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New Research Reveals Hundreds of Undiscovered Black Holes (phys.org)
An anonymous reader quotes a report from Phys.Org: New research by the University of Surrey published in the journal Monthly Notices of the Royal Astronomical Society has shone light on a globular cluster of stars that could host several hundred black holes, a phenomenon that until recently was thought impossible. Globular clusters are spherical collections of stars which orbit around a galactic center such as our Milky-way galaxy. Using advanced computer simulations, the team at the University of Surrey were able to see the un-see-able by mapping a globular cluster known as NGC 6101, from which the existence of black holes within the system was deduced. These black holes are a few times larger than the Sun, and form in the gravitational collapse of massive stars at the end of their lives. It was previously thought that these black holes would almost all be expelled from their parent cluster due to the effects of supernova explosion, during the death of a star. It is only as recently as 2013 that astrophysicists found individual black holes in globular clusters via rare phenomena in which a companion star donates material to the black hole. This work, which was supported by the European Research Council (ERC), has shown that in NGC 6101 there could be several hundred black holes, overturning old theories as to how black holes form.
hundreds of black holes all at once? or is it just grit on the scanner scope?
http://arxiv.org/abs/1609.0172...
From the article
"This research is exciting as we were able to theoretically observe the spectacle of an entire population of black holes using computer simulations. The results show that globular clusters like NGC 6101, which were always considered boring are in fact the most interesting ones, possibly each harbouring hundreds of black holes. This will help us to find more black holes in other globular clusters in the Universe. " concluded Peuten.
Therefore still undiscovered, as this was just a simulation that provided an explanation of the makeup of the specific cluster under examination - when they added black holes to the simulation, the results matched what the actual cluster looks like while without black holes it didn't
This is definitely very cool, but "reveals" is a strong word. They've demonstrated that it's a plausible explanation for the puzzling distribution of stars in this cluster, but there are still other explanations that have not been ruled out.
What's puzzling about the cluster is that the stars appear well-mixed -- the high mass stars follow the same distribution as the lower mass stars. That's weird because globular clusters should undergo mass segregation, where the high mass stars slowly congregate towards the center while the lower-mass stars migrate towards the outside (interestingly, this is because self-gravitating systems have negative heat capacity, which is a concept that tends to freak out non-astronomers). And we indeed see that most clusters are mass-segregated.
So why do black holes help? They form from the most massive stars, which died early, and they end up being significantly more massive than the lower-mass stars that are left. So if there are lots of black holes, then the effect of mass segregation is to make the *black holes* congregate towards the center. In other words, mass segregation is still happening, but it's operating on black holes (which we can't see, so we don't notice its effect) instead of stars (which we can see).
There are other ways you can explain this, though. If there's a massive-enough intermediate-mass black hole at the cluster center, that makes the process of mass segregation take longer, so it might not have had time to make any significant change. A sufficiently large fraction of binary stars within the cluster could have a similar effect (i.e. make the mass segregation timescale much longer). Or, more speculatively, you could posit that there was some dynamical event that happened to the cluster since its formation that mixed the stars, so mass segregation has not had as long to operate as we assume. So their explanation is a plausible interesting one that they have demonstrated can indeed cause the desired effect, which is really cool! But these other options also need to be investigated.
Some novae occur though a gentle accretion process, such as a burnt out star with a companion, and some occur through expending all of thier fuel and the lack of thermal pressure causes collapse. Rarely one can be created through a merger of two stars but it's not exactly the same thing. In the first two cases it's not very clear what causes this but there is some evidence the process is not always symmetrical. A supernova often expends as much energy over a few hours to days as the star previously expended in its lifetime. Much of the material is blown off at up to 10% light speed. With the release of so much energy, even a very small deviation from being spherical can provide enough velocity on the black hole to exceed the pull of the gravity in these small globular clusters. So the result of the simulation is interesting and points the way forward for follow up observation.
