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--------------------- 2629 - GALAXIES - how do they form and grow?
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- Our Sun is only one of the billions of stars in our galaxy, the Milky Way. It’s also quite small compared to other stars, many are at least eight times more massive.
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- These massive stars influence the structure, shape and chemical content of a galaxy. And when they have exhausted their hydrogen gas fuel and die, they do so in an explosive event called a supernova. This explosion is sometimes so strong that it triggers the formation of new stars out of materials in the dead star’s surroundings.
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- See Review 2628 about gravity waves and supernova explosions.
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- One theory is that a rotating disc of gas and dust funnels materials into the growing star.
Astronomers have recently found that the funneling of matter into a forming star happens at different rates over time.
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- Sometimes the forming star swallows up a huge amount of matter, resulting in a burst of activities in the massive star. This is called an “accretion burst event“. It is incredibly rare. Only three such events have been observed, out of all the billions of massive stars in the Milky Way. The first detection of an accretion burst was in 2016
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- A “maser” is the microwave, the radio frequency equivalent of laser, “microwave amplification by stimulated emission of radiation”. Masers are observed using radio telescopes and most of them are observed at centimeter wavelength They are very compact.
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- A maser flare can be a sign of an extraordinary event such as the formation of a star. Since 2017 radio telescopes have been working together to detect a flare stimulated by a burst in the funneling of materials into a massive star.
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- In January 2019, astronomers noticed that one such massive proto star showed signs of new activity. The masers associated with the object brightened significantly over a short period of time. The theory is that masers brighten when excited by an accretion burst.
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- Follow-up observations with the Australian Long Baseline Array revealed something astronomers are witnessing for the first time, a blast of heat wave coming from the source and traveling through the surroundings of the forming big star. Blasts can last for about two weeks to a few months.
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- Blasts like this were not observed in the previous two accretion bursts in massive stars. This may imply that it’s a different kind of accretion burst. There may even be a “zoo” of accretion burst types. There may be a whole range of different types which act in different ways that may depend on the mass and evolutionary stage of the young star.
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- Although the burst activity has died down, the masers are still a lot brighter than they were before the burst. Astronomers are watching with interest to see whether a similar burst will occur again, and at what scale. Collaboration is astronomy is crucial for new, important discoveries.
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- An enormous effort that stunned the world, scientists last year unveiled the first direct picture of a black hole. Now, astronomers have used a different technique involving x-ray “echoes” to peer even closer at one of these gravitational monsters.
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- The black hole coming into focus is in the middle of a galaxy that is a billion light-years away. The supermassive object is surrounded by a swirling disk of million-degree matter and is sheathed by an x-ray corona with a temperature exceeding a billion degrees.
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- By charting how those x-rays behave, scientists created an extremely detailed map of the region around the black hole’s event horizon, the zone beyond which not even light can escape.
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- At the center of our galaxy is a supermassive black hole. Black holes don’t give off any light themselves, so the only way we can study this is by watching what matter does as it falls onto it.
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- The new measurements of the black hole helped scientists pin down its mass and spin, properties that can reveal vital clues about the black hole’s evolution. If similar measurements can be made for a larger population of nearby supermassive black holes, they could help scientists learn more about how galaxies grow.
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- Understanding the spin distribution of black holes in many galaxies tells us about how we go from the early universe to the population we see today.
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- This is one of the most exciting galaxies in the x-ray sky. It is an active galaxy, meaning that its innermost region shines more brightly than can be explained by stars alone, and its x-ray brightness fluctuates by a factor of 50, sometimes over just a few hours. Astronomers wanted too find a dynamic, fluctuating source that could help them nail down specific properties of the central supermassive black hole.
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- An Earth-orbiting telescope studied the cosmos in x-rays over the course of 16 orbits, totaling more than 550 hours, between 2011 and 2016. From those many hours’ worth of data astronomers could assemble a map of the supermassive black hole’s x-ray corona and its accretion disk, a ring of swirling matter that’s just outside the event horizon.
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- Some of the emitted x-rays head directly into the cosmos, but others slam into the accretion disk and take a little longer to exit the immediate environment. This extra path length causes a time delay between the x-rays that were produced originally in the corona. The echo. or time delay, is called a “reverberation.”
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- The reverberation mapping, helped the scientists probe the gassy material around the black hole. The process works like echolocation, the way bats bounce sound off objects to help them navigate in flight. Reverberation mapping can be used to study objects that are far, far away and probe regions even closer to the event horizon. It uses light echoes within the object to tell us about structures, even very small and very far away ones.”
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- The light echoes captured was used to determine the precise geometry of the material surrounding the black hole, including the dimensions of its dynamic x-ray corona, which powers those echoes. That information was used to calculate the black hole’s mass and spin.
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- Based on the new mapping, the team concluded that this supermassive black hole contains as much mass as two million suns, and that it is spinning nearly as fast as it possibly can without breaking the laws of physics.
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- Every large galaxy in the universe is likely anchored to a central supermassive black hole. Deciphering the ways in which those anchors rotate could offer clues to how they, and their host galaxies, formed and evolved over the age of the universe.
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- One way in which galaxies could form involves multiple small galaxies colliding and merging. As these galaxies merge, so do their central black holes. If those collisions are chaotic, they could not only contribute to the resulting bigger black hole’s mass, but also to the way it spins.
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- Another way in which black holes might bulk up is through a continual stream of inflowing gas. In that case, the resulting spin might be speedier.
