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THE CURIOUS CASE OF THE FERMI BUBBLES
Hello, there!
I am NASA's Fermi Gamma Ray Telescope. I was sent to space to look at the cosmos using the most energetic form of light --- the gamma rays.
The frequency of visible light is of the order 10^14 Hz but gamma rays have frequency greater than 10^19 Hz! So obviously you humans can't see them. That's why I scan the space for all gamma ray emissions and report them to the ground station to help the scientists understand the space.
Nearly two years after my launch, the scientists on Earth filtered the 'noise' from the data that I had provided and two gamma ray ‘bubbles’ ( they prefer to call it fermi bubbles) were discovered- one above and another below the black hole at the center of our Milky Way galaxy.
NASA's Fermi Gamma Ray Telescope
Although it is not easy to collect 'ground data' when you're in space, I was truly interested in learning the secrets of the bubbles. So here I share whatever I have learnt.
At first, the scientists were a bit amused as they never expected something like this. However, soon they started to process all the data that I had supplied to them and found out that the total power for both bubbles is 4×10^37 erg/s or 2.5×10^40 GeV/s. They also found out that these bubbles have a smooth surface, sharp edges and flat intensity distribution.
They soon understood that these gamma ray bubbles were counterparts of the microwave haze, first detected by the Wilkinson Microwave Anisotropy Probe and later confirmed by the Planck Satellite. Scientists had thought that the microwave haze and fermi bubbles were caused due to some kind of dark matter annihilation but after the discovery of the sharp edges of these emissions, scientists were sure that some other phenomenon was the root cause of this.
I also heard that scientists have come up with some models to explain Fermi Bubbles and the Microwave Haze(as always, models are an integral part of predictions)!
One of the models predict that these emissions are caused by Cosmic Ray Protons accelerated at the Galactic Center and transported by Active Galactic Nuclei or Nuclear Star Formation winds. These have velocities of hundreds of kilometres per second and the bubbles are formed on timescales of greater than 10 Million yr. To form the lobular shape, the quasi spherical winds were proposed to be collimated for eg. by the Central Molecular Zone.
Another hypothesis is that the bubble has been formed due to outflows from the Active Galactic Nucleus. This model is further supported by 3-D stimulation which showed that these bubbles could have been formed by a combination of primary Cosmic Ray Protons and secondary Cosmic Ray Electrons.
There are in fact several other models which are both interesting and complicated but still a huge amount of research is going on in this field. It is predicted that if we are able to solve the origin of Fermi Bubbles, we will be able to gather information about the star formation for the past 10 million years or more!
I am trying my best to give the scientists enough data so that they can figure out the origin of Fermi Bubbles and all its other mysteries. For now, though, I must take my leave to complete another voyage around the Earth.
See you all later!
Written by Abhijnan Kar, Shamik Niyogi and Subharthi Paul
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