by Paul Gilster | Sep 19, 2007 | Exoplanetary Science |
Neon isn’t an unusual find in spectroscopic studies of massive stars or, for that matter, in observations of novae or the galactic core. Energetic X-ray or ultraviolet emissions can ionize the gas, at which point it produces infrared light at characteristic wavelengths. Not expecting to find it around low-mass stars like our Sun, researchers have been surprised to find four Sun-like stars showing neon in their disks as measured by a Spitzer Space Telescope project run by the University of Arizona.
That project, called Formation and Evolution of Planetary Systems (FEPS) is run out of Steward Observatory. The idea is to study planet-forming gas around 35 young, solar-type stars. Before this work, none of these stars would have been thought energetic enough to radiate the amount of X-ray and ultraviolet light needed to ionize neon.
Unexpected though they might be, the observations are useful because neon, while hardly abundant, offers a precise spectral signature that makes it easier for astronomers to track the gas content in circumstellar disks. The neon signature, says Michael R. Meyer (Steward Observatory), reminds us that the planet formation period can be a violent one. And future detections of the gas may help to differentiate between stars retaining their dust and gas disks and those that have already begun to form planets.
“It serves as a valuable reminder that the environment in which the planets formed was harsh, too, in a way. And it could turn out to be an important tracer of remnant gas in circumstellar disks — a kind of ‘vacancy/no vacancy’ sign for planets.”
Image: In this artist’s conception, a possible newfound planet spins through a clearing in a nearby star’s dusty, planet-forming disk. (Image credit: NASA/JPL/R. Hurt, SSC).
If so, neon makes a nice fixture in the toolkit of researchers anticipating the launch of future planet-hunter missions like Kepler and ESA’s Darwin. The more methods we can bring to bear in choosing targets for precious telescope time, the better our chances of success. Tracking stars whose inner disks show gases that can circularize the orbits of Earth-like planets will speed the process. Future studies of stellar systems of different ages are being developed to show how the gas dissipates with time.
The paper is Pascucci, “Detection of [Ne II] Emission from Young Circumstellar Disks,” The Astrophysical Journal 663 (July 1, 2007), pp. 383-393 (abstract).
by Paul Gilster | Sep 18, 2007 | Deep Sky Astronomy & Telescopes |
Centauri Dreams has always been captivated with the Magellanic Clouds, two galaxies that are the Milky Way’s nearest neighbors in space. The fascination is in many respects visual. Knowing that they’re a beautiful sight to those below the equator, the counter-thought came quickly to mind — what would the Milky Way look like from one of these small satellite galaxies? How bright would it be, how much of the sky would it fill? While pondering such questions, have a look at the Large Magellanic Cloud below, and be sure to click to enlarge this gorgeous image.
Pondering such things, I wrote a story called “Magellanic,” a sort of Weird Tales-era fantasy (I realize that Weird Tales still exists, but I refer to the fabled issues of the 20’s and 30’s). Mixing in a first contact scenario in 1920’s Tibet, a mountain-climbing adventurer at the end of his career, a bit of intelligence agency intrigue and throwing in Edwin Hubble for good measure, I thought I had a winner, but the story remained sadly unpublished, reminding me that my talents lie in other directions.
Image: The Large Magellanic Cloud, a fixture in my imagination since childhood. New observations indicate that many of our previous theories about the Magellanics must be radically revised. Credit: Copyright Robert Gendler and Josch Hambsch 2005.
The latest news about the Magellanics is that they may not be satellites at all, but independent galaxies that have approached comparatively recently. Astronomers from the Harvard-Smithsonian Center for Astrophysics have measured anomalously high velocities for the duo, implying that they are not bound to the Milky Way. Thus we throw out many previous theories about the Magellanics and their presumed effects.
For one thing, the Milky Way’s gaseous disk is known to be warped, a fact hitherto explained by gravitational tides due to the Magellanics. The new theory has the Clouds arriving between one and three billion years ago, making it unlikely they are the cause of the warp. And the long hydrogen trail called the Magellanic Stream that extends behind the Clouds was thought to be formed from similar interactions. Knowing that the Magellanics are only passing by tends to rule out this scenario as well.