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- Astronomers hope to use reverberation mapping to pin down the spins, and thus the formation histories, of hundreds of nearby supermassive black holes, in effect taking a census of these objects. Then, based on how far away those black holes are, scientists can look at how galaxies grew.
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- Astronomers are not the only ones trying to learn where we came from and how we got here. What are we going to do now that we are here?
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--------------------------------- Other Reviews to learn about galaxies:
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- 2628 - GRAVITY WAVES - from supernovae explosions? Is the speed of gravity instantaneous, or is there a speed limit on how fast the force of gravity can travel. This is not as simple a question. After all, we know how fast light travels, and if the Sun were to suddenly wink out of existence, we’d still receive light from it for just over 8 minutes after it disappeared!
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- 2436 - GALAXIES - what rotating galaxies tell us? The conclusion is that most of what contributes to the galaxy’s weight does not shine. We call it “Dark Matter“. The weight of Dark Matter is 10 times greater than the weight of what we see. (Do not believe “truth” without evidence. Is 95% of the Universe really Dark Matter?)
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- 2371 - The farthest galaxy in our observable Universe?- Astronomers have found a galaxy believed to be the farthest detected as 2004. As we leaned from Edwin Hubble in 1920 the further away a galaxy is the faster it is receding, or moving away from us. The light from a galaxy that is moving away from us has its wavelength stretched out. This is called the Doppler effect.
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- 2340 - How to weigh a galaxy? How to do the math? About half the mass of the Milky is inside the Sun's orbit and half is outside. This fact has proven to be a real problem for astronomers. The inside orbit is much, much denser with visible light than the outside orbits. The mass of the outside orbits is larger than we can visible see. This fact has caused astronomers to invent another object in the Universe, Dark Matter. The mass of the Milky Way inside the orbit of Earth is 1.9*10^41 kilograms. The total mass of the Milky Way is 3.9*10^41 kilograms
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- 2283 - Galaxies are structures of stars, and they in turn are structures of the Universe. The Universe forms itself into filaments and treads that are all interconnecting with galaxies at the nodes where the filaments come together. Starts with our closest galaxy, M31, The Andromeda Galaxy. Discovered in 1923 by Edwin Hubble. The Andromeda Galaxy is visible with the naked eye in the north-east horizon you can see a spiral shaped cloud.
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- 2227 - How did galaxies form? Large galaxies devour smaller galaxies. The estimate of the total number of galaxies in the Observable Universe is 2 trillion in a volume 27.7 billion lightyears across.
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- 2062 - All disk galaxies complete one rotation about once every billion years. Stars orbiting the edges of galaxies have the same orbital periods. It is like a giant 78 RPM vinyl record. But, this structure is not following mathematical laws that require orbital periods sweep out equal areas in equal times. The planets orbiting the Sun follow this mathematical law, Kepler’s Law. But, galaxies do not?
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- 2060 - Galaxies are the structure of the Universe. Each individual galaxy has an ever expanding velocity, riding on a wave of space. This is the result of a fight between gravity and space expanding, but gravity falls off at the square of distance. Expanding space is constant mysterious force that is the same regardless of separating distances. It wins the battle.
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- 2046 - How do galaxies form and grow? Blackholes shape the cosmos. How does Dark Matter enter into this picture? Running the state of the art project using a mathematical model to form the universe. It sheds new light on how blackholes shape the cosmos and how galaxies from and grow. Astronomers have discovered that all galaxy disks rotate about one rotation in a billion years. This is regardless of their size or mass.
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- 1994 - How many galaxies are there?
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- 1887 - Galaxies galore - astronomers have mapped the positions and velocities of 8,000 galaxies reveling nested galactic structures of voids, sheets, filaments and nodes giving us a picture of the structure of the Universe.
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- 1832 - Dwarf galaxies and WIMPS?
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- 1813 - Galactic Storms, Quakes, and Waves. Seismic like quakes occur across our Galaxy. We can analyze these waves to map out the Galaxy in 3D very similar to how analysis of Earthquake waves are used to analyze the Earth’s interior.
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- 1760 - The birth of galaxies? - When and how did the first galaxies form. How do galaxies regulate star formation?
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- 1754 - “The Tides of Gravity” Astronomers are studying tidal streams to locate the center of gravity in our Galaxy.
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- 1751 - “Einstein’s Theory of Gravity” All bodies accelerate in a gravitational field the same regardless of mass or composition.
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- 1585 - Andromeda and Milky Way Collision in 6.3 billion years. What is the tug of war between gravity and Dark Energy? When will the collision happen? The Universe is expanding and galaxies are flying away from each other. A better description would be that the space between galaxies is expanding and pushing galaxies apart from each other. However, this is only on the grander scale. On large scales Dark Energy is dominate.
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- 1456 - “Gravity’s Tidal Forces” The ground you stand on can rise more that a foot as the Moon passes overhead.
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- 1132 - Why don’t galaxies follow the laws of gravity?
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- 1121 - - Why Do We Think There Is a Blackhole at the Center of Our Galaxy?
Dozens of stars have now been plotted orbiting the Galaxy’s Blackhole, which is called Sagittarius A. These dozen stars are orbiting in a clockwise direction. Some in elliptical orbits of 17 light hours to 10 light days.
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- 1120 - What happens when galaxies collide?
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- 933 - Galaxy evolution? Most have a Blackhole at their center.
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- 892 - How galaxies grow up?
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- 403 - “ The Gravity of it All” If the Earth was spinning 5 times faster ( a 5 hour day) what would happen to gravity?
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- 53 - The farthest galaxy in our Universe is traveling 98% the speed of light away from us.
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- February 21, 2020 2629
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