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Finding Hidden Black Holes

by Paul Gilster | Jul 31, 2006 | Deep Sky Astronomy & Telescopes | 7 Comments

The super-massive black holes thought to lurk in nearby galaxies present us with a problem. They should suck in surrounding gas and dust to produce x-rays, and it has been the assumption that black holes hidden by such materials, also known as 'Compton-thick objects,' are responsible for much of the overall x-ray background. Yet an x-ray census using data from Integral, ESA's orbiting International Gamma Ray Astrophysics Laboratory, showed that a mere 15 percent of black hole galaxies detected were of the hidden Compton-thick variety. And later work at NASA (GSFC) and the Integral Science Data Centre (Geneva), using two years of Integral data, shows an even smaller fraction. So where do the x-rays come from? "Naturally, it is difficult to find something we know is hiding well and which has eluded detection so far," says Volker Beckmann (NASA GSFC, and lead author of an upcoming paper on the subject). "Integral is a telescope that should see nearby hidden black holes, but we have come...

Extraterrestrial Inflows and Ice Ages

by Paul Gilster | Jul 29, 2006 | Interstellar Medium | 1 Comment

40,000 tons of extraterrestrial matter are believed to hit the Earth every year. This from the current issue of Science, where researchers from New York (Columbia University) and Bremerhaven (Alfred-Wegener-Institut) present a study of helium isotopes found in Antarctic ice cores. Over the last 30,000 years, the scientists believe, the amount of 3He, a rare isotope found in cosmic dust, exceeds that found in terrestrial dust in ice by a factor of 5000. We have, the investigation indicates, been subject to a constant rain of cosmic dust particles over this period. Which is interesting in its own right, but becomes more pointed when you look at the measurements of the helium isotope 4He, which is much more common on Earth. Indications point to a change of origins in terrestrial dust between the last Ice Age and the current interglacial warm period. Says Gisela Winckler (Lamont-Doherty Earth Observatory, Columbia University): "The terrestrial dust coming down on Antarctica during the...

A Fine Drizzle on Titan

by Paul Gilster | Jul 28, 2006 | Outer Solar System | 7 Comments

The current issue of Nature features a look at Huygens data with a big payoff: rain is falling on Titan, continues to fall as we speak, and will probably keep falling for a long time. Says Christopher McKay (NASA Ames), a co-author of the paper, "The rain on Titan is just a slight drizzle, but it rains all the time, day in, day out. It makes the ground wet and muddy with liquid methane. This is why the Huygens probe landed with a splat. It landed in methane mud." All this from low, methane-nitrogen clouds that are barely visible but appear to be widespread, affecting weather globally. A Nature feature on this work, from which the McKay quote is drawn, can be found here. Methane rains are what you get at temperatures of minus 179 degrees Celsius, as are the river-like features also found by the probe as it descended on January 14, 2005. The latter surely derive from the ceaseless rains as well. McKay says the rain equals roughly two inches a year, about as much as Death Valley gets on...

Zoom in on COSMOS

by Paul Gilster | Jul 27, 2006 | Research Tools | 1 Comment

We are entering a great era when it comes to research tools for the study of deep space. But as new technologies create datasets we're able to distribute globally, we need to consolidate our gains to make them available to broader audiences. That's why the creation of a Web-based utility called COSMOS SkyWalker is such heartening news. Using it, huge and minutely detailed images from sources like the Hubble Space Telescope's Advanced Camera for Surveys can be managed for presentations and study over the Internet. The problem is no small one. Compare the Hubble Ultra Deep Field (UDF), which contains some 10,000 galaxies, to the Cosmological Evolution Survey (COSMOS), housing no less than 2 million. The image areas on these surveys are contiguous and made up of an extraordinary number of data pixels, some 1010 pixels for COSMOS. That kind of scale makes it all but impossible to show both size and detail at the same time. Shipping the complete COSMOS ACS image over the Internet, even in...

55 Cancri: Modeling a Terrestrial World

by Paul Gilster | Jul 26, 2006 | Exoplanetary Science | 3 Comments

For Centauri Dreams, the most exciting part of the exoplanet hunt is the refinement of our models. We know, for example, of numerous planetary systems dominated by gas giants. Now we're trying to figure out which of these may contain smaller, rocky worlds, and that means learning more about solar system dynamics. A step in the right direction emerges from a June paper that analyzes what happens to moon-sized protoplanets as they evolve in systems with gas giants. Based on computer simulations, the work assumes a giant planet the size of Jupiter and manipulates the position and mass of the protoplanets in these settings over time, testing four systems with known planets: 55 Cancri, HD 38529, HD 37124 and HD 74156. The most interesting result is the ready formation of terrestrial worlds around 55 Cancri, often with orbits in the habitable zone. HD 38529 also produced a rocky world, one about the size of Mars, and showed conditions favorable to an asteroid belt as well. No further...

