- 3247 - BLACKHOLES - the more we learn the less we know? New observations of a blackhole not only confirmed behavior predicted by General Relativity, they also allowed the team to study processes taking place behind a blackhole for the first time.
----- 3247 - BLACKHOLES - the more we learn the less we know?
- A blackhole emitted a flare away from us, but its intense gravity redirected the blast back in our direction. Starting to learn more about blackholes:
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- In 1916, Albert Einstein put the finishing touches on his Theory of General Relativity, a journey that began in 1905 with his attempts to reconcile Newton’s own theories of gravitation with the laws of electromagnetism.
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- Einstein’s theory provided a unified description of gravity as a “geometric property” of the cosmos, where massive objects alter the curvature of spacetime, affecting everything around them.
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- Einstein’s field equations predicted the existence of blackholes, objects so massive that even light cannot escape their surfaces. General Relativity also predicts that blackholes will bend light in their vicinity, an effect that can be used by astronomers to observe more distant objects.
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- Relying on this technique, an international team of scientists made an unprecedented feat by observing light caused by an X-ray flare that took place behind a blackhole.
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- Using the ESA’s XMM-Newton and NASA’s NuSTAR space telescopes, astronomers observed bright X-ray flares coming from around a supermassive blackhole located at the center of “I Zwicky 1“, a spiral galaxy located 1,800 light-years from Earth.
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- Because of the blackhole’s extreme gravity which comes from 10 million Solar masses, flares from behind the blackhole were made visible to the XMM-Newton and NuSTAR.
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- This “corona” is thought to be the result of gas that falls continuously into the blackhole and forms a spinning disk around it. As the ring is accelerated to near the speed of light, it is heated to millions of degrees and generated magnetic fields that get twisted into knots.
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- Eventually, these fields get twisted up to the point that they snap and release all the energy they have stored within. This energy is then transferred to matter in the surrounding disk, which produces the “corona” of high-energy X-ray electrons.
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- The X-ray flares were visible as light echoes, which were reflected from infalling gas particles being accreted onto the face of the blackhole. The X-ray flare observed was so bright that some of the X-rays shone down onto the disk of gas falling into the blackhole.
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- As the flares subsided, the telescopes picked up fainter flashes, which were the echoes of the flares bouncing off the gas behind the blackhole. The light from these flashes was bent around by the blackhole’s intense gravity and became visible to the telescopes, with a slight delay.
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- Astronomers were able to discern where the X-ray flashes came from based on the specific “colors” of light (their specific wavelength) they emitted. The colors of the X-rays that came from the far side of the blackhole were slightly altered by the extreme gravitational environment.
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- The fact that X-ray echoes are seen at different times depending on where on the disk they were reflected from, contain a lot of information about what is happening around a blackhole.
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- These observations not only confirmed behavior predicted by General Relativity, they also allowed the team to study processes taking place behind a blackhole for the first time.
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- These missions will continue to rely on the XMM-Newton space telescope, as well as the ESA’s proposed next-generation X-ray observatory, known as the Advanced Telescope for High-ENergy Astrophysics (ATHENA).
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- The idea of an object in space so massive and dense that light could not escape it has been around for centuries. Blackholes predicted by Einstein's theory of general relativity, showed that when a massive star dies, it leaves behind a small, dense remnant core. If the core's mass is more than about three times the mass of the Sun, the equations showed, the force of gravity overwhelms all other forces and produces a blackhole.
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- Scientists can't directly observe blackholes with telescopes that detect x-rays, light, or other forms of electromagnetic radiation. They can, however, infer the presence of blackholes and study them by detecting their effect on other matter nearby.
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- If a blackhole passes through a cloud of interstellar matter it will draw matter inward in a process known as accretion. A similar process can occur if a normal star passes close to a blackhole. In this case, the blackhole can tear the star apart as it pulls it toward itself.
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- As the attracted matter accelerates and heats up, it emits x-rays that radiate into space. Blackholes have been found emitting powerful gamma ray bursts, devouring nearby stars, and spurring the growth of new stars in some areas while stalling it in others.
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- Most blackholes form from the remnants of a large star that dies in a supernova explosion. Smaller stars become dense “neutron stars“, which are not massive enough to trap light. If the total mass of the star is large enough, about three times the mass of the Sun, it can be proven theoretically that no force can keep the star from collapsing under the influence of gravity.
