Archives For black holes


Imagine a problem with seemingly countless solutions, a paradox that’s paradoxically solved by completely unrelated mechanisms some of which violate the rules of physics as we know them, while others raise more questions than they provide answers. That paradox is what happens to an object unfortunate enough to fall into a black hole. Last time we talked about this puzzle, we reviewed why the very concept of something falling into a black hole is an insanely complicated problem which plays havoc with what we think we know about quantum mechanics. Currently, a leading theory posits that tiny wormholes allow for the scrambled particles of the doomed object to maintain some sort of presence in this universe without violating the laws of physics. But not content with someone else theories, and knowing full well that his last finding about black holes made them necessary in the first place, as explained by the linked post, Stephen Hawking now claims to have found a new solution to the paradox and will be publishing a paper shortly.

While we don’t know the exact wording of the paper, we know enough about his solution to say that he has not really found a satisfactory answer to the paradox. Why? His answer rests on an extremely hard to test notion that objects falling to a black hole are smeared across the edge of the event horizon and emit just enough photons for us to reconstruct holographic projections of what it once was. Unfortunately, it would be more scrambled than the Playboy channel on really old TVs, so anyone trying to figure out what the object was probably won’t be able to do it. But it will be something as least, which is all that thermodynamics needs to balance out the equations and make it seem that the paradox has been solved. Except it really hasn’t because we haven’t the slightest idea of how to test this hypothesis. It still violates monogamous entanglement, and because the photons we’re supposed to see are meant to be scrambled into unidentifiable flash of high speed, high energy particles, good luck proving the original source of the information.

Unless we physically travel to a black hole and dropping a powerful probe into it, we would only have guesses and complex equations we couldn’t rule out with practical observations. Sadly, a probe launched today would take 55.3 million years to get to the nearest one, which means any practical experiments are absolutely out of the question. Creating micro black holes as both an experiment for laboratory study and a potential relativistic power source, would take energy we can’t really generate right now, rendering experiments in controlled conditions impossible for a long time. And that means we’re very unlikely to be closer to solving the black hole information paradox for the foreseeable future unless by some lucky coincidence we’ll see something out in deep space able to shed light on the fate of whatever falls into a black hole’s physics-shattering maw, regardless of what the papers tell you or the stature of the scientist making the claim…

black hole accretion disk

Falling into a black hole is a confusing and complicated business, rife with paradoxes and weird quantum effects to reconcile. About a month ago, we looked at black holes’ interactions with the outside world when something falls into them, and today, we’re going to look into the other side of the fall. Conventional wisdom holds that inside a black hole gravity is exponentially increasing until time, space, and energy as we know it completely break down as the singularity. Notice I’m not talking about matter at all because at such tremendous gravitational forces and with searing temperatures in the trillions of degrees, matter simply can’t exist anymore. Movies imagine that singularity as some sort of mysterious portal where anything can happen, while in reality, we’re clueless about what it looks like or even if it really exists. We don’t even know if anything makes it down to the singularity in the first place. But what we do know is that somewhere, whatever is swallowed by the black hole should persist in some weird quantum state because we don’t see any evidence for black holes violating the first law of thermodynamics. Enter the fuzzball.

Quantum fuzzballs aren’t really objects or boundary layers as we know them. Instead, they’re a tangle of quarks and gluons made up of the matter that gave rise to the black hole and what it’s been eating over its lifetime. They don’t have singularities, just loops of raw energy trapped by the immense gravitational forces exerted on them. On the one hand, thinking of a black hole as just a hyper-dense fuzzball eliminates the anomalies and paradoxes inherent in descriptions of singularities, but on the other, simply making a problem go away with equations doesn’t mean it was solved. And that’s the real problem with quantum fuzzballs. They appear as exotic math in general relativity being extended deep into a realm where its predictive powers begin to fail, so while it’s entirely possible that we identified in what direction we need to explore and what we’d expect were we to look into a black hole, it’s equally likely that the classic idea of their anatomy still holds. Unless we drop something into one of those gravitational zombies nearby, we won’t know if the current toy models of what lies inside of it are right. All we have is conjecture.

