by Paul Gilster | Mar 25, 2006 | Breakthrough Propulsion |
An effect that far exceeds what would be expected under Einstein’s theory of General Relativity has been produced in a laboratory. The fact that the effect — the gravitational equivalent of a magnetic field — is one hundred million trillion times larger than what General Relativity predicts has raised the eyebrows of more than a few researchers. But Martin Tajmar (ARC Seibersdorf Research GmbH, Austria) says that three years and 250 experimental runs have gone into this work, and encourages other physicists to examine and verify it.
If confirmed, the new findings could be a key result in the search for a quantum theory of gravity. We know that a moving electrical charge creates a magnetic field, and General Relativity assumes that a moving mass likewise generates a gravitomagnetic field, one that should, by the tenets of GR, be all but negligible. To test this, Tajmar and colleague Clovis de Matos (European Space Agency HQ, Paris) used a ring of superconducting material rotating 6500 times per minute. From an ESA news release:
Spinning superconductors produce a weak magnetic field, the so-called London moment. The new experiment tests a conjecture by Tajmar and de Matos that explains the difference between high-precision mass measurements of Cooper-pairs (the current carriers in superconductors) and their prediction via quantum theory. They have discovered that this anomaly could be explained by the appearance of a gravitomagnetic field in the spinning superconductor (This effect has been named the Gravitomagnetic London Moment by analogy with its magnetic counterpart).
The result: acceleration sensors placed close to the spinning superconductor show an acceleration field that seems to be produced by gravitomagnetism. In other words, a superconductive gyroscope seems to be capable of generating a gravitomagnetic field, making it the gravitational counterpart of the magnetic coil used in Michael Faraday’s classic experiment of 1831. In that groundbreaking work, Faraday moved a magnet through a loop of wire and observed electric current flowing in the wire, thus demonstrating electromagnetic induction.
Despite being far vaster than what General Relativity predicts, the effect is nonetheless just 100 millionths of the acceleration due to Earth’s gravitational field. It could, nonetheless, represent a breakthrough in engineering acceleration fields. “If confirmed, this would be a major breakthrough,” says Tajmar, “it opens up a new means of investigating general relativity and its consequences in the quantum world.”
Further research and confirmation of these findings will be a fascinating process to watch. The results were presented on March 21 at ESA’s European Space and Technology Research Centre in the Netherlands. The two papers to study right now are:
Tajmar, Martin, F. Plesescu, K. Marhold, and Clovis J. de Matos, “Experimental Detection of the Gravitomagnetic London Moment,” submitted to Physica C and available here.
Tajmar, Martin and Clovis J. de Matos, “Local Photon and Graviton Mass and its Consequences,” submitted to International Journal of Modern Physics D, available here.
by Paul Gilster | Mar 24, 2006 | Exoplanetary Science
If the goal is to find terrestrial planets around nearby stars, the transit method is our best bet. Sure, microlensing can deliver powerful results, and is fully capable, we believe, of finding a small, rocky world around a distant star. But microlensing as currently used is limited to stars that are tens of thousands of light years from Earth. In other words, find a terrestrial planet with microlensing and you can’t do much by way of follow-up study.
But transit methods are different. If a star’s system of planets is oriented so that the planets cross in front of the star as seen from Earth, it is possible not only to find the planets but to do spectroscopic analysis and learn something of their composition. All that makes Transitsearch.org an exciting thing to be a part of. As discussed earlier in these pages, it’s a cooperative project that gets amateur astronomers and smaller observatories into the transit hunt, supplying dates and times when transits are thought to occur.
Greg Laughlin (University of California, Santa Cruz), who heads the Transitsearch collaboration, now reminds participants that we have a transit opportunity coming up on March 28. The star is the M-class red dwarf GL 581, which is known to have a Neptune-class planet on a tight 5-day orbit. Laughlin reports that the planet has not been checked for transits, and is thereby a candidate for scrutiny as the observing window opens. Observing a transit of this planet would be a major step forward for exoplanet studies, and would help us refine the tools that will eventually find that Earth-like world.
Here are the coordinates as given by Laughlin:
ICRS 2000.0
RA 15 19 26.8250 DEC -07 43 20.209
Predicted transit midpoint: JD 2453822.79 (2006 Mar 28 06:59 UT)
Predicted central transit duration: 88 minutes.
Predicted transit depth: 1.6%
A-priori transit probability: 3.6%
The full ephemeris table is found on the candidates page at Transitsearch.org site. If you are an amateur astronomer with CCD capability, give serious thought to getting involved in Transitsearch. The effort concentrates on planet-bearing stars with high probabilities of displaying transits, and it needs coverage on a global basis for best results. It’s a remarkable fact that transiting worlds can be observed using commercial telescopes with CCD detectors — what an upgrade for amateur astronomy since the days when, as a star-struck teenager, I used to lug my little 3-inch reflector out into the yard for 1960’s era astronomy!
by Paul Gilster | Mar 23, 2006 | Exoplanetary Science
How many brown dwarfs await discovery near the Sun? Nobody knows, but the most recent is an interesting object indeed. Found some 12.7 light years from Earth as a companion to the red star SCR 1845-6357, it is the third closest brown dwarf yet discovered. “If you think of the galaxy as being the size of Tucson,” says Laird Close (University of Arizona), “it’s kind of like finding someone living in the upstairs of your house that you didn’t know about before.”
And that’s not all that makes the new dwarf interesting. Its surface temperature of 750 degrees Celsius makes it a remarkably cool object, one of the lowest-temperature dwarfs ever found. SCR 1845-6357 is some ten times less massive than our Sun; it is located in the southern hemisphere constellation Pavo (the Peacock). The small size of this star is interesting because until now, no brown dwarfs had been found around stars with less than half the mass of the Sun. And what we can deduce about its companion is that the brown dwarf is 4.5 AU from the star, and anywhere between 9 and 65 times as massive as Jupiter. Few brown dwarfs are known to come within 10 AU of their primary.
