Friday, January 20, 2006

Intelligent Design and the Big Bang

Science 6 January 2006:
Vol. 311. no. 5757, pp. 54 - 57


The Distance to the Perseus Spiral Arm in the Milky Way

Y. Xu,1,2,3 M. J. Reid,2 X. W. Zheng,1,2 K. M. Menten4

We have measured the distance to the massive star–forming region W3OH in the Perseus spiral arm of the Milky Way to be 1.95 ± 0.04 kiloparsecs (5.86 x1016 km). This distance was determined by triangulation, with Earth's orbit as one segment of a triangle, using the Very Long Baseline Array. This resolves the long-standing problem that there is a discrepancy of a factor of 2 between different techniques used to determine distances. The reason for the discrepancy is that this portion of the Perseus arm has anomalous motions. The orientation of the anomalous motion agrees with spiral density-wave theory, but the magnitude of the motion is somewhat larger than most models predict.

1 Department of Astronomy, Nanjing University, Nanjing 210093, China.
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
3 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 20030, China.
4 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany.

Massive stars and their associated bright regions of ionized hydrogen trace the spiral arms of galaxies. However, for our galaxy, the Milky Way, our view from the interior makes it difficult to determine its spiral structure. In principle, one can construct a simple model of the rotation speed of stars and gas as a function of distance from the center of the Milky Way. Then, if one measures the line-of-sight component of the velocity of a star or interstellar gas, one can determine its distance by matching the observation with the model prediction (that is, a kinematic distance). Knowing the distances to star-forming regions, one can then locate them in three dimensions and construct a "plan view" —a view from above the plane—of the Milky Way. Unfortunately, many problems arise when constructing a plan view of the Milky Way, including (i) difficulties in determining an accurate rotation model (which requires values for the distance and orbital speed of the Sun from the center of the Milky Way), (ii) distance ambiguities in some portions of the Milky Way (where an observed velocity can occur at two distances), and (iii) departures from circular rotation (as might be expected for spiral structure). Progress has been made on the first two problems. For example, many kinematic distance ambiguities can be resolved by interferometric studies of hydrogen absorption at radio frequencies, because distant sources will show a greater velocity range for hydrogen absorption than will near sources (1). However, the third problem, noncircular motions, is fundamentally much harder to address


BrooklynDodger comments: For all the controversy over Intelligent Design, there seems little contest over the origin of the universe, the real creation. Why are there no fundamentalist efforts to substitute 7 day creation for cosmological theories? The Big Bang gives at least a metaphorical role for a Deity [the Big Banger]. However, if the Banger just set a machine in motion, with no further supernatural intervention, there's little point in hoping that going to church on Sunday will get you a better deal on Monday.

The Dodger thought this story was cool because the star map put the world in its place. Our solar system looks to be in a not very dense region of the galaxy, and pretty far out from the center. Stars are still forming, but matter is not still being created.

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