black hole eating planet

Black holes are, needless to say, strange places, and over the years, I’ve written much about all the bizarre paradoxes and extreme questions they pose. All this weirdness is what makes them fun to study because solving some of these paradoxes and questions ultimately gets us closer and closer to figuring out how time and space works. Consider the science this way. When you build an airplane wing, you want to flex it as hard as you can until it snaps because that will tell you the limits of the materials you used and the soundness of your design. Much the same way as destructive testing helps engineers hone their craft, so does studying a place where physics seems, well, broken, helps scientists test the outer limits of their discipline. Of course when you have the broken fabric of space-time to piece together, some problems will be much harder to solve than others and one of the most persistent ones is whether black holes have firewalls.

What exactly is a black hole firewall? We don’t really know because it’s not supposed to be one of the defining features of its anatomy. Instead, it’s what happens when spontaneous quantum particles litter the cosmos in the wrong place. These particles constantly blink into existence as particle and anti-particle pairs which instantly annihilate each other, and where this won’t pose any problem anywhere else in the cosmos, when they appear too close to an event horizon of a black hole, one particle will get drawn in while the other is repelled into space, with a small flash of energy from the maw of the black hole which it must give up to keep with the laws of physics. It’s a fraction of a fraction of a nanowatt, but over the eons a black hole will exist, this adds up and the black hole would eventually be unable to hold itself together and explode. At least this is the theory behind what we call Hawking radiation, which will balance out the escaping particle’s energy and returns the swallowed matter back to the universe. So what’s the problem?

Well, the problem lays in a technicality that’s actually quite a big deal because it breaks a very fundamental principle of how quantum systems work. Entangled quantum particles are said to have a monogamy of entanglement, meaning that once you entangle one particle in a system, you can’t entangle it with another. To paraphrase a great explanation the source of which I just can’t recall, imagine quantum entanglement as rolling some dice and no matter what numbers come up for each individual dice, the sum of those numbers is the same with every roll. This is important because it lets us know that if we entangle a pair of dice and get 12 in our first throw, when we throw them again and one comes up as a 7, we understand that the other is 5 without even looking at it. Understanding how this works allows us to do some amazing experiments on the very nature of causality itself. But to make this balance out, we would have to know for sure that our 5 isn’t also being used to change the sum of another roll, elsewhere.

And this is exactly what a black hole’s event horizon allows. When one of our virtual particles is swallowed and the black hole gives off the teeny Hawking emission, the remaining particle and the emission are entangled. But the infalling anti-particle is still there, and the outgoing one is still entangled with it. Two independent quantum systems have created a mass-energy surplus, which is a very blatant violation of the laws of thermodynamics, and most solutions to this weird state of affairs involve even further violations of the laws of physics. Enter the firewall. Not really an ongoing phenomenon just beyond the event horizon, it’s instead a line crossing which would permanently sever the entanglement between the outgoing and infalling particles, leaving just a Hawking emission and the outgoing particle as a quantum system. This would release massive amounts of energy proportional to the event, and trap the particle in the black hole forever. It’s not a tidy solution, but it sort of works if you try not to think about it too hard.

Of course thinking too hard about things is what scientists do and they quickly pointed out that breaking quantum entanglement on a whim just doesn’t work, no matter how much energy you release to compensate for the inequality in the resulting equations. And that means, the firewall isn’t really the answer to what happens to the energy and information when black holes devour something. A new solution proposes that black holes actually spawn wormholes when they eat entangled particles. Those aren’t the conventional kind of wormholes we think of, they couldn’t be used to cross space and time on a whim, but they’re essentially a connection which keeps both the escaping and the infalling particle entangled. Recall our dice-based quantum system, and imagine that you roll a dice in NYC while someone else in Hong Kong rolls the other. Both will still amount to 12, and if your dice shows a 6, the one in Hong Kong will as well. But should you be unable to see what you rolled, you can count on a call telling you what the other dice is showing at the moment. That phone call? That’s more or less the wormhole in question.

