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Astronomers Discover 33 Pairs of Waltzing Black Holes

ScuttleMonkey posted more than 4 years ago | from the teach-them-to-foxtrot dept.

Space 101

Astronomers from UC Berkeley have identified 33 pairs of waltzing black holes, closing the gap somewhat between the observed population of super-massive black hole pairs and what had been predicted by theory. "Astronomical observations have shown that 1) nearly every galaxy has a central super-massive black hole (with a mass of a million to a billion times the mass of the Sun), and 2) galaxies commonly collide and merge to form new, more massive galaxies. As a consequence of these two observations, a merger between two galaxies should bring two super-massive black holes to the new, more massive galaxy formed from the merger. The two black holes gradually in-spiral toward the center of this galaxy, engaging in a gravitational tug-of-war with the surrounding stars. The result is a black hole dance, choreographed by Newton himself. Such a dance is expected to occur in our own Milky Way Galaxy in about 3 billion years, when it collides with the Andromeda Galaxy."

cancel ×

101 comments

Waltzing? (3, Funny)

CannonballHead (842625) | more than 4 years ago | (#30646092)

Apparently, the definition "waltzing"/a waltz has been diminished to the extent that now it just refers to two objects moving together. Hum.

I guess I'm just a cranky music theory lover though.

Re:Waltzing? (2, Funny)

Z00L00K (682162) | more than 4 years ago | (#30646184)

Time to play Waltzing Matilda then?

Re:Waltzing? (1)

miruku (642921) | more than 4 years ago | (#30647688)

Re:Waltzing? (2)

FlyingBishop (1293238) | more than 4 years ago | (#30646442)

Yeah I would've expected them to oscillate in a frequency that is a multiple of 3.

Re:Waltzing? (0)

Anonymous Coward | more than 4 years ago | (#30646622)

Or, in effect the galaxies, us included, have already collided. We, being on the temporal edge of the black hole's event-horizon are as of yet incapable of truly appreciating our doomed status.

Re:Waltzing? (1)

Monkeedude1212 (1560403) | more than 4 years ago | (#30646634)

Are you saying that you don't feel closer whenever you waltz with a member of the opposite sex?

They are merely using waltz to describe the effects of said motion, not the actual motion itself, which is confusing since waltzing (the dance) implies motion.

However, if you were expecting some similarity between the black holes and music, I have a My Chemical Romance CD I could send to you.

Re:Waltzing? (1)

BlaisePascal (50039) | more than 4 years ago | (#30647304)

The issue is that a waltz is characterized by a beat with an emphasis on every third beat ("Oom-pa-pa-Oom-pa-pa"). If you want to get closer but without the emphasis on thirds you can do a swing or a pivot, either of which would better describe the motion of two massive orbiting bodies.

Re:Waltzing? (2, Informative)

RichardDeVries (961583) | more than 4 years ago | (#30647576)

Other similarities are that in a waltz, the dancers usually remain in closed position and that the pair makes circular motions. You know, like waltzing black holes.

Re:Waltzing? (1)

Suki I (1546431) | more than 4 years ago | (#30649076)

I think it's romantic. Harrumph!

Re:Waltzing? (1)

mykos (1627575) | more than 4 years ago | (#30652022)

As a cranky literature lover, I'll have you know that utilizing "waltzing" for personification diminishes the term in no way.

Can Black Hole A eat Black Hole B? (0)

Anonymous Coward | more than 4 years ago | (#30652116)

Get two very hungry black hole together, can one eat up another?

The big question (3, Funny)

Drummergeek0 (1513771) | more than 4 years ago | (#30646100)

Who leads and who follows?

Re:The big question (1, Funny)

gstoddart (321705) | more than 4 years ago | (#30646400)

Who leads and who follows?

Well, it's governed by orbital mechanics and gravity ... so the bigger one technically 'leads', but the smaller one also exerts some influence. :-P

Cheers

Re:The big question (1)

OakDragon (885217) | more than 4 years ago | (#30646696)

I'm assuming it's black tie only?

Re:The big question (1)

MBGMorden (803437) | more than 4 years ago | (#30656420)

They learn as they go. Sometimes one leads, sometimes it follows. They don't worry 'bout what they don't know. Galactic collisions is a dance you learn as you go.

- JMM

OH NO! (2, Funny)

madddddddddd (1710534) | more than 4 years ago | (#30646154)

the Y3B bug already being dismissed as irrelevant

Newton? (4, Insightful)

sznupi (719324) | more than 4 years ago | (#30646214)

At those masses, the choreographer is most likely Einstein (nvm that dark matter might be not the underlying cause of some discrepancy between how we think gravity works and what we are observing at galactic scales; we might as well have a different choreographer yet)

Re:Newton? (2, Informative)

bcrowell (177657) | more than 4 years ago | (#30647992)

At those masses, the choreographer is most likely Einstein

That's incorrect. The paper [arxiv.org] gives the orbital velocities as being ~100 km/s. If the black holes were close enough to one another for their orbits around their mutual center of mass to be significantly affected by relativity, their distance from one another would have to be comparable to the radii of their event horizons. But at a distance that's comparable to the radius of the event horizon, orbital velocities are a significant fraction of the speed of light. Since we observe that their orbital velocities are very small compared to the speed of light, it follows that their orbits are Newtonian to a good approximation.

that dark matter might be not the underlying cause of some discrepancy between how we think gravity works and what we are observing at galactic scales; we might as well have a different choreographer yet

I assume you're referring to something like MOND [wikipedia.org] , in which case this is also incorrect. MOND gives significant corrections for objects with very small accelerations. These black holes actually have very big accelerations compared to the accelerations of ordinary disk stars, which are what MOND was invented to explain. Therefore even if MOND were right (which seems increasingly unlikely), it wouldn't be relevant for understanding these binary black holes' orbits.

Re:Newton? (1)

sznupi (719324) | more than 4 years ago | (#30649200)

Mercury orbits at half of those 100 km/s, and yet also at those orbital energies, curvature of space, you have to take into account relativistic effects to have any understanding of its orbit.

