Forget Black Holes, Let’s Look For Black Rings

A bubble ring. Could a black hole take on this shape at higher dimensions? (©

Black holes are as extreme as anything can get. When a massive structure can no longer sustain its own gravity, it will collapse to a point known as a singularity. For example, a massive star after it has gone supernova may leave one of these singularities behind, a remnant of massive star death, sucking any local matter into a one-way trip to the guts of space-time.

At a certain point, when light itself succumbs to the black hole’s gravity, an event horizon forms, beyond which universal physics breaks down; we have very little idea about what lies inside the event horizon. All we do know is that you don’t want to fall into one, you’d be stretched and spaghettified. Spaghettification is due to extreme (and when I say extreme, I mean as-extreme-as-it-can-get) tidal forces between your head to your toes.

So, the message is: Don’t play with black holes, it can only end in tears.

Now the Black Hole Health & Safety lecture is over, it’s time to talk about “black rings”. Under certain conditions, black holes may not be the mathematical singularities we once knew and (thought we) understood.

In a recent publication by Masashi Kimura at Osaka City University in Japan, the black ring idea is explored in 5-dimensional space. In the space-time we know and love, there are three spatial dimensions and one temporal dimension. We are four-dimensional creatures. When string theory came along in the 1980’s we really began to appreciate that there could be more than the four dimensions we live in.

Previously, cosmologists have entertained the thought that black rings may exist in our 4D space-time. However, the big problem comes when trying to understand how these structures maintain their shapes; surely they should simply collapse and form your regular black holes? Actually, it depends on how big they are and how the competing forces balance out.

As the Universe is expanding, it is thought black rings could exist if they are of scales similar to the cosmological constant (this constant was derived by Einstein to explain a “flat” Universe, but later it was found the constant was required to characterize the universal expansion as observed by Edwin Hubble in 1929). If a black ring exists in 4D space-time, its gravitational collapse would be countered by the expansion of space-time (as characterized by the cosmological constant).

A bubble ring, as made by a dolphin, for fun (©
A bubble ring, as made by a dolphin, for fun (©

The only analogy I can relate this to in the terrestrial world is bubble rings (or, indeed, smoke rings). When under water, a bubble will rise to the surface. However, under the constriction of surface tension, the bubble will form the smallest possible shape. When a bubble ring is produced, there needs to be a balance between surface tension and a vortex. The surface tension pulls in, while the vortex maintains the bubble ring shape, pushing out.

In the case of the black ring, gravity is pulling inward, while the expansion of space-time is countering it, pushing out. In this situation, in an expanding Universe, there could be enduring examples of black rings out there.

In Kimura’s research, not only are black rings a possibility, there could be a number of different complex shapes that could form when considering these extra dimensions. When the Universe was young, multiple interacting black rings may have been possible, eventually coalescing to form black holes.

Although this research is very interesting, it is hard to imagine how we could observe these higher-dimensional black rings. Would we see them as a singularity (i.e. a black hole) in our 4D space-time? Or would they even be unobservable for lower-dimensional beings such as ourselves?

Publication: Dynamical Black Rings with a Positive Cosmological Constant, Masashi Kimura, 2009. arXiv:0904.4311v2 [gr-qc]

Via: arXiv blog


I Wish Office Work Was This Interesting

Having just stumbled around the space blogs, I was enthusiastic that I would find some inspiration toward my next article. Along the way, I found this rather entertaining short film on Phil Plait’s Bad Astronomy website. As Phil points out, “black holes don’t work this way.” Although, that is a shame.

There’s a strong moral to this story: don’t photocopy alone, as you never know when your Xerox machine will print out a singularity. Well, not really, perhaps the guy should have stopped at stealing a snickers bar, a lesson we could all learn from. Actually, I might have walked off with just one wad of cash… actually, maybe two… you get the picture.

Needless to say, this isn’t actually how a black hole works… it’s not even how a wormhole would work. But take the short film at face value and get some entertainment from it, I thought it was quite good fun.

Probing Variable Black Holes

Artist impression of a black hole feeding off its companion star... and a rogue Higgs particle (ESO/L. Calçada)
Artist impression of a black hole feeding off its companion star... and a rogue Higgs particle (ESO/L. Calçada/Particle Zoo)

Black holes are voracious eaters. They devour pretty much anything that strays too close. They’re not fussy; dust, gas, plasma, Higgs bosons, planets, stars, even photons are on the menu. However, for astronomers, interesting things can be observed if a star starts to be cannibalized by a neighbouring black hole. Should a star be unlucky enough to have a black hole as its binary partner, the black hole will begin to strip the stars upper layers, slowly consuming it on each agonizing orbit. Much like water spiralling down a plug hole, the tortured plasma from the star is gravitationally dragged on a spiral path toward the black hole’s event horizon. As stellar matter falls down the event horizon plug hole, it reaches relativistic velocities, blasting a huge amount of radiation into space. And now, astronomers have taken different observations from two observatories to see how the visible emissions correlate with the X-ray emissions from two known black hole sources. What they discovered came as a surprise
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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...
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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Meet Sagittarius A*, Our Very Own Supermassive Black Hole

Yearly location of stars within 0.2 parsecs from Sagittarius A* orbiting the common, compact radio source (A. Ghez)
Yearly location of stars within 0.2 parsecs from Sagittarius A* orbiting the common, compact radio source (A. Ghez)

We are told there is a supermassive black hole living in the centre of our galaxy. Apparently, supermassive black holes can be found in the centre of most galactic nuclei, and all the stars within the surrounding galactic disk will orbit around it. But how do we know there is a huge black hole in the centre of the Milky Way? What evidence is there? It turns out there is quite a lot, actually.