Yes, this does basically jettison Hawking radiation and leads to its own weird conclusions about the fabric of the universe being composed of a constantly entangled quantum mesh, but that’s how science works. Slowly and carefully, we chip away at complex problems and flesh out all of the toy models until we can simulate real systems, and try and observe them and their behavior out in the wild. What happens to matter that falls into a black hole and if it’s still connected to a quantum system on the outside is still a wide open question. But the fact that it’s just so difficult to even try to answer what seems like a simple question at first glance, shows just how bizarre, complex, and self-contradictory the universe can be. Far from a steady, ordered system, it’s an incredibly wild mess that seems to barely be governed by its own rules should we look just a bit too close, and nowhere is this more evident than with black holes. They’re places where all we know about time and space is broken. But they’re also the places that could teach us the most about these laws, especially because that’s where they’re being tested at their extremes…

black hole accretion disk

Apologies for the sudden hiatus everyone. In the last several weeks, life has interfered with any possibility of writing and when there has been time for anything, it’s been occupied by Project X which actually does concern this blog and will be detailed in the future. But I’m finally back, and back with an astronomical bang, or FRBs to be exact. You see, recently astronomers have been puzzled by extremely energetic bursts that last for fractions of a second and vanish forever. It’s like a GRB, the birth cry of a newly born black hole, but it all happens in less than the blink of an eye rather than depending on the size of the cataclysm. These bursts are currently called FRBs and no one is really sure what they are, where they generally originate in the night sky, and how much energy they’re really emitting, repeating the original dilemma with GRBs when they were first discovered. Now we have our first theoretical contender called SURONs, or Supramassive Rotating Neutron Stars, the end result of supernovae that should have created black holes but didn’t, not yet at least. They’re essentially ticking black hole time bombs floating in space.

When our sun will die, it will slowly pulsate and cool into a white dwarf because its mass is below the Chandrashekhar limit, the point at which a star becomes too heavy not to collapse on itself as a supernova. There are some objects that challenge exactly where this limit comes into play, but it seems to be about 1.44 solar masses. Stars heavier than that produce iron in their cores during the last stages of their lives and the unique thing about iron is that fusing it produces no net energy output. Bascially, the strong nuclear force’s interactions with iron’s nucleons create a point of diminishing returns on the nuclear binding energy and the tightly wound nuclei of iron is the first element from which a nuclear reaction can’t extract anything worthwhile. No matter how much iron is being fused, there’s just not enough energy to keep its outer layers from collapsing inward and detonating as a supernova. This is when another important astronomical limit comes into play, the Tolman-Oppenheimer-Volkoff limit. (Yes, that Oppenheimer.) If a neutron star left after a supernova is about two solar masses, it will collapse on itself as a black hole.

Although "will" is kind of a strong word really, a better one would be "should." And this is exactly where the SURONs come into play. Neutron stars are made of degenerate matter, or particles in such a high density environment that the only thing keeping them from falling into each other is, well, each other. Compressing them any more shatters matter as we know it and creates chaotic maelstroms of energy that flow into each other. Degenerate matter at the core of neutron stars can be so hot and dense that it’s basically a weird quantum fluid with no viscosity already, so it’s not going to take all that much to turn it into a black hole. In fact, SURONs are just over the limit and the pressure of its outer layers should’ve triggered a collapse but the particles in their cores were given a brief reprieve. Stars spin and whatever momentum is left after their fiery death has to transfer to the pulsar left behind. Because the star was well over a million miles across and a typical pulsar is tens of miles across, that energy sends the little pulsar spinning wildly arouns its axis, sometimes as fast as 1,122 times per second. This releaves just enough pressure to keep the core from imploding and leave the SURON a neutron star spinning wildly through space.

But there’s a catch. SURONs have extremely strong magnetic fields and those fields will interact with the nebula left behind as will the interactions between its radioactive death beams and gas and dust. Over thousands of years, this will all put a brake on how quickly the neutron star spins which means that at a certain point, the pressure on its core will start building back up until the inevitable happens and the degenerate matter swallows itself and becomes a black hole. Since the SURONs is relatively puny, this collapse happens in a fraction of a second. Its fearsome and powerful magnetic fields will be severed from the just formed event horizon and re-connect very, very violently just outside of it, generating a potent and very short radio pulse. An FRB. This is a nice and tidy explanation because SURONs would be roughly the same size and the event will be pretty much uniform, almost like a Type Ia supernova used as a standard unit for measuring the rate of the universe’s expansion. We don’t know if these neutron stars ticking away into new black holes really do dot the sky and this is not the only possible explanation of FRBs, but it is a pretty good one and it seems quite solid. And that’s often as good as it gets in astronomy…

