Slashdot Mirror
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.
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