Astronomers Discover 33 Pairs of Waltzing Black Holes

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."

Comments

Waltzing?

[CannonballHead]

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?

[Z00L00K]

Time to play Waltzing Matilda then?

Re:Waltzing?

[FlyingBishop]

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

Re:Waltzing?

[RichardDeVries]

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.

The big question

[Drummergeek0]

Who leads and who follows?

Newton?

[sznupi]

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?

[bcrowell]

At those masses, the choreographer is most likely Einstein

That's incorrect. The paper 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, 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?

[bcrowell]

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 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?

[bcrowell]

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?

[bcrowell]

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?

[bcrowell]

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 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, 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.

and this...

[owlnation]

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

Einstein!

[mbone]

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:Wake Me Up When

[Red Flayer]

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!

Wow!

[gstoddart]

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!

[gstoddart]

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

Good news for gravitational waves hunters

[photonic]

Great, the collision of these things is exactly the kind of event we need for detecting gravitational waves. 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-based kilometer long observatories, which are measuring right now. This is probably more something for the space-based LISA mission, which can probe much lower frequencies since it has a base-line of millions of kilometers.

Re:Good news for gravitational waves hunters

[bcrowell]

The same thing occurred to me. Here 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, even before they merge. I guess the orbital periods would be very long, though.

Re:*golf clap*

[Chris Burke]

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?