Sunday, September 29, 2013

Mysterious Radio Bursts Detected - Of Alien Origin?

The Parkes 64 m radio telescope which detected the strange radio bursts.

Six years ago, radio astronomers were baffled on detecting 4 energetic bursts of radio waves that lasted only a few milliseconds. Their bafflement was engendered by being unable to associate the bursts with a specific object.  Now, more recently, we find in the July 5 issue of Science, that Dan Thornton of University of Manchester and colleagues also reported 4 mysterious bursts.

Interestingly, they exhibited energies similar to the 2007 events,  and also resembled them in appearing only once. While researchers still aren't sure what might have caused such a signal they know it wasn't a fluke. The parameters for the radio telescope and the observed events all check out and conform to radio astronomy physics.  So we do know in order to be detected at all,  radio waves must fall within certain physical limits, i.e. brightness temperature, received flux, solid angle etc. One also needs to look at properties of the antenna -receiver such as beam width, gain, antenna temperature, etc. Since all the detected parameters were within conformance to standard radio physics we know the bursts aren't flukes.

In the Science paper, the radio astronomers reported scanning the sky with the 64 m Parkes radio telescope in New South Wales, Australia (see image).  They'd actually been searching for the rapidly spinning compact remnants of once massive stars as well as other transient radio sources. In the first case, one expects a supernova would have erupted leaving a neutron star (at least) in its wake. (The 4 newly observed bursts originated in the high latitudes of the Southern hemisphere, and roughly 40 degrees south of the Milky Way's disk.)

The first order of business was to determine the distance of the events. We know as radio wavelength radiation propagates through gas and dust it impacts electrons which smear the signal. The four strange burst emissions showed such a smearing, indicating the bursts were from space and not from Earth. Also, since the point of origin was 40 degrees off from the galaxy's disk the researchers concluded the burst originated outside the Milky Way. Following a computation of how much material the radiation had to travel through, they estimated the bursts' distance at between 5.5 and 10.5 billion years.

As for the energy signature, it was astounding. Each of the four bursts released as much energy in its brief emission time as the Sun puts out in 3,000 years.  So what is the source?

Could it be an advanced alien civilization which has somehow managed to exploit the energy of powerful astronomical objects to dispatch brief, but energetic signals? Granted, this hypothesis can't be totally excluded, since one must recall E.A. Milne's rubric of always dealing with physical proposals by using the concept of a bead on a wire and never letting the bead get to one end (certainty) or the other (impossibility). However, if the distance calculation for the events holds up - it is doubtful aliens are the source. At such immense distances, in effect looking that far back in time, it is improbable advanced alien civilizations existed.

In an article appearing 25 years ago, in The Journal of the Barbados Astronomical Society, I also argued against the likelihood of extra-terrestrials using radio signals to communicate. In order to communicate, say over thousands (or even hundreds) of light years' distance, information is transmitted. It requires energy to do this. Interestingly, a relation between energy and information is available. It can be written as:

E = 0.693 kT

Here, E is the energy associated with transmission of 1-bit of information. T is the temperature of the environment in which it is sent (say the radio transmitting antenna) and k is a physical constant known as the Boltzmann constant. Imagine an alien civilization sending the equivalent of a small novel to humans. This would be approximately 1020  bits of information. The associated energy would be about 0.3 (three tenths) of a Joule.  The energy required, from a practical standpoint, would be much, much larger - maybe 100 million times larger. Why? Because in the process of pure transmission (over light years distance) a significant fraction of signal dilutes. So, at least 30 million Joules would be needed, to have it get to Earth in a useful form.

Arguably, aliens genuinely interested in contact would not waste time or effort with anything so puny as a small novel. It is more probable, if they went to the trouble of first contact (as in the film 'Contact') they'd send a lot of information. Say, equal to an alien encyclopedia of mathematics, or their most prevalent language. In this case, the information content soars to billions of megabytes, and the energy accordingly. For one million megabytes (1012    bits) the aliens are looking at an energy for transmission on the order of 3 x 1019  Joules.

It is well to realize that time factors into this as well. If the aliens kept the transmission going for at least one hour (Earth time), 3 x 1019   kilowatts of power are needed (assuming the aliens are able to sustain a rate of energy conversion of 1 Joule per second). In the civilization classification scheme of the late Russian astrophysicist I.S. Kardashev, this would put them at a bit beyond Type I, but not quite Type II. Kardashev's three-class scheme is:

I: Able to harness the equivalent power of the planet Earth

II: Able to harness the power equal to a typical star (1023  kw)

III: Able to harness the power equal to a typical galaxy (1033  kw)

While the burst energies appear to be close to the last category, there is one problem: no decipherable or intelligible communication was recorded. In this case, it leaves a powerful astronomical object as the likely source.

The astronomers themselves, in their Science paper, propose the most convincing cause is a neutron star known as a magnetar.  Thornton and colleagues suggest some 1,000 of these magnetar bursts occur across the sky every year. We will wait for confirmation to see if this is in fact, the best explanation

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