As for as somebody else being the choreographer, I wasn't standing by the notion of it; just mentioning the possibility (and hey, for supermassive black holes acceleration resulting in orbital velocity of 100 km/s might fall under rather small BTW)

Re:Newton? (2, Informative)

bcrowell (177657) | more than 4 years ago | (#30650366)

Mercury orbits at half of those 100 km/s, and yet also at those orbital energies, curvature of space, you have to take into account relativistic effects to have any understanding of its orbit.

No, that's incorrect. Newtonian physics is an excellent approximation to the orbit of Mercury. The famous relativistic effects on Mercury's orbit are tiny. To see them, you have to subtract out a whole bunch of other effects, some of them a hundred times bigger [wikipedia.org] than the relativistic one.

and hey, for supermassive black holes acceleration resulting in orbital velocity of 100 km/s might fall under rather small BTW

No, because the adjustable parameter in MOND is specifically tuned up so that you only get significant anomalous effects for stars farther out in the disks of galaxies. Comerford's paper says they expect the black-hole pairs to be separated by ~1 kpc, which is small compared to the size of a galaxy. If you estimate the acceleration from their numbers, you get a=v^2/r=(100 km/s)^2/(0.5 kpc)=6x10^-10 m/s2, which is about 5 times bigger than the a0 parameter in MOND, so you won't see any significant effect. This isn't a coincidence, because supermassive black holes are observed at the *centers* of galaxies, not out in the disks, whereas the MOND parameter is chosen so as to have an effect on the disk while leaving things at smaller radii alone.

Re:Newton? (1)

pnewhook (788591) | more than 4 years ago | (#30650864)

GPS satellites need their internal clocks corrected to take into account relativistic effects based on the speed they are going. And they are only travelling at about 4km per second.

So yeah, relativity does have an effect.

Re:Newton? (2, Informative)

bcrowell (177657) | more than 4 years ago | (#30650996)

GPS satellites need their internal clocks corrected to take into account relativistic effects based on the speed they are going. And they are only travelling at about 4km per second. So yeah, relativity does have an effect.

Absolutely. But the relativistic effects are extremely small at those speeds. For instance, the relativistic time dilation aboard a GPS satellite is about 1 part in 10^10.

Re:Newton? (1)

pnewhook (788591) | more than 4 years ago | (#30651098)

Absolutely. But the relativistic effects are extremely small at those speeds. For instance, the relativistic time dilation aboard a GPS satellite is about 1 part in 10^10.

The relativistic effects on the GPS onboard clock due to its relative motion to the GPS receiver would result in the position calculation being shifted by 7 miles per day if it were not corrected for.

Re:Newton? (2, Informative)

bcrowell (177657) | more than 4 years ago | (#30651142)

The relativistic effects on the GPS onboard clock due to its relative motion to the GPS receiver would result in the position calculation being shifted by 7 miles per day if it were not corrected for.

Sure. The error in locating yourself on the earth's surface equals the time error multiplied by the speed of light. Since the speed of light is big, the technique is extremely sensitive to tiny time errors.

Re:Newton? (1)

arminw (717974) | more than 4 years ago | (#30651264)

....because supermassive black holes are observed at the *centers* of galaxies...
Black holes, supermassive or otherwise have never been OBSERVED anywhere. They are mathematical constructs that are theorized to exist in the center of galaxies and maybe other places, but no one has ever seen one anywhere. They, as well as dark matter and energy are theorized to exist, because of the unexplained motion of heavenly bodies we CAN observe. Clearly something is causing stars and galaxies to move differently than our knowledge of the laws of gravity predict. The operation of gravity is understood well enough and has been understood, to enable us to launch satellites and rockets to the moon and other parts of the solar system.

There are theories that besides gravity, electrical and magnetic forces may be also involved. Scientists and researchers who even mention electricity being involved in the operation of large-scale universe are labeled as crackpots and nuts by well-funded mainstream scientists. Quite often in science, these so-called nuts were later vindicated by mainstream science.

Re:Newton? (1)

sznupi (719324) | more than 4 years ago | (#30652946)

I still have the impression you think I was embracing alternative theories of gravity...oh well.

But as for Mercury; well, the fact stands that even with all other factors, with tiny mass of the planet, we were seeing it in different orbit than it "should" be...with our capabilities from centuries ago. Never mind even that this effect would be only slightly stronger - it's there. Newton isn't the choreographer.

Re:Newton? (2, Informative)

bcrowell (177657) | more than 4 years ago | (#30656092)

I still have the impression you think I was embracing alternative theories of gravity...oh well.

No, I pointed out that you'd misunderstood those alternative theories of gravity.

But as for Mercury; well, the fact stands that even with all other factors, with tiny mass of the planet, we were seeing it in different orbit than it "should" be [...]

Both in your original post [slashdot.org] and in this one, you seem to be displaying a misconception that the mass of the object is what matters. That's incorrect. What makes a black hole a black hole isn't its mass, it's the fact that the mass is compressed into such a small space. When an ordinary, main-sequence star collapses into a black hole, it actually loses mass in the process. Likewise the mass of Mercury is completely irrelevant to the discussion. You seem to think that Mercury's small mass reduces the relativistic effect on its orbit. That's incorrect. The relativistic precession of Mercury's perihelion is 43 seconds of arc. If Mercury's mass was half what it is, or double what it is, the precession would still be 43 seconds of arc.

Never mind even that this effect would be only slightly stronger - it's there. Newton isn't the choreographer.

Similarly, you could analyze the motion of two human bodies doing a literal waltz, and say that Newton isn't the choreographer. You'd be absolutely right. There would be relativistic effects on the motion of their bodies. That would be absolutely irrelevant, however, because the effects would be too small to measure compared to other effects that you couldn't even quantify, like air currents. Similarly, the relativistic effects on the orbits of these black holes are far too small to measure. The gamma factor for an object moving at 100 km/s is 1.00000006. The difference from 1, which is 5x10^-8, quantifies the size of the relativistic effects. If you take a look at the paper [arxiv.org] , they weren't even able to resolve the black holes well enough to determine their distances from one another. That means that their orbits are not known at all, much less to a precision of parts per billion. Also, if we assume that their order-of-magnitude estimate of 1 kpc for the orbital separation is roughly correct, each one is swimming in the gravitational field of a whole bunch of other densely packed stars near the galactic core. That effect, which is impossible to measure or calculate with any precision, is going to completely swamp the relativistic effect.

