Gravitational Waves – Page 2

The Naked Singularity Recipe: Spin a Black Hole, Add Mass

naked_singularity

The event horizon of a black hole is the point of no return. If anything, even light, strays within the bounds of this gravitational trap, it will never escape. The event horizon is what makes a black hole black.

But say if there was a way to remove the event horizon, leaving just the black hole’s singularity to be “seen” by the rest of the universe? What if there is a special condition that would allow this infinitely small, yet massive point to become naked?

Generally physicists agree that this is a physical impossibility, but the mathematics says otherwise; a naked singularity could be possible.

Previously on Astroengine, one “special condition” was investigated when an extreme black hole collision was simulated by a Caltech researcher. In this case, the black hole pair was smashed together, head-on, at a velocity close to the speed of light. The gravitational waves travelling away from the collision were then modelled and characterized. It turns out that after this insanely energetic impact, 14% of the total mass was converted into gravitational wave energy and both black holes merged as one.

While this might not be very realistic, it proved to be a very useful diagnostic tool to understand the conditions after the collision of two black holes. As an interesting observation, the Caltech researchers found that although the collision was extreme, and there was a huge amount of mass-energy conversion going on (plus, I’d imagine, a rather big explosion), neither black hole lost their event horizons.

Case closed, wouldn’t you think?

Actually, another theory as to how a black hole could be stripped naked has been knocking around for some time; what if you added mass to a black hole spinning at its maximum possible rate? Could the black hole be disrupted enough to shed its event horizon?

It turns out there’s a natural braking system that prevents this from happening. As soon as mass is dropped into the black hole, it is flung out of the event horizon by the black hole’s huge centrifugal force, preventing it from coming close to the singularity.

However, Ted Jacobson and Thomas Sotiriou at the University of Maryland at College Park have now improved upon this idea, sending mass in the same direction as the spinning black hole. Only this time, the black hole isn’t spinning at its fastest possible rate, the simulation lets the orbiting matter fall into the event horizon, speeding up its spin. The result? It appears to disrupt the black hole enough to strip away the event horizon, exposing the singularity.

The most interesting thing to come of this research is that swirling matter is falling into black holes all over the universe, speeding up their spin. Jacobson and Sotiriou may have stumbled on a viable mechanism that actually allows naked singularities in the cosmos. Unless nature has found another way to prevent the cosmic censorship hypothesis from being violated that is…

Source: New Scientist

Did Gravitational Waves Ring a Bell in 1987?

Gravitational waves generated by a binary system (MIT)

The hunt for gravitational waves continue, but unfortunately all gravitational wave hunters around the world are churning up nothing. Just noise. Could it be that this consequence of Einstein’s theory of General Relativity is horribly flawed? Probably not. Still, the search for these elusive waves has foxed physicists for many years. It has even come to the point that the laser interferometers used in an attempt to detect the tiny (and I mean TINY) changes in distances (as when the gravitational wave passes through us, space-time experiences a minuscule compression or expansion) have become so precise, the director of Fermilab thinks a German-UK gravitational wave detector is starting to detect the quanta of space-time itself.

However, do you ever get the feeling that we might be trying too hard? What if gravitational waves have already been detected? Say if these notoriously difficult ripples in space-time were detected over 20 years ago without using a laser interferometer? It turns out that an overlooked scientist may have found the answer to the gravitational wave problem by using nothing more than some aluminium bars and a well-timed supernova…
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Gravitational Waves and Gravity Waves, What’s the Difference?

I’ve received this question so many times, so I thought I’d post, for reference purposes, the difference between a gravitational wave and a gravity wave. Yes, they are different creatures (although many authors would have you believe otherwise).

Gravitational waves are theoretical perturbations (ripples) in space-time. Much work is going into the discovery of gravitational waves using gravitational wave detectors like the US Laser Interferometer Gravitational-Wave Observatory (LIGO) or German-British GEO600, but so far, they have proven to be very elusive. In a previous Astroengine post, there is a new theory that perhaps gravitational wave detectors have reached a limit on their precision (i.e. the quanta of space-time, leading to the holographic universe conjecture). Gravitational waves, as predicted by Einstein’s theory of general relativity, are thought to exist, but have yet to be detected. There are indirect observations of gravitational waves, from observations of the slowing period of binary stars; energy is most likely being lost through gravitational wave generation. Gravitational waves are thought to be generated also by black hole collision, pulsars and supernovae. More on Gravitational Waves…

Gravity waves are physical perturbations driven by the restoring force of gravity in a terrestrial environment. A common example of this are waves formed at an air-water boundary (i.e. the surface of the ocean). Wind creates an instability in the ocean, the restoring gravity force pulls down on the water, while the buoyancy of the water pushes it back up. A perturbation then propagates (i.e. ocean waves). Extreme examples include tsunamis and tides. Perturbations in the atmosphere can also be caused by gravity, where rising/falling air tries to regain equilibrium (after being forced over a maintain range, say), but gravity and buoyancy forces will cause it to propagate as a wave. More on Gravity Waves…

So, gravitational waves are perturbations in space-time (over universal scales). Gravity waves are perturbations in atmospheres (planetary scale). They most certainly are not the same thing.

