What can I say other than I am a strong supporter for dark matter theory. Dark matter is thought to make up 80% of the matter in the universe and because they do not interact with ordinary matter except via gravity, we have no clues what it is made of. But we know it is there holding all the stuffs within our galaxy or else it would have flown apart a long time ago. We have seen a collection of strong and yet indirect evidence supporting dark matter theory. Among some of the most significant are from NASA’s Fermi space telescope which spotted a brilliant haze of gamma rays coming from the center of the Milky Way and the same signal coming from dwarf galaxies is making this case even stronger. It is the most compelling signal for dark matter particles. The theory is that dark matters are their own anti-particles, and when they collide, they annihilate each other and produce intense energy in the form of X ray and Gamma ray radiation. This is precisely what NASA”s Fermi space telescope spotted back in 2009.
The leading candidate is called a Weakly Interactive Massive Particle ( WIMP) and formed a halo around the galaxy so dark matter would come from all direction in space. The latest finding showed that the gamma rays form a sphere around the galactic center where the radius extends nearly 5000 light years which is much further than any of the previous measurements and much further than you would expect from some other astronomical objects such as pulsars. As of now, it is difficult ( but not impossible) to propose any other astronomical sources or astrophysical mechanisms to account for such a continuous emission of gamma rays coming from every direction like it’s supposed to be. This excess of photons spread out evenly in a sphere and not from some isolated point sources one would expect to see if it came from pulsars.
But of course we may not be able to eliminate completely that the signal could be coming from pulsars spinning so fast that the magnetic fields can accelerate charged particles to nearly the speed of light , which then emit high energy photons in the gamma-ray wavelength. But the question of why so many pulsars are clustered in a sphere around the hub of the Milky Way? One suggestion is that star clusters orbiting the Milky Way might have been disrupted by the strong gravity from the center of the galaxy ( due to dark matter) and causing them to spill out pulsars into a spherical shape around the galaxy. This is really in line with the observation of the Fermi signal.
As a scientist, I don’t think the evidence is hard enough to supporting dark matter theory or pulsars theory or any other theories being proposed including Modified Gravity. But I must admit that I am still in favor of dark matter theory and more substantial evidence is needed to confirm the theory. LHC has upgraded the accelerator and more collision experiments will be carried out to look for dark matter (WIMP). Underground experiment such as Xenon 1T is also gearing up to detect dark matter. The Xenon 1T detector measures tiny flashes of light and charge which are generated when the dark matter particle interacts with the xenon atom. The scientists use this information to reconstruct the position of the particle interaction within the detector and also the energy to determine whether or not the interaction is due to dark matter. This international XENON Collaboration consisting of 21 research groups from United States, Germany, Italy, Switzerland, Portugal, France, Netherlands, Israel, Sweden, and United Arab Emirates, celebrated the inauguration of their new XENON 1T back in Nov 11, 2015, just a little over a week ago today. This XENON 1T will search for dark matter with unprecedented sensitivity.
Until we find direct evidence, we can only speculate and continue to show support for the scientific work and respect their collaboration and await for the results. This is the nature of doing great scientific work.