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back to article Black hole boffins close in on gravity waves

While the world looks for ways to directly observe gravity waves, boffins at Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) say they've used information about the Einsteinian prediction to examine huge black holes in space. In what they call a “new chapter in astronomy”, post-doctoral CSIRO …

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A "tenth of a microsecond"

That's the accuracy they say they're measuring it with in the press release. I know what they're doing is pretty complicated, but shouldn't they be able to get much better accuracy than that? Or is this just a first cut and they don't need more accuracy for what they're doing so far? Or is there a limit to the time resolution delivered by radio telescopes?

Maybe I'm assuming this is easier than it really is, based on other scientific studies where they deal with fractions of nanoseconds or smaller.

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Re: A "tenth of a microsecond"

These are pulse times of arrival (TOA), you record them at a radio telescope and compare with a reference clock, probably using GPS satellites. So your precision is limited by the synchronisation procedure. 0.1us corresponds to a light signal travelling about 30m - this is very impressive.

Don't knock it - the very much related binary pulsar TOA measurements (Hulse and Taylor, http://www.nobelprize.org/nobel_prizes/physics/laureates/1993/press.html, you can easily find, e.g., their Nobel lectures that should be a very good read) allow determination of the pulsars' orbital parameters with precision unmatched in all science (IIRC, down to 14 significant digits, on a par with the precision of measurements of electron charge - there is nothing better).

This precision allowed to measure binary pulsar slowdown that was found to be consistent with gravitational wave emission as predicted by Einstein's general theory of relativity. Since the Australian guys look at massive back holes rather than objects of ~1 solar mass I am guessing they are hoping to observe a much larger effect.

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Re: A "tenth of a microsecond"

Well, if the pulses are a few microseconds wide, and include spectral components in the Gigahertz range, then 100 nanosecond accuracy (10 MHz) is actually pretty good.

I suspect that they are either noise limited or speckle limited.

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Planck time

There is a theory that says that 1 unit of Planck Time is the smallest measurable unit of time. But it currently does not account for the sped a New York Taxi Driver can hit the horn after the lights turn green :-)

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Anonymous Coward

Re: Planck time

"does not account for the sped a New York Taxi Driver can hit the horn after the lights turn green ". Simple, the brain receives a new signal from the environment 6 seconds behind realtime as we know it. Yes, 6 seconds, there are research/experiements proving this. So how can we function in "realtime" as we know it ?!. Well, it seems our MIND (not brain, but mind) seems to have a pre-cog to allow it to off-set the 6 second delay. Or else, everything else out there will be colliding into each other and nothing will function the way we think, it should. Back to the issue, I have a simple question "How do they know it IS Gravity waves that is causing the narrowing ???". Could a super-gamma brust nearby have caused this ?. Gamma waves, or Dark-matter waves from some nearby Black holes arriving .... could be a million things and we could still be wrong!.

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Re: Planck time

"Simple, the brain receives a new signal from the environment 6 seconds behind realtime as we know it. Yes, 6 seconds, there are research/experiements proving this."

Call me skeptical, but I bet if I held an anvil above your head at such a height that it would take just 5 seconds to hit you, and if I dropped it at a random moment of my choosing giving you no warning, you'd still be able to step out of the way.

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Wile E. Ciotie ...

would like to disagree with <THWACK>

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I'm confused. Although far from being an astro- (or any other kind of) physicist, it's unclear to me why Black Holes must collide. I can understand that when galaxies collide the black holes at there centers compete for the resulting mess, er mass. But why must they combine? Wouldn't the additional fuel be sufficient to cause a wave?

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Disclaimer: No kind of physicist here either.

That said, the emission of gravitational waves is a theoretically predicted mechanism for orbital decay between two black holes (or other massive objects) in mutual orbit, which is a process that will eventually result in their collision. Being able to detect those waves to compare their strength to prediction will allow the physicists to narrow down their theories. The other outcome is the existence of gravitational waves being conclusively ruled out, which I understand will have big consequences...

Due to the weakness of the gravitational force, detection of gravitational waves is very difficult, so extreme objects or events such as supermassive black holes orbiting or colliding are considered to be good targets for observation.

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Well, you just don't get a serious (and detectable) "wave" without at least two mightily density things doing a complex dance with mightily high acceleration. So it's good to have a few million-solar-masses black holes merging or in near orbit.

See This Wikipedia Entry:

A more dramatic example of radiated gravitational energy is represented by two solar mass neutron stars orbiting at a distance from each other of 1.89×108 m (only 0.63 light-seconds apart). [The Sun is 8 light minutes from the Earth.] Plugging their masses into the above equation shows that the gravitational radiation from them would be 1.38×1028 watts, which is about 100 times more than the Sun's electromagnetic radiation.

Mathematically, this is hairy because the solutions to the equations are nonlinear (adding two solutions does not yield a solution), so numerical approximations are needed.

It is also evidently not easy to depict. The first part of the video doesn't show a black hole; it shows a black ball. In the second part, the third space dimension seems to have been dropped so these should be "circles" (but what is the "time" of that plane? This is not a Newtonian space that allows constant-time planes).

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As for the "why must they combine" (from the press release When galaxies merge, their resident central black holes are doomed to meet. They first waltz together then enter a desperate embrace and merge.), this seems to come from models that predict merger via interaction with the dust and gas of the surrounding disks (first slow down via interaction with gas and dust, then get rid of momentum via gravitational waves, if I understand correctly

I found this for example: Massive Black Hole binaries in gas-rich galaxy mergers; multiple regimes of orbital decay and interplay with gas inflows.

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Joke

So.... 11 years from now...

....flying cars!!!

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Re: So.... 11 years from now...

Pff. Proper jet packs or I'm going back to bed.

