Centauri Dreams will not publish on January 1. The regular publication schedule resumes on the afternoon of the 2nd. Happy New Year to all!
Schedule Update
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A Celestial Companion for 2007
The last regular posting of 2006 is a good time to remind you that Tammy Plotner's What's Up 2007 is now available. It's a 410 page PDF file that takes you through celestial events on a day to day basis for the entire year. Loaded with photographs and charts, What's Up 2007 is free to download, or you can buy a printed version for $25. A third alternative is to check the Astronomy What's Up weblog daily, where each day's entry will be posted as the year progresses. I skipped ahead at random and landed on February 14, which I learned from Plotner's book is not only Valentine's Day but also the birthday of astronomer Fritz Zwicky, who catalogued galaxy clusters and did yeoman work on supernovae. The celestial object for the day is the Spirograph Nebula, whose image (taken by the Hubble telescope) adorns the page. Plotner's clear prose walks us through the basics: ...the light you see tonight from the IC 408 planetary nebula left in the year 7 AD. Its central star, much like our own...
Tightening the Focus on Dark Matter
Interesting things happen when gravitational lenses go to work. The earliest observations of the phenomenon involved entire clusters of galaxies. When the alignment is right, a galaxy cluster between the observer and a still more distant galaxy will bend the light of that galaxy. It will appear as one or more luminous arcs which are actually made up of its multiple images distorted (and magnified) by the gravitational lens. All this happens because, as Einstein told us, spacetime is curved by the presence of matter. Here's how gravitational lensing looks. Notice the blue arcs of the lensed galaxy in the background surrounding the galaxies at their center, which have distorted spacetime enough to make this image possible. The latest work on the lensing phenomenon focuses on smaller structures like groups -- rather than entire clusters -- of galaxies. Astronomers using the Canada-France-Hawaii Telescope (Hawaii) are devoting 500 nights of telescope time to a survey of an area of the...
Meanwhile, on Centauri B…
With COROT on its way, the search for exoplanets moves into a new phase with an active, space-based transit study. Launched from Baikonur (Kazakhstan) yesterday, the mission's status reports will be available online and should provide fascinating reading. After all, COROT will monitor 120,000 stars with its 30-centimeter telescope, looking for the signatures of planetary transits. That means the kind of 'hot Jupiters' we've already found around many stars, but it should also involve smaller rocky worlds, some perhaps not all that much larger than Earth. But notice what COROT stands for: 'Convection Rotation and Planetary Transits.' The first part of that phrase refers to asteroseismology, the study of stellar interiors by examining the acoustic waves that move across the surface of stars. That means COROT will be able to detect so-called 'starquakes' that well up from deep inside the star. Examining their strength and duration tells astronomers much about the star's mass and...
The Darkening of Centauri A
Take a look at the image of Alpha Centauri in the Centauri Dreams logo. It's the bright object at far left, not the single star that it appears but a triple system whose glare masks its two major components. Centauri A is a G2 star much like our Sun, while Centauri B is a K1. The two are separated by an average of 23 AU, with an orbital period of some eighty years. Indiscernible in the image is Proxima Centauri, an M-class dwarf which is actually the closest star to Earth. Bright, nearby and highly studied, the Centauri stars would seemingly be well characterized. But new results from the European Space Agency's XMM-Newton x-ray satellite show anomalies. Unlike optical wavelengths, where the larger Centauri A dominates, Centauri B is the brighter object in x-ray emissions. What's odd is that repeated monitoring of the two by XMM-Newton shows that Centauri A faded by no less than an order of magnitude in x-rays during the two-year observing range, a behavior out of keeping with all...
