Thanks Jim, that's the craziest noise reduction work ever heard of.
tom fowle WA6IVG

On Fri, Feb 12, 2016 at 08:18:27PM -0800, Jim Gammon wrote:
> Got this from a ham friend yesterday.
> Gravitational Waves Exist: The Inside Story of How Scientists Finally Found
> Them
> By Nicola Twilley
> 
> Just over a billion years ago, many millions of galaxies from here, a pair
> of black holes collided. They had been circling each other for aeons, in a
> sort of mating dance, gathering pace with each orbit, hurtling closer and
> closer. By the time they were a few hundred miles apart, they were whipping
> around at nearly the speed of light, releasing great shudders of
> gravitational energy. Space and time became distorted, like water at a
> rolling boil. In the fraction of a second that it took for the black holes
> to finally merge, they radiated a hundred times more energy than all the
> stars in the universe combined. They formed a new black hole, sixty-two
> times as heavy as our sun and almost as wide across as the state of Maine.
> As it smoothed itself out, assuming the shape of a slightly flattened
> sphere, a few last quivers of energy escaped. Then space and time became
> silent again.
> 
> 
> 
> 
> The waves rippled outward in every direction, weakening as they went. On
> Earth, dinosaurs arose, evolved, and went extinct. The waves kept going.
> About fifty thousand years ago, they entered our own Milky Way galaxy, just
> as Homo sapiens were beginning to replace our Neanderthal cousins as the
> planet’s dominant species of ape. A hundred years ago, Albert Einstein, one
> of the more advanced members of the species, predicted the waves’ existence,
> inspiring decades of speculation and fruitless searching. Twenty-two years
> ago, construction began on an enormous detector, the Laser Interferometer
> Gravitational-Wave Observatory (LIGO). Then, on September 14, 2015, at just
> before eleven in the morning, Central European Time, the waves reached
> Earth. Marco Drago, a thirty-two-year-old Italian postdoctoral student and a
> member of the LIGO Scientific Collaboration, was the first person to notice
> them. He was sitting in front of his computer at the Albert Einstein
> Institute, in Hannover, Germany, viewing the LIGO data remotely. The waves
> appeared on his screen as a compressed squiggle, but the most exquisite ears
> in the universe, attuned to vibrations of less than a trillionth of an inch,
> would have heard what astronomers call a chirp—a faint whooping from low to
> high. This morning, in a press conference in Washington, D.C., the LIGO team
> announced that the signal constitutes the first direct observation of
> gravitational waves.
> 
> 
> 
> 
> When Drago saw the signal, he was stunned. “It was difficult to understand
> what to do,” he told me. He informed a colleague, who had the presence of
> mind to call the LIGO operations room, in Livingston, Louisiana. Word began
> to circulate among the thousand or so scientists involved in the project. In
> California, David Reitze, the executive director of the LIGO Laboratory, saw
> his daughter off to school and went to his office, at Caltech, where he was
> greeted by a barrage of messages. “I don’t remember exactly what I said,” he
> told me. “It was along these lines: ‘Holy shit, what is this?’ ” Vicky
> Kalogera, a professor of physics and astronomy at Northwestern University,
> was in meetings all day, and didn’t hear the news until dinnertime. “My
> husband asked me to set the table,” she said. “I was completely ignoring
> him, skimming through all these weird e-mails and thinking, What is going
> on?” Rainer Weiss, the eighty-three-year-old physicist who first suggested
> building LIGO, in 1972, was on vacation in Maine. He logged on, saw the
> signal, and yelled “My God!” loudly enough that his wife and adult son came
> running.