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Re: So.... 11 years from now...

and a millisecond later flying traffic cops and parking wardens.

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Thumb Up

Impressive work

Note they have already ruled out certain theories about such black holes.

Personally I've never understood the interaction between masses at high velocity and gravity waves.

It always seemed obvious that a GW detector near a big particle accelerator should be picking up feint but repetitive pulses when the accelerator was running.

But thumbs up for reducing the search range and pinning things down.

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Re: Impressive work

It always seemed obvious that a GW detector near a big particle accelerator should be picking up feint but repetitive pulses when the accelerator was running.

LOL what?

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Re: Impressive work

"It always seemed obvious that a GW detector near a big particle accelerator should be picking up feint but repetitive pulses when the accelerator was running."

I don't think the minute amount of protons being run around the accelerator even with relativistic mass would generate any measurable gravity wave esp. as ( AFAIK) the usual detectors probably wouldn't be tuned to the frequency of any such wave. A single bunch of protons at the LHC must have an orbital rate of ~10000 orbits/s

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Re: Impressive work

Yes, one would have probably want to whump an asteroid-mass black hole around the ring. Using electrostatics...

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Re: Impressive work

It always seemed obvious that a GW detector near a big particle accelerator should be picking up feint but repetitive pulses when the accelerator was running.

The key number to bear in mind is the relative stength of the Gravitational force and the Electromagnetic one. Electromagnetism is about 10^42 times stronger. This is one of the most staggering numbers in physics!

In fact, you can deduce this from thinking about the everyday world. You can dangle a few kilogrammes on a fine thread. Attracting in one direction, the entire Earth. Balancing in the other direction, electrostatic forces between the atoms in the thread. Which are themselves mostly self-cancelled within the atoms (electron charge cancelling proton charge): the attraction between atoms is the result of small asymmetries of charge distribution, which is still sufficient to hold molecules and crystals together against the pull of an entire planet.

The same number is the reason you aren't going to observe gravitational waves for anything less than extreme cosmological situations where there's a star or a galaxy's worth of mass moving close to the speed of light.

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Pint

Re: Impressive work

surf's up!

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Limits of doubt

It is not clear from the article whether they have actually detected Gravitational waves or just put a limit on their size.

If it is the latter, there must still be some doubt about whether they actually exist even though this would require major changes to Einstein's theories?

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Re: Limits of doubt

Not detected and there may be weird / unelegant / unlikely gravities with no gravity waves indeed.

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Re: Limits of doubt

Not detected, therefore limited. Not enough so at this time to cast doubt on GR. Enough so to cast doubt on some models of galaxy formation (in particular, on the formation of multiple large black holes in their cores and subsequent merger dynamics of these hypothesized large black holes).

A thought I had was that the cosmic era of large black hole mergers may be over (i.e black holes in galaxy centres interact strongly enough that they merge into one within, say, a billion years of the galaxy forming. Since all neaby galaxies formed longer ago than that, mergers won't be happening any more, bar rare events such as colliding galaxies.

One might even be able to apply the Anthropic principle to this (would a universe with frequent mergers of large black holes in our cosmological neighbourhood be compatible with mamalian life on a planet's surface? I'm thinking about cosmologically nearby Gamma-ray busts. )

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Headmaster

Gravitational waves, not gravity waves

Pedant point: correct in the article, incorrect in the headline, it should say "gravitational waves". Gravity waves are something else entirely, i.e. a meteorological phenomenon that produces seriously cool cloud formations (worth checking out on Google Images).

Having said that, the term "gravity waves" is used loosely all too often so El Reg is far from alone.

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Gravitational waves?

IF there are gravitational waves, their propagation peed through space must be instantaneous, and will modify the "nothing travels faster than light" rule.

Consider this: let's assume that earth is at a point in its ellipticl orbit where it is getting cliser to the sun (approaching winter in the northern hemisphere). Further, let us assume rhe existence of gravity waves travelling at some speed y. That would mean the gravitational force keeping earth in orbit left the sun some time in the past (since it takes time for the wave to reach earth). However, each subsequent wave arrives faster than the previous wave, by virtue of the distance between the sun and earth growing smaller. Add to that the logical fact that each wave is attracting earth to where the Sun WAS when the wave left, not where the sun IS when the wave reaches earth. Earth will be trying to orbit a point 'behind' the sun, with the perturbation growing daily as the earth approaches the sun. This would result in an orbital death spiral unless the wave travelled at infinite speed through space.

Studies of planetary orbits show conclusively that they orbit around the instantaneous location of the center of mass, not some past location of the mass. For something we experience daily, and can make predictions about with great accuracy, we know little about just what - and why - gravity is.

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Re: Gravitational waves?

An orbital death spiral is exactly what will happen to every orbiting system in the universe, given enough time. "Enough" is a lot (hint: many powers of ten times the current 15-billion-year age of the universe). Gravitational wave emission becomes humanly measureable only where nature throws stellar or greater masses around in really tight orbits at significant fractions of the speed of light.

You aren't upset about the electromagnetic death spiral that will overtake orbiting electrically charged bodies at a rate many orders of magnitude faster, are you?

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Facepalm

Re: Gravitational waves?

IF there are gravitational waves, their propagation peed through space must be instantaneous, and will modify the "nothing travels faster than light" rule.

This has been done to death on alt.space.discussion in the early nineties.

Yeah, checking for stable orbits in Einstein gravity is so beyond those dumb physicists.

Do the math. I'm sure it will work out.. What's that? Can't into 4-D tensors? Then why are you posting?

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Re: Gravitational waves?

Can't into 4-D tensors?

Not sure what that means but have you tried solving Einstein's equations for two black holes rotating about each other? You dont actually get gravity waves if you do that.

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Black hole boffins close in on gravity waves

Spanish home in on El Dorado.

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