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------------ 1879 - Fermi Bubbles and Radio Bursts?
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- August 24, 2001 astronomers discovered an ultra-bright, ultra - brief flash of radio waves. We have spent over a decade trying to identify the source and explain the physics involved with these phenomena.
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- The radio signal was 100 times brighter, but vanished in 5 milliseconds. It was not until 2006 that closer analysis discovered the flash was smeared over a wide range of radio frequencies. The lower frequency waves were calculated to have traveled 3 billion lightyears over an expanding Universe. If that were true the flash must have had more energy than our Sun emits in 1,000 years.
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- In the last 15 years astronomers have discovered 16 of these Fast Radio Bursts. But, those are only the ones we “ hear”. Astronomers calculate that a Radio Burst arrives at Earth every 15 seconds.
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- If these bursts get smeared across many frequencies and over time it is an indication that the signal traveled through clouds of plasma ( charge particles ). The speed of light , 671 million miles per hour in a vacuum, slows down when traveling in plasma. Lower frequencies interact more with free electrons. The greater the “ dispersion” the more distant the source. The data suggests that the pulses traveled through the inter-galactic medium encountering plasma clouds.
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- The radio telescope has tunnel vision, able to see, “ hear”, only 14.4 arc minutes across. (half the angular size of a Full Moon). An ekxact source has not yet been conclusively identified. Hear are some speculations:
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----------------- Neutron stars pack the mass of 500,000 Earths into a sphere 10 kilometers across. The flashes could come from Neutron stars inspiraling, colliding , or collapsing into Blackholes.
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---------------- Neutron stars could produce powerful magnetic fields producing flares when star quakes break the Neutron stars crusty surface. ( called Magnetars ).
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--------------- “Cosmic Strings” , defects in the structure of space-time, could release bursts of energy.
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--------------- Pulsars are spinning Neutron stars known for regular, even bursts of radiation, but, occasionally give off a much stronger burst.
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- One reason astronomers are so anxious to find the source for these bursts is that an accurate distance measurements would allow an accurate density measurement of intergalactic medium. This in turn would allow a new calculation of the Universe’s visible matter. Then , new calculations for the ratios of Dark Matter and Dark Energy. Stay tuned and announcement will be made shortly.
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- Another new discovery happens right here at home, in our Milky Way Galaxy. We are sitting 27,000 lightyears from the center of the Galaxy. The diameter is 100,000 lightyears so we live about half way out to the edge of this flat disk of stars.
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- The center is a bulge of stars but the galaxy still looks like a phonograph record. Does anyone remember what these records look like? Extending vertically above and below the bulge an the center of the galaxy are hourglass lobes that extend above and below by 25,000 lightyears.
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- These gigantic lobes are known as the “ Fermi Bubbles”. They were first discovered 6 years ago. Astronomers studying them believe they are evidence of some violent activity that once occurred at the center of our galaxy. Astronomers “ see” these lobes in the Gamma Ray and Microwave frequencies
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- Microwave radiation can be created by electrons spiraling around a magnetic field. If the electrons are high enough energy they can also produce Gamma Ray radiation, called the “Inverse-Compton Effect“.
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- Much of this discovery comes from the Fermi Gamma Ray Space Telescope launched in 2008. In 2010 the Fermi Bubbles were discovered in the data collected. The Gamma Ray bubbles have distinct edges, almost appearing as the edge of a shock wave. Other theories suggest a magnetic field traps charged particles at the edge.
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- The lobes could be the result of jets of material exiting the poles of the Blackhole at the center of the galaxy. The jets slamming into interstellar gas could compress into shockwave fronts. Or, the lobes could have resulted from the stellar winds of stars and supernovae exploding near the galactic center.
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- Astronomers have identified carbon and silicon atoms in the gas. These heavier elements are only the result of fusion in the core of stars and supernovae explosions. Measuring the redshift and the blueshift of the spectra of these elements tell astronomers the gas structures must be 2 to 4 million years old. Further the gas slows down as it approaches the edges. The flowing material abruptly stops at the edges.
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- 3-D computer modeling is busily trying to simulate these Fermi Bubble formation. The model uses massive stars exploding as supernovae. The outgoing material traveling a supersonic speeds creates shock waves laced with magnetic field lines. The shock waves sweep up electrons and accelerate them to high energies. Maybe, multiple generations of exploding massive stars over 10 million years best fit the observations.
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- Still not every thing simulated matches all the observations taken from radio frequencies out to Gamma Ray wavelengths. Astronomers need more data and more analysis to solve the puzzle of Fermi Bubbles.
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- As you have likely gathered astronomers do not have a clear explanation for Fermi Bubbles or Radio Bursts. Stay tuned an announcement will be made shortly.
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