> 
> 
> 
> 
> The collaborators began the arduous process of double-, triple-, and
> quadruple-checking their data. “We’re saying that we made a measurement that
> is about a thousandth the diameter of a proton, that tells us about two
> black holes that merged over a billion years ago,” Reitze said. “That is a
> pretty extraordinary claim and it needs extraordinary evidence.” In the
> meantime, the LIGO scientists were sworn to absolute secrecy. As rumors of
> the finding spread, from late September through this week, media excitement
> spiked; there were rumblings about a Nobel Prize. But the collaborators gave
> anyone who asked about it an abbreviated version of the truth—that they were
> still analyzing data and had nothing to announce. Kalogera hadn’t even told
> her husband.
> 
> 
> 
> 
> LIGO consists of two facilities, separated by nearly nineteen hundred
> miles—about a three-and-a-half-hour flight on a passenger jet, but a journey
> of less than ten ten-thousandths of a second for a gravitational wave. The
> detector in Livingston, Louisiana, sits on swampland east of Baton Rouge,
> surrounded by a commercial pine forest; the one in Hanford, Washington, is
> on the southwestern edge of the most contaminated nuclear site in the United
> States, amid desert sagebrush, tumbleweed, and decommissioned reactors. At
> both locations, a pair of concrete pipes some twelve feet tall stretch at
> right angles into the distance, so that from high above the facilities
> resemble carpenter’s squares. The pipes are so long—nearly two and a half
> miles—that they have to be raised from the ground by a yard at each end, to
> keep them lying flat as Earth curves beneath them.
> 
> 
> 
> 
> LIGO is part of a larger effort to explore one of the more elusive
> implications of Einstein’s general theory of relativity. The theory, put
> simply, states that space and time curve in the presence of mass, and that
> this curvature produces the effect known as gravity. When two black holes
> orbit each other, they stretch and squeeze space-time like children running
> in circles on a trampoline, creating vibrations that travel to the very
> edge; these vibrations are gravitational waves. They pass through us all the
> time, from sources across the universe, but because gravity is so much
> weaker than the other fundamental forces of nature—electromagnetism, for
> instance, or the interactions that bind an atom together—we never sense
> them. Einstein thought it highly unlikely that they would ever be detected.
> He twice declared them nonexistent, reversing and then re-reversing his own
> prediction. A skeptical contemporary noted that the waves seemed to
> “propagate at the speed of thought.”
> 
> 
> 
> 
> Nearly five decades passed before someone set about building an instrument
> to detect gravitational waves. The first person to try was an engineering
> professor at the University of Maryland, College Park, named Joe Weber. He
> called his device the resonant bar antenna. Weber believed that an aluminum
> cylinder could be made to work like a bell, amplifying the feeble strike of
> a gravitational wave. When a wave hit the cylinder, it would vibrate very
> slightly, and sensors around its circumference would translate the ringing
> into an electrical signal. To make sure he wasn’t detecting the vibrations
> of passing trucks or minor earthquakes, Weber developed several safeguards:
> he suspended his bars in a vacuum, and he ran two of them at a time, in
> separate locations—one on the campus of the University of Maryland, and one
> at Argonne National Laboratory, near Chicago. If both bars rang in the same
> way within a fraction of a second of each other, he concluded, the cause
> might be a gravitational wave.
> 
> 
> 
> 
> In June of 1969, Weber announced that his bars had registered something.
> Physicists and the media were thrilled; the Times reported that “a new
> chapter in man’s observation of the universe has been opened.” Soon, Weber
> started reporting signals on a daily basis. But doubt spread as other
> laboratories built bars that failed to match his results. By 1974, many had
> concluded that Weber was mistaken. (He continued to claim new detections
> until his death, in 2000.)
> 
> 
> 
> 
> Weber’s legacy shaped the field that he established. It created a poisonous
> perception that gravitational-wave hunters, as Weiss put it, are “all liars
> and not careful, and God knows what.” That perception was reinforced in
> 2014, when scientists at BICEP2, a telescope near the South Pole, detected
> what seemed to be gravitational radiation left over from the Big Bang; the
> signal was real, but it turned out to be a product of cosmic dust. Weber
> also left behind a group of researchers who were motivated by their
> inability to reproduce his results. Weiss, frustrated by the difficulty of
> teaching Weber’s work to his undergraduates at the Massachusetts Institute
> of Technology, began designing what would become LIGO. “I couldn’t
> understand what Weber was up to,” he said in an oral history conducted by
> Caltech in 2000. “I didn’t think it was right. So I decided I would go at it
> myself.”
