Caltech Press Release

Caltech Scientists Awarded 2017 Nobel Prize in Physics

https://www.ligo.caltech.edu/page/press-release-2017-nobel-prize

"I am humbled and honored to receive this award," says Barish. "The detection of gravitational waves is truly a triumph of modern large-scale experimental physics. Over several decades, our teams at Caltech and MIT developed LIGO into the incredibly sensitive device that made the discovery. When the signal reached LIGO from a collision of two stellar black holes that occurred 1.3 billion years ago, the 1,000-scientist-strong LIGO Scientific Collaboration was able to both identify the candidate event within minutes and perform the detailed analysis that convincingly demonstrated that gravitational waves exist."

Some Info on what is referred to as 'Blind Injections' of data, taken from the LIGO site.... Like WTF?

https://www.ligo.org/news/blind-injection.php#sthash.xcYObjtZ.dpuf

Blind injections:

The LIGO Scientific Collaboration and the Virgo Collaboration conducted their latest joint observation run (using the LIGO Hanford, LIGO Livingston, Virgo and GEO 600 detectors) from July, 2009 through October 2010, and are jointly searching through the resulting data for gravitational wave signals standing above the detector noise levels. To make sure they get it right, they train and test their search procedures with many simulated signals that are injected into the detectors, or directly into the data streams. The data analysts agreed in advance to a "blind" test: a few carefully-selected members of the collaborations would secretly inject some (zero, one, or maybe more) signals into the data without telling anyone. The secret goes into a "Blind Injection Envelope", to be opened when the searches are complete. Such a "mock data challenge" has the potential to stress-test the full procedure and uncover problems that could not be found in other ways.

The outcomes from previous blind injection exercises were reported in 2010, in https://journals.aps.org/prd/abstract/10.1103/PhysRevD.81.102001 and https://journals.aps.org/prd/abstract/10.1103/PhysRevD.82.102001

The signal:

A rather strong signal was observed on September 16, 2010, within a minute or so of its apparent arrival at the detectors. The scientists on duty at the detector sites immediately recognized the tell-tale chirp signal expected from the merger of two black holes and/or neutron stars, and sprang into action. They knew that it could be a blind injection, but they also knew to act like it was the real thing.

The event was beautifully consistent with the expected signal from such a merger. The figures below show the strength of the signal (redder colors indicate more signal power) in time (horizontal axis) and frequency (vertical axis). The signal sweeps upwards in frequency ("chirp") as the stars spiral into one another, approaching merger. The first plot is what was seen in the LIGO Hanford detector, and the second is what was seen at the same time in the LIGO Livingston detector. Despite apparent differences, the two signals are completely consistent with one another. The dark and light blue regions are typical of fluctuating noise in the detectors.

The detector network is capable of locating the source in the sky only crudely; it seemed to be coming from the constellation Canis Major (the "Big Dog") in the southern hemisphere (the event was dubbed "the Big Dog" shortly thereafter). They sent alerts to partners operating robotic optical telescopes in the southern hemisphere (ROTSE, TAROT, Skymapper, Zadko) and the Swift X-ray space telescope, all of which took images of the sky on that and/or subsequent days in the hope of capturing an optical or X-ray "afterglow".

Is it real?

In the subsequent days and weeks, numerous teams of scientists tried to get definitive answers to many questions. The event was seen strongly in the two LIGO detectors, less strongly in the Virgo detector, and nothing was seen in the less sensitive GEO detector. Could the event be explained as an accidental coincidence of noise fluctuations? The initial estimate was that the chance of the event being due to noise in the detectors was "much less than 1%", but much more work was required to say how much; after careful analysis, the teams agreed that such a noise coincidence might happen once in 7,000 years.

Could the detectors have exhibited some never-before-seen instrumental effect just then, maybe one that could somehow be correlated between sites that are separated by thousands of kilometers? Despite many investigations and much thought, no plausible scenario for this could be found (except for a blind injection).

