NASA’s Telescope Detects Strongest Hint Yet of Dark Matter Particles from Galactic Center
By on April 6th, 2014

NASA’s Fermi Gamma Ray Telescope has spotted something which should interest every physicist. Looking at the heart of our Milky Way galaxy, Fermi has unequivocally showed a bright gamma-ray glow. Scientists have then removed all known gamma-ray sources and, while it removes quite a bit of the contributing source, it still leaves a bit unaccounted for. We don’t know what’s causing this excess gamma ray glow. Given that gamma rays are some of the most energetic radiations known, it is unlikely that they are caused by some thermal event. The best explanation at the moment is that something unknown – some unknown particles – are annihilating each other and giving off these radiations. The question is then, what are these particles.

The signal that Fermi saw. On the right, we have the same signal with all the known sources removed. A strong glow still remains - we don't know what that is!

The signal that Fermi saw. On the right, we have the same signal with all the known sources removed. A strong glow still remains – we don’t know what that is!

These particles ought to be quite heavy; the gamma ray emission hints at their mass. One very likely explanation for these particles is that they are Dark Matter particles. Humorously called WIMPs, short for Weakly Interacting Massive Particles, these heavy particles are likely candidates for Dark Matter (DM). In other words, the gamma ray lines seen by NASA’s Fermi telescope are because of DM annihilation.

Dark Matter 101

But what is DM you ask? DM is conjectured to be a type of matter beyond which we already know about, responsible for about 27% of the total mass-energy of the Universe. It was first hypothesized by Fritz Zwicky to explain why some galaxies can actually rotate as fast as they do without breaking apart. He surmised that there must be some invisible form of matter, which does not have any electromagnetic interaction, and thus doesn’t give off light, but are massive and, thus, can interact via the gravitational force. Today that conjecture stands on firmer grounds, with observations of known deviation from expected rotation speeds spanning thousands of galaxies. DM has been indirectly hinted at by many experiments such as the CoBE, WMAP and the recent Planck experiment, which all map out the distribution of Cosmic Microwave Background Radiation in our Universe. A host of other experiments also detect strong anomalies which can be easily explained away by the DM hypothesis.

In other words, we are quite sure that DM exists.

The mass-energy estimate of the Universe as given by the Planck experiment.  Courtesy: Planck/ESA

The mass-energy estimate of the Universe as given by the Planck experiment.
Courtesy: Planck/ESA

The clinching evidence would be to a actually detect it and one way is to let it annihilate each other into two known particles. These two particles then annihilate and produce some radiation which we can detect. The heavier the DM particles, the more energetic the final radiation; thus by knowing the final states, we can figure out the masses of the initial particles.

It is to be noted that no-one is jumping up and saying that DM has been found. While the evidence is highly suggestive, it’s not yet clinching, because, as most scientists like to say, not enough data has been collected. They would conservatively err on the side of mundane humility rather than make a mistake making an extraordinary claim.

Keep watching this space for more.

The official paper: http://arxiv.org/abs/1402.6703

The following video was released by NASA:

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Author: Debjyoti Bardhan Google Profile for Debjyoti Bardhan
Is a science geek, currently pursuing some sort of a degree (called a PhD) in Physics at TIFR, Mumbai. An enthusiastic but useless amateur photographer, his most favourite activity is simply lazing around. He is interested in all things interesting and scientific.

Debjyoti Bardhan has written and can be contacted at debjyoti@techie-buzz.com.
 
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