"How far is Moreno Valley from Pasadena?"
"Oh, about one hour."
"Why does everybody speak in times instead of distances?"
This brief conversation with my friend occurred shortly after I moved to California from Iowa. While distances between cities might be tricky, distances to other galaxies are downright daunting. However, new X-ray and maser measurements (masers are like lasers except they use microwaves instead of visible light) provide astronomers with unprecedented accuracy that bolsters confidence in a big bang creation model.
For anyone familiar with the Los Angeles area, it is relatively easy to translate a "one-hour distance" to about 45 miles based on how fast freeway traffic moves. So, a "distance" of one hour makes sense because that is the relevant quantity that most people measure; namely, how long it takes to drive somewhere. In fact, in some large cities freeway signs tell commuters how many minutes they are from downtown or other destinations--despite tall buildings that appear just ahead.
A problem arises when converting the measured driving time into an actual distance. People in more rural areas will likely travel a greater distance in the same measured driving time because traffic on Southern California freeways moves more slowly than on Iowa interstates. Even by confining the measurement to Southern California, the measured driving time depends greatly on the time of day, accidents, weather, and other factors. Thus, traffic can flow anywhere from 5 to 65 mph (or more!).
Astronomers face a similar problem when measuring distances to objects outside this solar system. Except for the stars in the local neighborhood, there are no "meter sticks" to use. The one measuring device astronomers do possess, stellar parallax, can only be used for stars within a few hundred light years of the solar system. This distance includes a few thousand stars-a small fraction of the billions of stars in the Milky Way Galaxy. Therefore, stellar parallax is hopelessly inadequate for measuring distances beyond the Galaxy.
Astronomers have developed many other techniques1 to measure more distant objects, but all of the methods require an accurate distance measurement to one relatively close object. A nearby dwarf galaxy called the Large Magellanic Cloud (LMC) serves as that object, but uncertainties in the measurements to the LMC indicate that distances beyond the LMC can be wrong by 5-10%.
A recent breakthrough resulted from two Princeton astronomers' research. They showed how the Chandra X-Ray Observatory, a NASA satellite launched in 1999, could be used to determine the distance to the Andromeda Galaxy (M31) to "an unprecedented absolute accuracy of 1%."2 The Andromeda Galaxy is roughly 2 million light years away-more than 10 times farther than the LMC. The increase in distance and improved accuracy of the new technique will reduce errors on all other distance measurements by a factor of 30-50.
The geometrical distance measurement requires an X-ray source behind Andromeda whose output varies in time. Conveniently, the active galaxy 5C 3.76 qualifies. As the X-rays from 5C 3.76 pass through Andromeda, they scatter from the galaxy's dust grains, creating an X-ray halo. Comparison of the X-ray variability from different parts of the halo with the variability of the active galaxy itself provides all the information necessary to geometrically determine the distance to Andromeda.
Another group of astronomers is developing a different technique to measure geometrical distances to galaxies using water masers.3 While distances measured using water masers have larger uncertainties (6-10%), masers can be seen in galaxies up to 100 times more distant than Andromeda, making them useful even as the technique develops. Recently, water masers were found in a dozen galaxies.4
Over the next few years, measurements of X-rays from Andromeda and the newly discovered maser galaxies will better establish the lower "mile markers" of the cosmic distance scale. Astronomers may soon determine distances to galaxies with the same precision as a map-equipped California motorist traveling from Pasadena to Moreno Valley. In turn, understanding of the cosmos and of RTB's biblical big bang creation model will stand on even more solid ground.
1. For a brief overview of the many different techniques developed to measure distances, see http://www.astro.ucla.edu/~wright/distance.htm.
2. B.T. Draine and Nicholas A. Bond, "Direct Extragalactic Distance Determination Using X-Ray Scattering," Astrophysical Journal 617 (2004): 987-1003; http://arxiv.org/abs/astro-ph/0407435.
3. J.A. Braatz et al., "A Green Bank Telescope Search for Water Masers in Nearby Active Galactic Nuclei," Astrophysical Journal Letters 617 (2004): L29; http://arxiv.org/abs/astro-ph/0412352.
4. J.R. Herrnstein et al., "A Geometric Distance to the Galaxy NGC4258 from Orbital Motions in a Nuclear Gas Disk," Nature 400 (1999): 539-41; http://www.nature.com/nature/journal/v400/n6744/abs/400539a0_fs.html.