by Paul Gilster | Dec 6, 2008 | Culture and Society, Outer Solar System |
Those of you who missed Tau Zero founder Marc Millis’ appearance on the History Channel the other day will get the chance for repeat performances on Tuesday the 9th at 8 PM EST and Wednesday the 10th at 12 AM. The show, called Light Speed, discusses the nature of light in the context of astronomical history, and goes on to consider it in relation to travel — will we ever break the light ‘barrier,’ or is c the ultimate constraint on our space journeys? Here’s the channel’s description:
According to the laws of physics we can never travel faster than the speed of light…or can we? Light speed allows us to see things instantly here on Earth, and shows us the entire history of the universe going back nearly 14 billion years. Learn all about light speed, the ultimate constant in the universe and discover ways scientists envision breaking the “light barrier” which may be the only way the star travel of our imaginations ever comes to reality.
We could have wished to see more of Marc, whose interview was squeezed into the end of the show, but what a pleasure to view the Tau Zero logo on-screen as we continue to tune up the TZF site.
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Also intriguing for interstellar mavens is Journey to the Edge of the Universe, running Sunday December 7 at 8 PM EST on the National Geographic Channel. This one is a tour of the cosmos using spectacular animation to take you places — newly forming stars, black holes, distant galaxies — that science is helping us to understand in greater detail than ever before. Check the remarkable trip to the surface of Venus, for example, and the view of Triton’s surface. This YouTube video offers an interview with director Yavar Abbas on the challenges of integrating computer effects with the data from our telescopes to create the journey. Wisely, I think, the decision was to go with straight animation coupled with rigorous adherence to current theory.
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Do we have a visitor from another star in our own Solar System? That’s one possible explanation for comet 96P/Machholz 1, whose chemistry sets it apart from the 150 other comets studied by Lowell Observatory astronomer David Schleicher. The molecule cyanogen (CN) is off the cometary average by a large amount, only one percent of what we would have expected. Machholz 1 is also depleted in C2 and C3 carbon, but the CN depletion is striking. No other comet has exhibited any CN depletion at all, much less this amount.
Says Schleicher:
“A large fraction of comets in our own Solar System have escaped into interstellar space, so we expect that many comets formed around other stars would also have escaped. Some of these will have crossed paths with the sun, and Machholz 1 could be an interstellar interloper.”
Other explanations are plausible, including the idea that the comet formed much further from the Sun than any other comet we’ve studied. Another possibility: Machholz 1 saw its chemistry altered by extreme heat. Because its orbit takes it well within the orbit of Mercury, and every five years at that, the repeated and frequent temperature changes could contribute to its composition. “However,” adds Schleicher, “the only other comet to show depletion in the abundance of CN did not reach such high temperatures. This implies that CN depletion does not require the chemical reactions associated with extreme heat.”
Bear in mind that before Machholz 1 revealed its secrets, we were working with two classes of comets based on their composition. The typical comet is thought to have come out of the Oort Cloud to move into the inner system, but to have been formed in the region of the giant planets, with some members of the group coming from the Kuiper Belt. But a second class of comets is known as ‘carbon-chain depleted’ — depleted in C2 and C3 like Machholz 1 — with orbits consistent with arrival from the Kuiper Belt. So the depletion may be the result of conditions in the places where the comets formed, perhaps farther out in the Kuiper Belt. Machholz 1’s unusual CN depletion sets it apart from either class, leaving us to wonder about celestial interlopers and the frequency of their journeys between the stars.
The paper is Schleicher, “The Extremely Anomalous Molecular Abundances of Comet 96P/Machholz 1 from Narrowband Photometry,” The Astronomical Journal 136 (November, 2008), pp. 2204-2213 (abstract).
by Paul Gilster | Dec 5, 2008 | Deep Sky Astronomy & Telescopes |
Brown dwarfs raise plenty of questions, not the least of which is how they form. Work up to some fifteen times Jupiter’s mass and the planet in question starts to look more like a brown dwarf, a ‘failed star’ that cannot sustain fusion at its core. Somewhere around 75 Jupiter masses long-term fusion ignites and you’re in the territory of a true star. This brown dwarf zone between the two poles makes these objects provocative — do they form the way most planets seem to do by collecting more and more rocky materials and eventually a gas envelope?
Or does a brown dwarf form, like a star, through the gravitational collapse of a gas cloud? The latter idea gets a boost from recent work from the Harvard-Smithsonian Center for Astrophysics. Astronomers have now found a stream of carbon monoxide flowing out from a young brown dwarf known as ISO-Oph 102. This gets interesting at several levels, the first being that the outflow from the dwarf resembles what happens in larger stars as they form, a stream of ejected materials pushing out from two opposite jets. The process helps the young star shed angular momentum as it draws in material from the surrounding disk.