See: Falcke, H., Rezzolla, L. (2013). Fast radio bursts: the last sign of supramassive neutron stars. Astronomy & Astrophysics arXiv: 1307.1409v1

black hole accretion disk

While many news outlets were reporting a new paper showing that a black hole’s accretion disk can accelerate gas to nearly the speed of light by the event horizon’s distortion of the very fabric of time and space around it, they missed something quite important. Yes, knowing for a fact that gas is screaming around the event horizon at relativistic speeds and beaming out violent X-rays we can see for millions of light years is definitely awesome. Every time the universe does such amazing things, just being able to witness it, document it, and understand how it happens tends to be a huge feat. But there’s more to what this tells us than just how the event horizon works or how relativistic frame-dragging is affecting the flow of gas in the accretion disk. It also tells us a little about what must have happened to the black hole to make it as large as it is.

You see, after analyzing the spectrum of X-rays from iron spinning around the event horizon of the supermassive black hole at the center of the galaxy NGC 1365, physicists can rule out the idea that instead of spinning around the event horizons, the gas was just obscuring what really went on around the black hole’s maw. There was too much distortion for gas to be in the way of the incoming radiation. But the measurements also show that the event horizon itself is zipping around its own axis that the “surface” of the event horizon, the point where tidal forces around the singularity are so strong, a particle would have to be traveling faster than the speed of light to escape, is traveling at nearly the speed of light itself. Not only is that astonishing, but there is only one way it could be spinning that quickly. Collisions with other giant black holes.

If a supermassive black hole gained its mass simply by sipping matter of stars and gas, it would have a low spin because the angular momentum of these objects is small. But merging with one or two other black holes could do the trick because these objects can spin as quickly as 1,000 times per second when they’re at stellar mass. When they collapse, the initial sin of the star that formed them is conserved and all that energy needs to go somewhere, so the black hole begins to church around its axis faster and faster. And when two fast-spinning black holes merge, they impart their energy tp each others’ spin, making the resulting object travel even faster. The sum of the mechanics involved is mind-boggling because the collision is between superheated quark and gluon streams of energy with zero viscosity, so there are few real world analogies we could refer to when talking about it, but the general mathematical results give us something not unlike the monster at the heart of NGC 1365 which shows us that we’re standing to understand more about how supermassive black holes feed on each other and shape the galaxies around them.

See: Risaliti, G., et al. (2013). A rapidly spinning supermassive black hole at the centre of NGC 1365 Nature, 494 (7438), 449-451 DOI: 10.1038/nature11938

[ illustration by NASA/JPL ]

primordial black hole

Usually a new discovery in deep space tends to further complicate our picture of the universe, almost as if the cosmos says "oh yeah, you think you have a good idea of how this works?" and throws a monkey wrench into the works, or sometimes, the whole screaming, angry monkey. So when it comes to phenomena as complex and exciting as black holes, surely there can’t be any data that makes them easier to understand. But this time, when physicists wanted to figure out if jets from black holes followed the same patterns as the mass of the objects went up, nature was willing to cooperate. As it turns out, the powerful jets of material shot from the accretion disks of black holes of 20 solar masses and 20 million solar masses follow the same mechanism. How do we know that? By plotting their strength against the mass of the black hole. If the data follows a linear trend, we know that the physics don’t require a new process to explain the numbers.

So what exactly is happening around black holes? As you may already know, black holes aren’t the cosmic vacuum cleaners far too many sci-fi movies made them out to be. They simply stay where they were very violently born and their immense tidal forces accelerate anything straying nearby into their maws. But black holes are tiny on an astronomical scale and only eat so much at a time. Whatever doesn’t fall directly into their event horizons is whipped around them until it heats up into a glowing accretion disk we can detect. And some of this material gets trapped in the powerful magnetic fields around the black hole and is launched into deep space at 99.9% of the speed of light in the form of highly energetic jets which produce powerful gamma rays. This process seemed to be the same for every black hole observed, but there’s no way to be sure if the black holes affected the jets beyond kinetic energy unless you start comparing gamma ray bursts to one another and plotting them along a trend line.