Re:Newton? (1)

sznupi (719324) | more than 4 years ago | (#30657402)

No, I pointed out that you'd misunderstood those alternative theories of gravity.

But I wasn't referring specifically to any of them, you did. I just left open the possibility that we might well still have some other choreographer in the future; my acceptance of general relativity notwithstanding.

Anyway I'm perfectly aware what makes a black hole a black hole, their Schwarzschild radius, and so on. Which is irrelevant here anyway, since when discussing orbits mass is the only thing that matters. Those two objects could be two compact swarms of butterflies for all we know. ;p

You are forgetting that all that matters in discussing whether the precession of orbit due to relativistic effects is not insignificant, is the size of orbit relative to the gravity well of participating bodies. And the fact is, those two supermassive black holes are comparably close to each other like Mercury and Sun, relative to the gravity wells of those bodies. Comparably deep in each others gravity well to the one in which Mercury is (nvm that for those black holes it can still go much further down). The effect is clearly there.

Yes, we might not be able to see it from this distance. But that doesn't change who the choreographer is, nothing more.

Re:Newton? (1)

bcrowell (177657) | more than 4 years ago | (#30658796)

Anyway I'm perfectly aware what makes a black hole a black hole, their Schwarzschild radius, and so on. Which is irrelevant here anyway, since when discussing orbits mass is the only thing that matters.

No, that's incorrect. There are three quantities that could be relevant: the mass of the primary M, the mass of the satellite m, and the radius of the orbit r. Contrary to your previous statements, m is irrelevant for a highly asymmetric system like the sun and Mercury. What quantifies the strength of the gravitational effects is the unitless quantity (G/c^2)(M/r), where m is the mass of the primary, and r is the radius of the orbit.

You are forgetting that all that matters in discussing whether the precession of orbit due to relativistic effects is not insignificant, is the size of orbit relative to the gravity well of participating bodies.

This contradicts your previous statements, but it is more or less correct, except that for the caveat about the irrelevance of m in the asymmetric case.

Comparably deep in each others gravity well to the one in which Mercury is

This is incorrect. In the case of Mercury and the sun, we have (G/c^2)(M/r)=3x10^-8. In the case where M is the mass of the supermassive black hole Sgr A*, and r is 1 kpc, (G/c^2)(M/r)=2x10^-10. Therefore the relativistic effects for the binary black holes are smaller by two orders of magnitude.

(nvm that for those black holes it can still go much further down).

The orbital radii for these binary black holes is estimated to be 1 kpc. It's true that you could get stronger relativistic effects if you made r smaller ("go much further down"), but in fact r is much bigger, even in proportion to M.

Wake Me Up When (1)

sexconker (1179573) | more than 4 years ago | (#30646246)

Wake me up when they've found some doing the Foxtrot or the Lindy Hop.

Re:Wake Me Up When (2, Funny)

Red Flayer (890720) | more than 4 years ago | (#30646606)

Wake me up when they've found some doing the Foxtrot or the Lindy Hop.

Meh, that's no big deal. Wake me up when a bunch of black holes line up to dance.

THEN you know we've got problems.

Doo doo doo de do de do doo doo/
Doo doo doo de do de do doo doo/
Do the hustle!

Collision is imminent (1)

Jim Hall (2985) | more than 4 years ago | (#30646372)

"[...] a merger between two galaxies should bring two super-massive black holes to the new, more massive galaxy formed from the merger. The two black holes gradually in-spiral toward the center of this galaxy, engaging in a gravitational tug-of-war with the surrounding stars. The result is a black hole dance, choreographed by Newton himself. Such a dance is expected to occur in our own Milky Way Galaxy in about 3 billion years, when it collides with the Andromeda Galaxy."

Don't worry - I'm sure Russia will have an ill-defined plan to divert this somehow. By then.

(Sorry, couldn't resist.)

Re:Collision is imminent (1)

AikonMGB (1013995) | more than 4 years ago | (#30646512)

In Soviet Russia, the Andromeda Galaxy collides with you?

Re:Collision is imminent (0)

Anonymous Coward | more than 4 years ago | (#30648152)

In Milky Way Galaxy, Andromeda Galaxy collides with you.

Re:Collision is imminent (1)

Talderas (1212466) | more than 4 years ago | (#30646528)

The dire threat of colliding galaxies in 3 billion years demands that we act now to save our planet!

Re:Collision is imminent (1)

arminw (717974) | more than 4 years ago | (#30651292)

If global warming doesn't get us first.

Re:Collision is imminent (1)

FiloEleven (602040) | more than 4 years ago | (#30652056)

Won't someone think of the children's children's children's children's children's [...] children's children's children's children???

So, would a pair of coupled black hole pairs... (1)

Biff Stu (654099) | more than 4 years ago | (#30646514)

be square dancing?

Re:So, would a pair of coupled black hole pairs... (1)

billstewart (78916) | more than 4 years ago | (#30647142)

No, square dancing needs four _couples_ to make a set.

Re:So, would a pair of coupled black hole pairs... (1)

Megahard (1053072) | more than 4 years ago | (#30649770)

33 pairs is enough for 8 squares, with one pair sitting out. They could do a Galaxy Circulate [tamtwirlers.org] .

and this... (3, Insightful)

owlnation (858981) | more than 4 years ago | (#30646530)

... is the only "Dancing with the Stars" I'd ever want to see.

Re:and this... (0)

Anonymous Coward | more than 4 years ago | (#30646690)

Doubly so if the partner was <Insert politician of opposite side of the spectrum here>.

Re:and this... (0)

Anonymous Coward | more than 4 years ago | (#30647492)

Woz?