> 
> 
> 
> 
> In the search for gravitational waves, “most of the action takes place on
> the phone,” Fred Raab, the head of LIGO’s Hanford site, told me. There are
> weekly meetings to discuss data and fortnightly meetings to discuss
> coördination between the two detectors, with collaborators in Australia,
> India, Germany, the United Kingdom, and elsewhere. “When these people wake
> up in the middle of the night dreaming, they’re dreaming about the
> detector,” Raab said. “That’s how intimate they have to be with it,” he
> explained, to be able to make the fantastically complex instrument that
> Weiss conceived actually work.
> 
> 
> 
> 
> Weiss’s detection method was altogether different from Weber’s. His first
> insight was to make the observatory “L”-shaped. Picture two people lying on
> the floor, their heads touching, their bodies forming a right angle. When a
> gravitational wave passes through them, one person will grow taller while
> the other shrinks; a moment later, the opposite will happen. As the wave
> expands space-time in one direction, it necessarily compresses it in the
> other. Weiss’s instrument would gauge the difference between these two
> fluctuating lengths, and it would do so on a gigantic scale, using miles of
> steel tubing. “I wasn’t going to be detecting anything on my tabletop,” he
> said.
> 
> 
> 
> 
> To achieve the necessary precision of measurement, Weiss suggested using
> light as a ruler. He imagined putting a laser in the crook of the “L.” It
> would send a beam down the length of each tube, which a mirror at the other
> end would reflect back. The speed of light in a vacuum is constant, so as
> long as the tubes were cleared of air and other particles the beams would
> recombine at the crook in synchrony—unless a gravitational wave happened to
> pass through. In that case, the distance between the mirrors and the laser
> would change slightly. Since one beam would now be covering a shorter
> distance than its twin, they would no longer be in lockstep by the time they
> got back. The greater the mismatch, the stronger the wave. Such an
> instrument would need to be thousands of times more sensitive than any
> previous device, and it would require delicate tuning in order to extract a
> signal of vanishing weakness from the planet’s omnipresent din.
> 
> 
> 
> 
> Weiss wrote up his design in the spring of 1972, as part of his laboratory’s
> quarterly progress report. The article never appeared in a scientific
> journal—it was an idea, not an experiment—but according to Kip Thorne, an
> emeritus professor at Caltech who is perhaps best known for his work on the
> movie “Interstellar,” “it is one of the greatest papers ever written.”
> Thorne doesn’t recall reading Weiss’s report until later. “If I had read it,
> I had certainly not understood it,” he said. Indeed, Thorne’s landmark
> textbook on gravitational theory, co-authored with Charles Misner and John
> Wheeler and first published in 1973, contained a student exercise designed
> to demonstrate the impracticability of measuring gravitational waves with
> lasers. “I turned around on that pretty quickly,” he told me.
> 
> 
> 
> 
> Thorne’s conversion occurred in a hotel room in Washington, D.C., in 1975.
> Weiss had invited him to speak to a panel of NASA scientists. The evening
> before the meeting, the two men got to talking. “I don’t remember how it
> happened, but we shared the hotel room that night,” Weiss said. They sat at
> a tiny table, filling sheet after sheet of paper with sketches and
> equations. Thorne, who was raised Mormon, drank Dr Pepper; Weiss smoked a
> corncob pipe stuffed with Three Nuns tobacco. “There are not that many
> people in the world that you can talk to like that, where both of you have
> been thinking about the same thing for years,” Weiss said. By the time
> Thorne got back to his own room, the sky was turning pink.
