Since it’s been a month since my conference, I think that this will be the last in my series of round-ups from the National Radio Sciences Meeting in Boulder last month. And this time, I’m going to stray away from mainstream science into something slightly out there but totally cool – the Search for Extraterrestrial Intelligence, or SETI.
There were two sessions dealing with new telescopes, techniques and observations. My talk on our epoch of reionization experiment* fit into the afternoon session of the first day. I got to shake off my nerves during a short coffee break, and we returned to hear a series of talks on SETI research. Joshua Von Korff from Berkeley gave the first talk on Astropulse, a project that is searching for all kinds of radio pulses with millisecond and even microsecond time resolution. This has a number of applications from evaporating black holes to rotating radio transients, giant pulses from pulsars to ET itself. Finding a pulse of radiation is not as simple as it seems, however. The interstellar medium (ISM), or the gas and dust that resides in the space between the stars, has refractive properties, meaning that it can “slow down” light. The measure of the refractive property is dependent on frequency of light that is being studied. So, if something gives off a pulse of radio radiation, that pulse will arrive at different times depending on what frequency that you are looking at. If you are using a broadband system, meaning you are looking at a wide swath of frequencies all at once, you may miss the pulse completely!
An example of dispersion measure for a pulsar. From the Handbook of Pulsar Astronomy by Lorimer and Kramer, explained in “Essential Radio Astronomy” by Condon and Ransom.
To find a pulse, you must guess for a wide range of dispersion measures relating to the properties of the ISM and the distance to your object, for an object that you haven’t even found yet! As you can imagine, this takes a lot of computing power. Pulsar astronomers are used to this fact, and so are SETI researchers. Many people are familiar with one solution to the computing problem, SETI@Home. This makes use of the personal computers of millions of users to comb through data from a radio telescope, searching for pulses that may indicate an extraterrestrial civilization, or one of the other cool transient phenomena that are formed naturally in our universe.
SETI@Home screenshot… my laptop looked like this a lot in college!
Next, Andrew Siemion, also from Berkeley, talked about another approach to radio SETI called “Fly’s Eye.” This uses the (mostly) privately funded Allen Telescope Array, or ATA, as a wide field of view survey instrument. In fact, each of its 42 currently working antennas points in a different direction in order to see 150 square degrees of the sky at a time. So it is like the eye of a fly, which is multi-faceted and thus has a large field of view, making them notorious hard to swat! Fly’s Eye has seen approximately 100 “events” to date, most of which were human-made signals, and at least one of which was a giant pulse from the Crab pulsar. Later in the session we heard from William Barott from Embry-Riddle about the digital backend of the ATA. The observatory at Hat Creek has multiple instruments on the backend, depending on the type of science that is being done. The racks of equipment and bright blue XAUI cables reminded me fondly of our own instrument in Green Bank, since we are using the same technology from the same group in Berkeley.
A real treat for me was listening to Jill Tarter speak about SETI. The previous talks were heavily weighted towards the instrumentation, but she delved into the SETI science and reasons for these surveys. Plus, I had seen her on a few Discovery Channel and other such specials, and I’m always amazed and energized by her explanations and motivation. You may think of her as the “real-life Ellie Arroway” if you are a Contact fan. What struck me the most from her talk was the real need that was expressed for surveys like Fly’s Eye and Astropulse. On the one hand, we’ve been looking for extraterrestrial signals since Frank Drake’s Project Ozma in Green Bank in 1960, and so far, nada. However, our radio telescopes started out more crudely and have been getting better and more sensitive with time. Thus, making some assumptions about a possible ET’s transmitting radio power, all the radio SETI searches to date have probed a region of the galaxy only a hundred or so light years across. Remember our galaxy is “a hundred thousand light years side-to-side,” so that’s an itty-bitty fraction! The ATA hopes to greatly expand that physical search space along with more frequency coverage and with greater sensitivity.
Search space of the ATA in the Milky Way, in comparison to Project Phoenix
Some searches are not unbiased scans of the sky. We know of one instance of life, ourselves. Since we aren’t finding habitable planets just yet, we can at least target sun-like stars. Some SETI searches will target those, while others will target stars that have been found to have exoplanets. Others will try a deep search of the Galactic Plane, the most likely part of the sky from which a signal will come. Some projects look for Dyson spheres in the infrared, while others will look for optical transmissions from other civilizations. The point is that there is a huge search space to explore, and we’ve only just begun. It makes me happy to know that someone, somewhere is keeping an eye out for that possible signal, even if the chances of ever receiving it are so small. Wouldn’t it be so fascinating and touch every part of our culture to learn that we are not alone?
* More about the project is forthcoming, I promise! But I talk a little about the science case here.
I’m a brand new post-doc in astronomy working as part of the 