Dust and Planet Formation in T Tauri Stars

by Paul Gilster | Jul 25, 2006 | Exoplanetary Science | 9 Comments

One of the beauties of the Spitzer Space Telescope is that it can pinpoint the swirling dust disks around distant stars. Such dust, heated by the star, puts out an infrared signature that Spitzer can analyze to a degree hitherto unattainable. Now a team of astronomers has observed some 500 young T Tauri stars in the star-forming regions of the Orion nebula. They've been looking at how young stars spin, and the effects that dusty disks have on slowing their rotation. T Tauri stars are ideal for this kind of work. They're young objects (less than 10 million years old) that are still in the process of gravitational contraction. Such stars often show large accretion disks, but a variant called weak-lined T Tauri stars have little or no disk. Figuring out the various phases of T Tauri formation and how they relate to planets is thus a substantial challenge. The answers Spitzer has provided are intriguing even if they leave many questions unanswered. Slow-spinning stars are five times more...

Calculating the Distance to a Star

by Paul Gilster | Jul 24, 2006 | Culture and Society | 0 Comments

Centauri Dreams' fascination with the history of science occasionally yields to forgetfulness. Which is why this piece on German mathematician and astronomer Friedrich Wilhelm Bessel, runs two days after his birthday rather than on the occasion itself. Bessel (July 22, 1784 - March 17, 1846) would go on to perform remarkable work in the study of stellar distances that in many respects anticipated the work of today's exoplanet hunters. He became, in fact, the first person to predict the existence of an unseen companion around another star. That was quite an accomplishment in 1844, when Bessel announced the find around Sirius, based on minute deviations in the motion of the star. The discovery would be verified by Alvan Graham Clark in 1862 with the first observations of Sirius B. We now know that Sirius B orbits the primary at a distance of roughly 20 AU, not so far off the 23.7 AU mean separation between Centauri A and B, although there the resemblance stops -- Sirius B is a white...

Exploration as Necessity

by Paul Gilster | Jul 22, 2006 | Culture and Society | 4 Comments

"The urge to explore, the quest of the part for the whole, has been the primary force in evolution since the first water creatures began to reconnoiter the land. We humans see this impulse as the drive to self-transcendence, the unfolding of self-awareness. The need to see the larger reality -- from the mountaintop, the moon, or the Archimedean points of science -- is the basic imperative of consciousness, the specialty of our species. If we insist that the human quest await the healing of every sore on the body politic, we condemn ourselves to stagnation. Living systems cannot remain static; they evolve or decline. They explore or expire. The inner experience of this imperative is curiosity and awe. The sense of wonder -- the need to find our place in the whole -- is not only the genesis of personal growth but the very mechanism of evolution, driving us to become more than we are. Exploration, evolution, and self-transcendence are but different perspectives on the same process." Wyn...

A Dead Star Brightens

by Paul Gilster | Jul 21, 2006 | Deep Sky Astronomy & Telescopes | 6 Comments

RS Ophiuchi, a binary system some 5000 light years from Earth, has given astronomers plenty to talk about since February, when it suddenly brightened. The phenomenon wasn't unusual -- RS Ophiuchi undergoes periodic outbursts -- but this was the first since 1985, allowing powerful radio telescope arrays to study the results. By coordination between radio telescopes from South Africa to China, Hawaii to the UK, astronomers have pieced together the sequence of events that led to the explosion and have studied its aftermath. The results are reported in the July 20 issue of Nature, revealing that a mere two weeks after first reports of the stellar eruption, an expanding blast wave extended to a distance of 10 AU. It was triggered by a nuclear explosion on the surface of a white dwarf that had been capturing gas from the nearby gas giant it orbits. Once enough gas collects on the white dwarf, a thermonuclear reaction begins, with the white dwarf's energy output increasing to over 100,000...

Radar Views of Xanadu

by Paul Gilster | Jul 20, 2006 | Outer Solar System | 2 Comments

Xanadu, that bright continent-sized aberration on the surface of Titan, begins to look somewhat familiar in new radar images from the Cassini orbiter. It's surrounded by darker terrain, cut by rivers and filled with hills and valleys. Cassini could identify a crater, probably created by asteroid impact, and flatter areas into which the rivers flow -- these are presumably lakes. Geologically and topographically (and ignoring for a moment the deep freeze), the place does look something like Earth, even if rain there falls in the form of methane. Image: A network of river channels is located atop Xanadu, the continent-sized region on Saturn's moon Titan. This radar image was captured by the Cassini Radar Mapper on April 30, 2006. These winding, meandering river channels start from the top of the image and run like a fork in the road, splitting to the right and left of the image. At Titan's chilly conditions, streams of methane and/or ethane might flow across parts of the region. Credit:...

