by Paul Gilster | Oct 26, 2006 | Deep Sky Astronomy & Telescopes |
Here’s something to think about, or better, try to visualize on an evening when there’s good celestial viewing outside. A typical globular star cluster holds several hundred thousand stars. Out on the periphery of such systems, the stars are relatively widely spaced. But move into the center and you’ll find stars packed thousands of times tighter than in our Sun’s neighborhood. Imagine the view in such a place — 10,000 stars closer to us than Alpha Centauri turning the night ablaze.
The Hubble Space Telescope paints this picture of conditions in the globular clusters that surround the Milky Way. And as part of these findings, the scientists involved say that such clusters sort out their stars on the basis of mass. You can imagine that in that tightly packed center, close encounters, collisions and mergers between stars would not be uncommon. The result: heavier stars sink toward the cluster’s core, while lighter ones move eventually to the periphery, a process never before witnessed but long suspected to occur.
The cluster in question is 47 Tucanae, a dense southern hemisphere object. Astronomers have been able to measure accurate speeds for 15,000 stars at its center, some of them a type called ‘blue stragglers’ that are thought to be the result of stellar collisions. Twice as massive as normal stars, they’re also found to move more slowly than their lighter counterparts. Seven years of measurements went into this work, the largest sample of velocities ever gathered for any globular cluster in our Galaxy.
Image: The 47 Tucanae globular cluster. Credit: Very Large Telescope/European Southern Observatory, R. Kotak and H. Boffin (ESO).
The work, by Georges Meylan (Ecole Polytechnique Federale de Lausanne) and collaborators appears in the September Astrophysical Journal Supplement Series. And it would be helpful to me if any of you know of science fiction settings involving globular clusters. I’m always curious about how writers portray unusual places but am having trouble coming up with many examples here. Talk about an exotic locale!
by Paul Gilster | Oct 25, 2006 | Culture and Society |
Finding single reasons for major events is curiously satisfying. Thus the notion that an asteroid strike did away with the dinosaurs — pinning their mysterious demise on one hammerblow from outer space makes sense out of what had seemed inexplicable. But a new theory challenges the single-cause notion of mass extinctions, and questions whether sudden catastrophes in combination aren’t needed to deliver the punch.
The work, to be presented today at the annual meeting of the Geological Society of America in Philadelphia, divides the last 488 million years of geologic history into distinct groups and characterizes each. So-called Pulses are times of sudden, catastrophic events like asteroid impacts, whereas Presses are periods of multigenerational stress on ecosystems, such as massive volcanic eruptions.
Nan Crystal Arens and Ian West (Hobart & William Smith Colleges) chart the history of marine organisms and extinctions through the fossil record to conclude that extinctions in times of Pulse or Press are statistically similar. It is only when Press and Pulse events coincide that a spike in extinctions occurs. “Statistically speaking, extinction rates are not significantly higher at times of impact or volcanism vs. no geologic events,” West said.
Centauri Dreams often cites evidence for extinction events seemingly triggered by incoming debris from the Solar System, such as the Chicxulub crater in the Yucatan associated with the dinosaurs’ demise, or the much larger crater recently found in Antarctica that may have been involved in the Permian-Triassic extinction. Arens and West would doubtless tell me to slow down because extinction events are complicated. Here’s Arens:
“In the modern world, species are commonly endangered by some stress before the final death blow falls. It seems likely that biological systems in the past worked in similar ways. By demonstrating that the coincidence of long-term stress and catastrophic disturbance is needed to produce big extinctions, we hope to break down some of the polarization characteristic of many discussions of extinction. We hope to send people back to the data with a more inclusive hypothesis to test.”
So much the better, and perhaps we can draw some useful inferences for today’s world out of all this. Arens’ comment about modern species relates to her idea that human beings can act as both Press and Pulse, manipulating the environment since the advent of agriculture (the Press) and triggering swift change by industrialization (the Pulse). Are we not entering an era of swifter extinctions by destroying habitats at a record pace? It’s a grim thought, but if Pulse and Press are now working simultaneously, we had better find out whether this link to ancient extinctions has genuine validity for a technological society.
by Paul Gilster | Oct 24, 2006 | Astrobiology and SETI |
From South Africa comes news of a striking find: bacteria living two miles beneath the surface and, more significantly, dependent only on the sulphur and hydrogen produced by geological processes rather than on the energy of the Sun. That life should form in such remote venues seems extraordinary, but the finding gives credence to the belief that similar microorganisms might have evolved on other worlds right here in our own Solar System.
Sure, we’ve found life in some hostile places before, including ocean vents and petroleum reservoirs, but their biological processes can all be traced at least partially back to the Sun, which provided the energy source for photosynthesis and therefore produced the needed nutrients for life. This new find, uncovered in a rock fissure that intersects the Mponeng gold mine near Johannesburg, uses radioactive decay as its power source, converting water molecules into hydrogen and ultimately producing hydrogen sulphide out of sulphate molecules in the rock.
Here’s Douglas Rumble (Carnegie Institution) on the process:
“We also believe that the sulfate used by these creatures is left-over from ancient groundwater mixed with ancient hydrothermal fluid. We can detect that because the chemical signature arises from interacting with the fracture’s wall rock. It is possible that communities like this can sustain themselves indefinitely, given enough input from geological processes. Time will tell how many more we might find in Earth’s crust, but it is especially exciting to ponder whether they exist elsewhere in the solar system.”