> 
> 
> 
> 
> At M.I.T., Weiss had begun assembling a small prototype detector with
> five-foot arms. But he had trouble getting support from departmental
> administrators, and many of his colleagues were also skeptical. One of them,
> an influential astrophysicist and relativity expert named Phillip Morrison,
> was firmly of the opinion that black holes did not exist—a viewpoint that
> many of his contemporaries shared, given the paucity of observational data.
> Since black holes were some of the only cosmic phenomena that could
> theoretically emit gravitational waves of significant size, Morrison
> believed that Weiss’s instrument had nothing to find. Thorne had more
> success: by 1981, there was a prototype under way at Caltech, with arms a
> hundred and thirty-one feet long. A Scottish physicist named Ronald Drever
> oversaw its construction, improving on Weiss’s design in the process.
> 
> 
> 
> 
> In 1990, after years of studies, reports, presentations, and committee
> meetings, Weiss, Thorne, and Drever persuaded the National Science
> Foundation to fund the construction of LIGO. The project would cost two
> hundred and seventy-two million dollars, more than any N.S.F.-backed
> experiment before or since. “That started a huge fight,” Weiss said. “The
> astronomers were dead-set against it, because they thought it was going to
> be the biggest waste of money that ever happened.” Many scientists were
> concerned that LIGO would sap money from other research. Rich Isaacson, a
> program officer at the N.S.F. at the time, was instrumental in getting the
> observatory off the ground. “He and the National Science Foundation stuck
> with us and took this enormous risk,” Weiss said.
> 
> 
> 
> 
> “It never should have been built,” Isaacson told me. “It was a couple of
> maniacs running around, with no signal ever having been discovered, talking
> about pushing vacuum technology and laser technology and materials
> technology and seismic isolation and feedback systems orders of magnitude
> beyond the current state of the art, using materials that hadn’t been
> invented yet.” But Isaacson had written his Ph.D. thesis on gravitational
> radiation, and he was a firm believer in LIGO’s theoretical underpinnings.
> “I was a mole for the gravitational-wave community inside the N.S.F.,” he
> said.
> 
> 
> 
> 
> In their proposal, the LIGO team warned that their initial design was
> unlikely to detect anything. Nonetheless, they argued, an imperfect
> observatory had to be built in order to understand how to make a better one.
> “There was every reason to imagine this was going to fail,” Isaacson said.
> He persuaded the N.S.F. that, even if no signal was registered during the
> first phase, the advances in precision measurement that came out of it would
> likely be worth the investment. Ground was broken in early 1994.
> 
> 
> 
> 
> It took years to make the most sensitive instrument in history insensitive
> to everything that is not a gravitational wave. Emptying the tubes of air
> demanded forty days of pumping. The result was one of the purest vacuums
> ever created on Earth, a trillionth as dense as the atmosphere at sea level.
> Still, the sources of interference were almost beyond reckoning—the motion
> of the wind in Hanford, or of the ocean in Livingston; imperfections in the
> laser light as a result of fluctuations in the power grid; the jittering of
> individual atoms within the mirrors; distant lightning storms. All can
> obscure or be mistaken for a gravitational wave, and each source had to be
> eliminated or controlled for. One of LIGO’s systems responds to minuscule
> seismic tremors by activating a damping system that pushes on the mirrors
> with exactly the right counterforce to keep them steady; another monitors
> for disruptive sounds from passing cars, airplanes, or wolves.
> 
> 
> 
> 
> “There are ten thousand other tiny things, and I really mean ten thousand,”
> Weiss said. “And every single one needs to be working correctly so that
> nothing interferes with the signal.” When his colleagues make adjustments to
> the observatory’s interior components, they must set up a portable clean
> room, sterilize their tools, and don what they call bunny suits—full-body
> protective gear—lest a skin cell or a particle of dust accidentally settle
> on the sparkling optical hardware.
