The universe it seems looks like a foggy night at the seaside, with a few lighthouses dotted around at random. At least, that’s the latest picture from NASA’s Fermi space telescope, it shows hundreds of the most violent & explosive objects in the universe, with just a hint of dark matter in the background.
Over the last 3 years, the Fermi Large-Area Telescope has been in orbit, scanning the sky for gamma rays with an energy of 10 – 300 geV (gigaelectronvolts), more powerful than those previously seen by satellites, but still too weak to spot from earthside.
Now NASA has released the first map of the entire sky at these higher energy levels. It shows over 500 individual sources, set against a hazy background of gamma rays.
The majority of the sources are blazars, distant galaxies with violent, massive black holes at their centres. Most of the rest are pulsars, intensely bright & dense neutron stars with powerful magnetic fields, spinning & flashing like interstellar lighthouses.
The background gamma ray haze is more equivocal: it is partly the result of high-energy cosmic rays, remnants of distant & massive explosions, seen as it collides with gas in our own galaxy. But the Fermi team is seeing almost a third more gamma rays at these energies than they would expect.
It has been suggested (as it always is when anything odd turns up in the cosmos) that this could be evidence of dark matter, the stuff thought that make up 85% of the universe. According to some theories, “Dark matter particles are their own antiparticles, colliding & annihilating with each other & producing gamma rays”. (Nope, that didn’t make any sense to me either.)
Fermi is no stranger to the hunt for the dark stuff. In 2012, it detected a spike in gamma rays at 130 geV, only for dark matter to be ruled out as the source 6 months later. Earlier this year, another Fermi signal started to look more like dark matter, as other possible explanations for it were ruled out.
This neighborhood just gets weirder & weirder, the more time you spend here, & so far all we are doing is looking out the window.
ThursdayAgain 
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