An Updated Catalog of Nearby Exoplanets

by Paul Gilster | Jul 19, 2006 | Exoplanetary Science | 4 Comments

Hard to believe that it's been over ten years now since the discovery of 51 Peg B, the first exoplanet found around a main sequence star. So much has happened since, including over 160 exoplanet candidates identified within 200 parsecs, with most of these discovered through Doppler search methods examining radial velocities (although the nearby planet TrES-1 was found via transit methods). The last published list of exoplanets appeared in 2002, which is why the just published "Catalog of Nearby Exoplanets" is so welcome. Appearing in The Astrophysical Journal, the catalog confines itself to the 200 parsec limit for good reasons. Yes, we have located exoplanets far beyond it, including some in the direction of galactic center found by the OGLE survey and several found through microlensing projects elsewhere. But within 200 pc, high resolution imaging and stellar spectroscopy allows satisfactory follow-up work, and we're also working with stars whose parallax has been studied through...

Terrestrial Planets and Close Binaries

by Paul Gilster | Jul 18, 2006 | Exoplanetary Science | 6 Comments

We've recently discussed Greg Laughlin and Jeremy Wertheimer's work on the possible role of Proxima Centauri in destabilizing the Centauri A and B debris disk and bringing volatiles to the inner system. Our deepening knowledge of the Centauri system is one of the most energizing aspects of the exoplanet hunt, for its proximity inexorably makes Alpha Centauri of high astrobiological interest. And no one has done more significant work on planet formation around binary stars than Elisa Quintana and Jack Lissauer (NASA Ames). The two have examined the possibilities of terrestrial worlds around Centauri A and B and are continuing with the study of other binary scenarios. Now they have extended their analysis to binary systems whose stars are much closer to each other than Centauri A and B. Their new paper is significant for planet hunters because more than half of all main sequence stars are in binary or multiple systems, whereas our basic models for planet formation have been based on...

Keeping an Eye on New Horizons

by Paul Gilster | Jul 17, 2006 | Outer Solar System | 1 Comment

With New Horizons now six months out and closer to Jupiter than it is to the Sun, the creatively-acronymed Jupiter Encounter Science Team (JEST) has turned in its observation plan. New Horizons will pick up a gravity assist from the gas giant in February of 2007, on its way to the 2015 encounter with the Pluto system. That also means that from January to June of 2007, the spacecraft will make more than 500 observations on everything from the Galilean satellites to the Jovian magnetosphere, with rich results expected. If you are tracking New Horizons, check out the mission locator page. Alan Stern's regular reports are also vital; Stern is principal investigator for the mission and has, throughout planning and launch, used the Web effectively to keep the public informed about its progress. In the latest update, he reports on a rare occultation of a star by Pluto in June. Such events provide the opportunity for studying Pluto's atmosphere, with the interesting result that conditions...

Two Ways to Look at the Future

by Paul Gilster | Jul 15, 2006 | Culture and Society | 6 Comments

Stewart Brand is a leading proponent of long-term thinking, the sort of thing that builds cathedrals and, perhaps one day, starships. In this excerpt from his book The Clock of the Long Now (New York: Basic Books, 1999), Brand discusses science fiction and the various forms of futurism. According to Kevin Kelly, 'Isaac Asimov once said that science fiction was born when it became evident that our world was changing within our lifetimes, and therefore thinking abut the future became a matter of individual survival.' The nanotechnology futurist Eric Drexler concurs: 'I have found over the years that people familiar with the science fiction classics find it much easier to think about the future, coming technologies, political effects of those technologies, and so on.' At Global Business Network (GBN), the scenario-planning business that employs me, we frequently send out science fiction books to the Network membership, and when we can get writers such as William Gibson, Bruce Sterling,...

ET in a Grain of Sand?

by Paul Gilster | Jul 14, 2006 | Astrobiology and SETI | 6 Comments

Centauri Dreams was amazed to realize that almost two years have passed since Christopher Rose and Gregory Wright posed a bold challenge to SETI researchers. In an article in the September 2 (2004) issue of Nature (a cover story, no less), the duo suggested that we are more likely to achieve extraterrestrial contact through artifacts -- organic material embedded in an asteroid or comet, say -- than through radio or optics. Larry Klaes, posting a link in a comment here on the Rose/Wright discussion, recently jogged my memory about this article, which deserves a renewed look. Rose (Rutgers University) is a professor of electrical and computer engineering; his work with wireless technologies convinced him that "...it's often MUCH (many many orders of magnitude) better from an energy use perspective (and perhaps from others like message persistence at the destination) to write a message down in some medium and LITERALLY toss it to the recipient than it is to radiate the message...