Quieting Mass Extinction Worries
I don't want to leave the subject of gamma ray bursts (GRBs) without considering findings that seem to reduce the potential threat from these events. And the revision of a significant GRB paper that I meant to discuss earlier gives me the chance to circle back around to it. The subject is intriguing because it bears on the spread of life in the cosmos. If gamma ray bursts -- powerful flashes of energy emitted in narrow jets -- are nearby, an evolving species might be destroyed before it could ever achieve sentience, much less technology. Krzysztof Stanek (Ohio State University) and collaborators approach the GRB question assuming that long gamma ray bursts (two seconds or more in duration) result from the death of massive stars. They also note two further facts about the unusual events. GRBs are highly beamed, and the supernovae remnants they leave behind are deficient in both hydrogen and helium in their spectra. And then we add this: Compared to average galaxies, those hosting GRBs...
Schedule Update
Merry Christmas! And for those of you who celebrate other holidays -- or none at all -- best wishes for the season. Centauri Dreams will not publish on December 24 or 25. The normal publication schedule resumes on the afternoon of the 26th.
A Gamma Ray Puzzle
When you're calculating the odds on life in any region of the galaxy, the rate of supernova explosions comes into play. As we saw yesterday, one factor Nikos Prantzos examined in his recent work on the galactic habitable zone was the effect that hard radiation could have on exposed land life. But what about gamma ray bursts (GRBs)? They're more powerful and, although rarer than supernovae, can create beamed energy that makes them lethal from larger distances. One theory is that because gamma ray bursts are associated with regions of low metallicity outside our galaxy, their frequency in the Milky Way is now close to zero. But a reminder of how little we actually know comes in the December 21 Nature, where four papers discuss GRB activity, and in particular a burst picked up by NASA's Swift satellite last June 14. It's a cosmic oddity, a kind of hybrid that probably marks the birth of a black hole. But, as Derek Fox (Penn State) says, "This burst -- unlike all other long gamma-ray...
Life Throughout the Galaxy?
Is there a galactic habitable zone, a region within the Milky Way where conditions for life are optimum? If so, we want to know its parameters, as they would help us define the search area for living worlds. The concept has kicked around for a while, and now surfaces again in an interesting paper by Nikos Prantzos (Institut d'Astrophysique de Paris). Prantzos ponders the main variables and, while concluding that the galactic habitable zone is far from well understood, believes it conceivable that the entire galactic disk may, at this stage of its evolution, be suitable for life. That conclusion goes further than Charles Lineweaver and team's work in 2004, the latter having found that the zone for complex life exists in a ring a few kiloparsecs wide surrounding the galactic center and gradually spreading outward as the Galaxy evolves (our earlier story on that work and habitable zones in general is here). Like Lineweaver, Prantzos looks at planet formation in terms of stellar...
Fermi Meets Elsie: SETI’s New Conundrum
"Simple and cheap, like onion dip." That's how Seth Shostak (SETI Institute) refers to our early optical search systems, which have involved limited equipment in the hunt for extraterrestrial intelligence, at least when compared to the much more demanding resources deployed by the radio search. Cheap is good, but not when you can only check one part of the sky at a time. All this gets Shostak pondering in a recent article about the parameters of a laser signal from an extraterrestrial civilization. For if we might miss a faint signal, what about a really big one? Suppose an intelligent species somewhere out there is deliberately trying to contact our planet. Wouldn't it make sense, Shostak muses, to create a huge optical impression, a signal that would catch our attention so obviously that we could then focus in to detect whatever message might be streaming from that same location? Bright objects in the sky do appear and are usually recorded, as witness historical records of...
Carl Sagan Remembered
When I think about Carl Sagan, the tenth anniversary of whose death we remember today, the first thing that comes to mind is a quote about the wonders of relativistic interstellar flight. It's worth quoting at length: If for some reason we were to desire a two-way communication with the inhabitants of some nearby galaxy, we might try the transmission of electromagnetic signals, or perhaps even the launching of an automatic probe vehicle. With either method, the elapsed transit time to the galaxy would be several millions of years at least. By that time in our future, there may be no civilization left on Earth to continue the dialogue. But if relativistic interstellar spaceflight were used for such a mission, the crew would arrive at the galaxy in question after about 30 years in transit, able not only to sing the songs of distant Earth, but to provide an opportunity for cosmic discourse with inhabitants of a certainly unique and possibly vanished civilization. Despite the dangers of...