> 
> 
> 
> 
> The first iteration of the observatory—Initial LIGO, as the team now calls
> it—was up and running in 2001. During the next nine years, the scientists
> measured and refined their instruments’ performance and improved their
> data-analysis algorithms. In the meantime, they used the prototype at
> Caltech and a facility in Germany to develop ever more sensitive mirror,
> laser, and seismic-isolation technology. In 2010, the detectors were taken
> offline for a five-year, two-hundred-million-dollar upgrade. They are now so
> well shielded that when the facilities manager at the Hanford site revs his
> Harley next to the control room, the scientist monitoring the
> gravitational-wave channel sees nothing. (A test of this scenario is
> memorialized in the logbook as “Bubba Roars Off on a Motor Cycle.”) The
> observatory’s second iteration, Advanced LIGO, should eventually be capable
> of surveying a volume of space that is more than a thousand times greater
> than its predecessor’s.
> 
> 
> 
> 
> Some of the most painstaking work took place on the mirrors, which, Reitze
> said, are the best in the world “by far.” Each is a little more than a foot
> wide, weighs nearly ninety pounds, and is polished to within a
> hundred-millionth of an inch of a perfect sphere. (They cost almost half a
> million dollars apiece.) At first, the mirrors were suspended from loops of
> steel wire. For the upgrade, they were attached instead to a system of
> pendulums, which insulated them even further from seismic tremors. They
> dangle from fibres of fused silica—glass, basically—which, although strong
> enough to bear the weight of the mirrors, shatter at the slightest
> provocation. “We did have one incident where a screw fell and pinged one,
> and it just went poof,” Anamaria Effler, a former operations specialist at
> the Hanford site, told me. The advantage of the fibres is their purity,
> according to Jim Hough, of the University of Glasgow. “You know how, when
> you flick a whiskey glass, it will ring beautifully?” he asked. “Fused
> silica is even better than a whiskey glass—it is like plucking a string on a
> violin.” The note is so thin that it is possible for LIGO’s
> signal-processing software to screen it out—another source of interference
> eliminated.
> 
> 
> 
> 
> Preparing Advanced LIGO took longer than expected, so the new and improved
> instrument’s start date was pushed back a few days, to September 18, 2015.
> Weiss was called in from Boston a week prior to try to track down the source
> of some radio-frequency interference. “I get there and I was horrified,” he
> said. “It was everywhere.” He recommended a weeklong program of repairs to
> address the issue, but the project’s directors refused to delay the start of
> the first observing run any longer. “Thank God they didn’t let me do it,”
> Weiss said. “I would have had the whole goddamn thing offline when the
> signal came in.”
> 
> 
> 
> 
> On Sunday, September 13th, Effler spent the day at the Livingston site with
> a colleague, finishing a battery of last-minute tests. “We yelled, we
> vibrated things with shakers, we tapped on things, we introduced magnetic
> radiation, we did all kinds of things,” she said. “And, of course,
> everything was taking longer than it was supposed to.” At four in the
> morning, with one test still left to do—a simulation of a truck driver
> hitting his brakes nearby—they decided to pack it in. They drove home,
> leaving the instrument to gather data in peace. The signal arrived not long
> after, at 4:50 A.M. local time, passing through the two detectors within
> seven milliseconds of each other. It was four days before the start of
> Advanced LIGO’s first official run.
> 
> 
> 
> 
> The fact that gravitational waves were detected so early prompted confusion
> and disbelief. “I had told everyone that we wouldn’t see anything until 2017
> or 2018,” Reitze said. Janna Levin, a professor of astrophysics at Barnard
> College and Columbia University, who is not a member of the LIGO Scientific
> Collaboration, was equally surprised. “When the rumors started, I was like,
> Come on!” she said. “They only just got it locked!” The signal, moreover,
> was almost too perfect. “Most of us thought that, when we ever saw such a
> thing, it would be something that you would need many, many computers and
> calculations to drag out of the noise,” Weiss said. Many of his colleagues
> assumed that the signal was some kind of test.