If the trend is exponential, that means new physics are needed to explain the sudden surges in power as we go up in the jet’s energy and vice versa. But the observed trend between kinetic energy of the jets and the power of the gamma ray bursts is linear, which means that it’s rather likely that the process behind forming the jets is the same across the entire spectrum of known black holes. The black hole’s mass affects how much is can swallow at a time and how powerful the jets it emits could be. The power of the jets affects the observed gamma ray bursts when a new black hole is formed and when it’s in the middle of a large meal consisting of stars and gas floating through interstellar space. So if we know that when we up the jets’ power, we also make the GRB stronger in a predictable way, that tells us that we can more or less confidently scale up what we learn about smaller black holes to their immense siblings, and estimate black holes sizes based on the GRBs’ strength. And that’s very useful for learning more about these prolific and extremely influential gravitational ghosts of giant stars.

See: Nemmen, R., et al. (2012). A universal scaling for the energetics of relativistic jets from black hole systems Science, 338 (6113), 1445-1448 DOI: 10.1126/science.1227416


As we discussed many times on Weird Things, black holes are the most amazing and terrifying things in the universe we know, and they’re not shy about gathering every law of physics we’re sure we understand, then laughing at them and doing something completely different. Well, not completely different per se, but the incredible heat and gravity of these objects makes time and space flow in ways they can’t anywhere else. One of these extreme phenomena is time dilation induced by gravity. We talked about the extreme effects of time dilation at relativistic speed over the last few years and mentioned that you could technically cross the entire universe in a human lifetime if you were traveling at 99% the speed of light. And the same effect applies when you’re exposed to an extremely gravitationally powerful object. Time would continue normally for you if you’re falling into a black hole, but to an outside observer, you’d be frozen in time and he won’t see you spaghettified and turned into quark-gluon soup past the event horizon.

Or at least that’s the theory which one physicist says might be wrong. According to his view, any particle falling into the black hole would never actually cross the horizon because the dilation is so extreme as to keep it falling until the black hole evaporates. Unfortunately for him, this really doesn’t sound even remotely right since that would prevent black holes from accreting mass. We know they do exactly that. If particles could never fall into a black hole, there would be absolutely no accretion and black holes would have the same mass with which they were created. It could be possible but it would make explaining hypermassive 10 billion solar mass beasts very, very difficult. You’d need a significant portion of a galaxy to implode in on itself just right, circling into itself over eons without enough gravitational nudges and tugs from the various stars and solar systems inside to maintain some semblance of equilibrium. And that just doesn’t sound right. It’s a lot more straightforward to assume that supermassive black holes are born maybe a thousand or so orders of magnitude smaller and work their way up through galactic collisions, gaining most of their mass during massive cataclysms rather than steady feedings.

The root of the problem with this paper lies with its author seemingly forgetting that dilation has an observable effect from the outside while time for the object in question continues as if nothing happened. Were the test particle in the paper see another particle going at the speed of light right next to it, it wouldn’t keep pace with it; the other particle would seem as if it was flying away from its point of reference at the speed of light. He achieves his result by removing a metric he doesn’t seem to have any grounds to remove, and while describing how a black hole accretes a good amount of matter, then evaporates over time due to Hawking radiation, he says that a test particle will just fall until the black hole unraveled into nothingness. These flows of events seem to contradict each other, unless I’m missing something crucial, and since the paper describes opposite outcomes to the same process, methinks it’s staying put on arXiv. The whole point of a black hole’s event horizon is that it must eventually be crossed and nothing can escape it, and once something crosses the event horizon, it’s effectively inside the black hole. If your paper doesn’t get the definition of this critical juncture right, it’s pretty much bound to be flawed.