Is the Universe a Holographic Projection?

Luke and Obi-Wan look at a 3D hologram of Leia projected by R2D2 (Star Wars)

Could our cosmos be a projection from the edge of the observable Universe?

Sounds like a silly question, but scientists are seriously taking on this idea. As it happens, a gravitational wave detector in Germany is turning up null results on the gravitational wave detection front (no surprises there), but it may have discovered something even more fundamental than a ripple in space-time. The spurious noise being detected at the GEO600 experiment has foxed physicists for some time. However, a particle physicist from the accelerator facility Fermilab has stepped in with his suspicion that the GEO600 “noise” may not be just annoying static, it might be the quantum structure of space-time itself…
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Can Gravitational Waves be Used for Evil?

Theoretical gravitational waves generated after a black hole collision. Can we surf them?

Gravitational waves are a theoretical consequence of a propagating energy disturbance through space-time. They are predicted by Einstein’s general relativity equations, and astrophysicists are going to great pains to try to detect the faint signature from the passage of these waves through local space. Unfortunately, even though millions of dollars have been spent on international experiments, the gravitational wave remains in equation form; there is little (direct) evidence to support their existence.

However, this doesn’t stop the US military from worrying about them and commissioned a 40-page report into whether high frequency gravitational waves could be used by an enemy. Excuse me? Gravitational waves… as a weapon?
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No Naked Singularity After Black Hole Collision

Black holes cannot be naked... the event horizon will always be there to cover them up...

You can manipulate a black hole as much as you like but you’ll never get rid of its event horizon, a new study suggests. This may sound a little odd, the event horizon is what makes the black hole, well… black. However, in the centre of a black hole, hidden deep inside the event horizon, is a singularity. A singularity is a mathematical consequence, it is also a point in space where the laws of physics do not apply. Mathematics also predicts that singularities can exist without an associated event horizon, but this means that we’d be able to physically see a black hole’s singularity. This theoretical entity is known as a “naked singularity” and physicists are at a loss to explain what one would look like.

Like any good physics experiment, an international team from the US, Germany, Portugal and Mexico have decided to simulate the most extreme situation possible in the aim of stripping a pair of black holes of their event horizons. They did this by constructing an energetic collision between two black holes travelling close to the speed of light, crashing head-on. Here’s what they discovered…
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Gravitational Wave Theory Takes Another Kick in the Teeth

Northern leg of the LIGO facility on the Hanford Reservation (LIGO)

Six years and nearly 400 million dollars later, the Laser Interferometer Gravitational-Wave Observatory (LIGO) still hasn’t turned up the evidence for gravitational waves. Gravitational waves are predicted by fundamental Einstein general relativity theories, but we haven’t been able to detect them. Is it because the first generation laser interferometers are not sensitive enough? Is it because LIGO needs more time to see through the cosmic noise to root out the gravitational wave signature? This is a deeply worrying non-development for physicists as a null result means that something isn’t quite right. We are certain (in theory) that these waves should be rippling through space-time (after all, massive objects are colliding and exploding all the time throughout the Universe), but if we can’t detect the things in our own cosmic back yard, something must be awry. In a recent publication, LIGO scientists have discussed the lack of evidence for gravitational waves, but remain upbeat that they can still be found…
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Recoiling Supermassive Black Holes and Stellar Flares

Astrophysicists love to simulate huge collisions, and they don’t get much bigger than this. From the discoverers of the first ever observed black hole collision back in April, new observational characteristics have been researched and Max Planck astrophysicists believe that after two supermassive black holes (SMBHs) have collided, they recoil and drag flaring stars with them. By looking out for anomalous X-ray flares in intergalactic space, or off-galactic nuclei locations, repelled black holes may be spotted powering their way into deep space at velocities of up to 4000 kms^-1…
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The Crab Pulsar is Probed By LIGO. Is it Really a Smooth Neutron Star?

Scientists working with the Laser Interferometer Gravitational-Wave Observatory (LIGO) have announced their first land-mark discovery. LIGO was built to detect gravitational waves (as predicted by Einstein’s general relativity), but this discovery is actually about not detecting gravitational waves. Hold on, what’s all the fuss about then? This sounds like a null result, and in some ways it is. But on the other hand it may be one of the most important neutron star observations ever. So what has LIGO (not) seen?
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When Stars Collide: LIGO and Gravitational Wave Astronomy

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is an ambitious project. The experiment is designed to detect and characterize gravitational waves generated by energetic and massive events in the cosmos. What’s more, as LIGO has two stations situated 3000 kilometres (1870 miles) apart, through triangulation, the location of a star collision or black hole event can be deduced in the sky. Completed two years ago, LIGO has been taking data ever since and the time has now come to begin analysing the results, seeing if the theoretical gravitational wave can actually be observed, bringing us into a new era of astronomy, gravitational wave astronomy…
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