viernes, 11 de febrero de 2011
E.T. Might Fire Up Intergalactic Lighthouses
The Kepler Space Observatory's discovery of over 1200 planet "candidates" announced last week left me with a chilling cosmic loneliness.
Although the Kepler finding makes me even more convinced that E.T. is out there, I can't help but ask the question: Where is everybody?
The evidence may be staring us in the face and we don't recognize it. It might even be buried as an obscure and mildly curious dataset in our ballooning vault of astronomical observations.
The thesis: advanced civilizations realize that two-way communication between stars is impractical given the roaming charges imposed by the speed of light. So instead they build a beacon that simply says: We Are Here!
But painting the sky with that beacon is costly. And, it is unlikely that it will be intercepted at just the right time to attract the attention of another civilization.
Radio signals, the staple of the 50-year old SETI effort, have to contend with background noise, selection of radio frequencies and the need for lots of power. Communications beyond our nearest neighbor stars is very difficult. Optical laser pulses are being looked for too, but they also suffer from the "needle-in-a-haystack" search challenge.
A better scheme may be to leave a "Rosetta Stone" artifact for an another civilization to discover as it becomes astronomically capable. This could take the form of a "galactic lighthouse," with a beacon that is so powerful it can be seen by inhabitants of other galaxies.
John Learned of the University of Hawaii has proposed using Cepheid variable stars as the lighthouses. These brilliant pulsating stars are invaluable for estimating intergalactic distances. Their rate of pulsation, which can range from 1-50 days, is also a measure of their intrinsic brightness.
This relationship can be used for calibrating intergalactic distances, a prerequisite for measuring the expansion rate of the universe, which is fundamental to nailing down other cosmological parameters. Therefore Cepheids would automatically get attention from scientifically inquisitive civilizations.
By twiddling with a Cepheid's pulsation cycle, the star could be used to broadcast, omnidirectionally, a modulated message.
But how do you twist with the dimmer knob on an entire star? This analogy is apt because a small change in voltage inside the dining room dimmer's circuitry is amplified to affect and entire chandelier of bright lights.
Learned proposes that an advanced civilization might build a neutrino beam that would be shot into the upper layers of a Cepheid variable star. Only neutrinos can penetrate matter as if it wasn’t there. So reaching the star's interior at nearly the speed of light would be easy.
When helium inside a Cepheid gets hot enough it is stripped of electrons, or ionized. During that ionized state the outer layers of the star are more opaque, absorbing more of the emitted light. And so, the star dims. As the star expands the outer layers of the star are less opaque. This lets more of the light escape and so appears brighter. As the star expands, the helium captures electrons and "de-ionizes" and the star contracts and cools. This heats the interior and the helium reionizes, and the cycle stars again. A neutrino beam could heat the star at the right moment to trip the expansion prematurely. A simple binary code might be broadcast by modulating the light curves this way.
The aliens would have anonymity because the neutrino projector would have to be sent to a nearby Cepheid variable star. The projector would be located at a safe distance from the seething star, say 100 billion miles. The device might collect stellar energy, storing it like an electronic flash capacitor, and then use it to fire up the neutrino beam.
Such an automated beam could continue working for centuries or even millennia, even after the host civilization has died out or lost interest in the experiment.
What's intriguing is that we have many decades worth of Cepheid light-curves in numerous galaxies. Perhaps buried in the archives is as anomalous Cepheid that simply has not been analyzed with this kind of scenario in mind.