Building Toward Computer Autonomy

by Paul Gilster | Jul 13, 2006 | Autonomy and Robotics | 0 Comments

We don't talk as much as we might about computer autonomy here, perhaps because it's obvious that the biggest challenge facing interstellar flight is propulsion. But it's clear that we need computer systems with fully autonomous characteristics on the kind of decades-long robotic missions that might eventually be flown. We'll want such probes to have human-like traits of curiosity and judgment, as well as repair and maintenace capabilities for the long journey. It's interesting to see, then, that Cambridge, MA-based BBN Technologies, which played such a pivotal role in the development of the ARPANET and later Internet protocols, has just received funding to create a so-called 'Integrated Learner.' Working to the tune of $5.5 million from the Defense Advanced Research Projects Agency (with a possible total of $24 million over four years), BBN's first phase effort will be to create a reasoning system that can apply itself to advanced tasks and master principles of the kind we all refer...

On Starshades and Planetary Threats

by Paul Gilster | Jul 12, 2006 | Culture and Society, Missions | 0 Comments

The possibility of deflecting an incoming asteroid became more problematic in early July. That's when David Polishook and Noah Brosch (both of Tel Aviv University) presented evidence that the number of binary asteroids near the Earth might be much higher than originally thought. Binaries might, in fact, comprise more than fifty percent of all NEAs. Now we're talking about moving two objects instead of just one, an indication that asteroid-nudging is more tricky than we thought. The paper "Many binaries among NEAs," available here, was presented at NASA's Near-Earth Object Detection, Characterization, and Threat Mitigation workhop in Colorado. It's a reminder that the environment incessantly nudges technological civilizations to extend their capabilities. Jose Garcia recently commented here on a story about the New Worlds Imager 'starshade' concept, noting that experience with starshades could come in handy in future attempts to mitigate the effects of global warming by covering up...

Anomalous Supernova Remnant Investigated

by Paul Gilster | Jul 11, 2006 | Deep Sky Astronomy & Telescopes | 4 Comments

Supernova remnant RCW103 is not exactly a new discovery. In fact, it was found over 25 years ago, the survivor of an explosion that took place in the early days of the Roman empire, though visible only in southern skies. And as you would expect, the area in question looks to be fairly standard issue for a supernova aftermath: a rapidly spinning neutron star and a surrounding bubble of material ejected by the explosion. But look again, as an Italian team using the European Space Agency's XMM-Newton x-ray satellite has done, and you spot some anomalies. The scientists, based at the Istituto Nazionale di Astrofisica (INAF) in Milan, find that emissions from the central source of the explosion repeat on a cycle of 6.7 hours, far longer than would be expected from such a neutron star. Another oddity is that the spectral properties found in these observations differ from another set of data made just five years ago with the same XMM-Newton equipment. So what we have is an object embedded...

A Relativistic Probe to Alpha Centauri

by Paul Gilster | Jul 10, 2006 | Missions | 24 Comments

Good space science comes from unexpected quarters. When I interviewed the Jet Propulsion Laboratory's James Lesh about his thinking on communicating with a probe around Alpha Centauri, he pointed out how much can be gained by simply studying the signal sent by a spacecraft. Here in the Solar System, we've seen how that signal is affected by passing through a planetary atmosphere as the vehicle moves behind a distant world, an event that tells us much about the atmosphere in question. So in many cases it's not just the data carried by the communications signal, but how that signal behaves, that tells the tale. Can we imagine something similar around Alpha Centauri? Lesh envisaged a 20-watt laser communications system sending data from a sophisticated probe. But a new paper takes a different approach, imagining a fast probe moving at relativistic speeds, one that would announce its arrival in the Centauri system and create effects that could be studied from Earth. At 10 ounces, such a...

On Migrating Gas Giants and their Effects

by Paul Gilster | Jul 8, 2006 | Exoplanetary Science | 10 Comments

We may not have images of terrestrial planets around another star yet, but many things can be learned about such worlds by computer simulation. A team of British astronomers, for example, has examined known exoplanetary systems in hopes of isolating those in which Earth-like worlds could exist in stable and habitable orbits. This is tricky business, because the massive planets present in almost every exoplanetary system we know about could disrupt such orbits long before life might have a chance to form on any worlds there. It's also tricky because to determine which systems could have life-bearing planets requires you to figure out the location of the habitable zone in each. Researchers Barrie Jones, Nick Sleep and David Underwood (Open University, Milton Keynes, UK) here use the classical definition of habitable zone: the distances from a star where water at the surface of an Earth-like planet would be in liquid form. Not surprisingly, they find that the question of planetary...

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In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).

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