by Paul Gilster | May 14, 2008 | Deep Sky Astronomy & Telescopes |
A tricky aspect of modern astronomy is keeping all the wavelengths straight. Take the case of G1.9+0.3, a supernova remnant (SNR) near the center of the Milky Way. If you look at an X-ray image of this object made with the Chandra satellite in 2007, you’ll see clear signs of growth compared to what the Very Large Array saw in 1985. But the VLA was working at radio wavelengths, making the image comparison problematic. Scientists studying G1.9+0.3 therefore went back to the VLA to observe the object for a second time in order to verify their initial impression.
The later study confirmed that this supernova remnant — consisting of the materials ejected by the vast explosion — really is growing at what seems to be an unprecedented pace. Fifteen percent growth in 23 years is no small matter in astronomical terms, and the growth also makes it possible to work backwards in time to arrive at the time the supernova went off, now pegged at 150 years ago. That makes G1.9+0.3 the youngest of the 250 known supernova remnants in the Milky Way.
Image: The growth of supernova remnant G1.9+0.3 is clearly visible in this comparison shot. The colour scheme (dark blue -> light blue -> green -> yellow -> red) is increasing radio intensity. The width of each of the above images is about 3 arcmin, i.e. 1/20th of a degree. Credit: VLA/Dave Green.
Intriguingly, this SNR holds one other distinction: Its brightness at radio wavelengths has been increasing over the last few decades, a process unique among galactic supernova remnants. We’ll learn much from future observations. Says Dave Green (University of Cambridge):
“The discovery that G1.9+0.3 is so young is very exciting. It fits into a large gap in the known ages of supernova remnants, and since it is expanding so quickly, we will be able to follow its evolution over the coming years.”
Those observations will continue to be made at X-ray and radio wavelengths for now, the object being obscured by gas and dust so that it is not otherwise visible. Nor would the supernova that created it have been detectable to Victorian astronomers, buried behind dust lanes whose nature and location they did not yet suspect. The paper, accepted by Monthly Notices of the Royal Astronomical Society, is Green, Reynolds et al., “The radio expansion and brightening of the very young supernova remnant G1.9+0.3” (abstract).
by Paul Gilster | May 13, 2008 | Deep Sky Astronomy & Telescopes |
With the GLAST mission near launch, keep in mind the possibilities of this unique observatory in terms of findings that could revolutionize our view of distant events. GLAST (Gamma-Ray Large Area Space Telescope) will be looking at things we’ve only recently learned about, such as the enigmatic gamma-ray bursts (GRBs) now flagged by the Swift satellite and quickly pinpointed for the use of Earth-based observatories. We know we’re pushing into uncharted waters given that GLAST represents a major step forward over all previous satellites designed to study gamma ray events. And major new instruments usually deliver new classes of objects.
Because of the increase in GLAST’s sensitivity over earlier tools like the EGRET instrument on NASA’s Compton Gamma-ray Observatory (CGRO), the satellite may find thousands of new point sources. And we have plenty of questions already on the table. Gamma-ray bursts, for example, may be the result of black hole mergers, or the merger of a black hole and a neutron star. But it’s also thought that some are markers for the collapse of a massive star into a black hole. What types of stars, then, become GRB’s, and why? What is the mechanism for producing the initial gamma rays in the burst? Because GRBs seem to come in numerous varieties, their study offers fertile ground for years of research.
Or consider dark matter, the leading candidate for which is the hypothetical weakly interacting massive particle (WIMP). Gamma rays may also derive from WIMPS, which according to supersymmetry theory act as their own antimatter particles, annihilating when they interact with each other, and in the process releasing gamma rays and secondary particles. The signature of such annihilations is potentially observable with GLAST’s Large Area Telescope (LAT), assuming that dark matter is indeed composed of WIMPs. Its continuous stream of gamma rays should differ markedly from the milliseconds-to-minutes time frame of GRBs.
Image: According to supersymmetry, dark-matter particles known as neutralinos (which are often called WIMPs) annihilate each other, creating a cascade of particles and radiation that includes medium-energy gamma rays. If neutralinos exist, the LAT might see the gamma rays associated with their demise. Credit: Sky & Telescope / Gregg Dinderman.
One other fascinating possibility in range of this observatory is the question of the speed of light in a vacuum. The special theory of relativity pins the speed of electromagnetic radiation to 299,792,458 meters (186,282.4 miles) per second, and it would be assumed that gamma-ray photons should move at the same speed. Some models of quantum gravity, however, predict that the speed of very-high-energy gamma rays may vary slightly from other forms of light, the result of the turbulence of spacetime at quantum scales. GLAST can thus test a prediction that could nudge us, if only slightly, toward a merger of general relativity and quantum mechanics.
