- 3325 - MILKY WAY GALAXY - still more to learn? Our celestial home galaxy is full of stars, supernovas, nebulas, energy and dark matter, but many aspects of it remain mysterious, even to scientists. How Gaia Satellite is helping us learn.
--------------------- 3325 - MILKY WAY GALAXY - still more to learn?
- Our planet, Mother Earth is the third planet orbiting out from the Sun. Our Sun is but one in over 200,000,000 stars in our Milky Way Galaxy. We are orbiting the center of this galaxy about 25,000 lightyears from the center. The center is a blackhole that is 4,000,000 more massive than our Sun.
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- Before the advent of electric lights, everybody on Earth had an unobstructed view of the night sky. The enormous milky band of stars crossing it was impossible to miss.
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- Ancient peoples gave different names to the cloud-like structure of our galaxy, but our modern version derives from the Greeks, who had a myth about the infant Hercules being brought to the goddess Hera, who nursed him while she was asleep.
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- When she awoke and pulled away, her breast milk spilled across the heavens. The source of the Greek name itself has been lost to the ages.
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- Counting stars is a tedious business. Even astronomers argue over the best way to do it. Their telescopes see only the brightest stars in our galaxy, and many are hidden by obscuring gas and dust.
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- One technique to estimate the stellar population of the Milky Way is to look at how fast stars are orbiting within it, which gives an indication of the gravitational tug, and therefore the mass, of the galaxy. How do you weigh the mass of a galaxy?
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- Divide the galactic mass by the average size of a star and you should have your answer. But these numbers are all approximations. Stars vary widely in size, and many assumptions go into estimating the number of stars residing in the Milky Way.
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- The European Space Agency's Gaia satellite has mapped the location of 1,000,000,000 stars in our galaxy, and its scientists believe this represents 1 percent of the total, so perhaps the Milky Way contains more than 100 billion stars.
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- Astronomers are still unsure exactly how much our galaxy weighs, with estimates ranging from 700 billion to 2 trillion times the mass of our sun. Getting a better grasp is no easy task. Most of the Milky Way's mass, perhaps 85 percent, is in the form of “dark matter“, which gives off no light and so is impossible to directly observe.
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- A recent study looked at how strongly our galaxy's humongous mass gravitationally tugs on smaller galaxies orbiting it and updated the estimate of the Milky Way's mass to 960,000,000,000 times the mass of the sun.
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- Several studies have indicated that the Milky Way and its neighbors are living out in the edges of the cosmos. From afar, the large-scale structure of the universe looks like a colossal cosmic web, with string-like filaments connecting dense regions separated by enormous, mostly empty voids.
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- At the center of our galaxy is a gigantic blackhole with the weight of 4,000,000 suns. Scientists know that it's there because they can trace the paths of orbiting stars in the Milky Way's center and see that they seem to orbit a supermassive object that can't be seen.
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- Astronomers have been combining observations from multiple radio telescopes to try and get a glimpse of the environment surrounding the blackhole, which is packed with gas and dust spinning around the blackhole's center. The project, called the “Event Horizon Telescope“, expects to have preliminary images of the blackhole's edge this year.
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- When Portuguese explorer Ferdinand Magellan sailed through the Southern Hemisphere in the 16th century, he and his crew were among the first Europeans to report on circular clusters of stars in the night sky.
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- These clusters are actually small galaxies that orbit our Milky Way like planets around a star, and they have been named the Small and Large Magellanic clouds. Many such dwarf galaxies orbit ours and sometimes they get eaten by our massive Milky Way.
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- Earlier this year, 2021, astronomers used new data from the “Gaia satellite” that showed millions of stars in our galaxy moving in similar narrow, "needle-like" orbits, suggesting they all originated from an earlier dwarf galaxy dubbed "the Gaia Sausage," .
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- Swirling through the mostly empty space between stars in our galaxy is a bunch of dirty grease. Oily organic molecules known as “aliphatic carbon compounds” are produced in certain types of stars and then are leaked out into interstellar space.
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- Researchers found that these grease-like substances could account for between a quarter and one-half of the Milky Way's interstellar carbon which is five times more than previously believed. Carbon is an essential building block of living things, finding it in abundance throughout the galaxy could suggest that other star systems harbor life.
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- We are currently speeding toward our neighbor, the “Andromeda galaxy“, at around 250,000 mph. The crash will comes in about 4 billion years.
