- 3238 - BLACKHOLES - act as gravity lenses? If there were a supernova, a super powerful explosion of a dying star, behind the blackhole, Astronomers would see that supernova go off multiple times. Each image would be delayed by a certain amount, depending on how many times it orbited the blackhole, allowing researchers to compare their theories with what‘s really happening.
------------------ 3227 - BLACKHOLES - act as gravity lenses?
- In two galaxies about 900 million light-years away, two blackholes each gobbled up their neutron star companions, triggering gravitational waves that finally hit Earth in January, 2020.
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- The two events were detected just 10 days apart. They mark the first-ever detection of a blackhole merging with a neutron star.
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- Gravitational waves have allowed us to detect collisions of pairs of blackholes and pairs of neutron stars, but the mixed collision of a blackhole with a neutron star has been a new discovery.
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- Two events in ten days, the astronomers observed the two new gravitational-wave events, GW200105 and GW200115, on January 5, 2020, and January 15, 2020, during the second half of the LIGO and Virgo detectors third observing run.
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- All three large detectors (both LIGO instruments and the Virgo instrument) detected the merger of a 6-solar mass blackhole with a 1.5-solar mass neutron star, roughly 1 billion light-years from Earth. With observations of the three widely separated detectors on Earth, the direction to the waves' origin can be determined to a part of the sky equivalent to the area covered by 2,900 full moons.
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- Just 10 days earlier, LIGO detected a strong signal using just one detector while the other was temporarily offline. While Virgo also was observing, the signal was too quiet in its data for Virgo to help detect it. From the gravitational waves, the astronomers inferred that the signal was caused by a 9-solar mass blackhole colliding with a 1.9-solar mass compact object, which they ultimately concluded was a neutron star. This merger happened at a distance of about 900 million light-years from Earth.
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- Although the signal was too quiet for Virgo to confirm its detection, its data did help narrow down the source's potential location to about 17% of the entire sky, which is equivalent to the area covered by 34,000 full moons.
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- While it is unclear where these binary systems form, astronomers identified three likely cosmic origins: stellar binary systems, dense stellar environments including young star clusters, and the centers of galaxies.
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- Blackholes are regions in space-time where gravity's pull is so powerful that not even light can escape its grasp. However, while light cannot escape a blackhole, its extreme gravity warps space around it, which allows light to "echo," bending around the back of the object. Astronomers have, for the first time, observed the light from behind a blackhole.
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- XMM-Newton and NASA's NuSTAR space telescopes have observed the light from behind a blackhole that's 10 million times more massive than our sun and lies 800 million light-years away in the spiral galaxy.
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- This study began with the researchers' desire to expand our understanding of blackhole coronas, which are the source of the X-ray light that often radiates from the vicinity of these objects. Bright flares of X-ray light are emitted by gas that falls into blackholes from their accretion disks, the disks of dust and gas that surround and "feed" these objects.
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- The team spotted an X-ray flare that was so bright that some of the light reflected on the gas falling back into the blackhole. When that reflected light was bent around the back of the blackhole by the object's extreme gravity, the team was able to spot it using space telescopes.
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- The astronomers also took note of how the X-ray light changed color as it bent and moved around the back of the blackhole. They hope to create a 3D map of the blackhole's surroundings. They also hope to better understand blackhole coronas and explore how the corona of a blackhole is capable of producing these bright X-ray flares.
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- Imagine a galaxy reflected in a fun house hall of mirrors. You'd see the galaxy, repeated again and again, with each image becoming more grotesque and distorted. That's how the universe looks near the event horizon of a blackhole, one of the most warped places in the universe.
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- If you were to place a galaxy behind the blackhole and then look off to the side, you'd see a distorted image of the galaxy. That's because some light from the galaxy would barely graze the edges of the blackhole, without falling in.
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- Because of the blackhole's extreme gravity, such light would get bent toward your line of sight. Strangely, the galaxy would appear to be far away from the blackhole, not directly behind it.
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- The gravity around blackholes is so intense, and space-time is so incredibly warped, that at a certain distance, light itself can orbit the blackholes. Some of the light from a background galaxy even gets trapped, looping forever, like a satellite.
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- However, the light would need to come the exact right distance from the blackhole to get trapped in an orbit. It can also hit the blackhole at an angle that allows it to make one ,or many, loops before eventually escaping.
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- Looking at the edge of the blackhole, your eyes would see one image of the background galaxy from its deflected light. Then, you would see a second image of the galaxy from light rays that managed to make a single orbit before escaping and then again from light rays that made two orbits, and then three and so on.
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- Physicists have known through simple estimates that each image is e^2𝜋 times closer than the last. In that formula, e is the base of the natural logarithm, and it equals roughly 2.7182. Pi is another irrational number that is about 3.14159, so e^2𝜋 comes out to a number very close to 500. That means each repetition of the same background object is about 500 times closer to the edge of the blackhole than the last.
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- Light from galaxies in the background of a blackhole circle the gravitational monster, creating endless "mirror" images of that universe. While physicists could get that simple result using pen-and-paper calculations, they weren't sure if that special factor of 500 would be completely accurate if they looked closely at the behavior of the complex space-time curvature near black holes.
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- Because the rotation of the blackhole twists space-time around it, each successive image of the background object appears flatter. Thus, the farthest image will appear relatively undistorted, while the closest image may be completely unrecognizable.
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- Technically, there are an infinite number of repeated images of background objects, each one closer to the event horizon. But those few that can be detected would provide a powerful perspective into the heart of general relativity, the mathematical theory that describes gravity.
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- In 2019, the Event Horizon Telescope, a network of dishes spanning the entire globe, generated the first image of the "shadow" of a blackhole cast on its surrounding gas and dust. That telescope wasn't powerful enough to capture the multiple fun-house-mirror images of background objects, but future telescopes could.
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- A supernova explosion of a dying star, behind the blackhole Would allow astronomers to see that supernova go off multiple times. Each image would be delayed by a certain amount, depending on how many times it orbited the blackhole. Researchers could then compare their theories with reality.
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- Astronomers just have to be willing to stare into the void long enough until the right thing happens.
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- July 29, 2021 BLACKHOLES - act as gravity lenses? 3238
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