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-------------------- 2462 - FERMI BUBBLES - strange Milky Way structures?
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- The Milky Way appears as a relatively flat structure when viewed along its plane in visible light. Gamma-ray emission, however , two huge structures billowing outward from the galaxy’s bulge like an enormous hourglass. Named the Fermi Bubbles, these structures are the result of the Milky Way’s supermassive black hole gorging itself on interstellar gas in the distant past.
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- Astronomers using distant quasars have traced the structure and motion of the northern Fermi Bubble, which rises 23,000 light-years above the plane of the Milky Way and contains enough cool gas to create 2,000,000 Sun-size stars. The radius of the galaxy is 50,000 lightyears.
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- By observing the ultraviolet light from 46 quasars astronomers have mapped out the motions of cool gas within the bubble to pin down its age at 6 to 9 million years.
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- Most galaxies contain a supermassive black hole at their center, and our Milky Way is no exception. Sgr A* black hole resides in the Milky Way’s bulge and has a mass equivalent to 4,500,000 solar masses. Today, Sgr A* is relatively quiet, accreting slowly as the galaxy ages.
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- By contrast, quasars are young, massive and supermassive black holes at the centers of galaxies in the early universe, sucking down huge amounts of gas and dust that shine brightly as the material is funneled into an accretion disk before finally passing into the black hole.
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- Like these younger black holes, astronomers believe that our own supermassive black hole was once more active, at a time when the galaxy was still forming and material was more plentiful for accretion.
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- Sometimes, matter can escape along the black hole’s spin axis, exiting the area as huge outflows that span tens or hundreds of thousands of light-years. The Milky Way’s Fermi Bubbles was an outflow discovered in 2015 and named after NASA’s Fermi Gamma-Ray Telescope, that spotted them.
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- Learning more about the origins of these outflows requires information about their motion. Because we are inside the Milky Way our vantage point gives us a front-row seat to map out the kinematic structure of the Milky Way outflow.
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- As the quasars’ light travels through the bubble to reach Earth, it highlights the gas in the bubble itself, allowing astronomers to determine information such as its chemical composition, temperature, and motion.
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- The “cool” gas in the northern Fermi Bubble, which contains elements such as silicon and carbon, was clocked at 2 million miles per hour and reaches temperatures of 17,700 degrees Fahrenheit.
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- Such “cool” gas is actually likely gas from the disk of the galaxy that has been swept up by and integrated into the outflow itself, which has temperatures of up to 18,000,000 degrees F. It is these high temperatures that cause the gas to shine in energetic light, such as gamma rays.
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- Once the gas’ velocity, speed and direction of movement, was measured, astronomers used this data to turn back the clock and pinpoint when the gas started moving. This origin is also the last known “big meal” enjoyed by Sgr A*, which hasn’t managed to suck down such a significant amount of matter ever since.
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- What we find is that a very strong, energetic event happened 6 million to 9 million years ago. It may have been a cloud of gas flowing into the black hole, which fired off jets of matter, forming the twin lobes of hot gas seen in X-ray and gamma-ray observations.
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- Fermi Bubbles do present a whole new picture and history of our Milky Way Galaxy.
Astronomy is full of surprises. What’s next?
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- November 2, 2019 2462
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--------------------- Sunday, November 3, 2019 --------------------
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