Since we last discussed the universe according to Roger Penrose, I thought the physics community wasn’t going to dedicate more time to the theory of cyclical cosmology, but apparently, I was wrong. It seems that the theory still lives and is being debated by scientists trying to figure out whether the concentric circles that could be spotted in CMBR maps mean anything significant, or if they’re just artifacts from the kind of anomalies we can expect after a Big Bang. Meanwhile, picking up on the criticism offered by many physicists about the need for a trigger to multiple incarnations of the universe, Penrose brought up a potential explanation for how we’d get an old universe out of gas to suddenly leave an imprint on a new one. Now, one could certainly see how a cyclical cosmology would be attractive. It all but eliminates the question of the source of the mass and energy behind the Big Bang, pointing back to the previous universe. However, were we to look past that, we’d find the theory making matters much more complex, especially when it comes to the cosmic reincarnation scheduled whenever entropy gets too low because the mechanism now given for it only introduces new problems.

First, let’s recap. When famed physicist Roger Penrose and his colleague Vahe Gurzadyan looked at a model of the cosmic microwave background radiation, or the CMBR, the universe’s first echoes of activity which give us the ability to see back to the very dawn of time as we know it, they spotted what resembled big, concentric circles of cooler temperatures. They then proceeded to theorize that these circles could well be scars left over from ancient Big Bangs and that each of them happened when a universe before them cooled and died. Their chosen method for explaining how this would work was to correlate low entropy just after a Big Bang and a similar state after an old universe has cooled completely, and leave it at that. In essence, they were saying that because countless tons of trillion degree quark-gluon plasma have an entropy value similar to that of icy nothingness, we can just flip the two and presto, a new universe is born from nothing, kind of like your can of pop suddenly turns into a fireball after you leave it in the freezer too long. So as you can imagine, cosmologist after cosmologist couldn’t figure out how Penrose actually expected the cyclical universe to work and how his past and future Big Bangs were being generated. They also couldn’t figure out what made those circles such unique features and noted that using current models also produced these features which puts their status as traces of something very special and significant in question. Why would they matter in the big picture?

Now we’re being told that these concentric circles are collisions between supermassive black holes from an earlier universe leaving anomalies in our current cycle. This is a puzzling statement to make since it means a few stray supermassive black holes will register on the CMBR of a new universe but past Big Bangs won’t, as well as clashing with Penrose’s earlier assessment that these features are evidence of other Big Bangs, not just activity in the previous universe. Maybe a collision of some ancient supermassive black holes triggered a birth of a new universe? After all, if a black hole is big enough and lasts long enough, it will eventually shed so much of its mass by Hawking radiation that it will no longer be able to self-gravitate, spewing out something a lot like raw quark-gluon plasmas which could then undergo baryogenesis and condense into matter. After all, the universe is expected to spend the vast majority of its time as a cold, empty stretch of vacuum dotted by an occasional supermassive black hole, and given the sheer length of time involved, even stranger things might happen. So we’ve got a plausible mechanism for cyclical cosmology then, right? Not so fast. Black holes are not magic and they don’t simply appear out of nowhere. Either vast clouds of hydrogen or an incredibly heavy star will need to collapse into one and it will take millions of years of feeding and collisions to grow one huge cosmic singularity. After it evaporates, it should release less matter then the universe that birthed it.

Using supermassive black holes as progenitors of new universes means that the amount of matter available for each new universe shrinks exponentially, and we’re actually on a course to a universe that will stay in near perpetual entropy after it cools off into nothing. And that brings us right back to the first Big Bang rather than a set of cycles which keep the universe bouncing back from its low entropy end. This may be why Penrose isn’t using black holes as his Big Bang generators, just as a source of gravitational waves to create little ripples in the CMBR map. However, we already know that a universe right after the Big Bang should have tiny variations since the blast itself did not need to be perfectly uniform and the tiniest little quantum fluctuation at the instant of the explosion could’ve left a major mark on the new universe as it expanded. And when modeling those tiny fluctuations, we also find concentric circles of slightly cooler temperatures in the CMBR without black holes of dead universes or complex cyclical cosmologies which imply bizarre universes that resurrect themselves. It’s not that there’s no way that we couldn’t all be children of primeval supermassive black holes starting a whole slew of Big Bangs or that the universe can’t be cyclical. It’s just that we have zero real evidence for these ideas past Penrose’s models and his repeated statements that his critics just don’t understand his work.

