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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.
The thing about space - the color of space... your normal space color - is its black. And the thing about black holes, is they're black. So how are you going to see them?
You "see" them by observing what they do to the stuff around them. X-ray emissions caused by charged particles being accelerated towards them. Lensing effects due to light being bent by their strong gravitational fields. Binary-star systems with an invisible companion that is too massive to be anything but a black hole. And so on.
If it weren't for deadlines, nothing would be late.
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