Image: This artist’s conception zooms in on the brown dwarf and its accretion disk. The discovery of a bipolar molecular outflow at ISO-Oph 102 offers the first strong evidence in favor of brown dwarf formation through gravitational collapse. Credit: David A. Aguilar (CfA)
The outflow from ISO-Oph 102, as we might expect, is considerably smaller than found in low-mass stars, as the paper points out:
We detect a bipolar molecular out?ow from the brown dwarf, demonstrating that this out?ow mechanism as seen in young stars continues to operate down to the masses of brown dwarfs. We show that the out?ow mass is much smaller than typical values found in low-mass stars by two to three orders of magnitude. We also combine our radio data with infrared data to estimate disk parameters. The infrared spectrum of ISO-Oph 102 shows strong crystalline silicate features. This demonstrates dust processing in the protoplanetary disk…of the brown dwarf. The coexistence of the molecular out?ow with the crystallization of dust grains could be of importance for models of planet formation.
So on the one hand, the picture of brown dwarfs forming through gravitational collapse is upheld, the major variable being the amount of disk material available, which would regulate how large a brown dwarf or star might emerge from a common star formation process. The other thing to note here is the impact on planetary formation around these objects. The authors surmise that the outflow from a brown dwarf may be longer lived than those coming from low-mass stars, perhaps a factor in sweeping gas out from the protoplanetary disk and forming rocky worlds.
The paper is Phan-Bao et al., “First Confirmed Detection of a Bipolar Molecular Outflow from a Young Brown Dwarf,” in press at Astrophysical Journal Letters and available online.
by Paul Gilster | Dec 4, 2008 | Exoplanetary Science |
The Optical Gravitational Lensing Experiment has thus far rewarded researchers with twelve exoplanets, the most recent announced just today. OGLE’s database is made up primarily of observations taken at the Las Campanas Observatory in Chile, its microlensing methods offering the chance to detect distant worlds that would be difficult if not impossible to study with radial velocity techniques. But because the project is all about parsing the light fluctuations of distant stars, OGLE has also found planets via the transit method, the most recent of them being the work of students at Leiden University in the Netherlands.
OGLE2-TR-L9b is a discovery that points to the wealth of potential data on such worlds that may already exist in our databases. Thus the university’s Ignas Snellen, who supervised the research project, found that the right software could tease a new planet out of OGLE data on some 15,700 stars, observed by the survey over a four year period between 1997 and 2000, even though other goals were in mind. No wonder the professor was surprised:
“The project was actually meant to teach the students how to develop search algorithms. But they did so well that there was time to test their algorithm on a so far unexplored database. At some point they came into my office and showed me this light curve. I was completely taken aback!”
All three students — Meta de Hoon, Remco van der Burg, and Francis Vuijsje — deserve to have their names prominently placed in this story, not only for their contribution to science but for the encouragement their work should give other students now being drawn to the field. Having found the new planet, the team then worked with the European Southern Observatory’s La Silla Observatory (Chile) and the Very Large Telescope at Paranal to confirm the discovery. Spectroscopic analysis from the latter showed not only a planet five times as massive as Jupiter, but also the hottest known star with a planet, a fast-rotating F3 some 1200 degrees Celsius hotter than our own Sun. [Addendum: My mistake re this being the hottest exoplanet star — see the comments below re Fomalhaut and HR 8799].
Image: Artist’s impression of the planet OGLE-TR-L9b. Circling its host star in about 2.5 days, it lies at only three percent of the Earth-Sun distance from its star, making the planet very hot with a bloated roiling atmosphere. The star itself is the hottest star with a planet ever discovered. Credit: ESO/H. Zodet.
OGLE2-TR-L9b circles its primary every 2.5 days at 0.03 AU, a massive, blindingly hot world discovered by a sharp-thinking team with excellent algorithms. And, as we have come to expect with exoplanet discoveries, this one leads to further questions. From the paper:
OGLE2-TR-L9b has a significantly larger radius than expected for a planet of about 4.5 times the mass of Jupiter, even if it is assumed that 0.5% of the incoming stellar luminosity is dissipated at the planet’s center… However, it is not the only planet found to be too large (e.g. CoRoT-exo-2b, TrES-4b, and XO-3b). Several mechanisms have been proposed to explain these ‘bloated’ radii, such as more significant core heating and/or orbital tidal heating…
We are, as I’ve opined before in these pages, in the golden era of exoplanet detection. Not that future technologies won’t yield spectacular results — including planets not so different from our Earth in the habitable zone of their stars — but it’s hard to imagine a better time for a young scientist to be entering the profession than now, when the questions become more multi-faceted with each new discovery and thesis topics abound. Congratulations to the discoverers of OGLE2-TR-L9b!
