by Paul Gilster | Feb 28, 2006 | Breakthrough Propulsion |
Can traversable wormholes be created, allowing us to achieve our wildest dreams of traveling between the stars? Mohammad Mansouryar says yes, and in a paper titled “On a macroscopic traversable spacewarp in practice,” the young Iranian theorist lays out his argument. Mansouryar bases his thinking on a needed prerequisite: the violation of the Averaged Null Energy Condition. He writes up its parameters in a 41 page document stuffed with conjectures, eight boxes of figures and 127 footnotes.
Mansouryar’s analysis is intractable to Centauri Dreams, demanding an examination from those far more competent in theoretical physics than myself. Especially given his startling conclusion: “In this paper, I have tried to review the literature, in the spirit of whether the TWs [traversable wormholes] in practice are far reaching or constructible by present knowledge & technology. The conclusion is they are quite possible to manufacture provided a sufficient determination of investment on improving computation tools & necessary materials.”
The goal, of course, is all but magical. A workable wormhole using Mansouryar’s methods would allow a spacecraft to take a cosmic bypass, riding a subluminal warp drive through the wormhole shortcut so that distances through space are radically altered while maintaining spacetime stability for passengers. The result is a hybrid of warp drive thinking a la Alcubierre and the classic wormhole as, more or less, conceived by science fiction.
On a Web site devoted to his work, the author notes that while increasing velocity in space is a desirable goal, the final goal is not the speed of light. For one thing, even c is too limiting when compared to cosmic distances, and the technical problems of accelerating closer and closer to c still stand. Mansouryar is also well aware of control problems at superluminal speeds, impacts from interstellar dust at high velocity, and the intractable issue of propulsion systems. His goal is to create a system in which local movement is much less than c but, as he says on his Web site “…the considered distance changes so that consequently would be less devoted time, finally in compared to a situation if a light pulse would be supposed to pass the same distance.”
A traversable wormhole is a solution if we can find a way to produce the negative energy needed to create and stabilize it. The paper discusses methods for producing exotic matter and muses on techniques to verify Mansouryar’s wormhole theories experimentally. Abstract and full text are available on the arXiv site, where the paper will doubtless produce controversy and discussion — particularly as to his experimental ideas — more illuminating than Centauri Dreams can provide.
by Paul Gilster | Feb 27, 2006 | Interstellar Medium
Are the Voyager spacecraft still doing good science? You bet, as witness the passage of Voyager 1 through the termination shock at the edge of interstellar space. Scientists had assumed the craft’s crossing of this boundary, where the solar wind abruptly slows, would confirm previous theories about anomalous, energetic cosmic rays that were thought to be produced in the region. But Voyager did anything but, finding the cosmic ray count to be far lower than predicted during its passage.
New work by David McComas (Southwest Research Institute) and Nathan Schwadron (Boston University), published recently in the Geophysical Research Letters, offers a theory why. They base their thinking on the shape of the shock itself, previously thought to be circular. The duo showed that a more realistic shape made sense. “In fact, the termination shock couldn’t be circular because the solar system is moving through the galaxy, which would create more of a flattened egg shape,” says Schwadron. “A flattening of the nose of the termination shock leads to a time dependant acceleration process.”
According to the new model, the nose of the acceleration shock (Voyager 1’s approximate location) is not where particles are best accelerated. Rather, they can only reach highest energies after moving along the sides, or flanks, of the shock, where the magnetic field has had longer connection times to accelerate particles.
Image: This schematic diagram cuts through the termination shock at the equator. Inside the termination shock, the magnetic field line spirals out and connects to the shock. Also shown are the approximate positions of Voyager 1 at the “nose” of the termination shock and Voyager 2 farther back. Credit and copyright: Southwest Research Institute.
Two other spacecraft will tell us more. Voyager 2 should pass the termination shock farther back from the nose in about 2-3 years, and the new model offers predictions about the jump in energetic particle fluxes that should occur. And then there’s IBEX (Interstellar Boundary Explorer), whose mission (with launch in 2008) will offer images of the interactions around the termination shock. The paper is “An Explanation of the Voyager Paradox: Particle Acceleration at a Blunt Termination Shock,” in the Geophysical Research Letters Vol. 33, No. 4 (17 February 2006), with abstract available here.
by Paul Gilster | Feb 25, 2006 | Exoplanetary Science |
The budgetary demise of Terrestrial Planet Finder has cast a pall over some researchers, but it may have energized an entirely different solution. What if I told you that in the 2013-2015 time frame we may get conclusive images that tell us whether or not there are terrestrial worlds around Tau Ceti, Epsilon Eridani, and Centauri A and B? Images that allow us to examine the habitable zones of as many as 100 stars over a three-year period? With TPF gone, the idea sounds like a fantasy, but my recent conversation with astronomer Webster Cash revealed it to be anything but.