After studying all of the evidence, the hundreds of scientists in the collaborations convinced themselves and each other that this was not an instrumental artifact.

Is there an afterglow?

Was there any sign of an optical or X-ray "transient" in the telescope images? A binary black hole merger would not be expected to emit any kind of light; but if one of the objects was a neutron star rather than a black hole, it would emit a burst of gamma rays that could be seen from across the universe, and an afterglow of X-rays and optical light. Teams worked with their partner astronomers to analyze the images, which only covered a small part of the sky that the signal could have come from. They looked for transients, and eliminated imposters such as variable stars, near-earth asteroids, distant supernovae, etc. Preliminary results revealed no candidate optical or X-ray transient event on the sky that could be associated with this signal.

What kind of merger?

Mergers of black holes and/or neutron stars are very rare, but they can come in many shapes and sizes. What were the masses of the two stars? If one was significantly less than 3 solar masses, it could be a neutron star, not a black hole, and this is an important distinction to astrophysicists. Whether black holes or neutron stars, they might be expected to be spinning; can this be determined from the signal? And where, precisely is the system located on the sky, and at what distance?

All told, there are fifteen parameters that can be extracted from the signals at the LIGO and Virgo detectors, and several different teams of scientists were able to measure them. The result, however, depended on the waveform models used, and the most realistic models were also the most complex.

Documenting the "Evidence":

The scientists gathered all this information together in a paper entitled "Evidence for the Direct Detection of Gravitational Waves from a Black Hole Binary Coalescence". (Coalescence refers to the inspiral of the two stars, their merger into a single perturbed black hole, and the "ringdown" into a final quiet black hole, all through the emission of gravitational waves). A second paper described the parameter estimation procedures and results. A third summarized the search for binary coalescence and the overall results (only one event was observed above the background noise).

Material was prepared for the open release of data relevant to this event, and a whole suite of resources for education and public outreach was assembled. The event was renamed "GW100916", for the year, month and date that it was recorded.

Opening the envelope:

An independent "Detection Committee" reviewed and double-checked all of this work, and reported their findings to the two collaborations. Everyone voted on whether the work, and all the documentation, was sufficient to announce the first detection; the result was a unanimous "yes". The Blind Injection Envelope was opened on March 14, 2011 at a joint meeting of the LIGO Scientific Collaboration and the Virgo Collaboration in Arcadia, CA. There were 300 people in the room and another 100 connecting through a video teleconference. The envelope was opened -- and there was the event: it was a blind injection, not the first direct detection of gravitational waves.

Did they get it right?

The event parameters were revealed: it was indeed a binary merger injected at the time when the "big dog" event was observed. The waveform recovered by the search was a good match to the one which was injected. However, there were some surprises: the injected signal was composed of a neutron star and a black hole, not two black holes; and it wasn't from anywhere near Canis Major. What happened?

Within hours, the answer became clear: there was a problem in the blind injection software. The team that injected the simulated gravitational wave signal into the detector had used some old software containing two "bugs": an old waveform model that had more recently been replaced by an improved one (this explained why the signal looked like two black holes), and a sign error in the injection to one detector that made it look like the signal was coming from a different part of the sky. When these errors were taken into account, the analysis easily recovered the "right" parameters. But most importantly, those bugs did not prevent the scientists from finding the injected event in the first place.

Lessons learned:

Aside from that one problem, everything else in the process seemed to go right. Procedures are now being established to ensure that problems like these will not happen again, which is one of the primary purposes of these mock data challenges.

The blind injection challenge was an extremely successful exercise for the LIGO and Virgo scientists, demonstrating their ability to detect gravitational waves from coalescing binaries and providing a concrete example of how the momentous first detection might play out.

Of course, the first real detection may well look nothing like this exercise: it could be a burst signal from a core-collapse supernova; a continuous sine wave from a spinning neutron star in our Galaxy; a hiss of noise from the earliest moment of the Big Bang; or something that they have not yet anticipated. It could be in the data already collected, since the searches for all anticipated signals are not yet complete. Or we might have to wait a few more years for the data from the next generation of detectors.

