will contribute $19 million to the effort, joining forces with the National Science Foundation ($12 million) and the Canada Foundation for Innovation ($3 million). The DOE’s SLAC National Accelerator Laboratory is managing the construction project for the international SuperCDMS collaboration of 111 members from 26 institutions, which is preparing to do research with the experiment.
The experiment will be at least 50 times more sensitive than its predecessor, exploring WIMP properties that can’t be probed by other experiments and giving researchers a powerful new tool to understand one of the biggest mysteries of modern physics, what is dark matter?
“Understanding dark matter is one of the hottest research topics – at SLAC and around the world,” said JoAnne Hewett, head of SLAC’s Fundamental Physics Directorate and the lab’s chief research officer. “We’re excited to lead the project and work with our partners to build this next-generation dark matter experiment.”
For more information go to: https://www6.slac.stanford.edu/news/2018-05-07-construction-begins-one-worlds-most-sensitive-dark-matter-experiments.aspx