> 
> 
> 
> 
> The LIGO team includes a small group of people whose job is to create blind
> injections—bogus evidence of a gravitational wave—as a way of keeping the
> scientists on their toes. Although everyone knew who the four people in that
> group were, “we didn’t know what, when, or whether,” Gabriela González, the
> collaboration’s spokeswoman, said. During Initial LIGO’s final run, in 2010,
> the detectors picked up what appeared to be a strong signal. The scientists
> analyzed it intensively for six months, concluding that it was a
> gravitational wave from somewhere in the constellation of Canis Major. Just
> before they submitted their results for publication, however, they learned
> that the signal was a fake.
> 
> 
> 
> 
> This time through, the blind-injection group swore that they had nothing to
> do with the signal. Marco Drago thought that their denials might also be
> part of the test, but Reitze, himself a member of the quartet, had a
> different concern. “My worry was—and you can file this under the fact that
> we are just paranoid cautious about making a false claim—could somebody have
> done this maliciously?” he said. “Could somebody have somehow faked a signal
> in our detector that we didn’t know about?” Reitze, Weiss, González, and a
> handful of others considered who, if anyone, was familiar enough with both
> the apparatus and the algorithms to have spoofed the system and covered his
> or her tracks. There were only four candidates, and none of them had a
> plausible motive. “We grilled those guys,” Weiss said. “And no, they didn’t
> do it.” Ultimately, he said, “We accepted that the most economical
> explanation was that it really is a black-hole pair.”
> 
> 
> 
> 
> Subgroups within the LIGO Scientific Collaboration set about validating
> every aspect of the detection. They reviewed how the instruments had been
> calibrated, took their software code apart line by line, and compiled a list
> of possible environmental disturbances, from oscillations in the ionosphere
> to earthquakes in the Pacific Rim. (“There was a very large lightning strike
> in Africa at about the same time,” Stan Whitcomb, LIGO’s chief scientist,
> told me. “But our magnetometers showed that it didn’t create enough of a
> disturbance to cause this event.”) Eventually, they confirmed that the
> detection met the statistical threshold of five sigma, the gold standard for
> declaring a discovery in physics. This meant that there was a probability of
> only one in 3.5 million that the signal was spotted by chance.
> 
> 
> 
> 
> The September 14th detection, now officially known as GW150914, has already
> yielded a handful of significant astrophysical findings. To begin with, it
> represents the first observational evidence that black-hole pairs exist.
> Until now, they had existed only in theory, since by definition they swallow
> all light in their vicinity, rendering themselves invisible to conventional
> telescopes. Gravitational waves are the only information known to be capable
> of escaping a black hole’s crushing gravity.
> 
> 
> 
> 
> The LIGO scientists have extracted an astonishing amount from the signal,
> including the masses of the black holes that produced it, their orbital
> speed, and the precise moment at which their surfaces touched. They are
> substantially heavier than expected, a surprise that, if confirmed by future
> observations, may help to explain how the mysterious supermassive black
> holes at the heart of many galaxies are formed. The team has also been able
> to quantify what is known as the ringdown—the three bursts of energy that
> the new, larger black hole gave off as it became spherical. “Seeing the
> ringdown is spectacular,” Levin said. It offers confirmation of one of
> relativity theory’s most important predictions about black holes—namely,
> that they radiate away imperfections in the form of gravitational waves
> after they coalesce.
> 
> 
> 
> 
> The detection also proves that Einstein was right about yet another aspect
> of the physical universe. Although his theory deals with gravity, it has
> primarily been tested in our solar system, a place with a notably weak
> gravitational regime. “You think Earth’s gravity is really something when
> you’re climbing the stairs,” Weiss said. “But, as far as physics goes, it is
> a pipsqueak, infinitesimal, tiny little effect.” Near a black hole, however,
> gravity becomes the strongest force in the universe, capable of tearing
> atoms apart. Einstein predicted as much in 1916, and the LIGO results
> suggest that his equations align almost perfectly with real-world
> observation. “How could he have ever known this?” Weiss asked. “I would love
> to present him with the data that I saw that morning, to see his face.”