Overall, it was an exhilarating and extremely valuable exercise, even if it was disappointing in the end. The LIGO and Virgo teams are now much more prepared for the first real detections.

More info from above link...

"In the initial phase of LIGO, in order to isolate the detectors from the earth's motion, we used a suspension system that consisted of test-mass mirrors hung by piano wire and used a multiple-stage set of passive shock absorbers, similar to those in your car. We knew this probably would not be good enough to detect gravitational waves, so we, in the LIGO Laboratory, developed an ambitious program for Advanced LIGO that incorporated a new suspension system to stabilize the mirrors and an active seismic isolation system to sense and correct for ground motions," says Barish.

The active seismic isolation system developed for Advanced LIGO works in a similar fashion to noise-canceling headphones, except it can measure and cancel out ground vibrations coming from many directions. In conjunction with this system, a new "quieter" way to suspend LIGO's mirrors was developed with the help of the Glasgow group, which involved hanging the mirrors with a four-stage pendulum. The combination of these two advances gave LIGO a huge improvement in sensitivity to lower frequencies of gravitational waves, which was ultimately what was needed to detect the crashing of two black holes.

Barish also created the LIGO of today: a collaboration of approximately 1,200 scientists and engineers at about 100 institutions in 19 nations called the LIGO Scientific Collaboration (LSC).

From a paper LIGO published with some more intel on their 'blind injections'

Following the completion of this analysis, the event

was revealed to be a blind injection. While the analy-

sis groups did not know the event was an injection prior

to its unblinding, they did know that one or more blind

injections may be performed during the analysis period.

Such blind injections have been carried out before: see [4]

for the results of a blind injection performed in a previ-

ous run. This event was the only coherent CBC blind

injection performed during S6 and VSR2 and 3. The in-

jection was identified as a gravitational-wave candidate

with high probability, and the blind injection challenge

was considered to be successful.

https://arxiv.org/pdf/1111.7314.pdf

Page 8

LIGO measurement claim lifted from their site, noticed some media outlets had suggested the ability to measure to 1/10,000 the diameter of a proton, LIGO only makes the claim of 1/1,000th the diameter of a proton....

LIGO's interferometers are the largest ever built. With arms 4 km (2.5 mi.) long, they are 360 times larger than the one used in the Michelson-Morley experiment (which had arms 11 m (33 feet) long).

This is particularly important in the search for gravitational waves because the longer the arms of an interferometer, the farther the laser travels, and the more sensitive the instrument becomes. Attempting to measure a change in arm length 1,000 times smaller than a proton means that LIGO has to be more sensitive than any scientific instrument ever built, so the longer the better. But there are obvious limitations to how long one can build an interferometer. Even with arms 4 km long, if LIGO's interferometers were basic Michelsons they would still not be long enough to detect gravitational waves...and yet they are. How is this possible?

https://www.ligo.caltech.edu/WA/page/ligos-ifo

But wait, LIGO DOES make the claim of 1/10,000th of a proton on a different page....

L-R: The LIGO Livingston Observatory, LIGO Hanford Observatory, and Virgo

These are "first-generation" detectors, designed to demonstrate the technologies that can sense motions at the level of one-ten-thousandth of the diameter of a proton (or 10-19 meter), which may only be barely sensitive enough to detect the waves.

https://www.ligo.org/news/blind-injection.php

I see now where the confusion in the media comes from, LIGO itself.... Poorly done LIGO.... Shame a scientific outfit that has had billions of dollars thrown at it can't seem to proof their own website very well....

Have to go with the SI unit they used in the second link, 10 to the minus 19 of a meter....

	Criado por Dee 8Tee mais de 5 anos atrás

Shenanigans in the scientific community? Nobel prize awarded in 2017 for the detection of gravitational waves, whilst the scientific community raises questions as to the authenticity of the signal interpretation.