On Ancient Starlight
What were the first objects in the universe? They may have been enormous stars a thousand times more massive than the Sun. If so, new observations suggest the apparent clusters found by the Spitzer Space Telescope could be the first galaxies, tiny by Milky Way standards and containing the mass of less than a million Suns. By contrast, the Milky Way today seems to house at least a 100 billion stars, and may be the result of the merging of far smaller galaxies like these. This is remarkable stuff. Spitzer is looking at patchy infrared light found across the entire sky, light that comes from vast objects more than 13 billion years away. That number catches the eye, of course, because the universe is now thought to be some 13.7 billion years old. The light, which is either from stars or violent black hole activity, was once ultraviolet or optical, but the expansion of spacetime has stretched it into the infrared. Image: The right panel is an image from NASA's Spitzer Space Telescope of...
Probing the Spaces Without and Within
Now here's a grand idea for a book: describe propulsion systems that can propel spacecraft with little or no fuel onboard. That's just what Greg Matloff and NASA's Les Johnson are doing with their new title Living Off the Land in Space (Copernicus & Praxis), which should be available come January. Matloff (New York City College of Technology) is well known in these pages as the co-author of The Starflight Handbook: A Pioneer's Guide to Interstellar Travel (Wiley, 1989). It's the seminal text, the one interstellar buffs return to again and again for the broad view of the kinds of technologies that might eventually get us to the stars. Matloff produced The Starflight Handbook with the late Eugene Mallove and went on to write Deep Space Probes (Springer/Praxis 2000), now in its second edition. His new book with Johnson grows out of their work together in Huntsville at NASA's In-Space Propulsion Technology Program, where mission concepts include everything from solar sails to solar...
Remembering Project Daedalus
Centauri Dreams defers to no one in admiration of Project Daedalus, the 1970s-era starship design that emerged from the British Interplanetary Society. It's a pleasure to see continuing interest in the craft, as witness Alan Bellows' backgrounder about it on the Damn Interesting site. Daedalus was the first serious and thorough design for a starship, a robotic interstellar probe that would reach Barnard's Star in about fifty years, moving at twelve percent of the speed of light. Be sure to check the Bellows story for the overview. But let me fill in a little more background: The British Interplanetary Society, founded in 1933, used to meet regularly at London's Mason's Arms pub on Maddox Street, a setting that Arthur C. Clarke readers may recognize from his later collection Tales from the White Hart. Daedalus was designed by about a dozen scientists and engineers, many of its sessions occurring in pubs and similar venues. When I talked to Geoffrey Landis about Daedalus some years...
A New Model for ‘Cold Faithful’
It would be easy to keep this site filled with outer Solar System news, so various and captivating are the images that stream in from our spacecraft. Exoplanet studies keep us focused primarily on nearby stars, but I do want to keep up with Cassini, and decided some time back that Centauri Dreams would leave inner system coverage to others and pick up the pace as we moved to Saturn and beyond. And what a story keeps unfolding there. For Cassini remains healthy and the news from Enceladus intriguing. We've known since last year about the plume erupting on the satellite, leading to speculation of liquid water beneath the ice of its surface. The south polar region of the tiny moon is geologically active in ways that challenge the imagination. After all, isn't the rest of Enceladus as cratered and ancient-looking as the surface of our own Moon? The 'Cold Faithful' model, which patterned the Enceladus geyser on Yellowstone's Old Faithful, has apparently run into problems. Susan Kieffer...
More on Red Dwarf Planet-Hunting
If you're thinking about detecting Earth-like planets around other stars, here's an item that may set the pulse racing a bit faster. Michael Endl, who is an expert at the planet hunt around red dwarf stars (he's searched for planets around 100 of them already), notes that the diminutive objects are prime targets for exoplanet hunters. And listen to this: "For the red dwarfs with the lowest masses, like Proxima Centauri, we are sensitive to planets down to two Earth masses using the standard radial velocity technique." Endl works at the University of Texas, out of which a study led by graduate student Jacob Bean has focused on planet formation around red dwarfs -- we looked at this work not long ago. Few gas giants have been detected around red dwarfs. The study examined the dwarfs known to have planets: Gliese 876, Gliese 436, and Gliese 581. Of the three, Gliese 876 is perhaps the most intriguing, as it's known to have two Jupiter mass planets and a likely third, lower-mass world...