Image: University of Arizona and European astronomers took this image of a very cool brown dwarf orbiting a star near our sun using the SDI camera on the Very Large Telescope in Chile. The substellar companion appears blue in this image. It is roughly 50 times fainter than its star, and 4.5 times the Earth-Sun distance away from its star. Credit: Beth Biller and Laird Close, UA Steward Observatory.
The payoff on the new discovery could be significant. Says Markus Kasper (European Southern Observatory, and a member of the discovery team):
“This newly found brown dwarf is a valuable object because its distance is well known, allowing us to determine with precision its intrinsic brightness. Moreover, from its orbital motion, we should be able in a few years to estimate its mass. These properties are vital for understanding the nature of brown dwarfs.”
The closest known brown dwarfs? They both orbit Epsilon Indi, 11.8 years away. And here’s an interesting thought: of the seven brown dwarfs within 20 light years of the Sun, five are known to have a companion. Brown dwarfs, at least from this evidence, seem to occur as part of larger systems rather than as solo objects. Only future observations of other nearby dwarfs will tell us whether this is coincidence or evidence of a pattern of brown dwarf formation.
The details of this work are slated to appear in a letter to the Astrophysical Journal as Biller, Kasper, Close et al., “Discovery of a Very Nearby Brown Dwarf to the Sun: A Methane Rich Brown Dwarf Companion to the Low Mass Star SCR 1845-6357.” Nice work indeed by University of Arizona graduate student Beth Biller on this exceptional find.
by Paul Gilster | Mar 22, 2006 | Astrobiology and SETI |
For years now, we’ve had our eye on Mars rocks that are known to occasionally fall to Earth, blown off their planet of origin in some primeval impact. But recent computer modeling suggests that a reverse process may also occur: rocks from Earth, potentially carrying life, could reach environments as distant as Europa and Titan.
The numbers are surprising. As presented by Brett Gladman (University of British Columbia, Vancouver) at the Lunar and Planetary Science Conference, from 30 to 100 objects from Earth would hit Europa after a period of 5 million years. Titan receives 20 hits. The question then becomes, can bacteria survive such a journey, given the violent heat and acceleration that would be involved in blasting them off the Earth?
Relevant work at the conference suggests that they can. As summarized by Mark Peplow in a Nature.com article, scientists at the University of Florida (Gainesville) have fired marble-sized pellets into plates containing bacterial spores in water. Their simulations find that a tiny number of bacteria survive the ordeal. That could mean that a place whose surface is not utterly inimical to life, such as Titan, could find itself hosting Earth-based life forms, provided the few bacteria that made the journey could adapt to temperatures of -170 degrees Celsius. Whether this is possible remains for future work to determine.
Centauri Dreams‘ take: I love this quote in the Nature.com story from Jeff Moore, a planetary scientist at NASA’s Ames Research Center: “Once one planet comes down with life, they all get it.” An abstract of Gladman, Dones, Levision et al., “Meteoroid Transfer to Europa and Titan,” is available here (PDF warning). And note: the abstract confusingly refers to Triton rather than Titan at one point, but the figure in question is clearly meant to depict impacts on the latter moon.
by Paul Gilster | Mar 21, 2006 | Communications and Navigation
Why is it so tricky to deliver large amounts of data from space? One key issue is frequency — because the amount of data that can be transmitted varies with the square of the frequency, higher frequencies give you more bang for the buck. Moving the Deep Space Network from today’s X-Band (between 8.40 and 8.45 GHz for deep space work and between 8.45 and 8.50 GHz for near-Earth operations) to the Ka-Band (31.80 to 32.30 GHz) will increase the network’s capabilities by a factor of four or five.
But the real goal is optical communications, where the far narrower signal carries a vastly increased amount of information. We need that kind of data-packing not only to get around spectrum-crowding as more and more spacecraft need to talk, but also to handle the high resolution imagery and video we’ll want to see from future deep space missions.
“It can take hours with the existing wireless radio frequency technology to get useful scientific information back from Mars to Earth. But an optical link can do that thousands of times faster,” said Karl Berggren, assistant professor in the Department of Electrical Engineering and Computer Science at MIT.
So news from Berggren’s team at MIT is heartening. Researchers there have developed a new light detector that can use optical links to surmount far slower radio technologies. The detector works at the same wavelength used by the optical fibers carrying broadband signals to homes and offices, and may eventually lead to startling results including color video from the far corners of the Solar System.
And just as critical, we’ll be able to move more and more of the high resolution imagery from missions like Mars Global Surveyor back to Earth. These are incredibly bulky datasets, including the results from observations made with synthetic aperture radar, terrain-mapping radar, and hyper-spectral imaging, and they gobble up plenty of precious bandwidth.
We need detectors like this one because spacecraft are starved for power. Using superconductor technology and nanowires, the MIT design is incredibly sensitive — working down to the level of a single photon — meaning it can receive signals from smaller lasers. The design is also speedy and efficient at light-gathering.
Such detectors are only one step, but they are markers of our progress on the road to an interplanetary infrastructure of laser installations that far surpasses conventional radio links. And that leads, ultimately, to the kind of optical network that will receive laser signals from our first generation of true interstellar probes.
For more, see Rosfjord, Yang, Berggren et al., “Nanowire single-photon detector with an integrated optical cavity and anti-reflection coating,” in Optics Express Vol. 14, Issue 2 (23 January 2006), pp. 527-534. A PDF is available here.