Hmmm.... (1)

Daimanta (1140543) | more than 4 years ago | (#30646538)

Finally I can post this link and not be offtopic:

http://www.youtube.com/watch?v=Cg1dMpu4v7M [youtube.com]

Re:Hmmm.... (1)

bmo (77928) | more than 4 years ago | (#30646732)

And this is what the Internet does to your precious Tchaikovsky.

http://www.youtube.com/watch?v=TvYOm89IcUU [youtube.com]

You're welcome.

--
BMO

Einstein! (2, Informative)

mbone (558574) | more than 4 years ago | (#30646552)

choreographed by Newton himself.

He might try, but the accurate calculation of black hole orbits requires the complete infrastructure of General Relativity, so Einstein is calling this tune.

Re:Einstein! (1)

mhajicek (1582795) | more than 4 years ago | (#30646960)

That depends on your frame of reference.

Re:Einstein! (1)

migla (1099771) | more than 4 years ago | (#30647214)

Yeah. Whomever. The real question is: What are we going to do about it?

Wow! (3, Insightful)

gstoddart (321705) | more than 4 years ago | (#30646610)

Wow, when I was in university, Black Holes were still a mostly theoretical idea and we had no real empirical evidence to support their existence.

Now we've got 33 pairs of them entwined in death spirals, and we're pretty sure every galaxy has one.

There's still a lot out there that we can't even conceive of ... I can't wait to see what the next 15-20 years brings us. I like the fact that the universe is vastly more complicated than we've ever really been able to guess at.

Cheers

Re:Wow! (0)

Anonymous Coward | more than 4 years ago | (#30647548)

You should have studied black holes in the Uni more!

Re:Wow! (1)

pnewhook (788591) | more than 4 years ago | (#30650906)

Wow, when I was in university, Black Holes were still a mostly theoretical idea and we had no real empirical evidence to support their existence.

Was this a creationist university?

Re:Wow! (2, Interesting)

gstoddart (321705) | more than 4 years ago | (#30651088)

Was this a creationist university?

*laugh* No, but it was pre-Hubble before they'd actually done the measurements to be fairly sure. There was strong theoretical evidence, but nothing they'd been able to hold up until '94 when they looked at M87. (Yes, there had been some evidence, but not yet conclusive.)

Some of us went to university a long time ago, and the world has changed a lot since then.

Like I said, I just continue to be amazed at the changes in my lifetime. You young kids think we've always known this stuff. :-P

begging your pardon sir, but it's a big-ass sky

;-)

Cheers

Re:Wow! (1)

arminw (717974) | more than 4 years ago | (#30651336)

....Black Holes were still a mostly theoretical idea and we had no real empirical evidence to support their existence....
They still are nothing but a mathematical construct, because nobody has ever observed one actually exists. They are inferred to exist, the same as dark matter and energy, because we observe stars and galaxies to move in ways that our incomplete knowledge can't explain.

Re:Wow! (1)

MBGMorden (803437) | more than 4 years ago | (#30656562)

They've been observed as much as we can. If you're looking for a photograph, then you're not going to get one because by nature they're invisible. Seeing something isn't the only way to observe it though. In this case, it's simply NOT going to be the way you observe it. We know how gravity and mass works. We can easily observe stars in our galaxy for example swinging around an incredibly massive object at the center of the galaxy that is invisible.

Invisible object, of that mass, at that size, IS a black hole.

Re:Wow! (1)

arminw (717974) | more than 4 years ago | (#30658498)

....swinging around an incredibly massive object at the center....
That assumes (a belief, not knowledge) that gravity is the ONLY force that can govern the motion of objects such as stars. If there is electricity and/or magnetism involved in addition to gravity, then the assumption of a black hole is false. Just the fact that the electric force is 36 orders of magnitude greater than gravity, makes it quite probable that electric and magnetic fields would be a large factor in controlling the motion we observe. This would be especially true in the center of the galaxy, with its dense population of stars. We know from our Sun, that large magnetic and electric fields are associated with it.

Because of this absolutely huge strength difference between gravity and electricity, even a tiny charge imbalance or a relatively small magnetic fields, can generate enormous forces that can completely overwhelm the weak gravitational interaction.

If scientists are going to make assumptions, is it reasonable at all, to totally exclude the electric and magnetic forces from consideration in the large-scale operation of the universe? There are theories, developed by scientists with just as many credentials and degrees, which explain the observations, without resorting to complicated mathematical constructs, such as black holes and relegating as much as 90% of all matter & energy in this universe invisible to direct observation. When fundamental assumptions fail to make sense of the data, it is time to throw out those assumptions and start over with new ones. That of course is very difficult to do by someone who has scribbled a ton or two of chalk onto some academic blackboard, writing complicated equations to try to explain the measurements.

Good news for gravitational waves hunters (4, Insightful)

photonic (584757) | more than 4 years ago | (#30646662)

Great, the collision of these things is exactly the kind of event we need for detecting gravitational waves [wikipedia.org] . These kind of 'inspirals' emit very distinct pattern, which can be retrieved very efficiently from the noise with matched filter banks. The higher the mass, the lower the frequency of this 'chirped' signal, so it is probable that these colliding super-massive black-holes cannot be detected with the ground [caltech.edu] -based [virgo.infn.it] kilometer long observatories, which are measuring right now. This is probably more something for the space-based LISA [nasa.gov] mission, which can probe much lower frequencies since it has a base-line of millions of kilometers.

Re:Good news for gravitational waves hunters (2, Interesting)

bcrowell (177657) | more than 4 years ago | (#30647124)

The same thing occurred to me. Here [arxiv.org] is what appears to be the paper describing the observations. It's remarkably silent on whether any of this has implications for gravitational wave astronomy or tests of general relativity. They basically seem to see it as purely a way of finding out about evolution of galaxies. I guess the fact that these pairs are reasonably frequent implies that you can make reasonable estimates, probably for the first time, of the rate at which black hole collisions should be expected. I wonder to what extent these black hole pairs can be used as laboratories for testing general relativity in the same sense as the Hulse-Taylor pulsar [wikipedia.org] , even before they merge. I guess the orbital periods would be very long, though.

