by Paul Gilster | Sep 9, 2009 | Exotic Physics |
Point a Voyager-speed spacecraft at Alpha Centauri and the travel time would be on the order of 73,000 years. Those of us obsessed with the idea of interstellar journeys are forced to hope for profound breakthroughs in physics and engineering. The word ‘breakthrough’ is, if anything, an understatement. An Alcubierre-style ‘warp drive’ would, so far as we know, require energies that would tax even a Kardashev Type III civilization, as physicist Richard Obousy points out. Hence the acknowledged ‘giggle factor’ that plagues serious discussion of these matters. Writes Obousy:
The giggle-factor is a consequence of using a name for a cutting edge propulsion concept that is taken straight from science fiction. In reality the name is a double-edged sword. When one mentions a ‘warp drive’ it should be immediately obvious (one would hope) that what is being dicussed is a hypothetical propulsion mechanism that utilizes an asymmetric manipulation of the fabric of spacetime to generate an exotic curvature which allows one to circumvent the traditional limitations of Special Relativity and travel at superluminal velocities.
Is a warp drive remotely possible? The answer may well be no, but scientists continue to look at the concept even if the pace of their study is slow. I’ve drawn the quotation above from Obousy’s new Interstellar Journey Web site, which includes not only the beginnings of a regular blog but also a short video introduction in ten sections (of which six are now online) to the issues involved. One emerging fact about warp drive is that it is the poor cousin of interstellar research when compared to the work that has been done on Einstein-Rosen bridges and forms of traversable wormholes.
Like the warp drive, a wormhole calls for negative energy and demands vast amounts of energy to remain functional. Oddly, wormhole papers greatly outnumber those on warp drive even though both ideas are almost absurdly speculative. Obousy runs a quick search and comes up with 1248 wormhole papers (ten released to arXiv in August alone), whereas the numbers for warp drive are miniscule: 33 papers, with no more than one or two being released per year.
We’re dealing with a fascinating idea, yet warp drive lacks the big-name backing (John Wheeler, Herman Weyl, Matt Visser) that wormhole physics enjoys. Consider Obousy’s new site an attempt to balance the books. The short background videos are well produced and visually effective, ranging from motivations for interstellar flight to proposed mission designs like Daedalus and on to the potential of dark energy to enable FTL concepts, an Obousy specialty.
Centauri Dreams readers will recall that Obousy’s work has appeared here on several occasions, in particular re his article in the British Interplanetary Society’s magazine Spaceflight that mines, among other ideas, the potential of higher dimensions of the sort emerging first from the work of Theodor Kaluza and, more recently, string theory. A new Obousy paper (with Aram Saharian) is “Casimir energy and the possibility of higher dimensional manipulation” (abstract), which relates the Casimir effect to dark energy. For this and other warp drive papers, see the archive at Interstellar Journey, which becomes a welcome addition to the online study of exotic concepts.
by Paul Gilster | Sep 8, 2009 | Deep Sky Astronomy & Telescopes |
I try to run interesting astronomical art wherever I can find it, but the image that accompanies this ESA news release on the discovery of an interesting white dwarf just doesn’t cut it. So use your imagination as I describe the results of a study using data from ESA’s XMM-Newton X-ray telescope, which have given us something we’ve long lacked — highly accurate mass information for an accreting white dwarf in a binary system, one that is growing close to the point of becoming a supernova.
Something in the vicinity of HD 49798 has been known to be giving off X-rays since 1997, but it has taken XMM-Newton to nail the culprit. The white dwarf near the larger star is twice as massive as expected, cramming about 1.3 solar masses into an object with a diameter about half that of our planet. Rotating every thirteen seconds, this object boasts the fastest white dwarf rotation known.
Why the larger mass? We’re looking at a white dwarf that is pulling gaseous material out of its companion star. The process points to an interesting future: When a white dwarf in this situation reaches 1.4 solar masses, it will doubtless explode, becoming what is known as a type Ia supernova. Such events are the ‘standard candles’ that astronomers use to study the expansion of the universe, and here we see a type Ia supernova in the process of developing.
Sandro Mereghetti (INAF-IASF Milan) describes the find in terms of a useful historical analogy:
“This is the Rosetta stone of white dwarfs in binary systems. Our precise determination of the masses of the two stars is crucial. We can now study it further and try to reconstruct its past, so that we can calculate its future.”
Not that we need wait up for this one. A supernova near HD 49798 shouldn’t occur for a few million years, and even when it does, it poses no danger to Earth. That will be an interesting event, visible in broad daylight with the naked eye, but for today’s astronomical purposes, this white dwarf tells us much about the supernovae so critical in our understanding of a universe whose expansion seems to be accelerating.
