Most easily detected: The Milky Way’s dark-matter halo contains a variety of structures of different sizes. But according to new research it is the diffuse, smooth component of dark matter in the halo where radiation signals from colliding dark matter particles are the strongest.
Credit: Virgo Consortium
SYDNEY: A massive computer simulation of the way galaxies form has revealed where exactly in the galaxy we should look to finally 'see' dark matter.
And it may be only a few years before astronomers first directly detect the mysterious substance, according to the research published in the British journal Nature today.
Dark matter makes up 85 per cent of matter in the universe. It pervades the Milky Way and forms massive haloes around our own galaxy and the smaller satellite galaxies surrounding it. So far its presence has only been indirectly inferred from its gravitational effects.
3.5 million computing hours
However, if particle collisions within dark matter give off gamma rays, under the right conditions the gamma rays should be detectable by NASA's Fermi Gamma-ray Space Telescope, launched in June 2008.
The researchers from the international Virgo Consortium's Aquarius Project used a computer simulation that took over 3.5 million computing hours create a virtual universe in order to find the best place to look for these gamma-ray signals.
"This calculation has redefined the state of the art in cosmological simulations. At times I thought it would never end," said lead author, astrophysicist Volter Springel from the Max Planck Institute for Astrophysics in Garching, Germany.
Some scientists have earmarked dense dark matter haloes within satellite galaxies as the prime contenders for dark matter gamma ray signals (see, Are scientists about to explain dark matter?, Cosmos Online). But Springel and colleagues disagree.
They say that these signals may be negligible. Instead, they argue that the dominant and most easily-detected signals will be in the diffuse dark matter that pervades the Milky Way itself, and the best place to look for them is in the area of sky looking towards the centre of the galaxy and nearest the Sun.
To annihilate, or not to annihilate
The researchers predict Fermi will see the first evidence of dark matter within a few years. "If we are really lucky, we may also detect sub-structures both without and with stars. This would provide a convincing confirmation of the [Cold Dark Matter] theory," they write.
Australian astrophysicist Geraint Lewis from the University of Sydney, commented that although the result was "very interesting", it relied on the assumption that dark matter emits gamma ray radiation from particle annihilations as ordinary matter does.
In space, colliding electrons and positrons (the antimatter equivalent of the electron) from normal matter emit energy in the form of gamma radiation as they 'annihilate' or wipe each other out.
But we "just don't know the physics yet" in regards to dark matter, warned Lewis. "Until we know about the physics of dark matter we don't know if it would annihilate or not," he said.