GLAST is now at Cape Canaveral with a planned launch in early June, having been moved to the Hazardous Processing Facility near Kennedy Space Center for fueling. I suppose it’s human nature that manned missions are what snare media attention, but this observatory may turn out to be one of the most significant we’ve launched in terms of probing out to the edges of physics and cosmology. Dark matter may not make CNN, nor will many gamma-ray bursts, but if GLAST can offer up some answers, we may get a far better read on how the universe functions, and if we’re really lucky, some clues to future propulsion possibilities.
by Paul Gilster | May 12, 2008 | Astrobiology and SETI |
How much would an extraterrestrial civilization resemble our own? The question resonates because on the one hand, the signature of our activities is what we tend to translate into the SETI search. We look, for example, for the signs of civilizations that are like us but more advanced technologically, which means we apply human thinking and motivations to cultures that are by definition not human. This is natural enough, because we’re the only technological civilization we know about, but it leads to results that may mislead us and obscure the actual situation.
Fermi’s Great Silence bothers us because we assume that what Milan ?irkovi? calls advanced technological civilizations (ATCs) will necessarily move out into the galaxy to colonize it. Yet we see no signs of this, no presence of an expansive power, no characteristic emissions telling us of any intelligence operating around nearby stars. This observation becomes a paradox only if we think in specifically human terms, relating what advanced cultures might do to our own history. If ATCs behave differently, then there may be no paradox — the galaxy may be rife with civilizations that simply operate according to a different set of principles.
?irkovi? (Astronomical Observatory, Belgrade) continues to be one of our most innovative SETI thinkers, pushing well outside the conventional paradigm to ask what truly alien intelligence might do. And in an upcoming paper to be published in the Journal of the British Interplanetary Society, the astronomer also questions our own understanding of human history, asking whether expansive colonization is necessarily emblematic of our species. If it is not, we should not be so quick to rule out alternative scenarios for alien action. We might re-think an expansive colonial model in favor of one ?irkovi? calls the ‘city-state.’
Moving Beyond Biology
Imagine for a moment that as humanity and technology continue to intertwine, we move into a period when human capacities become extended so far beyond those of present day people that what is widely called a ‘posthuman’ civilization emerges. Would such a culture still be bound by biological motivations that characterize us today? ?irkovi? sees a contradiction in the thinking of many technological optimists, who support evolutionary explanations for mankind’s origin but seem unprepared to abandon the biological paradigm when considering what future civilizations might do when they move beyond it.
The situation seems to be as follows: if we agree that specific biological motivations have been a determining factor in the biological (human) phase of the history of our species, it would be only reasonable to argue that, with the transition to the postbiological (posthuman) phase, the old biological impetuses and motivations will become largely irrelevant. Paradoxically, it is rare to encounter such attitude in tech-optimists/transhumanist circles; in general, the predominant view is that the posthumanity will enable faster, better, larger, etc. steps toward achieving the same old, biological, Darwinian aims and goals. In other words, just new means toward old ends. I hereby argue that such view is old-fashioned, illogical and ultimately untenable. Rejecting it could throw some new light on issues in both future studies, as well as the discussions of advanced extraterrestrial civilizations and ongoing SETI projects.
That ‘new light’ considers the possibility that, as Sir Julian Huxley surmised in an essay written as far back as 1957, natural selection will have little to do with a true posthuman future. Instead, we have to look to other modes of evolution encompassing technological and cultural change. We may consider advanced technological civilizations as outcomes of such evolution that have now become immune to existential risks, societies that can manipulate the surrounding universe to a high level of precision, reaching what Nikolai Kardashev called a Type II level, able to use all the energy resources of their own planetary systems.
The Expanding Empire vs. the City-State
And because ?irkovi? questions what the expansive colonial model implies, he is drawn to ask what a Type II civilization would do with its power. The ‘city-state’ model is one focused on optimizing its activities, heeding the problems of further expansion and drawing heavily on its computational abilities. Rather than looking for signs of outward-reaching super-civilizations (much less Kardashev Type III societies, which ?irkovi? sees as unlikely to arise), we should ponder cultures that have a keen eye on their own limitations and an ability to use resources close at hand.
