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Scientific Progress Goes “Chirp”!
Northern leg (x-arm) of LIGO interferometer on Hanford Reservation. By Umptanum – wikipédia, CC BY-SA 3.0.
Ladies and Gentlemen, we have detected gravitational waves! We did it!” And with that, the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced the discovery of a strange feature of General Relativity that’s been hiding since the 1960s.
Gravitational waves are ripples in the fabric of space, caused by the acceleration of mass. The bigger the mass and the faster it’s accelerated, the better, and there’s nothing that better fits that description than two black holes orbiting each other. These waves expand and compress space, which slightly changes distances between objects in their path. Two objects floating freely in deep space far from any forces, would find themselves carried a little towards each other and then a little away from each other and back and forth, as the wave passed over them. If you could measure the distance between them accurately, like with a laser range-finder, you’d detect that oscillation. But this is tough to do on the Earth, because you can’t have the two objects floating freely any more. The best you can do is to hang them from fine threads, like a swing. They’re not free to move in every direction, but they can swing back and forth.
So, how did we find them? LIGO shines laser beams down two 4-kilometer (2.5-mile) vacuum pipes, arranged in an “L” shape. At the end of each pipe is a mirror that reflects the beam back and measures its length, with an accuracy of 10^-18 m, a thousandth the width of a proton. This always amazes me, because the mirror itself is made out of atoms, which are bumpy and much larger than protons. And yet, it works because the bumps average themselves out. When a gravitational wave comes by, it shrinks the distance along one pipe while expanding the distance along the other (as they’re at right angles) and then it switches.
What they’ve announced today is the detection of gravitational waves coming from the merger of two black holes, spiraling into each other a billion light-years away from us. At 29 and 36 times the mass of the Sun, these aren’t very big for black holes: the ones in the centers of galaxies have millions or billions of solar masses. But the smaller ones are more plentiful, which means they’re more likely to collide. As the two in question orbited each other, the gravitational waves carried away more and more of their energy, making them spiral inward, until they finally collided and released massive amounts of energy (the equivalent of the mass of three Suns converted directly into energy).
Take a look at the wave patterns that LIGO felt:
The vibration is vertical, and time goes to the right. Early on, the waves are slow (i.e., broad) and weak (i.e., short). As the black holes spiral inward, the waves strengthen and increase in frequency until they make a loud “chirp!“ when they collide. Then, there’s a faint wiggling at the end, as the new, combined black hole rings like a bell until it settles down.
This pattern is so clear, you can see it without needing the computer to sort it through for you. What are the odds of detecting this? My wife — who works in numerical relativity (the computer simulation of the waves) — tells me that it was entirely possible they’d run this for decades before they heard anything. Instead, they found this within days of turning the machine on. That suggests that these black holes are colliding all over the place, and we’re going to find plenty more.
So what good is this? The press is mostly writing headlines shouting, “Einstein is proven right!” This is true in a simplified sense, but not too many of us were expecting otherwise and that’s not really why all of this was built. With more detections and better signals, we’ll get to the point where we can test theories that go beyond General Relativity, which is interesting. But I think the real value of this discovery will be observational.
Until now, astronomy has almost exclusively relied on what we can see with light: i.e, electromagnetic radiation, ranging from radio waves on one end to gamma rays on the other. We can see the gas falling into black holes — glowing x-ray hot before it disappears — and we can see supernovas from the light they emit. But there’s a lot going on down in the compact centers of these things that we can’t see with light. Gravitational waves will give us an entirely different way to probe them.
Already, the gravitational wave people and the visible light astronomers have teamed up to do joint searches for flashes of light that might accompany a gravitational wave burst. My wife, for example, is working on the computer simulations for these. This photo shows her working out the algorithm for her models.
The discovery of gravitational waves has been a long time coming. Searches started in the 1960s, and there’s even a detector on the Moon, placed there by Apollo 17. But the evidence up to this point had always been indirect. Now, we’ve finally got something both direct and obvious.
That’s big news.
Published in Science & Technology
Catch a wave and you’re sittin’ on top of the world.
Not stupid at all. In fact, it was one of the two main contenders for being dark matter for a while.
