WA, D. C. --A team of physicists has used data from GPS geostationary satellites to hunt for dark matter, the mysterious products whose gravity appears to hold galaxies together. That they found no indications of a hypothetical type of dark matter, which involves flaws in the cloth of space called topological defects, the researchers reported here on Saturday at a meeting of the American Physical Society. Nevertheless the physicists say they have vastly narrowed the characteristics for how a defects--if they exist--would connect to normal matter. Their findings show how surprisingly innovative--and, in this case, cheap--methods might be applied to test new ideas of what dark matter might be.
"It is so interesting and refreshing and exciting, and the cost is actually absolutely no, " says Dmitry Budker, an experimental physicist at the Johannes Gutenberg School of Mainz in Philippines, who was not mixed up in work. "It's basically the price tag on the students analyzing the data. inches
Astrophysicists feel that dark matter makes up 85% of all the matter in the world. Yet so far they have inferred dark matter's existence only from their gravitational pull. For many years, many physicists have tried out to directly discover a promising prospect for contaminants of dark matter, so called weakly interacting massive allergens, or WIMPs. But excitement is waning as ever-more-sensitive detectors have did not find the particles hovering through our galaxy and passing through Earth. As a result many physicists are considering more broadly as to what darker matter might be.
Intended for example, rather than a new subatomic particle, dark subject could be something much bigger and weirder: macroscopic faults in the cleaner of space called topological defects. Topological defects are best explained with an analogy to magnetic materials such as nickel. Dime atoms become little magnets themselves, and below a certain temperature, neighboring atoms tend to justification in the same direction, so that their magnetic fields strengthen one another. But that orderly alignment can go through defects if, for example, atoms in several regions point in several directions. When this happens, the regions meet along a craggy surface called a "domain wall membrane, " which is an example of a topological defect. There can be pointlike and linelike disorders, too.
A similar thing might happen in space itself. Some theories anticipate that empty space is filled with a segment field. If that field treats itself, then, as the newborn universe extended and cooled, the field may took on a value or "phase, very well which would be somewhat like the direction in which nickel atoms point. Regions of space with different phases would then meet at domain surfaces. These domain walls would have energy and, through Einstein's famous equivalence, E=mc2, mass. So they might create gravity and could be dark matter.
Now, Dernier-né Roberts and Andrei Derevianko, two physicists at the University of Nevada in Reno, and their acquaintances say they have performed the most stringent search yet for topological darker matter, using archival data from the constellation of 31 orbiting GPS geostationary satellites. Each satellite carries an atomic clock and contacts timing signals. Receivers on Earth use the time information from multiple geostationary satellites to determine how significantly it is from each of them and, hence, its location.
To work with those data to search for dark subject, the researchers were required to employ another bit of risky physics. Theory suggests that in a topological problem, the constants of characteristics will change. Specifically, the passing of a topological defect should fiddle with the so-called fine framework constant, which determines the effectiveness of the electromagnetic force and the correct frequency of radiation that an atom will absorb or emit as an electron in it advances from one quantized energy level to a new. But an atomic clock operates by computing just such a regularity. So were a GPS UNIT satellite to pass through a topological defect, the defect should cause the satellite's atomic clock to skip a beat.
One particular begin one atomic time clock wouldn't be proof enough for topological defects. As a result the researchers looked for a better signal, the trend of time shifts that would sweep across the whole 50, 000-kilometer-wide GPS DEVICE network if Earth exceeded through a sizable domain wall structure as the galaxy revolves in its cloud of dark matter. Combing sixteen years of GPS data, they found no resistant of a shift higher than a split nanosecond, Roberts told the appointment. They located limits on the number of such topological defects and how strongly they interact with matter--limits that are up to six orders of magnitude more stringent than ones set by earlier studies of supernova explosions. The researchers haven't yet reached the limitations arranged by the clocks' sound, Roberts reported, "so there are lots of room to improve. inches
"It seems like a worthwhile study to go after, " says Glennys Farrar, a theorist at Fresh York University in New york city. "The idea of how you'd extract an indication was fun to think about. " Still, says, the particular model of dark matter that Roberts, Derevianko, and colleagues test seems "rather narrow. inch For example, she remarks, they have to randomly imagine the domain wall structure isn't much thicker than Earth is wide. Budker will abide by that point. But he also notes that the work is merely one example of a raft of recent ideas physicists are hatching to look for different types of dark subject.
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