In a recent review of the subject, the radio emissions observed since the 1950’s are examined. However, probably the most striking piece of evidence is the figure to the left. Of course, we know black holes exert a massive gravitational pull on local space, and by observing the centre of our galaxy, we find there is a huge gravitational influence over a compact cluster of stars, all orbiting a common point, reaching orbital velocities of 5000 km/s…
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New Exotic Particle May Explain Milky Way Gamma-Ray Phenomenon

Chandra observation of Cassiopeia A, a young supernova remnant in our galaxy - a prominent source of high-energy particles (NASA/CXC/MIT/UMass Amherst/M. D. Stage et al.)
Chandra observation of Cassiopeia A, a young supernova remnant in our galaxy - a prominant source of high-energy particles (NASA/CXC/MIT/UMass Amherst/M. D. Stage et al.)

There is something strange happening in the core of the Milky Way. A space observatory measuring the energy and distribution of gamma-rays in the cosmos has made an unexpected (and perplexing) discovery. It would seem there is a very high proportion of gamma-ray photons emanating from our galactic core with a very distinctive signature; they have a precise energy of 511 keV (8×10-14 Joules), and there’s a lot of them. So what could possibly be producing these 511 keV gamma-rays? It turns out, 511 keV is a magic number; it is the exact rest mass energy of a positron (the antimatter particle of the electron). So this is fairly conclusive evidence that positrons are dying (i.e. annihilating) in vast numbers in our galactic nuclei. Still, this is of little help to astrophysicists as there is no known mechanism for producing such high numbers of annihilating positrons. Ideas have been put forward, but there’s a new possibility, involving some new particle physics and some lateral thinking…
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Recoiling Supermassive Black Holes and Stellar Flares

Simulation of black holes colliding. In a word, awesome (Max Planck Group)

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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Are Primordial Black Holes Antimatter Factories?

A black hole, artist impression (NASA)
A black hole, artist impression (NASA)

Could small, primordial black holes be efficient antimatter generators? It is well known that cool planetary bodies, surrounded by equal numbers of protons and electrons in thermal equilibrium, will eventually become positively charged. Why? Because electrons, with their low mass, have a higher velocity than the larger protons. Although they undergo the same gravitational acceleration, electrons are able to attain “escape velocity” more readily as the more massive protons get stuck in the gravitational well. The result? The planet has a net positive charge as more electrons, than proton escape into space.

Primordial black holes are thought to exist in our Universe (left-overs from the Big Bang), and although they may be small, they may influence ionized cosmic clouds in the same way, more electrons escape than protons left behind. However, should a threshold be reached, the extreme gravitational force surrounding the black hole could set up a powerful electrostatic field, kick-starting a strange quantum phenomenon that generates the electron’s anti-matter partner (the positron) from the vacuum of space…
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Supermassive Black Holes are Not Fussy Eaters

The core of M81 (Chandra/NASA)

By combining observations from a multitude of observatories, all looking at spiral galaxy M81, astronomers have taken a very close and intimate look at a supermassive black hole’s feeding habits. As supermassive black holes (of tens of millions of solar masses) and stellar black holes (of a few solar masses) exist in entirely different environments, astrophysicists were uncertain as to what supermassive black holes feed on. Stellar black holes eat away at the gas from companion stars, creating an accretion disk, generating a range of emissions as stellar gas falls into the disk. But where do supermassive black holes get their food? It turns out they feed off gas in the central region of galactic cores, generating similar emissions as their smaller stellar cousins. What’s more, this finding supports Einstein’s theory that all black holes, regardless of mass, share the same characteristics…
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The Case of the Supermassive Black Hole, the Infrared Object and Perceived Accuracy of Science

There is a trend in astronomical observations to label strange and exotic objects with superlative names. Take “supermassive” black holes for instance. Yes they are more massive than intermediate black holes, bigger than stellar black holes, and in a whole different league to theoretical micro-black holes. But is the label “supermassive” an accurate description? Is it even scientific?

After reading a very interesting article written by Michael Gmirkin on “Incorrect Assumptions in Astrophysics“, I began to relate his investigation into the use of terms to describe astronomical phenomena with very expressive names. Terms like “super-massive”, “ultra-luminous”, and “beyond-bright” are mentioned by Gmirkin, perhaps leading astronomers to incorrect conclusions. Whilst this may be perceived as an issue amongst scientists, what if the media or non-specialist individuals misinterpret the meaning of these grand statements? Could it lead to public misunderstanding of the science, possibly even causing worry when a scientist describes a particle accelerator collision as “recreating the conditions of the Big Bang”?
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