Titan’s Peaks and Other Lands Unknown
If you've seen the Sierra Nevadas, you know what Bob Brown is talking about when he likens the mountain range found on Titan to those beautiful peaks in the western United States. Brown (University of Arizona) is team leader of the Cassini visual and infrared mapping spectrometer. Cassini was able to resolve features down to 400 meters (1300 feet) on its October 25 flyby. And suddenly we have a mountain range, dunes, and something resembling a volcanic flow under Titan's inscrutable atmosphere. Fascinatingly, at the top of the ridges are deposits of a white material that may be ethane snow or some other form of organic substance. Here's Cassini scientist Larry Soderblom (USGS) on the organics: "There seem to be layers and layers of various coats of organic 'paint' on top of each other on these mountain tops, almost like a painter laying the background on a canvas. Some of this organic gunk falls out of the atmosphere as rain, dust, or smog onto the valley floors and mountain tops,...
Focus on Massive Stars
What got me interested in Pismis 24-1 was simply the image. It's one of those spectacular displays we've come to expect from Hubble, obtained using the telescope's Advanced Camera for Surveys. Pismis 24-1 is part of the open cluster Pismis 24, some 8000 light years from Earth in the nebula NGC 6357 in Sagittarius. The cluster is filled with massive stars, but what seizes the attention is the juxtaposition of the cluster itself (the brightest stars in the image) and the gorgeous tapestries of the nebula in which it is embedded. Pismis 24-1, the brightest star in the cluster, was originally thought to weigh up to 300 solar masses, making it twice the assumed upper mass limit for individual stars. But as the image below shows, it's at least a binary, and ground based observations suggest that it may even be a triple system, with the third star too tightly bound to be resolved. If so, it's a whopper of one, each of the three stars averaging about 70 solar masses. Ahead for these...
Excluding Alpha Centauri Planets
You would think Alpha Centauri would be a prime hunting ground for extrasolar planets simply because of its proximity. But the problem for direct imaging is the sheer brightness of Centauri A and B, creating a halo of diffuse light around the pair. Getting through the glare isn't easy, but a search based on twin techniques -- adaptive optics and CCD imaging -- covering a wide-field around the Centauri system has just been completed. Results on the CCD work, using European Southern Observatory equipment, have now been made available and they've come up short on planetary detections. As reported by Pierre Kervella (Observatoire de Paris-Meudon) and Frederic Thévenin (Observatoire de la Côte d'Azur), the team found no co-moving companion objects between 100 and 300 AU. And that's useful information, because it puts some constraints on possible planets around these stars. From the paper: Within the explored area, this negative result sets an upper mass limit of 15-30 M J to the...
Solar Sailing in the Near Term
I don't want to move past Gregory and James Benford's interesting sail ideas without pausing to examine another paper that ran in the preceding issue of JBIS. It's a look at what we might do in the near-term with solar sails, written by Gregory Matloff (CUNY), Travis Taylor (BAE Systems) and collaborators. And it focuses on what inspired Centauri Dreams (the book) in the first place, the question of where we stand right now in terms of deep space propulsion. In other words, never mind the politics or the economics. If we had to launch a mission soon (obviously with a robotic rather than a human payload), how far could we go and how fast? Matloff and Taylor lay out the near-term possibilities for reaching the heliopause (roughly 200 AU) and the Sun's inner gravity focus (550 AU) using both sails and other propulsion options. The reference sail used here is a 100 meter disc massing some 157 kilograms, with structure and payload adding up to 100 kg for a total mass of 257 kg. Let me...
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