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- As the surface of the star nears an imaginary surface called the "event horizon," time on the star slows relative to the time kept by observers far away. When the surface reaches the event horizon, time stands still, and the star can collapse no more. It is a frozen collapsing object.
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- Even bigger blackholes can result from stellar collisions. Soon after its launch in December 2004, NASA's Swift telescope observed the powerful, fleeting flashes of light known as gamma ray bursts.
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- Chandra and NASA's Hubble Space Telescope later collected data from the event's "afterglow," and together the observations led astronomers to conclude that the powerful explosions can result when a blackhole and a neutron star collide, producing another blackhole.
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- Blackholes appear to exist on two radically different size scales. On the one end, there are the countless blackholes that are the remnants of massive stars. Peppered throughout the Universe, these "stellar mass" blackholes are generally 10 to 24 times as massive as the Sun.
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- Astronomers spot them when another star draws near enough for some of the matter surrounding it to be snared by the blackhole's gravity, churning out x-rays in the process. Most stellar blackholes are very difficult to detect. Scientists estimate that there are as many as ten million to a billion such blackholes in the Milky Way alone.
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- On the other end of the size spectrum are the giants known as "supermassive" blackholes, which are billions, of times as massive as the Sun. Astronomers believe that supermassive blackholes lie at the center of virtually all large galaxies, even our own Milky Way. Astronomers can detect them by watching for their effects on nearby stars and gas.
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- Astronomers have long believed that no “mid-sized blackholes” exist. Recent evidence from Chandra, XMM-Newton and Hubble strengthens the case that mid-size blackholes do exist.
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- One possible mechanism for the formation of supermassive blackholes involves a chain reaction of collisions of stars in compact star clusters that results in the buildup of extremely massive stars, which then collapse to form intermediate-mass black holes. The star clusters then sink to the center of the galaxy, where the intermediate-mass blackholes merge to form a supermassive blackhole.
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- The term "blackhole" was coined in 1967 by American astronomer John Wheeler. After decades of blackholes being known only as theoretical objects, the first physical blackhole ever discovered was spotted in 1971.
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- In 2019 the Event Horizon Telescope (EHT) collaboration released the “first image” ever recorded of a blackhole. The EHT saw the blackhole in the center of galaxy M87 while the telescope was examining the event horizon, or the area past which nothing can escape from a blackhole. The image maps the sudden loss of photons (particles of light).
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- Astronomers have identified three types of black holes:
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--------------- stellar blackholes,
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--------------- supermassive blackholes
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-------------- intermediate blackholes.
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- Stellar blackholes are small but deadly. When a star burns through the last of its fuel, the object may collapse, or fall into itself. For smaller stars the new core will become a ‘neutron star” or a “white dwarf “ star. But when a larger star collapses, it continues to compress and creates a stellar blackhole.
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- Blackholes formed by the collapse of individual stars are relatively small, but incredibly dense. One of these objects packs more than three times the mass of the sun into the diameter of a city. This leads to an amount of gravitational force pulling on objects around the object. Stellar blackholes then consume the dust and gas from their surrounding galaxies, which keeps them growing in size.
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- Supermassive blackholes are giants at the center of galaxies. Small blackholes populate the universe, but supermassive blackholes dominate the universe. These enormous blackholes are millions or even billions of times as massive as the sun, but are about the same size in diameter. Such blackholes are thought to lie at the center of every galaxy, including the Milky Way.
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- Scientists aren't certain how such large blackholes spawn. Once these giants have formed, they gather mass from the dust and gas around them, material that is plentiful in the center of galaxies, allowing them to grow to even more enormous sizes.
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- Supermassive blackholes may be the result of hundreds or thousands of tiny blackholes that merge together. Large gas clouds could also be responsible, collapsing together and rapidly accreting mass.
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- A third option is the collapse of a stellar cluster, a group of stars all falling together.
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- A fourth option, supermassive blackholes could arise from large clusters of “dark matter‘. This is a substance that we can observe through its gravitational effect on other objects; however, we don't know what dark matter is composed of because it does not emit light and cannot be directly observed.
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- Intermediate blackholes are stuck in the middle. Scientists once thought that blackholes came in only small and large sizes, but recent research has revealed the possibility that midsize, or intermediate, blackholes could exist.
