- 3285 - GRBs - and Blackholes. Gamma-ray bursts (GRBs) are the brightest, most energetic blasts of light in the universe. Released by an immense cosmic explosion, a single GRB is capable of shining about a million trillion times brighter than Earth's sun.
--------------------- 3285 - GRBs - and Blackholes.
- Astronomers can not explain how these immense bursts of power is created. Part of the problem is that all known GRBs come from very, very far away, usually billions of light-years from Earth.
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- The GRB's home galaxy is so far away that the burst's light appears to come from nowhere at all, briefly blipping out of the black, empty sky and vanishing seconds later. These "empty-sky" gamma-ray bursts have presented an ongoing cosmic mystery for more than 60 years.
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- Astronomers are beginning to model the interactions between gamma rays and other powerful energy sources, such as cosmic rays. Those nebulous empty-sky bursts could be the results of massive stellar explosions in the disks of distant galaxies.
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- Astronomers favor two leading explanations for the empty-sky gamma-ray mystery. In one explanation, the rays occur when gas falls into the supermassive blackholes that sit at the centers of all galaxies in the universe.
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- As gas particles get sucked into the blackhole, a small fraction escape and instead radiate in large, near-light-speed jets of matter. It's thought that these powerful jets could be responsible for gamma-ray bursts.
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- Gamma Rays are very high frequency light. With light waves the higher the frequency the more powerful the light packing higher energy. Ultraviolet light is higher frequency than visible light That is why it burns your skin.
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- Another explanation points to stellar explosioning supernovas. When large stars run out of fuel and erupt in these violent supernovas, they can send nearby particles blasting away at near-light speed. These highly energetic particles, called cosmic rays, may then collide with other particles sprinkled through the gassy hinterland between stars, producing gamma-rays.
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- In this 2021 study, the researchers focused on that second explanation by modeling the interactions between cosmic rays and interstellar gas in various types of star-forming galaxies.
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- Astronomers found that the rate of gamma-ray emissions was influenced by the size of the galaxy, the rate of star formation, which affects the rate of supernovas, and the initial energy of the cosmic rays created by each supernova.
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- Blackholes are probably still responsible for some of the gamma-rays that our satellites pick up. But the mysterious “empty-sky GRBs“, these blackholes are not necessary, exploding stars in faraway corners of the universe are sufficient to explain the phenomenon.
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- Still for 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.
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- With all the normal rules of physics breaking down inside them, it's tempting to dismiss blackholes as the stuff of science fiction. Yet there's plenty of evidence, both direct and indirect, that they really do exist in our universe.
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- Blackholes were predicted as a theoretical possibility, in 1916 by Karl Schwarzschild, who found them to be an inevitable consequence of Einstein's theory of general relativity.
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- If Einstein's theory is correct then blackholes must exist. Later 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.
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- If that star is really big, 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.
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- 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 which was another prediction of Einstein's theory of relativity.
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- With observatories like the “Laser Interferometer Gravitational-Wave Observatory” and “Virgo“, we have the ability to detect these gravitational waves.
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- The first gravity wave discovery, involving the merger of two blackholes, was announced in 2016, and many more have been made since then. As detector sensitivity improves, other wave-generating events besides blackhole mergers are being discovered.
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- A crash between a blackhole and a neutron star took place beyond our own galaxy at a distance of 0.65 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. There's one way to detect the dark beasts, though, and that's through their gravitational effects on other stars.
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- When observing the ordinary-looking binary system, or pair of orbiting stars, known as HR 6819 in 2020, astronomers noticed oddities in the motion of the two visible stars that could be explained only if there was a third, totally invisible, object there.
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- When they worked out its mass, at least four times that of the sun, the researchers knew there was only one possibility left. It had to be a blackhole. It is the closest yet discovered to Earth, a mere 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. Called Cygnus X-1, the system produces some of the universe's brightest X-rays.
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- The X-rays don't emanate from the blackhole itself, or from its visible companion star which is 33 times the mass of our own sun, according . 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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- At the center of our galaxy is a supermassive black hole in the region known as Sagittarius A.
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- Blackholes are 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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- In the case of active galaxies, the evidence for these heavyweights is spectacular. The central black holes in these galaxies are surrounded by accretion disks that produce intense radiation at all wavelengths of light.
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- Our own galaxy has a blackhole at its center. Astronomers 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 around 4 million solar masses.
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- Another piece of evidence for the existence of black holes is … “spaghettification“. Spaghettification is what happens when you fall into a blackhole. You get stretched out into thin strands by the blackhole's extreme gravitational pull.
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- Last year, in October 2020, astronomers witnessed this shredding as a flash of light from a star as it was ripped apart. Fortunately, the spaghettifying didn't happen anywhere near Earth, but instead in a galaxy 215 million lightyears away.
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- Astronomers have plenty of compelling indirect evidence for blackholes: 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 of the supermassive blackhole at the center of active galaxy Messier 87 was created. This stunning photo was taken by the Event Horizon Telescope which 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 blackhole against the orange glow of its surrounding accretion disk.
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- September 26, 2021 GRBs - and Blackholes. 3285
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