- 3733 - BLACKHOLES - what have we learned? Black holes have three "layers": the outer and inner event horizon, and the singularity. The event horizon of a black hole is the boundary around the mouth of the black hole, past which light cannot escape. Once a particle crosses the event horizon, it cannot leave. Gravity is constant across the event horizon.
--------------------- 3733 - BLACKHOLES - what have we learned?
- A black hole about 10 times more massive than our sun lurks just 1,560 light-years from Earth. That is twice as close as the previous proximity black hole.
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- The stellar-mass blackhole, “Gaia BH1“, resides in a binary system whose other member is a sunlike star. That star is about as far from its companion black hole as Earth is from the sun.
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- Astronomers think that our Milky Way galaxy harbors about 100 million of these stellar-mass black holes, light-gobbling objects that are five to 100 times more massive than the sun.
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- Their small size makes these bodies relatively hard to detect, however, especially by telescope. Gravitational-wave detectors have had more success recently, finding evidence of mergers involving these objects. The ones that scientists do see tend to be "X-ray binaries," black holes that pull material from a companion star into an accretion disk around themselves. This fast-orbiting dust and gas emits X-rays, high-energy light that some powerful telescopes can observe.
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- Not all stellar-mass black holes that inhabit binary systems are actively feeding, however. Finding these dormant objects is even more difficult and requires different strategies.
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- The researchers pored over data gathered by the European Space Agency's (ESA) “Gaia” spacecraft, which is precisely mapping the positions, speeds and trajectories of about 2 billion Milky Way stars. One of those stars is the companion to Gaia BH1. Its motion displays tiny irregularities, an indication that something massive and unseen is tugging on it gravitationally.
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- The Gaia measurements suggested that a black hole could be that tugger. Astronomers studied the star with a number of ground-based instruments, including the Gemini North and Keck 1 telescopes in Hawaii and the Magellan Clay and MPG/ESO telescopes in Chile.
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- They were able to take the system's measure in detail. The unseen object contains the mass of 10 suns and orbits the system's center of mass about once every 186 Earth days.
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- The binary contains a normal star and at least one dormant blackhole. If the unseen object in Gaia BH1 were a star it would be far brighter than its companion, and therefore easier to see. But none of the team's observations revealed a hint of a second star in the system.
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- The Gaia BH1 system is intriguing, and not just because it's relatively close to us. The Milky Way's spiral disc is about 100,000 light-years wide. Gaia BH1's mass indicates that the star that died and gave rise to it must have been at least 20 solar masses. Such giants live for just a few million years, and they puff up tremendously.
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- Modeling work suggests that such puffing would likely have destroyed the companion before it had a chance to evolve into a sunlike star if the two were born at the same time. Or, if it survived, it should have ended up on a much tighter orbit than the one it currently occupies.
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- Black holes are some of the strangest and most fascinating objects in space. They're extremely dense, with such strong gravitational attraction that not even light can escape their grasp.
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- The Milky Way could contain over 100 million black holes, though detecting them is very difficult. At the heart of the Milky Way lies a supermassive blackhole, “Sagittarius A*”. The colossal structure is about 4,000,000 times the mass of the sun and lies approximately 26,000 light-years away from Earth.
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- The first image of a black hole was captured in 2019 by the Event Horizon Telescope (EHT) collaboration. The striking photo of the black hole at the center of the M87 galaxy was 55 million light-years.
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- Albert Einstein first predicted the existence of black holes in 1916, with his general theory of relativity. The term "black hole" was coined many years later in 1967 by American astronomer John Wheeler.
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- After decades of black holes being known only as theoretical objects the first black hole ever discovered was Cygnus X-1, located within the Milky Way in the constellation of Cygnus, the Swan.
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- Astronomers saw the first signs of the black hole in 1964 when a sounding rocket detected celestial sources of X-rays. In 1971, astronomers determined that the X-rays were coming from a bright blue star orbiting a strange dark object. It was suggested that the detected X-rays were a result of stellar material being stripped away from the bright star and "gobbled" up by the dark object, an all-consuming black hole.
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- According to the “Space Telescope Science Institute” (STScI) approximately one out of every thousand stars is massive enough to become a black hole. Since the Milky Way contains over 100 billion stars, our home galaxy must harbor some 100 million black holes.
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- Though detecting black holes is a difficult task and estimates from NASA suggest there could be as many as 10 million to a billion stellar black holes in the Milky Way.
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- The closest black hole to Earth is dubbed "The Unicorn" and is situated approximately 1,500 light-years away. The nickname has a double meaning. Not only does the black hole candidate reside in the constellation Monoceros ("the unicorn"), its incredibly low mass, about three times that of the sun, makes it nearly “one of a kind“.
