News from the Frontiers of Cosmology: A companion to the book The Edge of Physics
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X-rays telescopes could solve the mystery of dark matter

Over the last two years, the FERMI and PAMELA satellites and the ATIC balloon-borne experiment have all tantalised us with hints of dark matter in our galactic neighbourhood. But how do we know that what they are seeing is not being produced by astrophysical sources such as pulsars? Well, a new paper suggests that advanced X-ray telescopes of the future could solve the mystery.

In August 2008, there was much hullabaloo about PAMELA and ATIC having seen an excess of positrons over the expected background of such particles in space. This excess could be coming from the mutual annihilation of dark matter particles. Even NASA’s FERMI satellite has seen such an excess. But, unfortunately, this does not constitute proof of the existence of dark matter particles in our galaxy. Such an excess can also be caused by nearby pulsars.

Now, Antoine Calvez of UCLA and colleagues are suggesting that we look at the dwarf spheroidal galaxies that hang around the Milky Way. These dwarfs should have abundant dark matter, but a paucity of pulsars. So, if dark matter is annihilating in such galaxies, then the high-energy electrons and positrons produced by the process should up-scatter – or bump up in energy – the photons of the cosmic microwave background into the X-ray energy band. So, if we see such X-rays, then it’ll constitute solid evidence that dark matter particles are creating the electrons and positrons and not pulsars.

The fly in the ointment is that today’s X-ray telescopes are nowhere near as sensitive as would be required for such observations. But, the researchers hope that the next generation of X-ray telescopes could do the trick.

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