- 3197 - MILKY WAY’S - blackhole at the center? For the last 30 years astronomers have been mapping the orbiting stars circling the Milky Way’s center. The orbit of the star “S2” and its stellar companions indicated that they were circling around a massive object, about 4,000,000 times the mass of the Sun. It could only be one thing, a massive blackhole.
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- By 1974, the blackhole was named “Sagittarius A*”, and was solidified as your own local supermassive blackhole. Since then, scientists have made several follow-up observations to reestablish the existence of this dark, lurking beast in the Milky Way, even turning one of the largest virtual telescopes in the world on it.
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- But not everyone seems to agree on the true nature of Sagittarius A*. A 2020 study claims that the blackhole of our galaxy is not a blackhole at all. Instead, it gives a more exotic take on physics that isn’t yet proven, that is, Sagittarius A* is an imposter, not a blackhole but a massive, fluffy ball of “fermionic dark matter“.
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- Although it’s difficult to provide definitive proof of Sagittarius A*, most scientists are 99.999% sure it’s there. So, how do you prove the existence of an invisible, massive cosmic blackhole that we cannot see?
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- An imposter blackhole theory is based on observations of a cloud of gas that had an encounter with the blackhole and surprisingly survived. In 2014, astronomers watched as a cloud of gas named “G2’ came dangerously close to the blackhole at the center of the Milky Way. But instead of being ripped apart and devoured by the blackhole’s gravitational tug, G2 kept on going.
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- Maybe Sagittarius A* is not a blackhole, but instead clumps of dark matter. Dark matter is an elusive form of matter that makes up around 85 percent of all matter in the universe and about 27 percent of its total mass, outweighing all visible matter around six to one.
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- This study suggests that an absolutely titanic blob of dark matter would produce the same amount of spacetime curvature. But the cluster of dark matter would have a slightly weaker gravitational tug, therefore allowing the cloud of gas to pass by without being torn to shreds. This would still provide enough gravity to keep the stars like S2 in orbit.
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- A blackhole is a region of space with a gravitational pull so strong that nothing can escape its influence, not even light itself. Blackholes grow by feeding off their surrounding material, swallowing up gas from neighboring stars or other celestial objects.
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- The largest-known blackholes lurk at the center of galaxies, and scientists believe that most large galaxies have a supermassive blackhole at their center.
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- In the early 2000s, scientists watched as the closest stars to the galaxy’s blackhole orbited around it, concluding that an object of roughly 4 million times the mass of the Sun was present within a region much smaller than the size of the Solar System.
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- If you use simple Newtonian physics, then you can figure out the mass of the object that the stars are orbiting. The blackhole at the center of our galaxy is very well studied because it is so close.
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- Amazing infrared telescopes can image very closely these regions closest to the blackhole than we've ever been able to see by mapping the trajectories of stars right as they get close to the blackhole.
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- The silhouette of the blackhole is surrounded by a glowing halo of fiery gas. Nicknamed a “ring of fire,” the hot gas formed a circular shape around the blackhole's event horizon. In the process, it confirmed predictions of what a supermassive blackhole looks like.
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- One theory that doesn’t invoke dark matter, is that the center of the Milky Way is not dominated by a blackhole of a giant mass, but perhaps by 4 million different objects in a very tight cluster that has the same gravitational effect.
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- A cluster of compact objects that would fit into that dense region would evaporate within years since the motions of the objects under the gravity of the cluster would be so high that they would get kicked out.
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- In contrast this blackhole is fairly quiet. Sagittarius A* lacks visible jets of material that is usually shooting out from blackholes of its size.
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- Some of the most distant objects that we see in the universe are blackholes, and they're blasting the universe with powerful radiation that’s generated by matter that's being accreted from them.
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- But, in the case of Sagittarius A*, it's very, very quiet and it's almost a billion times less luminous. This suggests that the blackhole isn’t spinning fast enough to create momentum for its accretion disc to send out jets of matter.
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- Observing a distant galaxy located some 320,000,000 lightyears away astronomers stumbled upon something oddly familiar. The galaxy, “UGC 10738“, had a thick disc containing ancient stars formed billions of years ago and a thin disc of relatively younger stars. The two star-filled discs were strikingly similar to those located in the Milky Way galaxy.
