- 3322 - BLACKHOLES - how we found them? In April 2019 a direct image was produced of the supermassive blackhole at the center of active galaxy Messier 87. This stunning photo was taken by the Event Horizon Telescope. The EHT consists of a large network of telescopes scattered all over the world rather than a single instrument.
--------------------- 3322 - BLACKHOLES - how we found them?
- Albert Einstein (1879-1955) is one of the most famous scientists of all time, and his name has become almost synonymous with the word "genius." His claim to fame comes from his contributions to modern physics, which have changed our entire perception of the universe and helped shape the world we live in today.
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- Einstein's ‘theory of special relativity” changed the way we think about space and time and established a universal speed limit of the speed of light. One of his earliest achievements, at the age of 26, was his theory of special relativity. It deals with relative motion in the special case where gravitational forces are neglected.
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- It was one of the greatest scientific revolutions in history, completely changing the way physicists think about space and time. Einstein merged these into a single space-time continuum.
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- One reason we think of space and time as being completely separate is because we measure them in different units, such as miles and seconds. But Einstein showed how they are actually interchangeable, linked to each other through the speed of light at 186,000 miles per second .
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- A consequence of special relativity is that nothing can travel faster than light. It also means that things start to behave very oddly as the speed of light is approached. If you could see a spaceship that was traveling at 80% the speed of light, it would look 40% shorter than when it appeared at rest.
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- And if you could see inside, everything would appear to move in slow motion, with a clock taking 100 seconds to tick through a minute. This means the spaceship's crew would actually age more slowly the faster they are traveling.
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- E = mc^2 is likely the only mathematical formula to have reached the status of cultural icon. The equation expresses the equivalence of mass (m) and energy (E), two physical parameters previously believed to be completely separate.
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- In traditional physics, mass measures the amount of matter contained in an object, whereas energy is a property the object has by virtue of its motion and the forces acting on it.
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- Energy can exist in the complete absence of matter, for example in light or radio waves. However, Einstein's equation says that mass and energy are essentially the same thing, as long as you multiply the mass by c^2, the square of the speed of light, which is a very big number to ensure it ends up in the same units as energy.
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- An object gains mass as it moves faster, simply because it's gaining energy. It also means that even an inert, stationary object has a huge amount of energy locked up inside it.
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- If sufficiently energetic particles are smashed together, the energy of the collision can create new matter in the form of additional particles. Lasers are an essential component of modern technology and are used in everything from barcode readers and laser pointers to holograms and fiber-optic communication.
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- Although lasers are not commonly associated with Einstein, it was ultimately his work that made them possible. The word laser, coined in 1959, stands for "light amplification by stimulated emission of radiation" and stimulated emission is a concept Einstein developed more than 40 years earlier.
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- In 1917, Einstein wrote a paper on the quantum theory of radiation that described, among other things, how a photon of light passing through a substance could stimulate the emission of further photons.
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- Einstein realized that the new photons travel in the same direction, and with the same frequency and phase, as the original photon. This results in a cascade effect as more and more virtually identical photons are produced.
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- When Einstein succeeded in adding gravity into the mix, in his theory of “general” relativity he found that massive objects like planets and stars actually distort the fabric of space-time, and it's this distortion that produces the effects we perceive as gravity.
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- Einstein explained general relativity through a complex set of equations, which have an enormous range of applications. Perhaps the most famous solution to Einstein's equations came from Karl Schwarzschild's solution in 1916, a blackhole.
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- Even weirder is a solution that Einstein himself developed in 1935 in collaboration with Nathan Rosen, describing the possibility of shortcuts from one point in space-time to another. Originally “Einstein-Rosen bridges“ which are now known by the more familiar name of “wormholes“.
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- Equations of general relativity applied to the universe as a whole gave answers that came out looked wrong to him. It implied that the fabric of space itself was in a state of continuous expansion, pulling galaxies along with it so the distances between them were constantly growing.
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- Common sense told Einstein that this couldn't be true, so he added something called the “cosmological constant” to his equations to produce a static universe.
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- In 1929, Edwin Hubble's observations of other galaxies showed that the universe really is expanding, apparently in just the way that Einstein's original equations predicted. It looked like the end of the line for the cosmological constant, which Einstein later described as his biggest blunder.
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- That wasn't the end of the story, however. Based on more refined measurements of the expansion of the universe, we now know that it's speeding up, rather than slowing down as it ought to in the absence of a cosmological constant. So it looks as though Einstein's "blunder" wasn't such an error after all. The acceleration is now the universal rate of expansion.
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- Einstein died in 1955, but his huge scientific legacy continues to make headlines even in the 21st century. This happened in a spectacular way in February 2016, with the announcement of the discovery of gravitational waves another consequence of general relativity.
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- Einstein never quite made up his mind whether gravitational waves were predicted or ruled out by his theory. And it took astronomers decades of searching to decide the matter one way or the other. Eventually they succeeded, using giant facilities such as the Laser Interferometer Gravitational-Wave Observatories (LIGO) in Hanford, Washington, and Livingston, Louisiana.
