Monday, February 1, 2016

Are There Alien Civilizations in the Galactic Bulge?

The galactic bulge, or the galactic center, or the galactic bar, is a bunch of stars in a spheroidal cluster at the center of the Milky Way. Because of the distance to it, and the dust between it and Earth, it has not yet been established exactly how big it is, or what its shape is. This is not unusual, as even the spiral arms of the Milky Way are not yet well understood. Other galaxies are much better mapped, so we can make analogies.

The stellar population of the Milky Way is also uncertain, with estimates in the low hundreds of billions of stars. A few things are known about the bulge. The stars there are old. The ages are like that of the globular clusters, dating back to a billion years or so after the date of the start of the universe. So, if we ask if there are aliens in that neighborhood of the galaxy, we have to ask the same questions that were asked about globular clusters. Is it possible for life to originate there? If so, how could they last until now?

Everything about the core of a globular cluster is true, and ten or a hundred times worse, in the galactic core. Stars are closer together, and stellar encounters are even more frequent. There may be no time for planetary systems to coagulate and form bodies, as some star is going to intrude into the vicinity of the proto-solar system, and disrupt planetary formation. Large rocks and small icebergs might form, but they will be tossed like flotsam out into interstellar space.

The density of stars is so great that there will be photon pressure moving gas around, and even small objects. Turbulence will be everywhere, as there is so much random motion of large stars. There may be some stellar collisions, leading to explosions, even if the supernova population disappears within the first hundred million years or two.

When Earth astronomers look at nearby stars and notice they all seem to have planets, that’s a nice conclusion, but it cannot be extrapolated to the whole galaxy. Just because it is nice and calm out here in the outer edges of the disk does not mean the same phenomena, for planetary formation, can occur in the galactic bulge. Stellar interactions tear apart planetary disks, preventing planets from forming. So, instead of saying that there are more planets than stars in the galaxy, it would be better to say there are more planets that stars in the disk portion of the galaxy. That reduces the number of possible worlds for aliens by a factor of ten, as the bulge has about 90% of the total number of stars. This alone is a significant contributor to the answer to the question of why no aliens are visiting us.

The galactic bulge is different from a globular cluster in that it does have some younger stars. Not all the gas was consumed in the initial formation of stars, and the turbulence formed by the stars whizzing around near to one another leads to some higher density blobs of gas, and with a little luck, it could last long enough to condense into a star. And with the star, a planetary disk. After that, planets only if no stellar encounter happens early, and the planets do not stay around if a stellar encounter happens later. So, likely, no aliens in the bulge.

It is possible to say that, since there are so many stars in the galactic bulge, 90% of them to be specific, that there probably are some which escape stellar encounters for long enough for life to form. Maybe even a few where intelligent life can form, except for one problem. There is a radiation hazard there. The closer a star is to a supernova, the more radiation impinges upon it. As an example, stars in the sun’s neighborhood might be 10 to 100 light years away, and because supernovas are rare, the nearest supernova during the time life was trying to evolve might be 1000 light years. Stars in the bulge are ten to a hundred times more densely packed. This means distances are of the order of ten times closer, and that means supernova radiation is a hundred times more intense. And a hundred times more stars means a hundred times more supernovas going off in the vicinity. So, life that lives underwater might not be affected too much, but anything that attempts to crawl out onto dry land would. Without land creatures, is intelligence possible? Only in exceptional circumstances.

This means, in the bulge, not too many planets, and those which do survive have some radiation problems. They would qualify as solo planets, as life could form, but would specifically be plateau planets, as they would have underwater life, but no dry land life to speak of. Of course, there are forms of bacteria that are much more resistant to UV and shorter wavelength radiation, but they do not have the capability to become intelligent. Even if insects can evolve to put up with that situation, there is not going to be intelligence. So, in the bulge, no star traveling aliens. We do not need to scan those stars for signs of life, and if we accidentally find it there, it would be inconsequential.

The same goes for hunting expeditions there. Would it be worthwhile for a species of aliens, who developed in a nice solar system somewhere out in the disk, to travel into the bulge to colonize planets there? They would have the ability to shield themselves against the radiation, to be sure, as they could live underground, once they managed to find the right planet and get there. The edge of the bulge would be nowhere near as bad as close to the galactic center, so perhaps tapping into the fringe area would be reasonable, just not the central part of the bulge. '

Certainly not the central part of the bulge as there is a black hole there, by reputation, which occasionally consumes a star and produces a lot of energetic photons doing so. Perhaps some alien civilization could develop observatories that monitor the galactic core and can indicate when such an event might take place, just as we look for sunspots or stellar eruptions on our star, and warn astronauts about the event. But in the main, the disk is the place to look for alien civilizations, to develop our statistics about stellar types and planetary populations, and perhaps go explore some day.

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