Re:Good news for gravitational waves hunters (1)

photonic (584757) | more than 4 years ago | (#30647484)

They do give a merger rate per galaxy in the introduction of the article. If you combine that with a density of galaxies and the sensitivity of your detector, this should give you a rate of observable events. In the final paragraph they confirm my suspicion that this coalescing SMBHs are LISA's business and that their observations should give an upper limit to the detection rate. I don't know if this is good or bad news, that depends on the earlier predictions.

Re:Good news for gravitational waves hunters (1)

budgenator (254554) | more than 4 years ago | (#30647536)

The orbit has decayed since the binary system was initially discovered, in precise agreement with the loss of energy due to gravitational waves predicted by Einstein's General Theory of Relativity. Hulse-Taylor binary [wikipedia.org]

Cool, maybe in a couple billion years we'll finally know what happens when two waltzing blackhole kiss each other.

Re:Good news for gravitational waves hunters (1)

pnewhook (788591) | more than 4 years ago | (#30650952)

I wonder to what extent these black hole pairs can be used as laboratories for testing general relativity

General relativity has been verified countless times, from the existence of black holes, to gravitational lensing, to even time dilation. General relativity effects are even needed to be compensated for in GPS clock calculations. Are there aspects of general relativity left to be tested?

Re:Good news for gravitational waves hunters (1)

bcrowell (177657) | more than 4 years ago | (#30656910)

General relativity has been verified countless times, from the existence of black holes, to gravitational lensing, to even time dilation. General relativity effects are even needed to be compensated for in GPS clock calculations. Are there aspects of general relativity left to be tested?

Sure. Of course you have to distinguish between falsifying Newtonian mechanics and verifying general relativity. It only takes one observation to disprove a theory, but proving a theory correct is a whole different matter.

A good (but somewhat out of date) popular-level description of this kind of thing is "Was Einstein Right?" by Clifford Will.

Some examples of things that are still left to test about GR:

  1. Nobody has been able to directly verify Einstein's century-old prediction that low-amplitude disturbances in the gravitational field propagate at c. A claim was made that it had been done in 2003, but it was wrong: [1] http://arxiv.org/abs/astro-ph/0302294 [arxiv.org] [2] http://arxiv.org/abs/astro-ph/0304006 [arxiv.org] [3] http://arxiv.org/abs/astro-ph/0301145 [arxiv.org]
  2. Nobody knows whether gravitational torsion [lightandmatter.com] exists. Einstein and Cartan played around with it as a way of making a GUT. String theory requires it to exist. The experimental evidence so far has put an upper limit on it.
  3. There are various theories of gravity that are consistent with GR in a certain limit, but differ from it in ways that should be empirically detectable. Two examples are the Brans-Dicke theory [wikipedia.org] and Oestvang's quasi-metric relativity [arxiv.org] . The selling points of the Brans-Dicke theory are that it's supposedly more "Machian" than GR, and at one time it was thought to reproduce certain solar-system measurements that GR couldn't reproduce, although that turned out to be wrong. Oestvang claims that he can reproduce the Pioneer anomaly [wikipedia.org] . Even if they turn out to be wrong, it's important to have them as "test theories." If you don't have any alternative theoretical framework, then it's impossible to decide what experiments to do to test GR, and it's impossible to interpret results of experiments unambiguously. This is basically the reason that it's been impossible to test propagation of gravitational effects at c; we don't have a viable test theory that predicts that they don't propagate at c, so there's no way to interpret the results of experiments.
  4. There are various open theoretical problems in classical GR (cosmic censorship, chronology protection conjecture), which may have some bearing on whether the theory is even self-consistent as a classical theory of gravity. There's a strong argument that if cosmic censorship fails, GR fails as a classical theory.
  5. There are significant questions, which could be resolved by observation, about the extent to which quantum effects alter the classical picture of the formation and structure of black holes. See, e.g.: http://arxiv.org/abs/0902.0346 [arxiv.org]

Re: "the orbital periods would be very long" (1)

Herve5 (879674) | more than 4 years ago | (#30653618)

Very very long indeed. I understand the timescales in TFA are in million to billion years, so the frequencies photonic expects to detect would be conversely so low that this'll just be a constant at our timescale... I fear we'll not see a turn ;-)

Re: "the orbital periods would be very long" (1)

photonic (584757) | more than 4 years ago | (#30655478)

If your detector is sensitive enough to observe lots of galaxies at the same time, you will be able to observe a few at the final stage of the inspiral. The system looses energy due to gravitational waves, thus the distance between the two objects will decrease and the rotation frequency will increase up to the point that they merge. It is this final stage that we want to detect, which the gravitational waves are sent with higher frequency and intensity.

Re:Good news for gravitational waves hunters (0)

Anonymous Coward | more than 4 years ago | (#30647928)

If I remember correctly, LISA is sensitive to gravitational waves with a period of minutes, which we would expect from a neutron star binary system. A supermassive black hole binary system will emit gravitational waves with a much longer period - years, at least. These are more likely to be detected through pulsar timing projects like PPTA [csiro.au] - essentially, these work similarly to observatories like LIGO or LISA, but instead of using an artificial laser as their input signal, they use radio pulses from pulsars. If the pulsars in one part of the sky seem to pulse a little earlier, and those in an orthogonal part of the sky pulse a little later, that would be an indication of a gravitational wave.

Re:Good news for gravitational waves hunters (1)

photonic (584757) | more than 4 years ago | (#30655574)

You might be right that super-massive black holes emit at frequencies that are even too low for LISA, for which the pulsar timing would help. Neutron star binaries, however, should emit up to a few hundred Hz, so they should be detectable with ground-based detectors. This leaves the normal black holes for LISA, so these three different methods nicely complement each other.

Is this really a discovery? (1)

Fluffeh (1273756) | more than 4 years ago | (#30646670)

Given that it's pretty common knowledge that a) galaxies have big black holes at their centers and b) that galaxies collide... is it really a discovery that black holes will orbit one another as their gravity catches hold of one another?