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- Astronomers have weighed Andromeda and found that it was roughly equivalent to 800 billion suns, or about the same as the Milky Way's mass. That means that exactly which galaxy will emerge less scathed from the future galactic crash remains an open question.
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- Astronomers were recently searching for hypervelocity stars, which get thrown at mind-bending speeds from the Milky Way after interacting with the giant blackhole in its center. What they found was even stranger rather than flying away from our galaxy, most of the fast stars they spotted were barreling toward ‘us‘.
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- These could be stars from another galaxy, zooming right through the Milky Way. These odd stars could have originated in the Large Magellanic Cloud or some other galaxy farther away.
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- There are mysterious bubbles arising out of the Milky Way. In 2010 astronomers uncovered gigantic, never-before-seen structures stretching for 25,000 light-years above and below the galaxy. Named 'Fermi bubbles' after the telescope that found them, these gamma-ray-emitting objects have defied astronomers' explanations ever since.
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- In 2020 a team gathered evidence suggesting that the bubbles are the aftermath of an energetic event 6 million to 9 million years ago, when the supermassive blackhole in the galactic center swallowed a huge clump of gas and dust and burped out these giant, glowing clouds.
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- Over the last decade, astronomers keep detecting odd flashes of light coming at them from the distant cosmos. Known as fast radio bursts (FRBs), these mysterious signals have no agreed-upon explanation. Despite knowing about them for more than 10 years, researchers had until recently captured only 30 examples of these FRBs.
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- In 2020 Australian scientists managed to find 20 more FRBs, nearly doubling the number of known objects. While they still don't know the odd flashes' origin. They were able to determine that the light had traveled through several billion light-years of gas and dust, which imparted telltale signs on the signal, suggesting that the FRBs were coming from a long way off.
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- One of these space missions ton learn more is “Gaia”. This satellite will make the largest, most precise three-dimensional map of our Milky Way Galaxy by surveying more than a thousand million stars.
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- Gaia will monitor each of its target stars about 70 times over a five-year period. It will precisely chart their positions, distances, movements, and changes in brightness. It is expected to discover hundreds of thousands of new celestial objects, such as extra-solar planets and brown dwarfs, and observe hundreds of thousands of asteroids within our own Solar System.
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- The mission will also study about 500,000 distant “quasars” and will provide stringent new tests of Albert Einstein’s General Theory of Relativity.
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- Gaia will create an extraordinarily precise three-dimensional map of more than a thousand million stars throughout our Galaxy and beyond, mapping their motions, luminosity, temperature and composition. Gaia will identify which stars are relics from smaller galaxies long ago ‘swallowed’ by the Milky Way. By watching for the large-scale motion of stars in our Galaxy, it will also probe the distribution of dark matter, the invisible substance thought to hold our Galaxy together.
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- Gaia will be repeatedly measuring the positions of all objects down to magnitude 20, 400,000 times fainter than can be seen with the naked eye. For all objects brighter than magnitude 15 (4,000 times fainter than the naked eye limit), Gaia will measure their positions to an accuracy of 24 micro-arcseconds. This is comparable to measuring the diameter of a human hair at a distance of 1,000 kilometers.
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- The nearest stars to have their distances measured to an accuracy of 0.001%. Even stars near the Galactic centrer, some 30,000 light-years away, will have their distances measured to within an accuracy of 20%.
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- Gaia contains two optical telescopes that work with three science instruments to precisely determine the location of stars and their velocities, and to split their light into a spectrum for analysis.
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- During its five-year mission, the spacecraft spins slowly, sweeping the two telescopes across the entire celestial sphere. As the detectors repeatedly measure the position of each celestial object, they will detect any changes in the object’s motion through space.
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- Gaia unfolded a ‘skirt’ just over 10 m in diameter that acts as both a sunshade to permanently shade the telescopes and allow their temperatures to drop to below –100°C, and as a power generator for the spacecraft. The underside of the shield is partially covered with solar panels and will always be facing the Sun, generating electricity to operate the spacecraft and its instruments.
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- Gaia is mapping the stars from an orbit around the Sun, at a distance of 1.5 million kilometers beyond Earth’s orbit. This special location, known as the L2 Lagrangian point, keeps pace with Earth as we orbit the Sun.
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- It offers a clearer view of the cosmos than an orbit around Earth, which would result in the spacecraft passing in and out of Earth's shadow and causing it to heat up and cool down, distorting its view. Free from this restriction and far away from the heat radiated by Earth, L2 provides a much more stable viewpoint.
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- November 3, 2021 MILKY WAY GALAXY - still more to learn? 3320
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