- 3338 - GRAVITY WAVES - detecting blackhole mergers? Gravity Waves are like light waves. They travel at the speed of light , 186,000 miles per second. Astronomers are just beginning to detect these waves. We had the theories but now we have physical evidence that large rotating masses create gravity waves.
-------------- 3338 - GRAVITY WAVES - detecting blackhole mergers?
- Astronomers have for the first time detected a collision between two blackholes of substantially different masses opening up a new vista on astrophysics and on the physics of gravity.
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- The event offers the first unmistakable evidence from these faint space-time ripples that at least one blackhole was spinning before merging, giving astronomers rare insight into a key property of these blackholes.
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- This exceptional event took place between blackholes with roughly equal masses. The collision was detected last year, 2020. The Laser Interferometer Gravitational-Wave Observatory (LIGO) detected the event, GW190412.
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- LIGO made the first discovery of gravitational waves in September 2015, detecting the space-time ripples from two merging blackholes. LIGO, later joined by “Virgo“, subsequently made ten more detections in two observing runs that ended in 2017, nine more blackhole mergers and one collision of two neutron stars, which helped to explain the origin of the Universe’s heavy chemical elements.
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- The third and most recent run started April 2019 and ended on March 2020, with a month-long break in October. Greatly improved sensitivity enabled the network to accumulate around 50 more ‘candidate events’ at a rate of roughly one per week.
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- A second merger between two neutron stars, dubbed GW190425, that was revealed in January, 2021
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- The latest event is unique. One of the two blackholes that merged had an estimated mass of around 8 solar masses, and the other was more than 3 times larger, at 31 solar masses. This imbalance made the larger blackhole distort the space around it, so the other’s trajectory deviated from a perfect spiral.
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- This spiral could be seen in the resulting gravitational waves, which were created as the objects spiralled into each other. All the other merger events that have been unveiled produced a wave that forms a similar ‘chirp’ shape, which increases in both intensity and frequency up to the moment of collision.
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- GW190412 was different, its intensity didn’t simply rise as in a chirp. Researchers were able to use this data to discern the ‘spin’ of blackholes. We know with confidence that this heavier object had to be spinning. The richer information in asymmetrical mergers helps to measure an event’s distance from the Milky Way with better precision.
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- Astronomers observed 39 cosmic events that released gravitational waves over a
6-month period in 2019, a rate of more than one per week. These observatories that detect these ripples have dramatically increased their sensitivity since the first identification was made in 2015.
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- Gravitational waves are ripples in the fabric of space-time that are released by accelerating masses, in particular when two massive objects spiral into each other and merge. Their detailed properties provide numerous tests of Albert Einstein’s general theory of relativity, including some of the strongest evidence to date for the existence of blackholes.
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- The detectors have also caught sight of a handful of collisions between two neutron stars and at least one merger of one neutron star and one blackhole. Mergers that involve neutron stars are especially interesting to astrophysicists because they are expected to release ordinary light as well as gravitational waves, which was confirmed in a merger of neutron stars seen in August 2017.
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- One surprising discovery is in the masses of the blackholes involved in the mergers. Astrophysicists expected a sharp cut-off, with no black holes weighing more than 45 times as much as the Sun. The catalogue includes three events with outlier masses, including one announced in September with a blackhole of 85 solar masses.
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- The blackhole mergers happening in an average galaxy appears to have peaked around eight billion years ago, following a period in which stars were forming. The mergers also provides information on how the blackholes spin, which holds the key to understanding how the objects came to orbit each other before they merged.
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- It shows that, in some binary systems, the two blackholes have misaligned axes of rotation, which would imply that they formed separately. But many other binaries appear to have roughly aligned axes of rotation, which is what astrophysicists expect when the two blackholes began their lives as a binary star system.
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- The latest 2021 catalogue of cosmic collisions, brings the total number of detections to 90. The new crop of 35 events includes one featuring the lightest neutron star ever seen, as well as two clashes involving these surprisingly large blackholes.
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- From the shape and frequency of the waves produced by mergers, researchers can calculate the details of a host of features for the objects involved, including their masses and their distance from Earth. The latest 35 events varied in distance from roughly 245 million to more than 2.2 billion parsecs (800 million to more than 7 billion light years) away.
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- Two events involved blackholes with masses more than 60 times that of the Sun. For astrophysicists, the mere existence of these blackholes is a problem for them. Typically, blackholes are thought to form from the collapse of a very massive star at the end of its life. But prevailing theories predict that some dying stars should explode rather than collapse, which should leave a dearth of blackholes in the range of roughly 65 to 120 solar masses.
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- A merger that challenged that assumption because it involved a blackhole of 85 solar masses.
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- The observatories spotted another intriguing event on December 19, 2019, involving a blackhole 30 times the mass of the Sun swallowing a minuscule neutron star. At just 1.17 solar masses, it is the one of the lightest known neutron stars and the lowest-mass object ever detected by LIGO–Virgo.
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- The bounty of blackhole mergers is getting large enough for researchers to be able to see patterns emerging. The most conspicuous of these is that blackhole mergers tend to happen more often in galaxies that are farther away from us in space and time.
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- The blackhole mergers have been getting less common as the Universe matures. There were more stars being created earlier in the Universe, and therefore it is natural to expect that there would be more blackholes created, and therefore more blackhole mergers.
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- LIGO and Virgo shut down on March, 2020, earlier than planned owing to the COVID-19 pandemic and have since been undergoing major upgrades. They are expected to reopen in late 2022 for another run of observations, which together with “KAGRA” could double the bounty.
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- Researchers expect that once they have hundreds of events to compare, they will be able to see trends that point to the origins and history of the binary systems involved in the mergers, as well as the history of the Universe itself.
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- Astronomers around the world are still hoping for a repeat of the August 2017 merger of two neutron stars, which is the only gravitational-wave event so far to have also been seen by conventional observatories.
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- November 10, 2021 GRAVITY WAVES - detecting blackhole mergers? 3338
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