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Stars Traveling Close To Light Speed Could Spread Life Through the Universe
KentuckyFC writes Stars in the Milky Way typically travel at a few hundred kilometers per second relative to their peers. But in recent years, astronomers have found a dozen or so "hypervelocity stars" traveling at up to 1000 kilometers per second, fast enough to escape our galaxy entirely. And they have observed stars orbiting the supermassive black hole at the center of the galaxy traveling at least an order of magnitude faster than this, albeit while gravitationally bound. Now a pair of astrophysicists have discovered a mechanism that would free these stars, sending them rocketing into intergalactic space at speeds in excess of 100,000 kilometers per second. That's more than a third of the speed of light. They calculate that there should be about 100,000 of these stars in every cubic gigaparsec of space and that the next generation of space telescopes will be sensitive to spot them. That's interesting because these stars will be cosmological messengers that can tell us about the conditions in other parts of the universe when they formed. And because these stars can travel across much of the observable universe throughout their lifetimes, they could also be responsible for spreading life throughout the cosmos.
http://www.wolframalpha.com/input/?i=number+of+olympic+swimming+pools+in+a+cubic+gigapasec
1.2×10^73
(2.93799895 Ã-- 10^79) liters in cubic gigaparsec divided by about 2.5 million liters per Olympic pool, so roughly 1.1751996e+73 pools.
That's what I thought, also. Even if they were dragging planets with them (is it possible for planets to orbit that fast?) wouldn't the planets have been sterilized by the conditions at the center of whatever galaxies they came from?
Just finding one of them should be cool enough. There's no need to postulate about "life".
The the term used in the paper is "semi-relativistic" - fast enough that relativistic effects cannot be ignored in even routine calculations about its properties. At 1/3 the speed of light the time dilation effect amounts to a 5.7% difference for example.
"Close to the speed of light" is the summary author's attempt to render "semi-relativistic" in sensible common place terminology.
Second class citizen of the New Gilded Age
Relativistic effects are a non-issue because there is no preferred reference frame in the universe. Our own sun is at this very moment moving at 99.9999999% of lightspeed, when observed from the appropriate position. When observed from there the relativistic effects are quite profound, but the beauty of relativistic effects is that their existence is entirely dependent upon the observer's frame of reference - a thousand different observers on a thousand different relativistic trajectories will see a thousand different sets of relativistic effects on us, and yet we, in a more local frame of reference see virtually none. And every one of those thousands of different observations are all mathematically equivalent.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
Unfortunately, space is not Euclidean on giga-parsec scales. Here, when talking about 5000 Gpc, they refer to a "comoving scale". That is a scale where the expansion of the universe has been divided out, so that e.g. the same number of galaxies remain in this box. So if you would place the atoms of the number of swimming pools you computed in the volume, they would be twice as dense at the largest distances, where the Universe was half the current size. Also, the largest distance within a 5000 Gpc^3 is 3200 Gpc (space is not Euclidean).
NB: The message above might reflect my opinion right now, but not necessarily tomorrow or next year.
Answers to various comments/questions on this sub-thread:
Time dilation at 1/3 c is 5.7%, quite a noticeable amount, but not remotely close to to turning billions of years into millions.
Tidal effects are small for super-massive galactic black holes. I doubt tidal disruption of Earth-like (i.e. fairly close) orbits would occur, especially for cool M-type stars (the most common kind).
While individual particles of cosmic dust hitting the planet at 1/3 c won't be a problem, (they will simply explode high in the upper atmosphere), the energy flux hitting the atmosphere from interstellar gas would be considerable. Average interstellar space has something like 1,000,000 hydrogen atoms per cubic meter. At 100,000 km/sec every second there would be 100,000*1,000*1,000,000= 10^14 hydrogen atoms hitting each square meter of atmosphere. The kinetic energy of those atoms would be about 1000 J, so roughly 1000 watts/m^2 of heating from interstellar hydrogen. Earth gets 1400 watts/M^2 of heat from the Sun, so it would roughly double the heating of an Earth-like world until it cleared the galaxy plane. If it ran into a denser patch (all of the region in the galactic center would be denser than the average I quoted) then the heating could be 10, 100, even 1000 times higher for a bit. I think this would cook any existing Earth-like planet.
Once in interstellar space though the heat load would drop by a factor of 10,000 to 100,000 of the average interstellar value and would cease to be significant. From there on the planet and star system would evolve on their own, and a new biosphere could come into existence.
Starships were meant to fly, Hands up and touch the sky - Nicky Minaj
Simple - because the more we learn about just how durable some life* is, the more it seems inevitable that panspermia happens. Almost certainly between planets within the same solar system, and quite possibly between solar systems as well. Whether it finds fertile ground or not is another question. Basically, even if you assume life "just happens" on a regular basis, panspermia allows it to then spread to places far less hospitable to biogenesis. For example, we have plenty of microbes on Earth that would probably have no problem thriving on Mars, Europa, etc, even if those worlds never offer the rich organic chemical soup and high energy gradients that are probably necessary to spawn life in the first place. When we finally start doing biological studies on those planets it will be very interesting to see if life (A) exists there currently, and (B) is related to Earth life.
* not to mention pseudo-living molecules like RNA and DNA, which don't necessarily need their host organism in order to reproduce and kick-start the evolutionary cycle on a new world.
The answers to those questions may tell us a great deal about the probably ubiquity of life in the universe, and is one of the reasons we try so hard to avoid contaminating them with Earthborn life from our probes. If they spawned their own life it may be less sophisticated than what has evolved here, on our lushly energy-rich plaent, and might be completely eradicate by invasive Earth organisms before we ever have a chance to detect it, depriving us of the knowledge that life likely arises pretty much everywhere. Or alternately, if they were colonized by Earth life long ago (Or perhaps we were all colonized by Mars life - it could potentially have supported life long before the Earth cooled sufficiently), then there is much to be learned about the ways that life evolved in (almost) completely isolated ecosystems. Even if there's only microbial life to be found, the evolutionary divergence could make the Galapagos islands look like just more of the same.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
OK, first of all, let's assume that the collision of two giant galactic black holes can fling stars out of the galactic center in a way that doesn't completely destroy any planetary systems within those star systems. How on earth does life get off of such a planet onto another? If a collision in the solar system were to launch a microbe-laden rock out of the star system, it's still traveling at a third of lightspeed. How do those microbes make a safe landing? For that matter, what about the planet that those microbes land on? Chicxulub is estimated to have released 100 million megatons of explosive energy, which is equivalent to giving every man woman and child on the planet a Hiroshima nuke and detonating them all at once. Now, the Chicxulub asteroid is estimated to have traveled around 20,000 km/sec. And .3 lightspeed is 100,000,000 m/sec, or about 5,000 times the speed of the Chicxulub asteroid. Since kinetic energy scales as velocity squared, we're dealing with an impact that is 25,000 Chicxulub asteroids. So imagine wiping the dinosaurs out. And then doing it again, 24,999 times. That's 2,500,000,000,000 megatons - 2.5 trillion megatons- of explosives. Even a much smaller asteroid- say, 1 km in diameter instead of 10 km- is still going to pack far more wallop than Chicxulub did, and create an extinction event. Even a single kilogram is going to come in with as much energy as a large H-bomb. My guess is that if these stars have any effect whatsoever on the evolution of life in the universe, it's probably not a terribly constructive one...