Image: Undergraduate students Francis Vuijsje, Meta de Hoon, and Remco van der Burg (left to right), whose work uncovered the new extrasolar planet. Credit: Leiden Observatory.
The paper is Snellen et al., “OGLE2-TR-L9: An extrasolar planet transiting a fast-rotating F3 star,” scheduled for publication in Astronomy & Astrophysics and available online.
by Paul Gilster | Dec 3, 2008 | Exotic Physics |
Planetary engineering on the largest scale might one day reveal itself to us through the observation of a Dyson sphere or other vast object created by an advanced civilization. But it’s interesting to think about alternative strategies for using celestial energies, strategies that assume vast powers at the disposal of mankind as projected into the distant future. Thus an interesting proposal from the Swiss theorists M. Taube and W. Seifritz, who consider what to do about the Sun’s eventual evolution into a planet-swallowing red giant.
A Sunshade and a Planetary Shift
Considering the possibilities of preserving the Earth during the Sun’s transition into a brighter and much larger object, the authors discuss alternatives like raising the Earth’s orbit to a safer distance or using a parasol to shield the planet from its rays. That might tide us over for a few billion years beyond the point where an unprotected Earth could survive as a habitable place. But the paper only begins here. After the sunshade, the authors go on to discuss their plan to create an artificial sun in the Kuiper Belt, where an Earth slowly moved into an outer orbit by gravitational swing-by techniques can eventually find its new home in a stable orbit around a life-giving source of heat and light. Call it an ArtSun, as they do, and ponder how much science fiction it might inspire.
Imagine, for example, an Earth gradually being shifted to a new orbit over a period of perhaps tens of millions of years as the Sun begins its inexorable growth to engulf the inner planets. And imagine our world, as the authors do, illuminated for the duration of the journey by a ring of fusion power stations encircling the planet at an orbital distance of 350,000 kilometers. This ring of whatever materials are best suited for the job is inescapably reminiscent of Larry Niven’s Dyson-esque Ringworld, though on a much smaller scale, and suggests a level of planetary engineering as beyond our present capabilities as the Large Hadron Collider would have been beyond the imaginings of Greek philosophers.
Given the changes in technology that make even a thousand years from now a vista too remote to analyze, it’s hard to know what might have transpired in a billion years, much less the five billion the authors contemplate during which the parasol might shield the Earth, or the billions beyond that it could survive around the new star. But the question is worth pondering from the standpoint of SETI, I think, where we might think about what an advanced civilization might do given enough time and powerful enough tools. And Taube and Seifritz’ ArtSun is a marvelous creation in any case, made up of gas giants culled from other stars. Surely that would throw an interesting astronomical signature?
Creating Sol II
The idea here is that within twenty light years of the Solar System there ought to exist enough planetary systems with gas giants, many of them much larger than our own Jupiter, to cull for use in the new stellar creation. Here’s the plan:
Some hundreds of such ‘gas giants’ will be transported to the Kuiper Belt by means of the ‘swing-by’ technique and fused together to form an ‘ArtSun’ which will ignite when its mass passes over a certain value. Unmanned spacecraft under fully autonomous control will explore those planetary systems and will find the corresponding asteroids for the ‘swing-by’ technique to accelerate the suited ‘gas giants’ out of their planetary systems. DD-fusion will be the source of energy for all these enterprises whereby deuterium will be separated out from the atmosphere of the ‘gas giant’. Although we do not know how to ignite a DD-explosive reaction for a Dyson-like space ship without the help of fissionable material we proceed on the assumption that we will have found a method in the far future.
Coincidentally, Adam Crowl just sent me links to two papers by Friedwardt Winterberg discussing DD fusion — creating propulsion solely through the non-fission ignition of pure deuterium — and thus opening up manned exploration of the entire Solar System. But more on this another day, because I’m not ready to leave Taube and Seifritz without a few more details about creating new stars. The duo discuss fusing twenty imported gas giants to create an M-class star, with the potential of using up to 100 such planets to create a G5 star not so different from the Sun. The M-dwarf would seem to be easier but a bit more problematic:
Under the assumption we let rotate Earth around such a Red Dwarf illuminated with the same ‘solar constant’ as today, we find a sidereal period for Earth being only 6.91% of a year, i.e. only 25.2 days but the not yet answered question is whether the photosynthesis will work satisfactorily under the red light.
Yes, and we’d best keep photosynthesis fully operational. On the other hand, an M-dwarf offers a tremendously increased lifetime over a G-class star. The authors go on to consider how to power up the fusion devices that will keep the Earth illuminated during its long orbit-shifting journey to 50 AU. All the deuterium to run these and the planet-shifting operations around other stars will come from a familiar source (familiar, at least, if you know the history of Project Daedalus, the British Interplanetary Society’s starship design) — the atmosphere of Jupiter and perhaps Saturn. Given the future technologies we’re discussing here, mining outer system atmospheres for fuel would doubtless be a trivial operation.