The paper is Mereghetti et al., “An ultra massive fast-spinning white dwarf in a peculiar binary system,” Science Vol. 325, No. 5945 (4 September 2009), pp. 1222-1223 (abstract).
by Paul Gilster | Sep 7, 2009 | Exoplanetary Science |
The exoplanet hunt has entered a significant new phase, one focused on transiting planets and the useful things we can learn about their physical properties and atmospheres through such events. Driven by CoRoT and Kepler, we’re now in position to use those transits to spot smaller worlds than ever, down to terrestrial size, and naturally the focus is on Earth analogs located in the habitable zones of their stars.
So think of it this way: We’ve gone from a broad-brush approach based largely on radial velocity methods to a more selective hunt, one that will take us to the realm of planets that can have liquid water on their surfaces and aren’t so different from our own. Not that the continuing work on characterizing planetary systems is of any less importance, but we’ve found plenty of gas giants, and now we’re trying to learn something about how common these smaller worlds may be.
Putting an exclamation point on this focus is a conference called Pathways Towards Habitable Planets, to be held in Barcelona from the 14th to the 18th of this month. The European Blue Dots Team (BDT) is an initiative made up of researchers who focus on finding habitable worlds, with international assistance. The purpose of its Barcelona conclave is to bring together space agencies from around the world to discuss how to learn more about planets of the kind Kepler and CoRoT may find.
A glance through the program shows how wide-ranging this discussion is likely to be. Some examples: Differing cultural views on the ‘are we alone’ question (Jean Schneider, CNRS-Paris Observatory). Tidal constraints on habitability (that one, as you might expect from discussions here) is from Rory Barnes (University of Arizona). A coronagraph concept for direct imaging and spectroscopy of exoplanetary systems (John Trauger, JPL). And an old Centauri Dreams friend: David Kipping (University College, London) discussing habitable exomoons.
Image: One way to study habitable exoplanets is through a space telescope coupled with a starshade concept like New Worlds Observer. This is a simulated image of the inner solar system taken at 10 parsecs with a 4-meter telescope. The Earth is clearly visible as a pale, blue dot. Venus is harder to make out due to the zodiacal light. The inclination of this image is 60 degrees. Credit: Phil Oakley.
The proceedings are to be published in the spring, but we should have copies of some of these papers for review in the near future. It’s good to see that Webster Cash (University of Colorado, Boulder) will be presenting the latest on his New Worlds Observer, a space-based starshade design that would be able to perform spectroscopy on exoplanetary light to look for biological markers. Long championed here, this powerful concept has had its ups and downs re funding but clearly remains viable.
by Paul Gilster | Sep 4, 2009 | Breakthrough Propulsion |
Both Tau Zero Foundation founder Marc Millis and JPL’s recently retired Robert Frisbee appear in an article in the Smithsonian’s Air & Space, where voyages to distant places indeed are discussed. Nothing is further from Earth, the article notes, than Voyager 1, which travels at a speed (almost 17 kilometers per second) that would get it across the US in a little under four minutes. Point that spacecraft toward Proxima Centauri and the journey at this speed would take 73,000 years. Clearly, something has to give, and writer Michael Klesius runs through the options.
From Ideas to Engineering
Voyager is actually headed in the vague direction of the constallation Camelopardalis, and won’t come near anything stellar in several hundred thousand years. We’d like to get mission times to a nearby star down to decades so that scientists and engineers working on the project could live to see its outcome.
How to achieve that is a question that has been at the back of Bob Frisbee’s mind for a long time now. To Alpha Centauri in just decades? Years? “We can see the theoretical possibilities of these things happening, but we just can’t get the engineering there,” Frisbee notes in the article, but he points out that this kind of brainstorming was what we used to do when thinking about a moon voyage, and that was a journey we made. It may take several generations of brainstorming but the ideas continue to fly.
Building a Breakthrough Concept
Let’s hope the Air & Space article provokes public discussion as it runs through the background of advanced propulsion studies in the 1990s, when wormholes were seriously tackled and warp drive began to be written up in scientific journals. Miguel Alcubierre’s concept of a spacecraft riding what is essentially a wave in spacetime kicked off a resurgence in breakthrough propulsion that led materially to projects like NASA’s Breakthrough Propulsion Physics, run by Millis until its termination in 2002. Funding issues are always problematic, but Tau Zero continues to probe these matters, and Frontiers of Propulsion Science, co-edited by Millis and Eric Davis, shows that the ongoing conversation is robust indeed.
