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Second Gravitational Wave Detected From Ancient Black Hole Collision (theguardian.com)
An anonymous reader quotes a report from The Guardian: Physicists have detected ripples in the fabric of spacetime that were set in motion by the collision of two black holes far across the universe more than a billion years ago. The event marks only the second time that scientists have spotted gravitational waves, the tenuous stretching and squeezing of spacetime predicted by Einstein more than a century ago. The faint signal received by the twin instruments of the Laser Interferometer Gravitational Wave Observatory (LIGO) in the US revealed two black holes circling one another 27 times before finally smashing together at half the speed of light. The cataclysmic event saw the black holes, one eight times more massive than the sun, the other 14 times more massive, merge into one about 21 times heavier than the sun. In the process, energy equivalent to the mass of the sun radiated into space as gravitational waves. Writing in the journal Physical Review Letters on Wednesday, the LIGO team describes how a second rush of gravitational waves showed up in their instrument a few months after the first, at 3.38am UK time on Boxing Day morning 2015. An automatic search detected the signals and emailed the LIGO scientists within minutes to alert them. The latest signals arrived at the Livingston detector 1.1milliseconds before they hit the Hanford detector, allowing scientists on the team to roughly work out the position of the collision in the sky. In February, LIGO scientists officially announced the first-ever observation of gravity waves.
Are the waves smaller than expect, thus harder to detect?
Indeed. They're very small. We're talking about a shift in space the size of a very small fraction of a proton. So yes, with the current detectors they're pretty hard to detect.
It took so long because the signal is mind-bogglingly weak. No detector was sensitive enough or well designed enough to rule out false positives. The LIGO experiment is much more sensitive and a lot of effort put in to detect false positives (including some social engineering). The detectors also underwent a very extensive testing phase before they were considered ready. We also weren't sure how frequent these events were, but now we are expecting a few more events.
But, it must be said indirect evidence of gravitational waves already were detected through the observation of two pulsars orbiting and closing in on each other at a rate predicted by the theory.
Those who do not learn from commit history are doomed to regress it.
Noise. All kinds of noise.
The system is an interferometer - basically two lasers set up in a large L shape with mirrors (massive simplification). When the lengths of the arms are the same, the beams cancel, when they differ a signal is recorded.
Now, the differences in length due to a gravitational wave is tiny, and the problem that kept LIGO from their detection is that there are huge numbers of sources of vibrations around the same frequencies as expected from gravitational waves that have far larger amplitudes. Thermal vibrations, for example, are a killer for experiments like this.
The waves themselves have almost exactly the waveforms that were predicted - the template fits from simulations match amazingly well in terms of amplitudes, frequencies and their evolution. What stopped experiments like this from making the observation was simply a lack of technical skill to make a precise enough instrument. Following the development of LIGO over the last decade, this is precisely what everyone working on the project said - once the noise curve is reduced to form Advanced LIOG (recent upgrade) the noise would be sufficiently small than an integrated signal against a template would be clearly visible, and now it is.
The current detectors are the most sensitive instruments ever developed by humanity, and in and of themselves mark a major leap forward in technical ability.
The world's burning. Moped Jesus spotted on I50. Details at 11.
Correction: It must be very tiny to be sensitive enough to accurately detect such distant large masses like GP's mom.
Still waiting on Serviscope_minor to wake up to fucking reality and realize that Jessica Price isn't going to fuck him.
They had a system to inject test data into the final stage analysis. The people doing it did it blind to publication ready point. Partly it was to ensure nobody leaked before the 'envelope was opened'.
There are three main detectors; two in the USA (LIGO) and one in Italy (Virgo). Currently, a detector is under construction in Japan and a fifth one using LIGO components will be built in India. Additionally, there is a smaller detector in Germany that is only sensitive in higher frequencies. It is mainly used to test technology, but it is also used for certain types of sources.
Having multiple detectors is very useful, because coincidence is used to determine the sky position. A single detector can only determine the distance, but with three or more detectors, a spot on the sky can be identified by triangulation. Moreover, having multiple detectors increases sensitivity, so weaker signals can be detected and more accurate measurements can be done on the properties of the system that is observed (e.g., the masses of merging black holes).
but the real ones detected by LIGO seem to propagate at something more on the order of 0.01 c. Does someone have a more exact value?
Sure, as far as we know, the exact value is c. Where did you find 0.01c?
The distance between Livingston and Hanford is 3002 km, and the signals were received 1.1 milliseconds apart. In a straight line that would be rougly 3 million km/sec, or 10c. But obviously the signal came in at an angle. If it had come in perpendicular to the line between the two detectors, they would have detected it simultaneously. So it must have come from somewhere in between, I would say around 6 degrees off the perpendicular plane between the two detectors.
Yes, but it's how much weaker. For a brief moment, those two blackholes released more energy that the rest of the entire observable Universe, that includes all of those quasars. Even gamma ray bursts only outshine their local galaxy.