Moving a Planet, or Moving Off-Planet?
Would an advanced civilization ever embark on such a task? If it did, would the astronomical signature of planetary re-location be something today’s astronomers in our own Solar System could flag as the likely sign of extraterrestrial engineering? My own guess, from a parochial 21st Century perspective, is that a civilization with the ability to travel to another solar system to move a gas giant to ours probably has the ability to consider massive re-location of population as needed to the nearest available habitable planet, or indeed, moving into vast space-based habitats that could survive a red giant’s depredations.
The authors choose planetary migration because they believe only a small number of Earth’s inhabitants could be evacuated via the creation of a starship. But their model is Freeman Dyson’s upgraded Project Orion vehicle from a classic 1968 paper, one that would carry a 10,000 ton payload at 10,000 kilometers per second via Orion-like nuclear bomb detonations. It’s hard to believe that a civilization that might survive billions of years into the future would be limited by 1968 starship design (a design that Dyson himself later gave up on as being unworkable). If anyone is around in five billion years, protected by Taube and Seifritz’ sunshade and hoping to avoid a swelling Sun, I think they’ll be opting for interstellar transport away from a soon to be devastated Earth.
But it’s fascinating to speculate on alternatives. Take a look at the discussion of planetary orbit changing using asteroid swing-bys, and ponder the risks of setting a large asteroid on a near-miss trajectory that, given the slightest mistake, could end all life on the planet anyway. One thing you can say about Taube and Seifritz — they’re not at all afraid to think big. And it’s worth your time looking this one up for the imaginative tinkering with the future that gets us thinking ultra-long-term, not to mention prompting those good SF story ideas. The paper is Taube and Seifritz, “The search for a strategy for mankind to survive the solar Red Giant catastrophe,” available online. That Dyson paper, by the way, is “Interstellar transport,” Physics Today 21, (October, 1968), pp. 41-45. And have a look at Crowlspace for other options for red giant survival.
by Paul Gilster | Dec 2, 2008 | Deep Sky Astronomy & Telescopes |
It hasn’t been all that long since Hanny van Arkel, a Dutch school teacher, lent her name to the anomalous object since known as ‘Hanny’s Voorwerp.’ Working with data from the Galaxy Zoo project, van Arkel was scanning galaxy images when she ran across what seemed to be a green blob of extremely hot gas with a hole in its center. That hole turned out to be 16000 light years across, its cause unknown, and the object itself seemed to be lit by an unseen source. Theories abounded, including a ‘light echo’ from a defunct quasar in a nearby galaxy.
And then there was the fact that the remarkably hot object (15000 degrees Celsius or more) was not only enormous but also empty of stars. Baffling astronomers for the past year, Hanny’s Voorwerp may now be swimming into sharper focus. An international team has been observing both the object and the nearby galaxy IC2497 using the Westerbork Synthesis Radio Telescope, with results that indicate the presence of a jet coming from a massive black hole at the center of the galaxy. Mike Garrett (ASTRON/Leiden) comments:
“It looks as though the jet emanating from the black hole clears a path through the dense interstellar medium of IC2497 towards Hanny’s Voorwerp. This cleared channel permits
the beam of intense optical and ultraviolet emission associated with the black hole, to illuminate a small part of a large gas cloud that partially surrounds the galaxy. The optical and ultraviolet emission heats and ionises the gas cloud, thus creating the phenomena known as Hanny’s Voorwerp.”
Meanwhile, the new data indicate that the huge hydrogen cloud, extending hundreds of thousands of light years and boasting a total mass amounting to five billion times that of the Sun, may well be the result of tidal interactions between IC2497 and another galaxy hundreds of millions of years ago. Hanny’s Voorwerp just might be the signpost of a cosmic mishap as these galaxies passed in the night, although even that theory leaves us with what Garrett calls ‘…a few more secrets to reveal.’ More radio telescope observations are planned in the near future.
Image (click to enlarge): WSRT observations reveal a radio jet (white contours) emanating from the center of the nearby galaxy IC2497, headed straight in the direction of Hanny’s Voorwerp (green). The observations also reveal a huge reservoir of hydrogen gas (colored orange) that probably arose from a previous encounter between IC2497 and another galaxy. The presence of strong neutral hydrogen absorption (top right plot) argues that the central regions of IC2497 are highly obscured. Credit: Main image left and top right hand corner (ASTRON). Hanny’s Voorwerp (bottom right) Dan Herbert, Isaac Newton Telescope.
