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Physics News Update
Number 668, January 9, 2004 by Phil Schewe, James Riordon, and Ben Stein

Large Galaxies Formed Surprisingly Early

Large galaxies formed surprisingly early, a new study finds. You'd expect that a census of the farthest, earliest galaxies would feature a lot of smaller, hotter, younger, bluer galaxies, perhaps in the act of smashing into and coalescing with their neighbors.

But a new survey made using the 8-meter Hawaii telescope of the Gemini Observatory shows rather that at only a comparatively short time after the big bang the universe was already well furnished with large, reddish, mature elliptical galaxies.

The Gemini Deep Deep Survey (GDDS) trawled the poorly patrolled "Redshift Desert" region of cosmic history, the epoch roughly 3 to 6 billion years since the big bang and found instead what team member Roberto Abraham (University of Toronto) calls a "Redshift Dessert"---plenty of massive old galaxies where you'd expect few. Abraham and his colleagues reported the results at this week's meeting of the American Astronomical Society (AAS) in Atlanta.

Patrick McCarthy (Carnegie Institution) said that what the survey shows is that at a point only 4 billion years into the life of the universe there were already galaxies up to 3 billion years old. This leaves very little time for the assembly of something as big as an elliptical galaxy.

Furthermore, the galaxies in the survey possess a plentiful stock of heavier "metal" atoms, the kind that would have to be cooked up in repeated cycles of star birth and supernova. To put the question in term of galaxy demographics: how could there be so many senior citizens so early? According to Roberto Abraham, all of this should make theorists sweat. (Gemini Observatory website)

Large-Scale Structures in the Early Universe

Large-scale structures in the early universe are also larger than expected. Like the presence of surprisingly early mature galaxies at a redshift of about 2 (see the item above) another result at the AAS meeting suggests that the standard cosmological model---or at least that part of it devoted to galaxy formation---is in need of revision.

A group of astronomers using the Blanco Telescope of the Inter-American Observatory in Chile and the Anglo-Australian Telescope in Australia reported seeing a grouping of 37 galaxies, all at a redshift close to 2.38, spread 300 million light years across the sky. Povilas Palunas (University of Texas) said that this constitutes the largest observed structure in the distant universe.

According to models that simulate how the hot diffuse matter of the infant cosmos distilled into a web of knots and filaments, such an immense agglomeration should not have arisen so quickly.

The statistical case for saying that this sampling of bright galaxies (fainter galaxies could not be seen) is truly a coherent structure and not just a chance juxtaposition can be expressed as a probability with 1000-to-1 odds, a likelihood obtained by looking not at the specific arrangement of galaxies themselves but at the daunting amount of void between the galaxies.

Gerard Williger (Johns Hopkins) said that he and his colleagues would naturally like next to sample adjoining volumes of deep space in order to test the proposition that the hasty filimentation of matter seen in this initial data set (the observed galaxies lie in the southern constellation "Grus") is not an isolated incident (See Goddard news release).

Negatively Misbehaving Muons

Negatively misbehaving muons bolster earlier evidence of new physics beyond the standard model, though further experimental and theoretical work may be needed to confirm this possibility.

At Brookhaven National Laboratory's "g-2" experiments, an international collaboration has been studying the decay of the muon, a heavy cousin of the electron, by measuring the muon's magnetic moment, a quantity that describes the strength with which the particle interacts with magnetic fields.

In 2001, researchers studied positively charged muons and found a discrepancy between the experimental value and the predictions of the standard model (see Update 524), though the discrepancy was later reduced after researchers discovered an error in the theory.

Yesterday, researchers reported measurements on negatively charged muons that matched the precision of the previously reported positive muon results. Combining the data on positive and negative muons, the researchers find a disagreement between the experiments and the standard model of as much as 2.8 standard deviations, about the same level of discrepancy that was originally reported in 2001 before the theory error was discovered. (For a discussion of the meaning of "standard deviation" and statistical significance in general, see Update 566.)

What would cause this discrepancy? Perhaps the muon's magnetic moment is being influenced by hypothesized but yet-undiscovered "supersymmetric" particles (with names such as "squarks") that are not included in the standard model. However, further work may be needed to check and refine the very difficult theoretical calculations on the muon's magnetic moment.

Unfortunately, additional experiments at Brookhaven are out of the question for the moment, as the project's funding has ended. However, experiment spokesman Lee Roberts of Boston University says that the new results are prompting his group to write a new proposal for continuing their experimental tests, and future accelerator experiments, such as those at the upcoming Large Hadron Collider in Europe, will search for supersymmetric particles. (More information at Brookhaven web page)