Default publications post thumbnail

Confirming Cosmic Expansion, Part 2 (of 4)

Continual cosmic expansion under fixed physical laws from an actual beginning of matter, energy, space, and time is the key to the biblical cosmic creation model. Efforts to further confirm continual expansion establish the validity of the biblical cosmic creation model and demonstrate the Bible’s capacity to accurately predict future scientific discoveries.

In part 1 of this series, I discussed the distance ladder method used to confirm the rate of cosmic expansion by using direct distance measurements on nearby objects to calibrate indirect methods for far away objects. I described how this method works, as well as its limitations.1 The shortcomings in these traditional measuring methods left room for much needed improvement in order to attain the cosmological ideal: measuring the cosmic expansion rate using only accurate direct distance calculations.

Thanks to new measurements on galaxies both near and far, that ideal has now been achieved. In this installment, I will describe and explain two of the three new techniques: measurements of the expanding shock fronts of supernova eruptions and observations of water maser sources orbiting about the center of the host galaxy.

Expanding supernova shock front 

In 1993, astronomers observed the beginning of a supernova eruption in the spiral galaxy M81. Since then astronomers have measured the growth of an expanding shock front emanating from that supernova. Spectral measurements of the light at the leading edges of the shock front informed researchers how rapidly in kilometers per second the shock front was growing, which in turn told them how many kilometers across the shock front was at various epochs in its expansion. An American and Canadian radio astronomy team then used a global network of radio telescopes to provide precise measurements of the angles subtended by the shock front at those same epochs.2 Simple geometry theorems gave the team an accurate direct distance measurement to M81.

The radio astronomy team determined the distance to M81 to be 12.9 million light-years ± 0.9 million light-years. This measurement, though slightly higher in value and slightly less precise than the best indirect determination, was consistent given the measuring errors. As the sample size of observed expanding supernova shock fronts grows from one to many, this technique will potentially deliver distance measurements superior to the best indirect methods.

Water maser orbits about galaxy centers

When using the water maser distance measuring method, astronomers replaced the traditional triangle baseline (diameter of Earth’s orbit) with the much larger diameters of the orbits of microwave laser, or maser, sources around the supergiant black holes located at the centers of large galaxies. The spectra of the maser sources yield the orbital velocities of the sources around the black hole. Newton’s laws of motion translate those velocities into measured diameters for the orbits. Next, because astronomers observe the maser sources at radio wavelengths, they are able to electronically link radio telescopes all over the globe. This creates an instrument with an angular resolving power a thousand times better than the biggest ground-based optical telescope and a hundred times superior to the Hubble Space Telescope. In addition, the long amount of observing time over which observations of the masers are made enables astronomers to gain another factor of a hundred improvement in the accuracy of their measurements. (For a more detailed description of this distance measuring method see here.)

To date, astronomers have used the water maser method to accurately determine the distance to two galaxies. The nearest of these galaxies, NGC 4258 (also known as M106), measures 25 million light-years away to within an accuracy of five percent. The farther galaxy, UGC 3789, lies at a distance of 150 million light-years. Currently, the cosmic expansion rate values derived from the water masers in NGC 4258 and UGC 3789 are precise to about six percent. Though not yet competitive with the precision of the gravitational lens time delay method (which I will discuss next week), the observing teams are confident that within three years they will have results superior in accuracy to the time delay method. Their current published values are consistent with the latest time delay determination of the cosmic expansion rate (based on recent measurements of the gravitational lens system B1608+656). Next week’s installment will explain in greater detail direct distance measuring via gravitational lens systems.

Part 1 | Part 2 | Part 3 | Part 4
  1. Direct cosmic distance measurements are based on the plane geometry theorems. For example, if one knows the length of the base of an isosceles triangle, then measurements of the angles at either end of the base will deliver the distance to the vertex of the triangle. The diameter of Earth’s orbit around the Sun (about 299,195,741 kilometers or 185,912,076 miles) has been the traditional base of the triangle in determining distances to nearby stars. Astronomically speaking, this base is so tiny that the accuracy of measurements to even the nearest stars is no better than a few percent. This particular direct method delivers accurate calculations only for stars located just over a thousand light-years away.

    To gain any measurement of the universe’s history, astronomers must use these limited direct distance measurements to calibrate indirect methods for far away objects. The indirect methods make certain assumptions about the properties of the observed objects. Only the direct methods are assumption free.
  2. N. Bartel et al., “SN 1993J VLBI. IV. A Geometric Distance to M81 with the Expanding Shock Front Method,” Astrophysical Journal 668 (October 20, 2007): 924–40.