- 2935 - GRAVITY WAVES - whole new astronomy. Whatever the future may hold for gravitational-wave science, one thing is for certain: Yet another confirmation of Einstein’s general theory of relativity, the detection of gravitational waves, has finally provided an entirely new way for astronomers to explore the universe.
------------------ 2935 - GRAVITY WAVES - whole new astronomy
- It was over 100 years ago that Albert Einstein published his “general theory of relativity“, laying the foundation for our modern view of gravity. Einstein proposed that massive objects can warp the fabric of space-time, with the heaviest, densest objects, such as stars and black holes, creating deep “gravity wells” in the fabric.
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- Einstein realized that when light passes through a gravity well, the photons' paths likewise get deformed. Gravity defines “straight lines”, and shortest paths through space.
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- Einstein’s theory also predicted that when two very massive objects spiral toward each other before colliding, their individual gravity wells interact. And as two whirlpools rotating around each other in an ocean would send out strong ripples in the water, two inspiraling cosmic objects send out ripples across space-time, known as “gravitational waves“.
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- Despite Einstein’s 1906 prediction of the existence of gravitational waves, it wasn’t until 1974 that two astronomers using the Arecibo Observatory in Puerto Rico found the first indirect evidence of gravitational waves.
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- After that it was another forty years before scientists found direct proof of gravity waves. On September 14, 2015, the “Laser Interferometer Gravitational-wave Observatory” (LIGO) detectors in Hanford, Washington, and Livingston, Louisiana, both captured the telltale “chirp” of gravitational-waves, generated when two black holes collided some 1.3 billion light-years away. (See other Reviews to learn about this event)
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- With this first detection of gravitational waves, astronomers proved the existence of an entirely new tool that they could use to explore the universe, ushering in an era of multi-messenger astronomy that will help answer the biggest questions in astrophysics and cosmology. Wow, like we have a whole new telescope on the universe.
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- Both LIGO and its sister facility, Virgo, take advantage of the fact that, as gravitational waves pass through Earth, they slightly expand and contract the space-time we live in. You probably did not notice it.
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- Thankfully, these passing gravitational waves are imperceptible to our human bodies, but the detectors of LIGO and Virgo are sensitive enough to pick them up. In fact, the gravitational waves from LIGO’s first detection only scrunched space-time by a distance of about 1/1,000 the size of an atomic nucleus.
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- Here is how LIGO was able to detect such a small fluctuation? The LIGO facility in Livingston, Louisiana, and its twin in Hanford, Washington, each have two interferometer arms inside tunnels that are 2.5 miles long.
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- This interferometer is a device, better known as a Michelson interferometer, which has a unique L-shape. For LIGO and Virgo, this familiar shape was blown up to a much larger scale than ever seen before.
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- Each of LIGO’s arms is 2.5 miles long. Each of Virgo’s arms is just under 2 miles long. Every one of these arms contains two mirrors one at the beginning of the arm, and one at the very end.
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- In LIGO’s case, once a beam splitter sends light into each perpendicular arm, it gets bounced back and forth between mirrors some 300 times, traveling a total distance of nearly 750 miles . This extended travel path, combined with the resulting laser light buildup, increases the sensitivity with which LIGO and Virgo can detect passing gravitational waves.
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- After the split light repeatedly bounces back and forth within each arm, the two beams then pass back through the “beam splitter” into a ‘photo detector‘. And if a gravitational wave passes through while the two light pulses are bouncing back and forth within each perpendicular arm, the space-time within the detector arms would be disproportionately distorted ecause the two arms are perpendicular and detect the waves in different phases.
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- The light bouncing around in one arm would travel a slightly different distance than the light bouncing around in the other arm, and LIGO and Virgo can pick up the tiny difference.
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- By making laser light travel up and down the arms and interfere with itself, scientists can deduce minute changes in the light’s path from a gravitational-wave encounter.
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- The initial LIGO facilities operated from 2002 to 2010 with no gravitational-wave detections. After 2010, LIGO underwent several years of upgrades and began observing again as Advanced LIGO in 2015. Virgo underwent similar upgrades beginning in 2011.
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- Since LIGO’s first detection in 2015, the Advanced LIGO and Virgo collaboration have detected some 50 confirmed gravitational-wave events, as well as many more candidate events. The observatories’ first run started in September 2015 and ran through January 2016. The second observing run went from November 2016 to August 2017.
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- And the third run was split into two parts, with the first half stretching from April 2019 to September 2019. The second half began in November 2019, but its remaining timeline is currently uncertain due to the COVID-19 pandemic. The COVID lockdown in California is what gives me the time to write this review.
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- Scientists have spent their time between each run performing routine maintenance and upgrading the detectors. And the most recent enhancement before the third run promised near-daily detections of gravitational-wave events. Despite the current COVID shutdown, LIGO/Virgo collaborations have already detected over 50 new merger candidates during this latest run, fulfilling that promise.
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- Besides proving that we can detect previously inaccessible ripples in the fabric of space-time, the first LIGO/Virgo run determined that at least three signals came from binary blackhole mergers. In August 2017, the collaboration detected the first gravitational waves produced by colliding “neutron stars“.
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- Over the past few years, LIGO and Virgo have steadily spotted more and more binary blackhole mergers. And in late 2019, they picked up a possible merger between a blackhole and a neutron star, an event that has never before been witnessed.
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- This year ,2020, the collaboration observed its second neutron star collision, as well as another potential first for the group: a light flare thought to be associated with the gravitational-wave detection of a binary black hole merger.
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- The pair of stellar-mass blackholes were likely orbiting their galaxy’s central supermassive black hole, which is also shrouded by a swirling disk of gas and dust. Once the binary black holes merged, they started careening through the supermassive blackhole’s disk. And as it plowed through the gas, the surrounding material flared up.
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- The timing, size, and location of this flare was spectacular. The collaboration has even captured the merger of a blackhole with a second confusing object, one that falls firmly in the observational “mass gap” separating a large neutron star from a small black hole.
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- The heaviest known neutron star is 2.5 times the mass of the Sun, while the lightest known black hole is about 5 solar masses. The strange object in this merger apparently has a mass of 2.6 solar masses.
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- What’s Next for Gravitational Waves? In 2024, LIGO will get yet another upgrade that will almost double its sensitivity, as well as lead to a seven-fold increase in the volume of space it can monitor. Later in the decade, scientists and engineers plan to kick off the third-generation of called “LIGO Voyager“.
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- Many other countries around the globe are also joining the international hunt for gravitational waves. India hopes to join the Advanced LIGO collaboration by the mid-2020s. By the mid-2030s, the European Space Agency and NASA hope to launch the Laser Interferometer Space Antenna (LISA), the world’s first space-based gravitational wave detector.
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- LISA would open the door for detecting a much more varied sampling of gravitational-wave sources than LIGO and Virgo can currently pick up. The European Union is also exploring the possibility of an underground gravitational-wave detector known as the “Einstein Telescope“.
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- Gravitational-wave science is yet another confirmation of Einstein’s general theory of relativity. The detection of gravitational waves, has provided an entirely new way for astronomers to explore the universe. A whole new generation of telescopes exploring the universe.
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- December 11, 2020 GRAVITY WAVES 2935
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