“We have known about the Clouds since the time of Magellan, and a single measurement has thrown out everything we thought we understood about their history and evolution,” says Gurtina Besla (Center for Astrophysics).
And that’s what makes astrophysics in our era so exciting. For that matter, consider the changes in perspective just since 1998, with the discovery of the universe’s continuing acceleration in expansion. As I keep saying (wishing I was young enough to do it myself, though realizing I was never any good at math), what a time to embark on a career in astrophysical research! In this case, add to the Magellanics mystery that star formation within them must now be completely re-thought and you’ll see that we have another example of reassessment that pushes existing theory to the limit.
The paper is Besla et al., “Are the Magellanic Clouds on their First Passage about the Milky Way?” (abstract).
by Paul Gilster | Sep 17, 2007 | Deep Sky Astronomy & Telescopes |
Considering that we can’t see dark matter and have little idea what it is, the notion that we could take its temperature seems preposterous. But new work out of Durham University (UK) points to a way of using visible astronomical sources to draw conclusions about dark matter’s effects in the early universe. Using computer simulations to examine the formation of the first stars, the researchers have applied ‘cold’ and ‘warm’ dark matter models, noting the effects we might expect to see today. These, in turn, should tell us something about how dark matter operates.
Cold, or slow-moving dark matter particles have a particular signature. After the first 100 million years of expansion, dark and more or less uniform, the universe would have begun to witness the birth of structure as dark matter’s gravity drew hydrogen, helium and lithium into the condensations that produced the first stars. In this model, the cold dark matter, clumping into spherical structures, would have produced stars in isolation, one for each dark matter concentration. These are the massive stars that produced the first heavy elements — carbon, oxygen and silicon — necessary for solid planets to emerge.
Warm dark matter is a different beast. Its particles in fast motion, the effect would be to replace the ripple-like spread of cold dark matter with long filaments in which large numbers of stars of differing sizes coalesced out of these strands more or less at the same time. Filaments like these would have been extraordinary structures, some 9000 light years long, according to the researchers, who believe the filaments would have fragmented in spectacular bursts of star formation.
Image: In the authors’ simulations, a gas filament condenses and then fragments to form the first stars. The gas heats as it gets compressed but then becomes cold in the center. The red shading in this image reflects changes in the gas’ temperature. Image copyright: Science.
The massive stars spawned by cold dark matter would have short lifespans that would not allow current observations. Stars formed from warm dark matter, on the other hand, should have varied considerably in mass. “A key question that astronomers often ask,” says Tom Theuns (Durham University),”is ‘where are the descendants of the first stars today’?’ The answer is that, if the dark matter is warm, some of these primordial stars should be lurking around our galaxy.”
That means stars we can observe today could hold valuable clues to star formation and dark matter’s nature. Moreover, collapse of the filaments themselves may have seeded the formation of black holes in the centers of massive galaxies. An exotic and far-ranging theory indeed! The paper is Gao and Theuns, “Lighting the Universe with Filaments,” Science Vol. 317. no. 5844 (14 September, 2007), pp. 1527 – 1530 (abstract).
by Paul Gilster | Sep 17, 2007 | Culture and Society, Research Tools |
By Bernd Henschenmacher
In Living off the Land in Space, Gregory Matloff, Les Johnson and artist C. Bangs discuss how mankind may colonize the Solar System and travel to nearby stars using energy and material resources provided by nature. The whole book is devoted to the ‘Living off the Land’ concept, which is introduced in the early chapters. Future space travelers, say Matloff et al., will use solar energy and mine the asteroids in order to reach other planets in our system and, later, stars like Alpha Centauri.
Given the huge distances involved and the difficulties of rapid transport from Earth, such methods are the only feasible way for mankind to leave its home. The authors draw on historical examples of colonization endeavors here on Earth to illustrate that living off the land is quite an old concept. Indeed, our species would still be confined to Africa if early humans had failed to use the resources they found along the way to new continents and islands.
After a short review of propulsion systems (Project Orion and Daedalus, interstellar ramjets, antimatter drives and even space warps), the authors focus on those concepts that may be available in the not too distant future. The reader will find chapters dealing with ion, solar thermal and chemical propulsion as well as space tethers and solar sails as methods of pushing into deep space. All have the advantage of requiring no fundamental breakthrough in physics to achieve the desired result.