I mean okay, it's cool to actually have proof of it but I am pretty sure I read about orbiting black holes a while back already. Not to take the icing off the cake here, I am probably more annoyed with the slashdot heading.

Re:Is this really a discovery? (1)

mhajicek (1582795) | more than 4 years ago | (#30646972)

There's a big difference between speculation and measurable data.

Confirmation of a theory is important (1)

jfengel (409917) | more than 4 years ago | (#30647114)

As with so much of science: if you went out there and didn't find it, that would be much bigger news, because it would cast doubt on your present theory.

Confirmation is never as exciting as falsification, but it's good that science isn't all that exciting, or nothing would ever get done. The more confirmations you get, the further you can speculate, with the chance of getting something that can be falsified.

Re:Is this really a discovery? (1)

MBGMorden (803437) | more than 4 years ago | (#30656648)

That's the "common sense" idea, and it's simply not a good way to do things.

To the average man a scientist trying to figure out why things fall, or measuring the speed at which they fall for example is wasting time. It's "common sense" that things just fall.

However, many, many things over the centuries that were "common sense" have been proven wrong when subjected to scientific analysis (after all, it was once common sense that the Sun went around the Earth).

Just dismissing every study as invaluable because you think you intrinsically know the results already is a recipe for a society full of misconceptions.

How long does the pair last before merger? (0)

Anonymous Coward | more than 4 years ago | (#30646758)

Given that the pair of orbiting supermassive black holes will be (presumably) spewing out gravitational waves at a prodigious rate, two questions come to mind:

1) How long does it take two such objects to coalesce? Are we talking millions, billions, or trillions of years?

2) My memory is foggy, but ISTR that a black hole merger results in a significant fraction (10-20%) of the black holes' masses being released as energy.

That sort of energy release is in gamma-ray-burst territory when you're talking about stellar-mass black holes, but downright awesome when you're talking about the potential for a merger between two supermassive black holes.

What happens when the holes merge? (1)

MMORG (311325) | more than 4 years ago | (#30646878)

So if a single magnestar can produce a truly massive gamma ray blast just by displacing its crust by a couple of centimeters http://science.slashdot.org/story/09/12/27/1639207/Fifth-Anniversary-of-a-Cosmic-Onslaught [slashdot.org] , what happens when two super-massive black holes finally merge?

Re:What happens when the holes merge? (1)

mhajicek (1582795) | more than 4 years ago | (#30647008)

Good question, but I imagine not a whole lot would make it past the event horizon(s). There would be a bunch of energy released by the collision of the matter orbiting them though.

Re:What happens when the holes merge? (1)

michelcolman (1208008) | more than 4 years ago | (#30647300)

From our point of view, they take an infinite amount of time to actually merge, since time around them slows down to pretty much a standstill due to the huge gravitational time dilation. So I guess there's nothing to worry about. In fact, even the black holes themselves don't really exist yet, they will forever be "almost" black holes (though admittedly very, very close). Unless you fall into one. But that would take an infinite amount of time from an outside observer's point of view, too.

*golf clap* (0, Troll)

drDugan (219551) | more than 4 years ago | (#30646924)

Okay, great. Exciting observations, but really, not that useful in the big scheme of where we are with physics today.

How about you physicists show us Higgs? How do quantum mechanics and gravity mesh into a coherent theory? Explain the disagreement of 107 orders of magnitude (yes, you read that right: 107 zeros) between the upper bound upon the vacuum energy density (from data obtained from Voyager, less than 10**14 GeV/m3) and the zero-point energy of 10**121 GeV/m3 - calculated using quantum field theory, or alternately: Why doesn't the zero-point energy of the vacuum cause a large cosmological constant? Why is there far more matter than antimatter? Are protons stable - if not, what's the half life? Is SUSY real or just implied? What governs the transition of quarks and gluons into pions (ie explain QCD)? What's the mass of a Neutrino? Explain why the fundamental physical constants have the exact and seemingly arbitrary yet interconnected values they have? Why did the universe have such low entropy in the past? What causes gamma ray bursts? and on and on and on...

But most of all, explain what causes the observed effects of hypothetical "dark matter" and "dark energy". My young children are smart enough to know that the dark matter story sounds like total and utter bull. The story goes like this: "We see something that looks like it causes things to move, but we don't know what it is, and we can't see it, or measure it, create it, or understand it at all. These unobservable matter blobs (and energy) may be 95% of everything we observe! We see something we can't explain, so we're calling it 'dark matter' and moving on with the old story that has worked for a while and still gets us grant funding." Why no one with a brain is calling out this story for its absurdity is astounding.

These issues are not subtle or small. The theories science (specifically physics) now promotes and teaches about the physical world, while highly accurate and highly reproducible in different areas, are *impossibly inconsistent* and *abundantly incomplete*. For science, inconsistency on this scale is a crisis requiring a revolution in thought.

The most dangerous hubris in science is the refusal to accept that we're far more ignorant about our physical environment than most would like to admit.

Re:*golf clap* (4, Insightful)

Chris Burke (6130) | more than 4 years ago | (#30647180)

But most of all, explain what causes the observed effects of hypothetical "dark matter" and "dark energy". My young children are smart enough to know that the dark matter story sounds like total and utter bull. The story goes like this: "We see something that looks like it causes things to move, but we don't know what it is, and we can't see it, or measure it, create it, or understand it at all. These unobservable matter blobs (and energy) may be 95% of everything we observe! We see something we can't explain, so we're calling it 'dark matter' and moving on with the old story that has worked for a while and still gets us grant funding." Why no one with a brain is calling out this story for its absurdity is astounding.

Because people with brains -- or at least those with brains and a bit of particle physics knowledge -- know that the idea of a type of matter that has mass but does not interact electromagnetically and is thus extremely hard to detect is not that outlandish. We already know of one such particle, the neutrino. A more massive neutrino-like particle is a prime candidate for dark matter, and is predicted by theory outside of dark matter. And while it's still highly speculative, there are teams out there right now who believe they are on the trail of detecting this particle.