The reason you’ve got more of the small ones is like having a certain amount of cookie dough, and some large and small cookie cutters. You can either make a whole lot of little cookies, or just a few big ones. So in astronomy, you’ve got a certain amount of matter to work with, and you can either get just a few big black holes, or a whole lot of smaller ones. In practice, you probably get both, and things are more plentiful when they’re smaller.
The mini-black hole model for dark matter is called MACHOs: MAssive Compact Halo Objects. (Everything has to be an acronym in astronomy.) This would be anything with a lot of mass in a compact space, orbiting the outer edge of the galaxy—its “halo.” Could be brown dwarfs, gas giant planets, or stellar-mass black holes.
I’ve always been told the MACHO model has been pretty well ruled out by looking for how their gravity bends the light behind them (gravitational lensing), but maybe we need to revisit this, given yesterday’s discovery.
One more note on this point: The black holes we’re most familiar with as astronomers are the stellar-mass black holes, weighing as much as a large star (a few times the mass of our sun), and the “super-massive” black holes at the centers of galaxies, which are millions or billions of times the mass of our sun. What we’ve long been missing is the “intermediate-mass” black holes, with, well, masses in between.
We’ve looked for evidence of them in the orbits of stars that might be near them, and in the light put out by gas falling into black holes, but I think we’ve only got evidence for one intermediate-mass black hole (~1000 solar masses), or maybe a handful by now. They’re a missing population, and yet surely they exist, if black holes start off small and grow to super-massive proportions. So where are they?
Yesterday’s catch was of black holes with about 30 times the mass of the sun. That’s still on the small side, but it’s getting up there, and I don’t think we’ve ever found any others with this mass. This might point to the missing population. “MACHOs” at last?
Blah blah blah, science nerd stuff… just let me know when I can buy an anti-grav flying car at my local Chevy dealership, ok? ;)
I’d agree with what you’ve written. “Model” would be a better label than “predicted.” My wife creates just this sort of thing, in fact. The field is called “numerical relativity,” since they’re doing models on supercomputers. This started in the 1970s, but it was decades (2005, I think) before anybody ever got a wave pattern to work at all. But once they did, then everybody else quickly managed to, as well, and the field took off.
The numerical models are very important for getting the wave pattern right where the black holes coalesce. That’s the trickiest part to simulate, and I wonder if it might give them a lot more information about the black holes if they can get this part right.
Ah, thank you. I’ve never quite gotten that one straight.
So, if the Sun were to magically disappear, we’d truly notice nothing for eight minutes?
Maxwell predicted radio waves in 1865. Hertz said “hey look … radio waves!” in 1886. Marconi started up with wireless telegraphy in 1895.
Watch this space.
I was fixing to ask what the speed of gravity waves in a vacuum was.
Why didn’t we build that thing on the Mexican border?
Great post. I wonder, has your wife got a name? ?
How is the speed of light not violated at that speed of orbit? Does intense gravity change the speed of light in the orbit?
I’ve known for a long time, from personal experience, that large masses can be “sensed”. I’ve been night-blind my entire life, and regularly experience total darkness. Even so, in a dark landscape, I can tell there is a tree nearby – from 5′ away I sense its mass, though I can’t see it. This probably has little or nothing to do with gravitational waves. More likely sound waves.
It’s an even more insane amount of power. In an instant, the event released power equivalent to the rest of the universe. Or so I read. This is all so exciting, and there’s so much to read and try to understand! The gravity (heh!) and import of this finding is analogous to the Wright brothers’ iconic event.
Okay…here are some more questions. If gravitational waves distort space-time, presumably they are they more intense closer to the origin of the event – in this case the spiraling of two black holes around each other at an amazingly high rate of speed – and then gradually recede over distance because the energy of the wave falls off proportionally, yes?
And if that is the case, how extreme or distorted could space-time get in close proximity of the event generated the waves? Are gravitational waves at close distance crashing into one another? Folding over one another? Is space-time in this region collapsing upon itself? And what are the implications if that is happening? What does it mean if space-time is collapsing upon itself or folding over itself? Are these even valid questions?
That’s what I thought. “What we’ve long been missing is the “intermediate-mass” black holes, with, well, masses in between.” Right – something on the middle of the scale that has a nice neighborhood black hole on one end and the incomprehensible all-devouring Heart of Moloch on the other. But what about really, really small black holes? Something the size of the Moon, or a basketball, or a marble?