Every propulsion system that has ever been envisioned for interstellar travel (even anti-gravity devices, the Zero Point Energy concept and the like are mentioned) is explained in an easy to understand way, laden with but a small amount of mathematics. Science fiction enthusiasts may be disappointed to read here that manned interstellar travel will probably take millennia and that warp drives are essentially impossible, but the authors’ admonition that breakthroughs happen leaves the matter open.
Nevertheless, the goal of the book is to provide a realistic view of what might be possible with technologies that are accessible in the near future. A wealth of references at the end of each chapter point the way to further resources. Living Off the Land in Space should satisfy anyone who wants to learn more about space colonization and the propulsion methods that will make it happen.
by Paul Gilster | Sep 15, 2007 | Culture and Society |
Too beautiful not to run immediately, this image of the Corona Australis region (be sure to click to enlarge) shows a relatively nearby hotbed of star formation. The Coronet cluster at its heart is a loose cluster of several dozen stars, all of them young but ranging widely in mass.
Here we’re looking at the Coronet in different wavelengths. The purple areas come from X-ray observations made by the Chandra observatory. The Spitzer Space Telescope contributes its infrared data, shown in orange, green and cyan. Regions like this offer valuable clues to star formation. Credit: NASA/CXC/JPL-Caltech/CfA.
——-
Next on my stack of reading material is Gregory Benford and Elisabeth Malartre’s Beyond Human: Living with Robots and Cyborgs (Forge, 2007), an overview of current thinking in robotics and artificial intelligence. Publisher’s Weekly notes the following, which is sure to be controversial:
[The] concluding argument, that consciousness and the intellectual power of the human mind emerge from the complexity of the brain, and thus cannot be reduced to the functioning of its individual components, leads them to doubt, convincingly, that robots (machines that mimic humans) and cyborgs (man-machine hybrids) will ever amount to more than sophisticated tools, enhancing human life but never replacing it.
Centauri Dreams agrees and looks forward to working through the arguments put forth by two powerful thinkers whose take on the future has ever been thoughtful and invigorating.
——-
An older title that deserves to be on your shelf is Timothy Ferris’ Seeing In the Dark, a deeply satisfying study of modern amateur astronomy. Those whose roots go back to 3-inch reflectors in the backyard will be stunned to see how powerful the range of amateur tools has become, including the use of CCD (charged coupled devices) for observations that not long ago would have been restricted to professional observatories. Don’t miss Ferris’ PBS documentary on these matters, scheduled to run September 19th at 8 PM Eastern Standard Time. And be sure to check the content-laden support site.
——-
A good idea a long time coming: The European Science Foundation, working with other organizations including the European Space Agency, will convene a conference in Vienna to bring scholars from the space sciences and the humanities together. Humans in Outer Space – Interdisciplinary Odysseys will look at the philosophical implications of contacting alien civilizations. Other issues addressed will be how space exploration is presented to the public and engaged in cooperatively by space-faring nations.
Here’s Luca Codignola (University of Genoa), a historian who looks at contact with extraterrestrial species in the context of past encounters:
“The so-called ‘Columbian Exchange’ that took place around 1492 was a typical case in point. It changed the Western way of conceiving the globe; it forcefully challenged its theology; it allowed for a free flow of bacteria, germs and microbes that almost wiped out the American peoples.”
Participants will discuss historical parallels like these, long examined by historians and ethnologists, in a SETI context when the two-day meeting begins on October 11. This meeting is reminiscent of the 1983 Los Alamos sessions that spawned the outstanding Interstellar Migration and the Human Experience (Berkeley, 1985), whose essays continue to shed light on possible outcomes as we look to human expansion into the cosmos.
——-
Interstellar migration can look a long way off when you’re living in a space-capable civilization that seems to be spinning its wheels. But the Google Lunar X Prize should spur those with big dreams and ready cash. Landing a privately funded robotic rover on the Moon is going to be no easy matter, but the first Ansari X Prize showed what could be done by a determined aviation community. Keep the dreamers engaged and great engineering should follow. Centauri Dreams applauds the sheer pluck of this renewed venture and anticipates great things to follow.