We’re in the area of postbiological evolution, as outlined here:
As an example, the imperative for filling the complete ecological niche in order to maximize one’s survival chances and decrease the amount of biotic competition is an essentially biological part of motivation for any species, including present-day humans… It would be hard to deny that this circumstance has played a significant role in colonization of the surface of the Earth. But expanding and filling the ecological niches are not the intrinsic property of life or intelligence – they are just consequences of the predominant evolutionary mechanism, i.e. natural selection. It seems logically possible to imagine a situation in which some other mechanism of evolutionary change, like the Lamarckian inheritance or genetic drift, could dominate and prompt different types of behaviour. The same applies for the desire to procreate, leave many children and enable more competitive transmission of one’s genes to future generation is linked with the very basics of the Darwinian evolution. Postbiological civilization is quite unlikely to retain anything like the genetic lottery when the creation of new generations is concerned.
The trick from the SETI perspective is to identify such a civilization, one without a pressing need for outward expansion beyond, perhaps, a few neighboring stellar systems. In fact, molecular nanotechnology might create such an efficient utilization of resources that an extraterrestrial culture would have little reason to look elsewhere, although ?irkovi? assumes that ATCs will, for reasons of research and prudence, become quite adept at monitoring the rest of the galaxy through a variety of observatories and nanotechnology-based interstellar probes. That model has a precedent in ancient Greek city-states that deployed networks of agents operating outside their own territories.
It’s a compelling argument, and you’ll find a rich science fiction treatment of some of its themes in Greg Egan’s Diaspora (1997), where a society of uploaded minds deals with the consequences of its freedom from biological motivations. Egan’s characters need not worry about their genetic heritage, their ecological boundaries, the pressures of population or any need for expansion through the colonial model. With access to information without the need of physical presence, the driving factors of the empire-state begin to dissipate. Even a dying star may not force expansion onto a culture like this, as ?irkovi? notes:
It has been claimed in the classical SETI literature that the interstellar migrations will be forced by the natural course of stellar evolution. However, even this “attenuated” expansionism – delayed by on the order of 109 years – is actually unnecessary, since naturally occurring thermonuclear fusion in stars is extremely inefficient energy source, converting less than 1% of the total stellar mass into potentially useable energy. Much deeper (by at least an order of magnitude) reservoir of useful energy is contained in the gravitational field of a stellar remnant (white dwarf, neutron star or black hole), even without already envisaged stellar engineering. Highly optimized civilization will be able to prolong utilization of its astrophysically local resources to truly cosmological timescales.
Image: The globular cluster 47 Tucanae, about 15,000 light years from Earth, and 120 light years across. The stars in 47 Tuc are about 10-12 billion years old, making them among the oldest stars in the galaxy (more than twice the age of our own sun). Could some of these stars be the home of non-expansive, ‘city-state’ civilizations? Credit: Southern African Large Telescope.
To Observe the Unobservable?
?irkovi? goes on to make the case against galactic empire in terms of both feasibility and cost, probing as well both political and ethical reasons for the city-state model to prevail. But back to the SETI question: Just how observable would a civilization following the city-state model actually be? We may find that our current technology is unable to make such detections, these being cultures whose very efficiency and adaptability to local resources renders them all but invisible to us. We do, however, get at least some relief from the otherwise inexplicable paradox of Fermi.
The paper is ?irkovi?, “Against the Empire,” slated for publication in JBIS and now available online. This paper is a comprehensive distillation of transhumanist ideas looked at in provocative new ways, its application to SETI one that challenges the basic assumptions of our radio and laser surveys. You’ll find much to mull over and much to argue with here. I wonder, for example, whether the lack of observed Type III civilizations in our cosmological neighborhood is truly a sign that galactic empires cannot form. Perhaps a Type III culture, able to harness the resources of its entire galaxy, would be even more difficult to detect than a nearby Type II, operating as it would be under assumptions that are even more alien to us than ?irkovi?’s city-states.
But opening up SETI to inquiries like these is heartening in many respects, and will be even more so if we continue to find no sign of intelligent life after another few decades. The astrobiological evidence thus far points in the direction of widespread life. If intelligence does arise on a modestly frequent basis, we may be living in a galaxy filled with thought whose pooled knowledge is simply unobservable, at least at this juncture of our own development. The thought that we are not alone, even if we are in the presence of moderate and sustainable societies much unlike our own, offers a satisfactory resolution to Fermi and a provocative picture of a possible (post)human future.
by Paul Gilster | May 10, 2008 | Culture and Society |
Alan Boyle uses the occasion of Neal Turok’s appointment as executive director of the Perimeter Institute for Theoretical Physics to interview the scientist on topics dear to the heart of Centauri Dreams readers. The ekpyrotic universe idea championed by Turok uses the idea of multidimensional ‘branes’ whose occasional collisions spark events like the Big Bang. A cyclic model emerges that sees multiple ‘bangs,’ using today’s accelerating universe as a condition for the arrival of the next cycle. It’s fascinating stuff, but does it assume the eventual validation of string theory? Boyle quotes Turok:
“In my opinion, string theory is the most promising avenue we have for the unification of gravity and the fundamental forces. But that doesn’t mean I’m not critical of it. I think sometimes people do exaggerate its achievements thus far. We need to keep an open mind.”