Says Millis:
“I think back to the era of Dirac and Schrödinger and Einstein. When they were having their pivotal meetings and sometimes heated debates, they weren’t being funded for that work. They were just doing it because that’s what they did. And they made significant advances… And I’m thinking to myself, Well, it would be great if we got funding, but even if we don’t, when we talk amongst ourselves and debate things and encourage each other to write papers, we’re going to make progress.”
That kind of progress is what Tau Zero is about. Not that robust funding is out of the picture — we are building a philanthropic model for the foundation that should be able to tap private sector sources (with all the good things that follow from not being channeled through endless layers of bureaucracy). But keeping an eye on the issues and encouraging debate is bound to produce good outcomes, if only in the synergies that result from putting propulsion theorists with good ideas in continuing contact.
Options for Infrastructure
But before we go to the stars, we’ve got to build up our capabilities right here in the system. On that score, the article is also noteworthy for its examination of NERVA, a nuclear thermal rocket design that Klesius describes this way:
It would produce thrust the way chemical rockets do: by heating a propellant—in this case, hydrogen—and ejecting the expanded gas through a nozzle. Instead of heating hydrogen through combustion, however, the nuclear rocket vaporizes it through the controlled fission, or splitting of atomic nuclei, of uranium. Because nuclear fuel has a greater energy density, it lasts a lot longer than chemicals, so you can keep the engine running and continue to accelerate for half the trip. Then, with the speedometer clicking off about 15 miles per second — twice the speed reached by returning Apollo astronauts — you’d swing the ship around to point the other way and use the engine’s thrust to decelerate for the rest of the trip. Even when factoring in the weight of the reactor, a nuclear engine would cut the transit time in half.
NERVA was a promising technology that delivered 850 seconds of thrust — twice the efficiency of chemical rockets — in 1960s-era tests, but the program faded in the 1970s. You’ll find more on NERVA, and on Franklin Chang-Díaz’ work on VASIMR, in Klesius’ article. Neither NERVA nor VASIMR has interstellar potential, but in terms of opening up the Solar System for exploration and infrastructure building, these are solid options to investigate.
An Insurance Plan for Human Survival
I like the Chang-Díaz quote that ends the piece:
“The space program began the day humans chose to walk out of their caves. By exploring space we are doing nothing less than insuring our own survival.”
Indeed. And all the technologies described here point to ways of making the insurance policy pay big dividends. Klesius writes about a fusion-powered 180-day trip to Jupiter, one dependent on breakthroughs in fusion itself and in materials science. Build the infrastructure here in the Solar System and gradually push the envelope outwards. It’s a plan that could pay off one day in making that journey to Proxima Centauri via fusion, antimatter or other means, and crossing the gulf in a single human lifetime.
by Paul Gilster | Sep 3, 2009 | Deep Sky Astronomy & Telescopes |
Here’s a surprise — a galaxy as large as the Milky Way that houses a supermassive black hole with the equivalent of a billion suns worth of matter. The surprise isn’t the object itself but its distance, some 12.8 billion light years (redshift 6.43). [See Adam Crowl’s comment below: This is not actually a ‘distance’ but the light travel time]. That makes this a young object, assuming a universe that began roughly 13.7 billion years ago, and has implications for how such galaxies form. Tomotsugu Goto (University of Hawaii), who led the team making the discovery, notes the unusual nature of his find:
“It is surprising that such a giant galaxy existed when the Universe was only one-sixteenth of its present age, and that it hosted a black hole one billion times more massive than the Sun. The galaxy and black hole must have formed very rapidly in the early universe.”
It seems odd to say it, but what complicates studying such distant objects is that host galaxies are often lost in the glare of the central black hole. The black hole emits no light, of course, but infalling material heated up by friction as it moves around the event horizon puts out a strong signature in visible and ultraviolet light. This University of Hawaii at Manoa news release notes that 40 percent of the light around 9100 angstroms comes from the host galaxy itself, while 60 percent is from the ionized materials around the black hole.
Image: False-color image of the QSO (Quasi-Stellar Object) CFHQSJ2329-0301, the most distant black hole currently known. In addition to the bright central black hole (white), the image shows the surrounding host galaxy (red). Credit: Tomotsugu Goto, University of Hawaii.
That light may make galaxy observations tricky, but it’s quite useful in the study of the central object. The amount of light emitted depends upon the mass of the black hole. Assuming a spherically symmetrical shell, the maximum brightness, called the ‘Eddington luminosity,’ allows us to calculate a maximum value for the mass. The huge black hole most likely formed from the merger of smaller black holes, of which the galaxy in question seems to provide a supply, but the formation mechanism is not fully understood.
The paper is Goto et al., “A QSO host galaxy and its Lyα emission at z=6.43,” to be published in Monthly Notices of the Royal Astronomical Society online edition, and currently available here.