In other words, they are doing exactly what you think they should be doing, and working on the problem. But surprisingly, doing actual useful work in this area requires more education than your children, or you for that matter, possess. Sorry!

The most dangerous hubris in science is the refusal to accept that we're far more ignorant about our physical environment than most would like to admit.

Stand in front of a mirror, look yourself directly in the eye, and say that fifty times.

All the things you point out, like what dark matter actually is, are holes in physics knowledge that physicists readily admit too. At least to the extent that you accurately describe the holes, rather than your gut feeling about what sounds too weird to be true. So who is showing hubris again?

Re:*golf clap* (1)

steelfood (895457) | more than 4 years ago | (#30658904)

I think the terminology used leads to confusion in the layman. "Dark matter" sounds like it's something real, like matter but that's undetectable. In actuality, it's just a placeholder for something unknonwn, like null in a database. It could be undiscovered matter, or it could be an undiscovered property of known matter. By giving it a term, most people end up with the impression that it's the former rather than both.

Re:*golf clap* (1)

Chris Burke (6130) | more than 4 years ago | (#30659660)

I think the terminology used leads to confusion in the layman. "Dark matter" sounds like it's something real, like matter but that's undetectable. In actuality, it's just a placeholder for something unknonwn, like null in a database.

Well it is in part just a placeholder for something unknown, not the name of some specific kind of matter. On the other hand, the reason it's called "dark matter" is because it is neither emitting nor reflecting enough light for us to see it directly. It is literally dark. And since the indirect gravitational evidence for this matter indicates that there is a ridiculously massive amount of it surrounding various galaxies, this is rather surprising. We can see clouds of hydrogen gas between galaxies, for example, so if this other matter was 'ordinary' we should be able to see it, too.

Thus the leading candidate for dark matter is in fact something that is like normal matter but undetectable by any of our long-range direct detection methods, all of which involve electromagnetism. If it is a type of particle that does not interact electromagnetically then, to the extent that "vision" implies photons, dark matter is literally invisible. And it is extremely hard to detect, unless you count the gravitational evidence in the first place.

So "dark matter" in a way really does give the correct impression to the layman. It's just that the layman, not having heard of a kind of matter that has mass but is invisible to telescopes sounds really weird and crazy. That's fine and dandy, until the layman decides that their lack of knowledge and gut instinct is enough to say that the scientists have no idea what they're talking about.

Of course the matter (heh) isn't fully decided yet or anything. The MACHO vs WIMP debate presses on. But as Hubble and other telescopes continue to fail to find enough objects in the galactic halo to account for dark matter, and with the still highly speculative but very exciting WIMP search showing several candidate events, things are definitely leaning in that direction.

Either way, neutrinos are a predicted and then subsequently observed form of the kind of non-baryonic matter we're talking about. So even if it's not WIMPs that make up the dark matter halo, it isn't a ridiculous idea.

Re:*golf clap* (1)

Beelzebud (1361137) | more than 4 years ago | (#30647220)

You do understand that science is a process right? We're in the process of figuring all of that stuff out. How else would you even know to ask those particular questions?

Your young children can be led to believe that Santa Claus and Easter Bunny exist, so I wouldn't exactly take their word for it on something like dark matter. The reason it's called 'dark matter' is because we don't know WTF it is. People are trying to figure that out. It's not as if they moved on, and decided to just not research it...

Re:*golf clap* (0)

Anonymous Coward | more than 4 years ago | (#30647582)

I don't have a degree in physics, but I have spotted the impudent jerk particle.

Re:*golf clap* (1)

jameskojiro (705701) | more than 4 years ago | (#30647786)

They shouldn't shows us a Higgs Boson particle as it would seal our fate as a "Type 13" civilization when our planet collapses into something the size of a pea due to experiments designed to find the mass of t6he Higg Boson Particle.

Re:*golf clap* (0)

Anonymous Coward | more than 4 years ago | (#30648092)

Think dark matter sounds quite plausible. Who said that all matter must reveal itself easily via other means than gravity under normal conditions ? We can't reach those conditions that existed right after the bigbang in our experiments, so well, if nature is that way that it produced an abundance of particles that fills the universe and doesn't interact much anymore with anything else, so that photons are produced somehow that interact with our detectors and shows us their existance, then we must accept that.

I'd say it's somehow arrogant of some people to believe that we must have easy access to everything that exists. Maybe it's only a fraction of the matter that we can easily detect and at some point we realise that there are things that are just beyond our scope of direct measurement for quite some time or maybe forever, because the majority of matter is just that way ... it's flying through space and does nothing except weakly interacting via gravity.

I just noticed that the argument is quite similar to the anthropic principle: We can only notice the matter that interacts a lot, which makes us think, the normal case is that everything there is must be easily detectable. But this is the wrong logic. Detecting something means it interacts. What we see are the things that interact via photons and our intuition tells us this is the standard form of matter in the universe. But in fact it tells us nothing about what's the standard case in the universe, because there could plainly be 1 mio times more matter that isn't easily detectable. Well, infact now, considering gravity, we come to the conclusion that it's not 2 times, 10 times, 100 times, 1 million times, but about 20 times more things that we can't easily detect via other means than gravity.
Not really a surprise then, if you ask me. It has to be some value, and if it turns out that the normal matter that we can see makes up about 5% of all matter, then well, fine. Doesn't surbrise me more than if it was 1% or 99.99% now thinking about it.

It's still just theory that has to be proven and could be easily wrong. But imho a quite plausable theory.

Re:*golf clap* (0)

Anonymous Coward | more than 4 years ago | (#30648578)

You sound like exactly the sort of person who ought to read this guy [milesmathis.com]

Whether you believe he's on to something or completely nuts, at least he's thinking about the paradoxes instead of ignoring them.