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- In 2019 the “Event Horizon Telescope” (EHT) collaboration released the first image ever recorded of a black hole. The EHT saw the black hole in the center of galaxy M87 while the telescope was examining the event horizon or the area past which nothing can escape from a black hole. The image maps the sudden loss of photons. It also opens up a whole new area of research in black holes, now that astronomers know what a black hole looks like.
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- In 2021, astronomers revealed a new view of the giant black hole at the center of M87, showing what the colossal structure looks like in polarized light. As polarized light waves have a different orientation and brightness compared to unpolarized light, the new image shows the black hole in even more detail. Polarization is a signature of magnetic fields and the image makes it clear that the black hole's ring is magnetized. Orange glowing ring with lines of light within surrounding a black circle.
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- The inner region of a black hole, where the object's mass lies, is known as its “singularity‘, the single point in space-time where the mass of the black hole is concentrated.
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- Scientists can't see black holes the way they can see stars and other objects in space. Instead, astronomers must rely on detecting the radiation black holes emit as dust and gas are drawn into the dense creatures. But supermassive black holes, 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 black hole, it ricochets off the event horizon and is hurled outward, rather than being tugged into the center. Bright jets of material traveling at near-relativistic speeds are created. Although the black hole remains unseen, these powerful jets can be viewed from great distances.
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- The EHT's image of a black hole 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 via the internet.
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- With time, researchers expect to image other black holes and build up a repository of what the objects look like. The next target is likely Sagittarius A*, which is the black hole in the center of our own Milky Way galaxy. Sagittarius A* is intriguing because it is quieter than expected, which may be due to magnetic fields smothering its activity.
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- Another study in 2019 showed that a cool gas halo surrounds Sagittarius A*, which gives unprecedented insight into what the environment around a black hole looks like.
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- Astronomers have identified three types of black holes: stellar black holes, supermassive black holes and intermediate black holes. Stellar Blackholes are small but deadly.
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- When a star burns through the last of its fuel, the object may collapse, or fall into itself. For smaller stars, those up to about three times the sun's mass, the new core will become a neutron star or a white dwarf. But when a larger star collapses, it continues to compress and creates a stellar black hole.
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- Black holes 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 a crazy amount of gravitational force pulling on objects around the object. Stellar black holes then consume the dust and gas from their surrounding galaxies, which keeps them growing in size.
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- Small black holes populate the universe, but supermassive black holes, dominate. These enormous black holes are millions or even billions of times as massive as the sun but are about the same size in diameter. Such black holes are thought to lie at the center of pretty much every galaxy, including the Milky Way.
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- Scientists aren't certain how such large black holes 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 black holes may be the result of hundreds or thousands of tiny black holes that merge. Large gas clouds could also be responsible, collapsing together and rapidly accreting mass. A third option is the collapse of a stellar cluster, a group of stars all falling together.
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- Fourth, supermassive black holes 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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- Scientists once thought that black holes came in only small and large sizes, but research has revealed the possibility that midsize, or intermediate, black holes (IMBHs) could exist. Such bodies could form when stars in a cluster collide in a chain reaction. Several of these IMBHs 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 black hole in the arm of a spiral galaxy. And in 2021 astronomers took advantage of an ancient gamma-ray burst to detect one.
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- Research suggested that these IMBHs may exist in the heart of dwarf galaxies (or very small galaxies). Observations of 10 such galaxies (five of which were previously unknown to science before this latest survey) revealed X-ray activity suggesting the presence of black holes of from 36,000 to 316,000 solar masses. The 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 black holes that are picking up nearby debris.
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- In 2015, astronomers using the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves from merging stellar black holes. LIGO's observations provide insights into the direction a black hole spins. As two black holes spiral around one another, they can spin in the same direction or the opposite direction.
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- There are two theories on how binary black holes form. The first suggests that the two black holes 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, black holes 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 according to LIGO Scientific Collaboration. LIGO's observations of companion black holes with different spin orientations provide stronger evidence for this formation theory.
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- If you fell into a black hole, theory has long suggested that gravity would stretch you out like spaghetti, though your death would come before you reached the singularity. But a 2012 study suggested that 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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- Black holes don't suck. Suction is caused by pulling something into a vacuum, which the massive black hole 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 black hole 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 black hole. In 1990, Hawking conceded defeat.
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- Miniature black holes may have formed immediately after the Big Bang. Rapidly expanding space may have squeezed some regions into tiny, dense black holes less massive than the sun.
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- If a star passes too close to a black hole, the star can be torn apart. Astronomers estimate that the Milky Way has anywhere from 10 million to 1 billion stellar black holes, with masses roughly three times that of the sun.
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- November 6, 2022 BLACKHOLES - what have we learned? 3733
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