Friday, January 29, 2016

Halo Stars

Halo stars are stars that reside in the halo. This has a few implications for aliens who might have originated there. First of all, a little background on the halo. It is inhabited by stars and globular clusters, which are clusters of stars shaped like globules. These stars and clusters orbit the Milky Way, and mostly the globular clusters have orbits which encircle the galaxy, but because the Milky Way is shaped like a plate, the orbits have a fairly funny shape. The stars also can orbit the whole galaxy, in the same kinds of orbits, but they can also penetrate the disk, maybe even the bulge at the thinner places, and come out on the other side. They are going to keep oscillating above and below the galaxy, until stellar encounters knock off some of their perpendicular velocity, and they go less far away. Eventually, they will just settle down into the galaxy, leaving the ones which orbit around the outside a bit more lonely.

Note that clouds of gas were not listed. There could be clouds of gas in orbit, but this is a very peaceful place, and a cloud of gas would condense and form stars and solar systems or even rogue planets. The orbit time is of the order of 200 million years, and a few orbits would be enough for condensation. This means that the stars out there in the halo are old. Of course there are exceptions. Every time some dwarf galaxy comes sailing through the disk or even right near it, it rips off some gas and maybe tosses it into extragalactic space, or the halo. By and large, the gas is not making new stars there, but there might be a few exceptions. Millions not billions.

Just exactly what does it mean to be an alien on an old halo star? It means you don’t have anything to eat or wear or drive around in or look at stars with or anything. You have used up the resources in your solar system one or two or three billion years ago, and nobody has come by with replenishments. You have tried every trick known to alienkind, like recycling to the ultimate possible, dropping your population down as low as sustainable, taking advantage of every form of energy on the planet and off it, and reducing your own needs with genetic engineering. It worked for a while, but a billion years is such a long, long time.

Every alien civilization on a halo star that did not start up star voyaging early in their history is forced to the same situation. Their living standards cannot be maintained, and so the only solution is to drop back to a very primitive level of existence, hunting, farming, or something else that does not require any resources, no fertilizer from mines, no oil or tar or gas, no gold, no copper, no rare earths. It means no interplanetary travel can be continued, so it is back to the home planet. No power stations. No power. No water supplies. No cities.

A planet is nice because it does 100% recycling, at its own pace, and so living in the bosom of the planet is a way for an intelligent species, or a non-intelligent one for that matter, to survive for a while. With luck, survival might last billions of years. No one would know, as history could not be preserved that long. Technology would consist of using the available organic growth. There might be some scrabbling around after some volcanic eruptions die off, a few millennia later for example, to see if any useful minerals were brought to the surface, if anyone remembered what they were and how they could be used. So, in that case, for a few tens of millennia there might be primitive use of metals. But for the most part, the planet does all the recycling, and it runs its life support on photosynthesis of the star’s photons.

This type of behavior could happen on planets around M stars, red dwarfs, if life is possible to originate there, or maybe K stars, as these evolve very slowly as well and the habitable zone does not sweep out and in in radius while the aliens are trying to make due on the planet. Hotter stars could present a problem, as a billion years is a long time to an A or an F class star, and even a G, like the Earth, could undergo changes. Of course, low mass stars may correlate with low total planetary mass, meaning there might not be so much to pick through among other planets sharing the same solar system. So, out in the halo, you would find widely separated small stars with alien civilizations hardly able to maintain a civilization after so much time.

An alien civilization out in the halo could go through the same grand transitions as one in the disk, and they would be able to understand early on that civilizations cannot last long times on one planet or one solar system. They would have to decide what they wanted to do, either take the very long voyages and seed their civilization on another distant sun, or be reduced to living almost like animals, but ones with language and stone implements. Without any advanced technology, they would be unable to stop evolution or genetic drift, and their species would likely not continue to exist as it was during the time of technology. They could have greatly improved their genetic code, but mutations would continue coming and accumulating, and eventually all those improvements would succumb to the random nature of genetic change, caused by indigenous sources such as chemicals or radiation. Their improved immune systems would gradually relax back to what could be stable under mutation. Genetic drift might take a hundred thousand years or a million, but not a billion. They would have a good ride for the first hundred thousand years or so, but after that, a hard life such as their pre-civilization ancestors experienced. Short life spans and little to distinguish them from a civilization that had not had a golden age.

Those that took the option of star traveling could, over some millennia, wrap up their civilization on the home solar system and start over somewhere else, perhaps on a lifeless planet somewhere, but one with resources that could be used to create life. Growing an ecology seems like it would take a million years, but if a high level of technology could be maintained during that period, the alien civilization might just decide that was the road they wanted to follow. And as the galactic clock continued to tick, at one revolution per 200 million years, they would gradually wend their way perhaps down to the very crowded area, in their point of view, of the galactic disk. That’s where we are waiting for them.

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