> 
> 
> 
> 
> Since the September 14th detection, LIGO has continued to observe candidate
> signals, although none are quite as dramatic as the first event. “The reason
> we are making all this fuss is because of the big guy,” Weiss said. “But we’re
> very happy that there are other, smaller ones, because it says this is not
> some unique, crazy, cuckoo effect.”
> 
> 
> 
> 
> Virtually everything that is known about the universe has come to scientists
> by way of the electromagnetic spectrum. Four hundred years ago, Galileo
> began exploring the realm of visible light with his telescope. Since then,
> astronomers have pushed their instruments further. They have learned to see
> in radio waves and microwaves, in infrared and ultraviolet, in X-rays and
> gamma rays, revealing the birth of stars in the Carina Nebula and the
> eruption of geysers on Saturn’s eighth moon, pinpointing the center of the
> Milky Way and the locations of Earth-like planets around us. But more than
> ninety-five per cent of the universe remains imperceptible to traditional
> astronomy. Gravitational waves may not illuminate the so-called dark energy
> that is thought to make up the majority of that obscurity, but they will
> enable us to survey space and time as we never have before. “This is a
> completely new kind of telescope,” Reitze said. “And that means we have an
> entirely new kind of astronomy to explore.” If what we witnessed before was
> a silent movie, Levin said, gravitational waves turn our universe into a
> talkie.
> 
> 
> 
> 
> As it happens, the particular frequencies of the waves that LIGO can detect
> fall within the range of human hearing, between about thirty-five and two
> hundred and fifty hertz. The chirp was much too quiet to hear by the time it
> reached Earth, and LIGO was capable of capturing only two-tenths of a second
> of the black holes’ multibillion-year merger, but with some minimal audio
> processing the event sounds like a glissando. “Use the back of your fingers,
> the nails, and just run them along the piano from the lowest A up to middle
> C, and you’ve got the whole signal,” Weiss said.
> 
> 
> 
> 
> Different celestial sources emit their own sorts of gravitational waves,
> which means that LIGO and its successors could end up hearing something like
> a cosmic orchestra. “The binary neutron stars are like the piccolos,” Reitze
> said. Isolated spinning pulsars, he added, might make a monochromatic “ding”
> like a triangle, and black holes would fill in the string section, running
> from double bass on up, depending on their mass. LIGO, he said, will only
> ever be able to detect violins and violas; waves from supermassive black
> holes, like the one at the center of the Milky Way, will have to await
> future detectors, with different sensitivities.
> 
> 
> 
> 
> Several such detectors are in the planning stages or under construction,
> including the Einstein Telescope, a European project whose underground arms
> will be more than twice the length of LIGO’s, and a space-based
> constellation of three instruments called eLISA. (The European Space Agency,
> with support from NASA, launched a pathfinder mission in December.) Other
> detectors are already up and running, including the BICEP2 telescope, which,
> despite its initial false alarm, may still detect the echoes of
> gravitational waves from even further back in the universe’s history. Reitze’s
> hope, he told me, is that the chirp will motivate more investment in the
> field.
> 
> 
> 
> 
> Advanced LIGO’s first observing run came to an end on January 12th. Effler
> and the rest of the commissioning team have since begun another round of
> improvements. The observatory is inching toward its maximum sensitivity;
> within two or three years, it may well register events on a daily basis,
> capturing more data in the process. It will come online again by late
> summer, listening even more closely to a celestial soundtrack that we have
> barely imagined. “We are opening up a window on the universe so radically
> different from all previous windows that we are pretty ignorant about what’s
> going to come through,” Thorne said. “There are just bound to be big
> surprises.”