Turok, as director of Cambridge University’s Center for Theoretical Cosmology, worked with Princeton’s Barry Steinhardt on Endless Universe: Beyond the Big Bang (Doubleday, 2007), which belongs on your bookshelf. Did an exhausted earlier universe help to spawn the one we live in today, and is another one likely to form a trillion years from now? Don’t look for experimental evidence any time soon, but the ekpyrotic universe is a model whose startling conclusions may offer insights into both dark matter and energy, and the role of each in the universe’s growth. Ekpyrotic, incidentally, derives from the Greek word for ‘conflagration.’
Other weekend reading might involve the latest Carnival of Space, held this week at the Space Cynics site. This week I’ll send you to Bad Astronomy‘s essay on the role our position in the galaxy may play in mass extinctions. This is Phil Plait’s take on a story we looked at briefly here on Centauri Dreams , involving the Solar System’s passage through the galactic plane, which may trigger a rain of comets from the outer system to move toward the Sun. So, at least, says a team at the Cardiff Centre for Astrobiology, which can point to our current galactic position as a sign that we may be nearing another such period. Check as well Brian Wang’s treatment of the laser comb technology we looked at yesterday.
by Paul Gilster | May 9, 2008 | Exoplanetary Science |
Boosting the sensitivity of our exoplanet search tools by a hundredfold is no small matter, yet that’s just what optical frequency combs, when implemented with an ultrafast laser, may be able to do. A frequency comb is created by a laser that generates short, equally spaced pulses of light. ‘Locking’ the individual frequencies — keeping them in phase with each other — is essential, as is producing pulses that are no more than a few million billionths of a second long. The image below explains the name, the graph giving the impression of nothing more than a fine-toothed comb (and see this National Institute of Standards and Technology backgrounder for further details on how these combs work).
We’ve looked at laser combs before, in particular in the work being performed at the Harvard Smithsonian Center for Astrophysics, which is involved in the deployment of such a comb at the William Herschel Observatory in the Canary Islands. The resultant instrument, called the HARPS-NEF (High-Accuracy Radial-velocity Planet Searcher of the New Earths Facility) spectrograph, should be useful in studying Earth-sized planets detected by the Kepler mission. The spikes on the comb can be used to measure the frequency of other light sources to a high degree of precision, useful to everything from the exoplanet hunt to making more accurate global positioning measurements.
Image: Experimental data from a NIST “gap-toothed” frequency comb that are false colored to indicate the range from low power (red) to high power (blue). The comb is specially designed for astronomy. Each “tooth” is a precisely known frequency, and the teeth are widely separated (by 20 gigahertz) in comparison to a standard comb. Credit: M. Kirchner & S. Diddams/NIST.
Now scientists at the University of Konstanz in Germany and the National Institute of Standards and Technology (NIST) have pushed a laser into record territory with a combination of high speed, short pulses and high average power. The new laser produces pulses ten times more often than a standard NIST frequency comb, creating shorter pulses than other lasers operating at comparable speeds. This is significant because the shorter the laser pulses, the wider the spacing between the ‘teeth’ of the comb. While standard combs use teeth too closely spaced for precise exoplanetary work, an ultrafast laser in this range offers the potential for more precise measurements of distant light.
The interest in laser comb technologies stems from the need to improve our Doppler methods of planet detection. Tiny shifts in the frequency of a star’s light as measured on a spectrograph tell astronomers about the presence of an otherwise unseen planet around a star. The trick is to measure those shifts with ever increasing detail, an area in which frequency combs hold out rich promise. The shifts induced by an Earth-like planet — equivalent to a wobble of only a few centimeters per second — are far beyond the capabilities of today’s instruments, which are limited to about one meter per second.
No wonder, then, that laser combs are under study at a widening number of institutions, a list that also includes the Max-Planck Institute for Quantum Optics. The new ultrafast laser is one way to push the envelope. Another is to spread the ‘teeth’ of the comb using other methods. The above mentioned CfA work pursues these, and such techniques are also under investigation by the NIST group and Steve Osterman (University of Colorado, Boulder), who are working with sets of mirrors to eliminate periodic blocks of teeth to create a ruler that should be more than adequate for such minute planetary detections.
