by Group 7
LIGO
LIGO stands for "Laser Interferometer Gravitational-wave Observatory". It is the world's largest gravitational wave observatory and a marvel of precision engineering. Comprising two enormous laser interferometers located 3000 kilometers apart, LIGO exploits the physical properties of light and of space itself to detect and understand the origins of gravitational waves (GW). LIGO (and other detectors like it) is unlike any other observatory on Earth. Ask someone to draw a picture of an observatory and odds are they will draw a gleaming white telescope dome perched on a mountain-top. As a gravitational wave observatory, LIGO bears no resemblance to this whatsoever, as the aerial photo of the LIGO Livingston interferometer at right clearly illustrates.
More than an observatory, LIGO is a remarkable physics experiment on the scale and complexity of some of the world's giant particle accelerators and nuclear physics laboratories. Though its mission is to detect gravitational waves from some of the most violent and energetic processes in the Universe, the data LIGO collects may have far-reaching effects on many areas of physics including gravitation, relativity, astrophysics, cosmology, particle physics, and nuclear physics. Nevertheless, since the "O" in LIGO stands for "observatory", below we describe how it differs from the observatories that most people envision. Three things distinguish LIGO from a stereotypical astronomical observatory: LIGO is blind, it is not round and cannot point at a particular part of the sky, and it is rare for a single detector to make a discovery on its own.
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LIGO is blind. Unlike optical or radio telescopes, LIGO does not see electromagnetic radiation (e.g., visible light, radio waves, microwaves). It doesn't have to because gravitational waves are not part of the electromagnetic spectrum. They are a completely different phenomenon altogether (though in some cases, we do expect to see some form of EM radiation coming from GW sources). In fact, electromagnetic radiation is so unimportant to LIGO that its detector components are completely isolated and sheltered from the outside world.
LIGO isn't round and can't point to specific locations in space. Since LIGO doesn’t need to collect light from stars, it doesn't need to be round or dish-shaped like optical telescope mirrors or radio telescope dishes, both of which need such structures to focus EM radiation onto a detector. Each LIGO detector consists of two arms, each 4km (2.5 mi.) long, comprising 1.2m-wide steel vacuum tubes arranged in an "L" shape, and covered by a 10-foot wide, 12-foot tall concrete shelter that protects the tubes from the environment. LIGO can also detect gravitational waves coming from any direction.
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A single LIGO detector could not initially confirm gravitational waves on its own. The initial discovery of gravitational waves required that similar signals arrive quasi-simultaneously in multiple detectors. Happily, GW150914 fulfilled that requirement, and we have now seen many signals which appeared in the two LIGO detectors and also in Italy's Virgo detector. Now that we understand both our signal sources and our instruments better, some detections can be confidently made with a significant signal in just one detector – a great step forward for our field. However, to help electromagnetic observers find a possible light source associated with our detections, we must have multiple detectors – ideally 3 or more – to localize the signal in the sky. This was the case for the first binary neutron star signal, GW170817
LIGO Mission
LIGO’s mission is to open the field of gravitational-wave astrophysics through the direct detection of gravitational waves. LIGO detectors use laser interferometry to measure the distortions in space-time occurring between stationary, hanging masses caused by passing gravitational waves. LIGO is a national facility for gravitational-wave research, providing opportunities for the broader scientific community to participate in detector development, observations and data analysis.
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LIGO is funded by the U.S. National Science Foundation and operated by the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT). LIGO's advanced detectors also received financial support for their construction from Australia, Germany, and the United Kingdom. LIGO detectors are available for use by members of the LIGO Scientific Collaboration (LSC), comprising researchers in partner institutions around the world.
LIGO Facilities
Although it is considered one observatory, LIGO comprises four facilities across the United States: two gravitational wave detectors, the interferometers, and two university research centers. The interferometers are located in fairly isolated areas of Washington, LIGO Hanford, and Louisiana, LIGO Livingston, and separated by 3,002 km . The two primary research centers are located at the California Institute of Technology (Caltech) in Pasadena, California, and the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts. The detector sites in Hanford and Livingston are home to the interferometers that make LIGO an "observatory". About 40 people work at each site, including engineers, technicians, and scientists who keep the instruments operating, and who monitor vacuum and computer systems. Administrative and business staff are also present, as are education and public outreach professionals who conduct public tours, facilitate field trips for local students, and arrange periodic public events.
The LIGO “observatory” is made up of two identical and widely separated interferometers situated in sparsely populated, out-of-the-way places: LIGO Hanford in southeastern Washington State in an arid shrub-steppe region crisscrossed by hundreds of layers of ancient lava flows; and LIGO Livingston, 3002 km away in a vast, humid, loblolly pine forest east of Baton Rouge, Louisiana. LIGO was designed with two detectors so far apart for good reason. LIGO’s detectors are so sensitive that they can 'feel' the tiniest vibrations on the Earth from sources very nearby to sources hundreds or thousands of miles away. Things like earthquakes, acoustic noise (e.g., trucks driving on nearby roads, farmers plowing fields, things that people can hear and feel), and even internal laser fluctuations can cause disturbances that can mask or mimic a gravitational wave signal in each interferometer. If the instruments were located close together, they would detect the same vibrations at the same times--both from Earth-sources and from gravitational waves and it would be nearly impossible to distinguish a vibration from a gravitational wave from the local noise.
