As if we needed another reminder of how much we have to learn about the galaxy, now comes word that an entirely new kind of cosmic object has been identified. Working with the Parkes radio telescope in eastern Australia, a multi-national team has found a type of neutron star that is all but undetectable most of the time, while occasionally releasing a single burst of radio waves. The time interval between bursts has thus far been observed to vary between 4 minutes to 3 hours.
Detection of these objects — called Rotating Radio Transients — is a formidable challenge due to the sporadic nature of their emissions. “These things were very difficult to pin down,” says Dr Dick Manchester, a member of the research team and a veteran pulsar hunter who works for CSIRO, Australia’s Commonwealth Scientific and Industrial Research Organisation. “For each object we’ve been detecting radio emission for less than one second a day. And because these are single bursts, we’ve had to take great care to distinguish them from terrestrial radio interference.”
That’s no easy challenge, and it leads the team to conclude that the objects, eleven of which have been identified so far, are indicators of a much larger population, perhaps a few hundred thousand in the Milky Way. The more studied and better understood form of pulsars, emitting regular radio pulses up to hundreds of times per second, are probably far outnumbered by the new objects.
Centauri Dreams note: It’s hard to use the term ‘conventional’ when describing pulsars, which is why I avoided it above. But the kind of pulsar we’re familiar with results from the supernova explosion of a massive star, leaving a collapsed core perhaps ten miles in diameter that is largely made up of neutrons. Such pulsars spin at enormous rates; a pulsar, known as PSR J0205+6449, for example, presently rotates 15 times every second. But the rotational rate slows as the pulsar ages, and after a few million years, such a pulsar will lose the energy needed to generate its radio and x-ray emissions.
How these newly identified objects fit in with the standard pulsar model will be interesting to follow. The paper is McLaughlin, Lyne, Lorimer et al., “Transient radio bursts from rotating neutron stars,” Nature 439 (16 February 2006), pp. 817-820. An abstract is here, and Nature.com also offers a helpful background article.
Together with the truly odd 10-min bursts spaced by 70 minutes, and from a point projected near our galactic center, these illuminate the role of sopratic events — a difficult task for astronomers to clarify. One might note that these are like what we would see from “industrial” use of microwave beams in distant solar systems, which occasionally
beam in our direction. Not all SETI should be devoted to conventional, regular events.
Gregory Benford
A fascinating thought, and a reminder that we can be too conventional in our SETI thinking. It has always seemed to me more likely that we would pick up sporadic evidence of extraterrestrial activities rather than a targeted beacon, though gearing up the needed equipment for tracking such events over time is a herculean challenge, and not just in the SETI context.
We have sadly, a long string of assumptions based on almost no information to speak of, and then to compound this uncertainty, we embellish it with man made theories and dodgy formulae.
Come on you young scientists, start using your instinctive facilities and your imagination, and start heading off in the other direction.
Brian Sallur
Astrophysics, abstract
astro-ph/0703019
From: Alice K. Harding [view email]
Date: Thu, 1 Mar 2007 16:14:23 GMT (204kb)
The Geminga Fraction
Authors: Alice K. Harding, Isabelle A. Grenier, Peter L. Gonthier
Comments: 10 pages, 7 figures, accepted for publication in Astrophysics and Space Science, as proceedings of “The Multi-Messenger Approach to High-Energy Gamma-Ray Sources”, Barcelona, July 4-7, 2006, J. M. Paredes, O. Reimer, and D. F. Torres, editors
Radio-quiet gamma-ray pulsars like Geminga may account for a number of the unidentified EGRET sources in the Galaxy. The number of Geminga-like pulsars is very sensitive to the geometry of both the gamma-ray and radio beams. Recent studies of the shape and polarization of pulse profiles of young radio pulsars have provided evidence that their radio emission originates in wide cone beams at altitudes that are a significant fraction (1 -10%) of their light cylinder radius. Such wide radio emission beams will be visible at a much larger range of observer angles than the narrow core components thought to originate at lower altitude. Using 3D geometrical modeling that includes relativistic effects from pulsar rotation, we study the visibility of such radio cone beams as well as that of the gamma-ray beams predicted by slot gap and outer gap models. From the results of this study one can obtain revised predictions for the fraction of Geminga-like, radio quiet pulsars present in the gamma-ray pulsar population.
http://arxiv.org/abs/astro-ph/0703019