By observing the patterns of evolution of life in Earth one can conclude a large part of the solution to the Fermi Problem - there is no general trend in evolution toward human-style intelligence with its complex symbol manipulation, communication, and complex tool making.
Examples of evolutionary trends that show up repeatedly include convergent evolution, and the filling up of ecological niches, which happen quite predictably. If the specific adaptations leading to human style intelligence are at all likely we should see them appearing repeatedly, independently in the evolutionary record.
But in the history of life on Earth the appearance of human-style intelligence appears to be a real fluke, which only very, very recently seems to have give our species and marked survival advantage.
There are about 60,000 vertebrate species today (lets assume that this is the only class of organism that can develop intelligence). If we take the estimate that 99.9% of all species that have ever existed have gone extinct, then this makes a history of 60 million evolutionary experiments over a span of 525 million years. Yet only the Simian branch of the Primates developed the dexterity adaptable to complex tool making - 60 million years ago.
Once the simian pre-adaptations were set toward manual dexterity, binocular vision, really all of the evolutionary tool-kit that hominids eventually exploited, do we see any trend within that family toward tool-using? Are there multiple independent branches with the simians that start using tools? No there are not, only one branch leads to that, the Apes (Hominoidea), and that sub-family emerged 20 million years ago. Is there a trend within the Hominoidea of multiple branches showing developing complex tool using? Again there is not. Orangutans for example split off 20 million years ago, but their adaptation pattern appears stable over that time, behaviorally orangutans today seem similar to their distant ancestors. This pattern is observable in each such branch of the Hominids (Great Apes). The Great Apes have existed for at least 8 million years, but none of the branches that split off from Homo has shown any tendency to follow the pattern of tool making and brain growth that Homo did. The other Great Apes have been stable in their brain size and propensity for simple tool use, but not tool making, for millions of years.
It is only within the genus Homo, which arose 2.8 million years ago that we start to see multiple experiments in tool making species with rapid brain growth appearing, this trend seems a real evolutionary fluke.
And finally intelligence has not really show to provide any marked survival advantage for the species possessing it until very recently. Within the last 70,000 years modern humans (who have existed in their present form around 250,000 years) appear to have undergone a population bottleneck where the entire human race shrank to about 2,000 individuals - a close brush with complete extinction.
Humans remained a rare species until about 40,000 years ago, when the first population surge occurred, bringing human numbers up only to levels similar to many other large mammal species (hundreds of thousands to the low millions) by 13,000 years ago. And only then did the intelligence help humans to start out-performing all other mammal species in success.
So this whole pattern suggests that the stable pattern of the last half-billion years, with many tens of millions of large complex animal species, and no trend toward human-style intelligence is the norm, and could be expected to continue indefinitely. But a long series of freak events (which we are still in the early stages of revealing and unraveling) seems to have led just one species to have civilization, and even there is was a late emergence and might not have happened at all if the species had not made it through that bottle-neck.
Starships were meant to fly, Hands up and touch the sky - Nicky Minaj
"you'd think one civilization would send out von Neumann probes"
Thats ridiculous! What are the chances of another civilization who had a scientist named "von Neumann"?
The "Great Filter" is a very poor answer, IMO. A Great Filter before where we are now is bad science on the level of thinking we're at the center of the universe: no, sorry, we're not special.
Could there be some future hurdle that many civilizations fail to jump? Sure. But there no reason to expect an alien civilization to think the way we do about anything, really. To propose that all civilizations would be blind to some danger is absurd.
Remember the uncertainty in the Drake equation is many orders of magnitude, and even so it doesn't much matter for the Fermi Paradox. A Great Filter that takes out 90% or even 99% of civilizations doesn't solve the paradox. It only take one civilization that built von Neumann probes.
Good post. You hit the salient points pretty nicely.
Agreed that invoking a purely speculative it-always-happens-no-matter-what genuine, permanent extinction event for advanced civilization is basically a magical solution for the Fermi Problem.