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Facilities located far apart, however, will not feel the same local vibrations but they will feel a gravitational wave vibration at (virtually) the same time. By comparing data from both sites, scientists can ignore the vibrations that differ between the sites and look only for identical signals that occurred at the same time at both locations. This is why two or more detectors are essential. One acts as a noise filter for the other, leaving only signals from gravitational waves as the stand-outs. Without working together in this way to confirm each other's detections, gravitational waves could never be positively detected with an interferometer like LIGO. LIGO’s collaboration with VIRGO adds a third interferometer to the mix thus significantly increasing the confidence that a detected signal is real.
The size of the interferometers (with arms 4 km (2.5 mi.) long) and LIGO's sensitivity to vibration presented significant challenges to LIGO designers when selecting an appropriate site for the instruments. For one, there are few places left where such a large portion of land can be dedicated to a massive science experiment requiring a lot of empty space around it and yet have access to the infrastructure it requires to run it. And secondly, just as astronomical telescopes are built far from city lights that pollute the night sky with an obscuring fog ("light pollution"), gravitational-wave observatories need to be isolated from the vibrations of human activity. Such vibrations can drown out the telltale signals of gravitational waves in a sea of noise, just as light pollution drowns out the fragile light of distant stars. In the end, the desert of eastern Washington, and the forests of Louisiana were chosen as the locations of LIGO's two detectors.
LIGO Detectors
Construction of LIGO's original gravitational wave detectors was completed in 1999. The first search for gravitational waves began in 2002 and concluded in 2010 during which time no gravitational waves were detected. Nevertheless, much was learned from the experience to prepare for the next phase of LIGO’s search for gravitational waves. The lessons learned during Initial LIGO's operation led to a complete redesign of LIGO's instruments, which were rebuilt between 2010 and 2014. This redesign and subsequent improvements made LIGO's interferometers 10 times more sensitive than their initial phase.
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A 10-fold increase in sensitivity means that LIGO will be able to detect gravitational waves 10 times farther away than before, which translates into roughly 1000-times more volume of space , and 1000-times more galaxies containing sources of gravitational waves.
This deeper search for gravitational waves began in September 2015, and within days, LIGO's upgraded detectors achieved what the previous version could not accomplish in 8 years of operation: On September 14, 2015, LIGO's interferometers in Livingston, LA and Hanford, WA made the world's first direct detection of gravitational waves, heralding a new era in astronomical exploration. The gravitational waves detected by LIGO on that day were generated by two black holes colliding and merging into one nearly 1.3 BILLION light years away from earth
Important discoveries and recent activities
As has been said before LIGO was the first to have proof of Gravitational Waves, and that made an enormous advancement on the scientific field, since for the past decades no one was able to accomplish that. The first discovery of a gravitational wave was on September 14, 2015, during the O1 as they call it. The “O”s consist of the continuum observation of the space to find as many gravitational waves of some kind. Up until now there have been 4 observation periods, the O1, O2, O3a and O3b, on the O1 they were able of witnessing 3 gravitational waves in 16 weeks, on O2 they saw 8 in 38 weeks, on O3a they saw 33 in just 26 weeks and finally on O3b they have seen 23 in 26 weeks as well. They created the O3a and O3b because of covid, since they had to stop for a period of time and continue again. The O4 has been postponed to 2022 since covid related issues are still a major problem.
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With that we can know what they have been up to, they have been preparing to do their “4th” observation period and on the meantime they have been upgrading their laser in order to be more sensible and capture even further, it's quite impressive since the computer machine works on an astonishing 14kHz of speed, they react 100 times faster than the human reaction time so every single bit of waves that can be detected are quickly sent to the scientists.
But why is LIGO so important?
They are important because they help on astrology and physics, what I mean with this is that they make possible to analyze phenomenons that are 100 Light years from us, and with that information we can know if our space station, astronauts, suits and so on need, its now that accurate but since every thing is affected by gravitational waves it can be quite helpful, imagine that a specific planet we are trying to go send a gravitational wave that disrupts our spaceship, with the help of the LIGO we can know if its harmful or not, we can also further study how Neutron Stars function since the information they get from the waves is impressive, they can also accurately tell what happened before something like a black hole they found last year that had been created with the collision of other 2 black holes.
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Every single bit of information they gather is posted on their site so that every person, scientist, civilian, curious, can have a peek on their discoveries, and it's quite rare for some foundation to even share a little bit of what they find, since all they want is profit, but LIGO, the only thing they want is to help make our world a better place, insure that we are safe where we are and don't hide anything from the public, willingly showing every single thing.