The microbes seem to have survived for tens of millions of years in this mode. Is there a similar kind of geologically-fueled life under the ice crust of Europa or in even more exotic environments further out in the Solar System? For that matter, how many other such communities exist elsewhere in our own planet’s crust? The paper is Li-Hung Lin et al., “Long-Term Sustainability of a High-Energy, Low-Diversity Crustal Biome,” now running in Science Vol. 314 No. 5798, pp. 479-482. An abstract is available.
by Paul Gilster | Oct 23, 2006 | Deep Sky Astronomy & Telescopes, Exoplanetary Science |
Among the plans for NASA’s Wide-field Infrared Survey Explorer (WISE) is a research agenda some of us have been hoping for for years. Designed to scan the entire sky in infrared light, the spacecraft should be able to locate nearby brown dwarfs. The possibility that one or more of these dim objects might actually be closer to us than Proxima Centauri cannot be ruled out, and if we were to find a brown dwarf one or two light years away, it would inevitably become the subject of mission speculation for next generation technologies.
Not that we know how to travel even one light year in a reasonable amount of time, but halving the distance to the nearest star would surely make such a mission more tenable. Note the progression: We’re already flying our first Kuiper Belt mission, if you take into account the plan for New Horizons to investigate icy objects beyond Pluto. We’re putting together mission concepts like Innovative Interstellar Explorer that could push well outside the heliosphere. Our studies of the Kuiper Belt lead eventually to the gravity focus and missions like Claudio Maccone’s FOCAL, designed to take advantage of the Sun’s lensing effects to study remote objects whose light is focused by gravity.
The Oort Cloud, which may extend as far out as a light year, is the domain of the long-period comets. And perhaps a brown dwarf? Assuming the primary Centauri A and B stars have a cometary cloud of their own, Proxima Centauri is well within it. Proxima is a larger, M-class red dwarf, but it reminds us that finding a dim object even in the local neighborhood would not be a surprise. Take into account possible brown dwarfs and you paint a picture of interstellar space that is far from empty. The exciting thing is that we don’t know much about brown dwarfs and can only speculate as to their numbers. Some researchers think they’re all over the sky:
“Brown dwarfs are lurking all around us,” said Dr. Peter Eisenhardt, project scientist for the mission at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We believe there are more brown dwarfs than stars in the nearby universe, but we haven’t found many of them because they are too faint in visible light.”
More brown dwarfs than stars… It’s quite a thought, and add to it that brown dwarfs seem to be able to support planetary systems of their own. The Spitzer Space Telescope has made those findings possible, and WISE will add significantly to our knowledge of the nearby infrared universe, not to mention what it might reveal about distant galaxies shrouded in dust. The image below, taken from the 2 Micron Sky Survey, gives a glimpse of what infrared imaging on a wide scale can accomplish. Be sure to click to enlarge this one for a breathtaking view.
Image: Panoramic view of the entire near-infrared sky reveals the distribution of galaxies beyond the Milky Way. The image is constructed from the more than 1.5 million galaxies in the 2MASS Extended Source Catalog (XSC), and the nearly 500 million Milky Way stars in the 2MASS Point Source Catalog (PSC). The galaxies are color-coded by their distances inferred from their photometric redshift (def.) deduced from the K band (2.2 microns) or as given in the NASA Extragalactic Database (NED). Blue are the nearest sources (redshift < 0.01); green are at moderate distances (0.01 < redshift < 0.04) and red are the most distant sources that 2MASS resolves (0.04 < redshift < 0.1). Credit: Two Micron Sky Survey (2MASS).
And for those of you who remember IRAS -- the Infrared Astronomical Satellite launched in 1983 -- WISE will be 500 times more sensitive. Launch is expected in 2009, but to follow WISE news in the interim, keep an eye on its news page.
by Paul Gilster | Oct 21, 2006 | Advanced Rocketry, Culture and Society |
Cory Doctorow offers a podcast with George Dyson that’s well worth your time, recalling among other things the remarkable days of Project Orion, in which Dyson’s father Freeman played so large a role. Note too that Dyson provided some documents from his own collection, now released for the first time and made available here. No surprises, but following the Orion story is a reminder of a day not so long ago when the outer planets were considered as viable an option for manned flight as the Moon. Let’s assume that one day they will be again.
Leonard David is out in Las Cruces for the Wirefly X Prize Cup, from which a live webcast has been in progress this morning. His weblog coverage is currently noting the apparent failure of Armadillo Aerospace in its attempt to win the NASA Lunar Lander Challenge. But whatever happens to the Armadillo venture, the Cup is a wonderful reawakening of the airshow spirit of the 1930s that inspired so much experimentation and drove aviation ever faster and farther. If you’re into space engineering, Las Cruces is the place to be. More on the Lunar Lander Challenge here.
Astronomer Phil Plait takes on Katie Couric in entertaining fashion, answering her recent assertions on what is supposed to be a news broadcast about the space program. Couric had opined that NASA’s budget request for $17 billion is way out of line, joining those who call for the money to be spent “…for medical research, social programs, and in finding solutions to poverty, hunger, and homelessness…”
Responds Plait:
“The irony is that the ability of Katie to appear to millions of people (well, fewer every day according to her ratings — oh, snap!) is due to the space program. Or does the term “satellite TV” mean something I’m missing? Maybe she could ask whoever the weatherman is on her show if (s)he thinks the space program is a waste of money.”
Centauri Dreams has many bones to pick with NASA’s budgetary problems — where is our commitment to science — but it’s good to see Couric challenged. It’s also sad to look at the trajectory CBS News has followed as it drives what was once a credible enterprise ever closer to tabloid territory.