Black holes don't exist (yet) (1)

michelcolman (1208008) | more than 4 years ago | (#30647046)

Funny how everybody is always talking about all those black holes in the universe while, in fact, none currently exist. Sure, there are objects that are very, very close to becoming a black hole, and for all practical intents and purposes they can be pretty much considered as such, but in our reference frame it will still take an infinite amount of time before that last bit of matter falling in makes it an actual black hole, with event horizon and all. That's because the intense field of gravity slows down time to an asymptotic halt, so the approaching last bit of matter required for the true black hole will pretty much stop before it gets far enough (from our point of view). The only person who will ever be able to say that black holes exist, is someone who is actually falling into one (which, from an outside observer's point of view, would take an infinite amount of time even though the person himself will experience the event in finite time).

Re:Black holes don't exist (yet) (1)

Fantastic Lad (198284) | more than 4 years ago | (#30647650)

Neat!

-FL

Re:Black holes don't exist (yet) (0)

Anonymous Coward | more than 4 years ago | (#30647700)

Hawking actually addressed this very problem in his most famous book. The one everyone has. To an outside, at rest, observer there's a "condensation" moment when the event horizon becomes larger than the observable object.

Just like in fluid physics, the condensation takes a finite amount of energy (in this case, mass and time) to occur... because it is a true phase change phenomenon.

What you say is true, we'll never be able to observe the matter infall to become a singularity, due to time dilation. But, we pass a point LONG BEFORE THAT where we are no longer able to observe, because the event horizon has formed.

Unlike so much else in mathematics and science, the event horizon isn't just some line we draw, saying "this is where this force equals that force and blah blah blah"... It's a real thing that is the black hole's ONLY remaining link to the universe around it. The horizon can move and shift, it can have irregularities, holds an electric charge, rotates, and exerts gravity (as well as being affected by gravity)

The electric charge is an important prediction. Unlike gravity, we know what carries electric charge; it's photons. And that means that any charge the black hole DOES have, has to exist on or outside the event horizon in order to escape, it's not electricity from inside the hole "leaking" out; it's actually ON the event horizon.

Hawking was interested in how the actual growing works, so he asked the question, if you drop something small and heavy into a black hole, when and how does the event horizon grow? He envisioned, as you probably do, that the size of the event horizon grew linearly as mass is added, but that's not how the field equations turned out. If you're the object, that's exactly what appears to happen, as the outside world gets dilated to nothing as you continue your infall. If you're outside though, the event horizon discretely increases in size as the object passes the NEW event horizon.

OT: today is Newton's birthday (0, Offtopic)

peter303 (12292) | more than 4 years ago | (#30647144)

The classical google portal has an interesting Newton animation.

A bit late (1)

ca111a (1078961) | more than 4 years ago | (#30647228)

For the holidays, isn't it. If they only did it before Christmas...

Multiple black holes become one; the time factor. (1)

zentechno (800941) | more than 4 years ago | (#30647618)

Well, as it's theorized the Milkyway has already swallowed others (reference missing), there should either be multiple black holes in our galaxy, or this provides a good estimation of how long it's been since that happened -- according to Einstein, of course.

Proof? (1)

FatdogHaiku (978357) | more than 4 years ago | (#30647872)

Such a dance is expected to occur in our own Milky Way Galaxy in about 3 billion years, when it collides with the Andromeda Galaxy.

I'll believe that when I see it...

Of course... (0)

Anonymous Coward | more than 4 years ago | (#30648226)

This is all caused by global warming :P

So that gives us (1)

mushroom blue (8836) | more than 4 years ago | (#30649264)

3 billion years for a species to not kill itself long enough to escape this galaxy, lest all life on it perish?

Re:So that gives us (1)

khallow (566160) | more than 4 years ago | (#30650234)

All life on what? The species in question? And how does a galactic collision threaten all life in the galaxies involved?

Re:So that gives us (1)

dryeo (100693) | more than 4 years ago | (#30651890)

When galaxies collided it can trigger a huge amount of star formation due to the gas clouds colliding. Many of these stars are blue super giants that put out large amounts of radiation as well as having a tendency to supernova.
This may raise the galactic radiation levels high enough to make most of the galaxy uninhabitable.
Also the odds of close passes by stars increases therefore increasing the odds of habitable planets orbits getting perturbed.
This would be most pronounced in the main part of the galaxy and inhabitable planets on the outskirts would be less likely to be affected.

Re:So that gives us (1)

al.caughey (1426989) | more than 4 years ago | (#30650418)

3 billion years for a species to not kill itself long enough to escape this galaxy, lest all life on it perish?

I expect that the cockroaches will be just fine where ever they end up.

3 mergers per billion years, really? (0)

Anonymous Coward | more than 4 years ago | (#30650176)

From TFA:

>The dual supermassive black hole pairs can in turn
>be used to estimate how often galaxies merge, and
>the team concludes that red galaxies from between 4
>and 7 billions years ago underwent 3 mergers every
>billion years.

Unless I'm not understanding something, that would mean that in the 3 billion year period (between 4 and 7 bya), the subject galaxies experienced an average of 9 mergers. If each merger results in two galaxies merging into one, then that means there were more than 500 times fewer galaxies (2^9) 4bya than 7bya

That's pretty dramatic, is there anything wrong with my math?

Nihil novi sub sole (1)

dragmyfeet (1712972) | more than 4 years ago | (#30651246)

1) nearly every galaxy has a central super-massive black hole 2) galaxies commonly collide and merge to form new, more massive galaxies. [...] The two black holes gradually in-spiral toward the center of this galaxy, engaging in a gravitational tug-of-war with the surrounding stars.

If this was a comment on the life of corporations, I would mod it "Insightful" (just substitue "galaxy" with "corporation" and "back hole" with "CEO").

Just goes to show you, micro and macro-scale ecology is eeringly similar. I think we need a lecture on fractals and how they apply to this situation.

What about the planets... (1)

hesaigo999ca (786966) | more than 4 years ago | (#30654084)

When the galaxies collide , what effect does it have on the inhabiting planets inside that galaxy, or is it something you would not feel, just all of a sudden (like in a crowded gym...) you look up to see twice as many people (or in this case planets and stars) then before?

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