I know, I know – you need a star of certain mass to turn on, burn out, collapse in (which sounds like Leary advice) but IRRC, there were worriers who thought the particle accelerators would create “mini black holes,” suggesting there’s another formation path.
I’d study the matter on Wikipedia, but suspect the entry is hideously technical.
All of this is my way of saying I don’t believe in dark matter, at least as currently described. It’s too convenient.
There was a theory being entertained for a while about a small black hole in Chappaqua, New York where information was thought to have disappeared over an event horizon and irretrievably down to a point of singularity…but it appears that this is now being disproved and information once thought to have been lost is now being detected.
It could be THE question, if the end result of the incident forms a singularity that has to create another dimension to handle all the traffic, and voila! Another big bang, somewhere else. Another cosmos, another 1000 billion galaxies, and a slight chance of duplicate Kardashians.
Hmm…a Big Rear End Theory of
CosmetologyCosmology. Fascinating.So anti-gravity travel is what we should expecting to gain from this discovery in the “real” world for those of us who don’t understand any of what’s under the hood of our universe. I’m just trying to be excited about something that everyone claims we should be excited about.
In other words, why should the average person care? Where is this knowledge supposed to lead us in terms of improving everyday life? Is this about time travel, contacting aliens, cloaking devices, real hover boards, faster transportation, smell-o-vision, the end of state run healthcare? Why should schlubs like me be excited? Because if it eventually means that you scientists just end up de-classifying planets like Pluto again, I couldn’t care less.
The story is told that Benjamin Franklin attended one of the ascents of the Montgolfier Brothers hot-air balloons, and in response to the question “of what use is it?” replied “of what use is a newborn babe?”
This might not be true, but if it isn’t, it ought to be.
I believe the Europeans will be launching a LIGO satellite in the near future. The coolest LIGO idea is to place three satellites in space shooting lasers at each other. I find it interesting that LIGO is an updated version of the original Michelson-Morley experiment, the greatest non-result in scientific history, which launched modern day physics
I actually thought the same thing when I read how the two LIGO sites were set up.
How did the scientists on this project determine which blackholes, in what part of our sky, caused these results?
Was a kind of triangulation within a site between each arm (by studying the signal), and then triangulation between the two sites, possible, and were those used?
That’s impressive long-range despond, James. I salute you, sir!
Yes – if either the current precision of the instrument is good enough, or future versions improve so more local observations are possible. Imagine if a device similar to LIGO could detect the gravitational waves of the moon orbiting the earth. You could, in some sense, refine observations originally made with other means, like electromagnetism or orbital path equations.
I’d really, really like to see this thing detect something more local. That would help laymen wondering about its utility. Sun spots perhaps, or maybe black holes closer to us.
Okay…to follow up…
What I’m trying to understand is how radically distorted space-time could be closer to the event that is creating the gravitational waves. As a thought experiment, if one lived on a planet close to the spiraling black holes (not that that might possible) where presumably the amplitude of the gravitational waves is far greater and possibly even more chaotic, crashing and folding down upon themselves could space-time be so distorted as to create a circumstance where a man wakes up, gets out of bed, makes coffee, eats breakfast and then walks back to his bedroom to find himself staring down at his bed where he is still fast asleep?
Gravity waves.
Ok, what’s a graviton and are we still looking for those?
Is this like light – can be a wave and a particle?
(not that I can grasp that either)
Larry Niven posited quantum black holes in several of his stories. I know he’s not a scientist, but he writes hard science fiction, and has tried to keep up with physics and cosmology. Apparently, there was a short period right after the big bang when quantum black holes were possible.
According to the Standard Model all four fundamental forces in physics have both a field and an associated particle. All particles associated with the field show characteristics of a wave and a point particle. Yes theoretically the graviton will have the wave-particle duality. The experiment did detect gravity waves but not the quanta, i.e. individualed packet, graviton.
To get a position fix with GPS you need four satellites. Similarly to know the position of the black holes they’d need four separate measuring stations. Unfortunately because all the stations would be on or near Earth, very close to each other compared to the distance to the black holes, such a measurement would have an enormous HDOP — Horizontal Dilution of Precision. HDOP is a metric that tells you how errors in your individual measurements multiply into errors in the position solution. That translates to uncertainty about the black holes’ place in the sky, possibly such a large uncertainty that it doesn’t narrow it down at all. As for the range, I think that quantity is probably unobservable.