See: Moss, A., Scott, D., & Zibin, J. (2011). No evidence for anomalously low variance circles in the sky Journal of Cosmology and Astroparticle Physics, 2011 (04), 33-33 DOI: 10.1088/1475-7516/2011/04/033

As the world keeps moving forward, our energy requirements are constantly increasing. Our cities and towns are consuming terawatt after terawatt, and as new technology comes online and old technology improves, the rate of consumption only grows. Surely, an incredibly advanced alien civilization that had a fairly sophisticated infrastructure for the last few million years would have energy needs far, far exceeding ours, measuring their demands in yottawatts and beyond, right? This seems to be the argument in a paper which suggest that one more SETI strategy we should consider is to look for black holes smaller than just a few solar masses since they could well be artificial, created by an extraterrestrial species which needs a constant stream of energy to run its exceptionally advanced society as per Kardashev’s predictions. After all, feeding black holes blast out torrents of extremely energetic beams that could be harnessed by an advanced enough species and all that energy could well exceed the output of an entire star, often concentrated in primarily two beams around what we could call their magnetic poles. So yes, why not look for alien life around oddly lightweight black holes?

feeding black hole

Well, the problem is that we don’t really know the lower limits of a natural black hole and the smaller they are, the harder they are to detect. How can you prove that a black hole is artificially made? Drawing a simple line between 3.5 solar masses and below, then saying that a gravitational well as dense as a black hole but any lighter than that is suspect raises the spectrum of primordial black holes, gravitational collapses of matter as small as a marble but with the mass of our planet, thought to have formed just after the Big Bang, first. An old alien civilization that can simply build a gravitational singularity is going to require a lot more proof than a very rudimentary weigh-in of a quirky astronomical object. Condensing the mass of three suns into a sphere just shy of 17 kilometers across requires an awful lot of energy, roughly just an order of magnitude less than your typical hypernova, so the creation of an artificial black hole on an astronomically relevant scale requires some very, very mighty aliens who can summon the energy of entire solar systems to do their bidding. But of course the paper’s author, Clement Vidal, doesn’t tell us to look for the biggest possible artificial black holes but that there may be something intrinsically interesting about a solar system in which a small black hole is accreting matter from an active star because that’s a very good way to get a torrent of raw energy for a long time.

However, his rather vague mechanism for manipulating matter into collapsing to a black hole state seems a little lacking since it equates our current ability to make nanomaterials by manipulating how chemical bonds come together on a molecular level, with the ability to compress atoms out of material existence, arguing that we can think of the latter as an extension of the former. In reality, making a string of carbon nanotubes and a tiny black hole are completely different capabilities. That said, I could see why a hypothetical alien species is going to be interested by manipulating microscopic black holes. As we discussed once before, an atom-sized gravitational singularity would be a great engine for a relativistic spacecraft, emitting enough energy to just balance on the edge of stability, evaporating quickly enough to do very little damage if things go wrong while it emits plenty of energy from the accretion of raw fuel keeping it alive. And the great thing about black holes in cores of reactors is that you can feed them with pretty much anything gaseous. Want to get rid of some highly noxious fumes you’ve trapped in a factory? Feed it to a tiny black hole. It will turn it into a shower of radiation to be turned into electricity that will power the closest city. However, triggering that initial collapse that will give a tiny black hole a fleeting chance at life is very, very difficult. The smaller the black hole, the smaller the energy input required, and the harder they’d be to detect here on Earth over all the noise made by natural objects.