It has been argued that in fact we have the history of many (most?) societies that reached a high level of organization and have collapsed - and so I seen a "civilization lifetime" parameter calculated from historical societies used in the Drake Equation. And that is a fair point. But none of the collapses were permanent, new ones have always arisen after, so it does not really support the extinction filter idea at all.
As I wrote on this thread below, extreme improbability of an advanced technological civilization arising in a biosphere is at least a partial explanation, since there the historical evidence is consistent with this idea. I did not mention though that the industrial revolution itself seems something of a fluke, it was completely unexpected and even with more than two centuries to study it, and abundant records and evidence, it is still not clear why it happened.
Also I did not point out the research about the habitable zone of the Universe, the region of space and time where the conditions permitting technological civilization could arise. This requires a very benign stable biosphere for half a billion years, since minor perturbations (on a cosmic scale) still bring about great extinction events. What with quasars and other active galactic cores, exploding stars, migrating planets and colliding bodies, necessary concentrations of heavy elements, etc. it turns out that a fairly small volume of cosmic history contains the necessary conditions. When you have enough "extremely unlikely" events in the chain, even the vast Observable Universe is perhaps not vast enough.
Then too, how far do we think a Von Neumann probe society would end up sending probes? The two major galaxies in the Local Group are 2.43 million light years apart. The next closest galaxy group is 10 million light years. At that distance even a 1% c probe takes a billion years. The closest galaxy cluster to ours is 53 million light years away. That's a billion years even at 5% c. And then there are the great voids in the Universe, separating super clusters, which are 200-600 million light years across. Even at substantial fractions of c the Universe is probably not old enough for a civilization to arise and send a probe to cross those. So at some scale distance does become a true barrier that technology and time cannot cross.
Starships were meant to fly, Hands up and touch the sky - Nicky Minaj
Not really, that's just one of the major theories for it's nature, that it's WIMPs - Weakly Interacting Massive Particles. Another popular theory is that it's MACHOs - Massive Compact Halo Objects, aka black holes orbiting outside the radius of the visible galaxy - a theory that has gained credence with the recent detection of two black whole mergers, both within the narrow size window which would remain consistent with observations to date, suggesting that such black holes are far more common than we believed. And there's several other theories as well - so far none has truly compelling evidence to separate it from the pack.
And of course, there's no guarantee that dark matter exists at all - it's basically just a "here there be dragons" kludge of current gravitational theory, necessary to make predictions consistent with observed reality. As we revise or replace General Relativity we may discover that the need for dark matter vanishes as well. You say that Newton could not say what gravity really was - today physicists realize that they understand it even less than he thought he did.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
Actually, tool making is fairly common throughout the animal kingdom, even among animals without hands - ravens, dolphins, etc. And manipulating hands have likewise arisen many times, though the added versatility of thumbs is more rare (though some, like Koalas, have us beat with two thumbs per hand)
And lets not make too many claims about the behavioral characteristics of animals millions of years ago, shall we? It is after all almost pure speculation since all we have left is skeletons, making even ancient archaeology look positively well-substantiated in comparison.
And speaking of archaeology, we have evidence of what, at least a half-dozen different tool-using hominid species that apparently arose independently? And, last I heard, none of those explain the discoveries of some of the apparently truly ancient stone tools we've discovered, predating any known tool-using primates.
On the other hand, you also missed one of the truly huge steps in primate evolution - brain size scaling independently of neuron size. Among most animals, neuron size scales roughly with brain size, so that bigger brains are just bigger. Primate brains are fairly unique in that neuron size remains relatively constant across species, so that a gorilla has far more neurons than a squirrel monkey. That was the key that let bigger brains actually be more useful. Of course there's no reason to assume that wouldn't be the normal state of affairs in an alien world, which would dramatically increase the odds of high-intelligence species emerging.
--- Most topics have many sides worth arguing, allow me to take one opposite you.