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---------------------------- 2544 - SUN - and stars at our galactic center?
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- Our Sun is our nearest star and it still holds many mysteries. Astronomers are studying stars all over the cosmos to better understand the physics that controls our solar system and our Universe.
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- A study, published December 6, 2019, gathered new images using the High Acuity Wide-field K-band Imager (HAWK-I) on the Very Large Telescope (VLT) in Chile, which is able to image the cosmos in near-infrared bands. The infrared frequencies are wider bandwidth than visible light and they allow the astronomers to peer through much of the dense gas and debris that clouds our vision of the Milky Way's center.
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- This survey included over 700,000 stars near the Milky Way's galactic center It has produced one of the most stunning images of our home galaxy. Astronomers studying the massive population of stars in the "nuclear disk" at the center of the galaxy hypothesize there were two major periods of star formation in the region, contradicting earlier beliefs it was in a near-constant state of star formation.
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- Analyzing the populations of stars overturns the currently accepted idea the galactic center has been constantly forming stars over its 13.5-billion-year life. Using theoretical models and the HAWK-I pictures, the team was able to tell a new story about the galactic center's star-forming history.
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- The new research shows the Milky Way's early life was the fastest growth period for nuclear disk at the center of our galaxy. During our galaxy's first 5 billion years, over 80% of the galaxy's stars were born, but then it dipped into a "quiescent" state, where star formation dropped away. A huge increase in activity occurred just 1 billion years ago, when approximately 5% of the center's stellar mass suddenly burst to life.
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- This burst of activity, which must have resulted in the explosion of more than a hundred-thousand supernovae, was probably one of the most energetic events in the whole history of our Milky Way.
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- The new evidence also suggests Sagittarius A*, the supermassive black hole at the center of our Milky Way Galaxy, may have acquired much of its mass during the early formation of the Milky Way.
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- How the Milky Way evolved to its current state is a contentious question. Whether populations of stars are built up continuously over billions of years or in a series of shorter bursts has been a long running argument in astronomy.
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- The findings come from the first wave of results from the spacecraft that launched in August 2018, provide important insights into two fundamental questions the mission was designed to answer:
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- Why does the Sun's corona get hotter as your move further away from the surface? What accelerates the solar wind that is an outward stream of protons, electrons and other particles emanating from the corona?
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- Both questions have ramifications for how we predict, detect and prepare for solar storms and coronal mass ejections that can have dramatic impacts on Earth's power grid and on astronauts that are above our atmosphere.
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- These observations will fundamentally change our understanding of the Sun and the solar wind and our ability to forecast space weather events."
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- The spacecraft revealed that the Sun's rotation impacts the solar wind much farther away than previously thought. Researchers knew that close in, the Sun's magnetic field pulls the wind in the same direction as the star's rotation. Farther from the Sun, at the distance the spacecraft measured in these first encounters, they had expected to see, at most, a weak signature of that rotation.
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- To the astronomers great surprise, as we neared the Sun, they already detected large rotational flows, 10 to 20 times greater than what standard models of the Sun predict.
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- This has huge implications. Space weather forecasting will need to account for these flows if we are going to be able to predict whether a coronal mass ejection will strike Earth, or astronauts heading to the Moon or Mars.
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- The Parker Solar Probe's findings regarding the Sun's magnetic field, which is believed to play a role in the coronal heating mystery, were equally surprising. From Earth's vantage point, magnetic oscillations called "Alfvén waves" were detected in the solar wind long ago. Some researchers though they may be remnants of whatever mechanism caused the heating phenomenon.
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- The unexpected results when you get closer to the Sun, you start seeing these 'rogue' Alfvén waves that have four times the energy than the regular waves around them. They feature 300,000 mph velocity spikes that are so strong, they actually flip the direction of the magnetic field.
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- Those polarity-reversing velocity spikes offer another potential candidate for what may cause the corona to get hotter moving away from the Sun.
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- The new evidence also suggests Sagittarius A*, the supermassive black hole at the center of the Milky Way, may have acquired much of its mass during the early formation of the Milky Way.
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- Whether populations of stars are built up continuously over billions of years or in a series of shorter bursts has been a long running argument in astronomy.
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- December 17, 2019 2544
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--------------------- Wednesday, December 18, 2019 --------------------
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