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- This revelation presented the astronomers with a rare opportunity to compare our own galaxy with its very own galactic twin, a galaxy that may have evolved in a similar fashion to the Milky Way. They found that the Milky Way may have evolved gradually over time rather than having formed as a result of a massive collision between galaxies.
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- Observations revealed that galaxy UGC 10738 has a thick disc consisting mostly of ancient stars, which have a low ratio of iron to hydrogen and helium, while its thin disc stars are younger and contain more metal, a sign that they formed from material left over by previous generations of stars.
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- Our Sun is a thin disc star, forming around 4.5 billion years ago. These discs have been observed in galaxies before, but it was nearly impossible to tell whether they hosted the same kind of star distribution between the two discs.
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- By confirming that this galaxy has a similar distribution of young and old stars between its thin and thick discs, the astronomers concluded that it had a similar origin story to that of the Milky Way.
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- 14 billion years ago, enormous clouds of gas and dust collapsed under the weight of their own gravity to form the Milky Way. These clouds then formed two main structures: a spherical halo, and a dense, bright disk.
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- Massive collision also formed the Milky Way, shaping it into the spiral galaxy it is today. Around 11 billion years ago, a small galaxy called “Gaia-Enceladus” slammed into the primordial Milky Way.
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- Based on previous evidence, scientists suggested that the Milky Way was unique in that it formed as a result of mergers with other, smaller galaxies and therefore its structure was not observable with other spiral galaxies.
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- Our Milky Way collided with other smaller galaxies over time, leading to its structure today. ---------------------------- Other reviews available:
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- 3130 - MILKY WAY - mysteries? The Dark Matter halo far outside and surrounding the Galaxy is the greatest mystery. We know the Dark Matter is there because we see the effect of its gravity. We see a constant orbital velocity of all the stars with ever increasing radius. Rotational velocity should fall off with the square root of velocity, if the mass is inside the radius.
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- 3129 - MILKY WAY GALAXY - When astronomers add up all the ordinary matter detectable around us, such as in galaxies, stars and planets, they find only half the amount expected to exist, based on predictions. This normal matter is "baryonic," which means it's made up of baryon particles such as protons and neutrons.
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- 2941 - MILKY WAY - it ain’t what it used to be? . Even after 14 billion years, mergers continue to sculpt the overall shape of our galaxy. This realization is just the latest change in how we understand the great stream of milk across the sky. Everything we thought we knew about the future and the history of the Milky Way, we need a new model to describe this.
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- 2854 - MILKY WAY GALAXY - learn more about our home? The satellite “Gaia” has truly revolutionized the study of the Milky Way. It ushered in “galactic archaeology“, a discipline that searches for evidence of past galactic events in the characteristics and behavior of the stars and stellar populations.
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- 2655 - MILKY WAY - our home in the cosmos? - This center of the Milky Way is located in the direction of the constellation Sagittarius, the “Teapot” group of stars low in the southern sky. The exact center is located just above the spout of the teapot. The center bulge would be much, much brighter if we could see through the enormous dust cloud of intergalactic dust that lies between us and the center.
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- 2411 - Our Milky Way, the Galaxy that is our home. It is an awe-inspiring place full of stars, supernovas, nebulas, energy and dark matter. But, many aspects of it remain mysterious, even to scientists.
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- 2325 - Calculating Milky Way’s Black Hole. Black Holes are both simple and complex. We can calculate their mass, radius, lifetime, energy consumption using simple algebra. At the same time, their immense gravity causes space to bend, lengths to shorten, time to slow and mass to increase.
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- 2324 - MILKY WAY - how to explain its rotation? This Review is about new things we are learning about our own Milky Way Galaxy. What is mysterious is that what we learn seems to defy the physics that we think we know. Certainly our solar system’s planets are rotating with different physics than stars in our galaxy or other galaxies. What’s going on? What are we missing?
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- 2057 -
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- 1919 - How did planets form? Theory is that gas and dust orbiting the star (our Sun) coalesced and multiple collisions created little planets ( planetesimals) that with further collisions created the large planets. Stars form into galaxies much the same way.
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- 1889 - Evolution of the galaxies Computer modeling and new extensive observations of our Milky Way Galaxy are telling us a story of galactic creation. The greatest mystery still is the you are here learning about it.
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- June 22, 2021 MILKY WAY’S - blackhole at the center? 3197
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--------------------- --- Wednesday, June 23, 2021 ---------------------------
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