Fermi uses gamma rays to unearth clues about 'empty' space

Apr 20, 2012 By David Reffkin
All-sky map of gamma rays observed in our galaxy by the Fermi Large Area Telescope. Found mostly in the plane of our galaxy (horizontal band) and toward the galactic center, gamma rays are present in. Credit: NASA/DOE/Fermi LAT Collaboration

The SLAC-built Large Area Telescope (LAT), the main instrument of the Fermi Gamma-ray Space Telescope, has been studying the gamma-ray sky for almost four years. During that time, the LAT has identified hundreds of gamma-ray sources, including pulsars and active galactic nuclei. It has shown that the Crab Nebula isn't the steady emitter of gamma rays it's long been thought to be. The LAT has catalogued lightning in the Earth's atmosphere and flares on the sun.

But, as reported in a paper soon to appear in The Astrophysical Journal, most of the detected by the LAT cannot be attributed to individual point sources.

The team discovered that the pulsars, active galactic nuclei, and the all the rest of the gamma-ray sources pinpointed by the LAT account for only about 10 percent of the gamma-ray photons that have been detected. Extragalactic diffuse emission, a glow that pervades the universe and originates in distant, indistinct sources, comprises approximately 15 percent of the total.

Most of the gamma rays detected by the LAT are "diffuse" emissions originating from our own Milky Way galaxy.

The main source of these pervasive, diffuse gamma-ray emissions are high-energy charged particles known as cosmic rays that interact with the gas and radiation fields between the stars, which is called the interstellar medium. The interstellar medium is far from empty space; scientists are busy gathering crucial information about the gas, dust and high-energy charged particles that fill it.

These cosmic particles can come from pulsars, supernova explosions and other powerful astrophysical sources. There may be an additional contribution from annihilating dark-matter particles or the black hole at the center of our galaxy.

The study was led by Gudlaugar Johannesson, a former postdoctoral researcher member and current affiliate of the SLAC- and Stanford-based Kavli Institute for Particle Astrophysics and Cosmology who is now at the University of Iceland; Andrew Strong of the Max Planck Institute in Garching, Germany; and KIPAC and Stanford scientist Troy Porter.

According to Porter, the new analysis leads to several conclusions. For example, it shows that the density of cosmic rays is higher than anticipated in the outer regions of the galaxy and beyond the central galactic plane. In addition, the total amount of gamma radiation from cosmic ray electrons due to interactions with infrared and visible light – which consist of photons of much lower energy than gamma rays – is larger than previously thought.

One of the major goals of the LAT collaboration is to better define these origins and the composition of the interstellar medium that permeates our galaxy, and this research has provided crucial input for their work.

Explore further: Hubble sees 'ghost light' from dead galaxies

More information: ApJ 747 121 2012. doi:10.1088/0004-637X/747/2/121

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Tuxford
1 / 5 (5) Apr 20, 2012
Diffuse emissions, rather than point sources, is aligned with LaViolette's contention that galactic superwaves of cosmic ray emissions originating from the central galactic core star can produce gamma ray emissions from throughout the galaxy, as they interact with local magnetic fields as they pass by.

And LaViolette has modeled the crab emissions in this way for decades. The Crab is currently illuminated in this way by the passage of the last major superwave, which passed Earth corresponding to the last ice age.

http://starburstf...og/?p=75

I wonder when astronomers will start to pay attention?
brodix
1 / 5 (2) Apr 20, 2012
"the density of cosmic rays is higher than anticipated in the outer regions of the galaxy and beyond the central galactic plane. In addition, the total amount of gamma radiation from cosmic ray electrons due to interactions with infrared and visible light which consist of photons of much lower energy than gamma rays is larger than previously thought."
Interesting this "halo" of cosmic rays is being discovered at the same time the issue of missing dark matter, presumably a halo on the perimeter of galaxies as well, is being examined.
To carry the conversation over here, could it be that gravity is a vacuum created by light turning into mass?
Ventilator
not rated yet Apr 20, 2012
brodix: "To carry the conversation over here, could it be that gravity is a vacuum created by light turning into mass?"

I still think that dark matter is, in my mind, absolute zero matter that is effectively frozen.

Light is an energy; what can it turn into besides other energy? That it slows down and gives off other light photons is likely, and most of the energy is absorbed by the object struck. Some of this energy turns into heat, however, when does light turn into mass? I know light does some things, just not that one.
brodix
1 / 5 (2) Apr 20, 2012
Ventilator,
I realize it's not in current theory. I'm just raising a possibility: Mass does turn into energy. Whether it's just striking a match or setting off a nuclear explosion, the energy expands. So if this process were reversed and energy collapsed into mass, it would create a vacuum. They can't find dark matter, but they do find this halo of cosmic rays around the galaxy. If there were an elemental process around the perimeters of galaxies, that was turning light into mass and creating that vacuum associated with mass, ie. gravity, wouldn't it potentially look like what is being described? Do we have any method of testing something this ephemeral? Looking at some of the other theories getting attention, this is at least moderately sensible.
Argiod
1 / 5 (3) Apr 20, 2012
Next they'll be telling us that this phenomenon is associated with quantum entanglement... new words, same old flim flam
typicalguy
not rated yet Apr 23, 2012
Ventilator,
I realize it's not in current theory. I'm just raising a possibility: Mass does turn into energy. Whether it's just striking a match or setting off a nuclear explosion, the energy expands. So if this process were reversed and energy collapsed into mass, it would create a vacuum. They can't find dark matter, but they do find this halo of cosmic rays around the galaxy. If there were an elemental process around the perimeters of galaxies, that was turning light into mass and creating that vacuum associated with mass, ie. gravity, wouldn't it potentially look like what is being described? Do we have any method of testing something this ephemeral? Looking at some of the other theories getting attention, this is at least moderately sensible.


This is done millions of times a day in particle accelerators. The discrepancy would have been noted. Matter creates gravity, not the action of light turning into matter. You can be deep inside the earth and still feel the effects

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