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- The discovery of gravitational waves has given astronomers a new tool for observing the universe including rare events like merging blackholes.
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- For all the far-out concepts in astronomy, blackholes may be the weirdest. A region of space where matter is so tightly packed that nothing, not even light itself, can escape, these dark behemoths present a pretty terrifying prospect too.
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- Blackholes were found to be an inevitable consequence of Albert Einstein's theory of general relativity. Blackholes were predicted in 1916 by Karl Schwarzschild, who found them to be an inevitable consequence of Einstein's theory of general relativity. In other words, if Einstein's theory is correct then blackholes must exist.
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- Roger Penrose and Stephen Hawking showed that any object collapsing down to a blackhole will form a “singularity” where the traditional laws of physics break down.
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- In the 1930s, Indian astrophysicist Subramanian Chandrasekhar looked at what happens to a star when it has used up all its nuclear fuel. The end result, he found, depends on the star's mass. If that star is really big, greater than 20 solar masses, then its dense core which may itself be three or more times the mass of the sun collapses all the way down to a blackhole.
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- The final core collapse happens incredibly quickly, in a matter of seconds, and it releases a tremendous amount of energy in the form of a “gamma-ray burst“. This burst can radiate as much energy into space as an ordinary star emits in its entire lifetime. And telescopes on Earth have detected many of these bursts, some of which come from galaxies billions of light-years away; so we can actually see blackholes being born.
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- Blackholes don't always exist in isolation, sometimes they occur in pairs, orbiting around each other. When they do, the gravitational interaction between them creates ripples in space-time, which propagate outward as gravitational waves, another prediction of Einstein's theory of relativity.
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- With observatories like the Laser Interferometer Gravitational-Wave Observatory and Virgo, we now have the ability to detect these waves. The first discovery, involving the merger of two blackholes, was announced back in 2016, and many more have been made since then.
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- As these detector’s sensitivity improves, other wave-generating events besides blackhole mergers are being discovered, such as a crash between a blackhole and a neutron star, which took place way beyond our own galaxy at a distance of 650 million to 1.5 billion light-years from Earth.
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- The short-lived, high-energy events that produce gamma-ray bursts and gravitational waves may be visible halfway across the observable universe, but for most of their lives blackholes, by their very nature, will be almost undetectable.
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- The fact that they don't emit any light or other radiation means they could be lurking in our cosmic neighborhood without astronomers being aware of it. Their gravitational effects on other stars can be detected when observing the ordinary-looking binary system, or pair of orbiting stars.
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- “HR 6819” observed in 2020 showed oddities in the motion of the two visible stars that could be explained only if there was a third, totally invisible, object there. When astronomers worked out its mass, at least four times that of the sun. It had to be a blackhole the closest yet discovered to Earth, one thousand light-years away inside our own galaxy.
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- The first observational evidence for a blackhole emerged in 1971, and this too came from a binary star system within our own galaxy. Cygnus X-1 system produces some of the universe's brightest X-rays. These don't emanate from the blackhole itself, or from its visible companion star which is enormous, at 33 times the mass of our own sun.
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- Matter is constantly being stripped from the giant star and dragged into an accretion disk around the blackhole, and it's from this accretion disk that the X-rays are emitted.
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- As they did with HR 6819, astronomers can use observed star motion to estimate the mass of the unseen object in Cygnus X-1. The latest calculations put the dark object at 21 solar masses concentrated into such a small space that it couldn't be anything other than a blackhole.
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- In addition to blackholes created through stellar collapse, evidence suggests that supermassive blackholes, each millions or even billions of solar masses, have been lurking in the centers of galaxies since early in the history of the universe.
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- Active galaxies show the evidence for these heavyweights. The central blackholes in these galaxies are surrounded by accretion disks that produce intense radiation at all wavelengths of light.
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- We have evidence that our own Milky Way galaxy has a blackhole at its center. That's because we see the stars in that region whizzing around so fast up to 8% of the speed of light that they must be orbiting something extremely small and massive. Current estimates put the Milky Way's central blackhole somewhere around 4,000,000 solar masses.
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- “Spaghettification” is what happens when you fall into a blackhole. Objects get stretched out into thin strands by the blackhole's extreme gravitational pull. In October 2020 astronomers witnessed this shredding. A flash of light from a star that was ripped apart. This happened in a galaxy 215 million light-years away.
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- Compelling indirect evidence for blackholes exists in bursts of radiation or gravitational waves, or dynamical effects on other bodies, that couldn't have been produced by any other object known to science.
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- In April 2019 a direct image was produced of the supermassive blackhole at the center of active galaxy Messier 87. This stunning photo was taken by the Event Horizon Telescope. The EHT consists of a large network of telescopes scattered all over the world rather than a single instrument.
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- The more telescopes that can participate, and the more widely spaced they are, the better the final image quality. The result clearly shows the dark shadow of the 6.5 billion-solar-mass black hole against the orange glow of its surrounding accretion disk. Can you believe your on eyes?
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- October 30, 2021 BLACKHOLES - how we found them? 3320
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