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- Such intermediate blackholes could form when stars in a cluster collide in a chain reaction. Several of these blackholes forming in the same region could then eventually fall together in the center of a galaxy and create a supermassive black hole.
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- In 2014, astronomers found what appeared to be an intermediate-mass blackhole in the arm of a spiral galaxy. Research, from 2018, suggested that these intermediate blackholls may exist in the heart of dwarf galaxies.
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- Observations of 10 such galaxies revealed X-ray activity that is common in blackholes and suggesting the presence of blackholes of from 36,000 to 316,000 solar masses.
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- This information came from the “Sloan Digital Sky Survey“, which examines about
1 million galaxies and can detect the kind of light often observed coming from blackholes that are picking up nearby debris.
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- Black holes have three "layers": the outer and inner “event horizon“, and the “singularity‘.
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- The “event horizon” of a blackhole is the boundary around the mouth of the blackhole, past which light cannot escape. Once a particle crosses the event horizon, it cannot leave. Gravity is constant across this event horizon.
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- The inner region of a blackhole, where the object's mass lies, is known as its “singularity“, the single point in space-time where the mass of the blackhole is concentrated.
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- Scientists can't see blackholes the way they can see stars and other objects in space. They must rely on detecting the radiation blackholes emit as dust and gas are drawn into the dense creatures.
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- But supermassive blackholes, lying in the center of a galaxy, may become shrouded by the thick dust and gas around them, which can block the telltale emissions.
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- Sometimes, as matter is drawn toward a blackhole, it ricochets off the event horizon and is hurled outward, rather than being tugged into the maw. Bright jets of material traveling at near-relativistic speeds are created. Although the blackhole remains unseen, these powerful jets can be viewed from great distances.
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- The Event Horizon Telescope's image of a blackhole in M87 (released in 2019) was an extraordinary effort, requiring two years of research even after the images were taken. That's because the collaboration of telescopes, which stretches across many observatories worldwide, produces an astounding amount of data that is too large to transfer by internet.
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- With time, researchers expect to image other blackholes and build up a repository of what the objects look like. The next target is likely Sagittarius A*, which is the blackhole in the center of our own Milky Way galaxy.
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- Sagittarius A* is intriguing because it is quieter than expected, which may be due to magnetic fields smothering its activity. A cool gas halo surrounds Sagittarius A*, which gives unprecedented insight into what the environment around a blackhole looks like.
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- The Event Horizon Telescope, a planet-scale array of eight ground-based radio telescopes forged through international collaboration, captured an image of the supermassive blackhole in the center of the galaxy M87 and its shadow.
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- In 2015, astronomers using the “Laser Interferometer Gravitational-Wave Observatory” (LIGO) detected gravitational waves from merging stellar blackholes.
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- There are two theories on how binary blackholes form. The first suggests that the two blackholes in a binary form at about the same time, from two stars that were born together and died explosively at about the same time. The companion stars would have had the same spin orientation as one another, so the two black holes left behind would as well.
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- Under the second model, blackholes in a stellar cluster sink to the center of the cluster and pair up. These companions would have random spin orientations compared to one another. LIGO's observations of companion blackholes with different spin orientations provide stronger evidence for this formation theory.
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------------------- Here are some more weird facts about blackholes:
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- If you fell into a blackhole, theory has long suggested that gravity would stretch you out like spaghetti, though your death would come before you reached the singularity.
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- The quantum effects would cause the event horizon to act much like a wall of fire, which would instantly burn you to death.
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- Blackholes don't suck. Suction is caused by pulling something into a vacuum, which the massive blackhole definitely is not. Instead, objects fall into them just as they fall toward anything that exerts gravity, like the Earth.
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- The first object considered to be a blackhole is Cygnus X-1. Cygnus X-1 was the subject of a 1974 friendly wager between Stephen Hawking and fellow physicist Kip Thorne, with Hawking betting that the source was not a blackhole. In 1990, Hawking conceded defeat.
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- Miniature blackholes may have formed immediately after the Big Bang. Rapidly expanding space may have squeezed some regions into tiny, dense blackholes less massive than the sun.
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- If a star passes too close to a blackhole, the star can be torn apart.
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- Astronomers estimate that the Milky Way has anywhere from 10 million to 1 billion stellar blackholes, with masses roughly three times that of the sun
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- August 15, 2021 BLACKHOLES - the more we learn the less we know? 3247
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