Cash (University of Colorado at Boulder) has been involved in the development of a concept most recently called New Worlds Imager, one that began as an enormous ‘pinhole camera’ design, as I discussed in Centauri Dreams (the book) in 2004. Within the last 18 months, the design has morphed into a low-cost mission using an occulter (call it a ‘starshade’) to mask the light of the star being observed so as to reveal planets. Observing the occulter from some distance away would be a second spacecraft equipped with a telescope. The key to Cash’s work is to suppress diffraction, for it is an odd fact of optics that when you put an occulter directly in front of a bright object like a star, you still have to deal with diffraction effects because of the wave nature of light.
In other words, you can’t just block starlight with the right-sized object and expect to see nearby planets, because a good deal of the star’s light still bends around your occulter and disrupts the image. Optics students will recognize the classic case of this phenomenon as Poisson’s Spot, although it grew out of work originally performed by Augustin Fresnel and was confirmed by Francois Arago early in the 19th Century. In any case, diffraction has played havoc with earlier attempts to suppress light sufficiently to discover terrestrial worlds.
And so a great deal of energy has gone into solving the diffraction problem, with what can only be described as middling results. What motivated Cash to attack it again were conversations with engineers from Northrop Grumman about his original design and the possibility of modifying it to use an occulter. Cash continues to pursue this work with funding from a Phase II grant from NASA’s Institute for Advanced Concepts, which had provided a Phase I venue for his original ideas.
The result? Cash now tells me the diffraction problem is well on the way to solution, meaning that his new theoretical and now laboratory work is demonstrating that it will be possible to screen out starlight effectively — we’ll be able to get a look at those terrestrial planets if they’re there. Moreover, a mission to make this possible is definitely feasible even given NASA’s budgetary constraints. Read on…
The mission built around Cash’s concepts would involve two spacecraft, a telescope and a free-flying occulter (powered by ion propulsion) that would block starlight and move from star to star; the telescope would thus acquire data from a multitude of stars as the occulter craft changes position.
And here’s what makes this realistic: Cash has made an arrangement to use the James Webb Space Telescope as the ‘eyes’ of the planet-finding mission. This means the cost of producing what would have been a two-spacecraft mission has been dramatically reduced, for all Cash has to supply is the occulter vehicle, which will involve a starshade and the necessary ion propulsion and electronics to move the shield in relation to the telescope. Both would be at the L2 point, with Cash’s occulter (launched three months after JWST in 2013) approximately 30,000 kilometers away from the space telescope.
The observing method? Move the occulter into position so that it masks the light from the star to be studied. Then turn the JWST instrument toward it to collect data. Imagine observing runs happening about once a week as the relative configuration of occulter and telescope changes. And imagine picking up planetary images from the inner habitable zone all the way out to the edge of the observed solar system. Cash believes the mission can acquire rich data from about 100 candidate stars in a three-year run.
As it turns out, NASA made an announcement of opportunity for Discovery missions in December that could allow the Cash design to happen. The Discovery program has already produced such spacecraft as Deep Impact and Mercury Messenger. Cash believes he can offer a proposal that will come in at or under the $425 million cap NASA places on such missions (bear in mind that $130 million is lost up-front in the cost of an Atlas V). He’ll be competing against other strong proposals, but with Terrestrial Planet Finder now out of the picture, the chance to do the entire TPF-C mission at a fraction of its earlier estimated cost seems too good to ignore.
Terrestrial Planet Finder had been assumed all along to be a two-part mission, with some designs for TPF-C using a visible light coronograph to observe terrestrial worlds, and the subsequent TPF-I (launched some years later) built around an interferometer using multiple spacecraft for infrared observations. Cash’s vehicle, operating in tandem with JWST, would be able to handle the observations originally demanded for TPF-C and at least some of the spectrographic analysis of TPF-I thrown in for good measure. “On some of the better targets, we can use some longer wavelength photometry and look for the water bands,” Cash added. “So we can not only find these things in the habitable zone but see whether they have methane or water atmospheres.”