And that brings us to a very important point that often goes unmentioned about the Kardashev scale. It’s not a set of good predictions, it’s a set of extrapolations which assume that an alien species jumps several orders of magnitude in its energy requirements at each level, sort of like a character in a video game ranking up one more notch. What if truly advanced alien species just don’t exist in very large numbers and don’t have such an insatiable thirst for energy that they need to build a black hole to siphon it form stars? What if they’re fine with just a tiny cluster of black hole reactors supplying all their needs? The very event of creating a black hole on a scale we could detect would be immediately flagged by astronomers as an immensely powerful and puzzling gamma ray burst (GRB) comparable to a Type Ia supernova in its might so if anything, that should be what we should consider suspect rather than a black hole on the lowest ends of scale appearing near alien suns. But then again, we’re back to assuming than an alien species would actually want to, or need to do something on such a drastic, astronomical scale to keep its civilization’s immense demands for energy sated…

Clement Vidal (2011). Black Holes: Attractors for Intelligence? arXiv: 1104.4362v1

[ illustration by NatGeo ]

When you’re reading sci-fi stories in which some of the characters find themselves in need to cover hundreds or thousands of light years very quickly without a warp drive, they manage to make it through time and space via a convenient wormhole. It’s not the worst way to go since wormholes are supposed to exist, we just don’t know how big they are. But how exactly do you go about spotting one, especially one a relatively small throat, big enough for a spacecraft to pass through but not exactly on a scale of a star or a planet? Well, according to one recent paper, you look for gravitational microlensing, a smaller version of the distortion of starlight which galaxies and massive black holes tend to create all the time by stretching and warping the space-time plane around them. Because the throat of a wormhole will also have extremely powerful gravitational tides, it would have the same effect on light. So all we really need to do to find real, actual, cosmic wormholes, is to look.

Depending on how far away those wormholes are, we could find one with an opening as small as a hundred kilometers across, or as big as a hundred quintillion kilometers wide. Sounds pretty neat, right? But does this mean that we could try and detect wormholes around us and build a network of interstellar routes based on a four dimensional map of these shortcuts through space and time? Well, not exactly. See, the problem is that a macro wormhole, one bigger than subatomic particles, has never been detected, and even we do see a slight bending of the light around a star, it might not necessarily be a wormhole. If there really are wormholes out in the cosmic wild, the physics of their formation seem to indicate that they’d be very turbulent and short-lived. As one throat reaches through the fabric of space, it has to be held open with a vast amount of energy, enough to overcome degeneracy pressure and create the kind of energy density that would puncture space itself, which is something that a black hole does at birth. And if the inflow at one end would have to be so extreme, imagine how much more complex the interactions become when we account for its tail end.

Conditions extreme enough to create a wormhole so resemble black hole physics that one hypothesis about how macro wormholes are formed involves the singularities of two black holes merging somewhere in deep space. But that idea throws up a few red flags about the notion of traveling through wormholes if they do exist and happen to form this way. The surges of energy would be so violent, anything that tries to travel through is more than likely to become a multi-trillion degree hot quark-gluon plasma slurped down into an event horizon by the immense gravitational tides of the objects than to travel to another galaxy. But even in the highly unlikely chance that there’s some small island of stability in the raging torrents of self-gravitating energy, kind of like a calm eye of a hurricane, an entering spacecraft won’t necessarily know where it’s going or when in time it may end up when it exits. Even worse, the converging black holes would be extremely unstable and the connection between them would be severed rather quickly. Anything caught up in the collapse will meet an end so violent, I really don’t know the adequate words to describe it. It wouldn’t just be vaporized, it may well be totally erased out of the visible universe after being hit with by a tsunami of energy powerful enough to move stars.

Just to pile on to the problems, there’s also the issue of the distance involved with such a wormhole. Since a black hole is actually a self gravitating spheroid rather than an actual tunnel into space and time, for two such objects to interact would mean that they’re very close to each other and the wormhole doesn’t really cover very much distance at all. So if after all those risk and death-defying leaps of faith you do manage to survive a trip through such a wormhole, you wouldn’t have traveled anywhere, probably far less than a million miles at best. So what about more stable, less dangerous, longer lasting, and deeper wormholes? Well, we don’t know the mechanism that would allow them to exist. However, if we do observe persistent microlensing that we could confirm isn’t being caused by a black hole or a dwarf galaxy in the way, the kind of microlensing that could be explained only by the throat of a wormhole, we’ll know that they exist. We just may not be able to travel through them because they’re much more likely to be far away from us than anywhere close.

See: Abe, F. (2010). Gravitational microlensing by the Ellis wormhole The Astrophysical Journal, 725 (1), 787- 793 DOI: 10.1088/0004-637X/725/1/787