Success at this mission might lead to renewed interest (and funding) for the interferometry mission that could follow. We’ll know more come April, when proposals for the Discovery program have to be submitted. Cash will enter his proposal with the backing of a consortium including Princeton University, Northrop Grumman, Ball Aerospace and Goddard Space Flight Center. Meanwhile, the more public interest that can be generated re saving the hunt for terrestrial worlds, the more likely this mission is to fly. If it does, then the budgetary disaster that swallowed the original TPF will be seen to be a blessing in disguise, allowing us to move to what appears to be a superior technology using existing equipment with a low-cost occulter. And that just might find us our first terrestrial exoplanet, far sooner than we had expected.
by Paul Gilster | Feb 24, 2006 | Deep Sky Astronomy & Telescopes
About 440 million light years away in the direction of the constellation Aries is the source of a curious gamma ray burst. Curious because it lasted for nearly 2,000 seconds, while most gamma ray bursts last anywhere from milliseconds to tens of seconds. Moreover, the burst is dimmer than one would expect, which makes scientists believe we may be viewing the event off-axis, although there is no consensus on the matter as yet.
Is GRB 060218 a new kind of explosion, a precursor to a supernova? The blast was detected on February 18, and since then satellite and ground-based telescopes have been focused on the area. There has never been a gamma ray burst detected this close to Earth — in fact, this one is 25 times closer than the average. A team in Italy believes a supernova may be building here, while the European Southern Observatory’s Very Large Telescope has picked up the kind of optical brightening that also suggests the supernova solution.
Image: The collapsing star scenario that is one of the leading contenders as the cause of gamma-ray bursts. Dr. Stan Woosley of the University of California at Santa Cruz proposed the collapsar theory in 1993. This artist’s concept of the collapsar model shows the center of a dying star collapsing minutes before the star implodes and emits a gamma-ray burst that is seen across the universe. Credit: NASA/Dana Berry.
“We expected to see the typical featureless spectrum of a gamma-ray burst afterglow, but instead we found a mixture between this and the more complex spectrum of a supernova similar to those generally observed weeks after the gamma-ray burst,” said Nicola Masetti of INAF’s Institute for Space Astrophysics and Cosmic Physics (IASF) in Bologna. “A supernova must be in the works.”
If so, this one is an observational gem. We may be looking at the collapse of a massive star, with stellar debris trapping optical light inside. GRB 060218 was detected by radio telescopes from the very day the Swift satellite first picked it up with all three of its instruments — the Burst Alert Telescope, the X-ray Observatory and the Ultraviolet/Optical Telescope. Scientists will thus be able to observe this explosion from start to finish in wavelengths ranging from radio through X-ray. And well-equipped amateurs with 16-inch telescopes may be able to see it as well as it reaches 16th magnitude brightness.
by Paul Gilster | Feb 23, 2006 | Deep Sky Astronomy & Telescopes, Exoplanetary Science |
Catching up on interesting stories, Centauri Dreams notes the bizarre case of the counter-rotating disk material around a young star 500 light years from Earth in the direction of Ophiuchus. Of course, we don’t actually know if planets exist there — we may just be looking at planetary formation — but astronomers using the Very Large Array radio telescope have determined that the inner part of the disk orbits in the opposite direction from the outer, and that’s a novel finding.
It seems reasonable to expect planets to orbit in the same direction; at least, it does if we take our own Solar System as a model, but exoplanetary findings have made it clear that planetary systems may be far more diverse than we originally thought. In this case, the assumption must be that the formative solar system drew material from not one but two prestellar clouds, both of which may provide enough material to form planets in the resultant disk.
Image: One protostellar cloud collapses further into a disk-like structure that rotates counter-clockwise (white arrows) about the newly-formed protostar. In addition, the protostar siphons off material from a second, passing protostellar cloud rotating in the opposite direction. Because of this, the outer part of the disk rotates clockwise (yellow arrows). Eventually, planets will form from the material in this disk, with the outer planets orbiting the star in the opposite direction from the inner planets. Credit: Bill Saxton, NRAO/AUI/NSF.
And how do we know that parts of the disk are moving in different directions? This work examined radio waves emitted by molecules within the star-forming clouds under investigation — these molecules emit radio waves at specific frequencies whose Doppler Shift can be measured. The key here proved to be observations of silicon monoxide (SiO) molecules. The April 1 edition of the Astrophysical Journal will contain a report on these findings.
Centauri Dreams‘ take: What was news to me in this story was a comment made by Jan Hollis (GSFC) to the effect that counter-rotation has previously been reported in the disks of galaxies (somehow I had missed this). That there should be protostellar disks exhibiting the same behavior is thus not unexpected, although understanding the dynamics that result in counter-rotating galactic material is a much greater challenge, given how much we have to learn about dark matter’s effect in determining just how a galaxy is going to form.
