February 26, 2020

08.02.11: A Standard Candle Re-tweak?

The size of a proton. The definition of a planet. The Periodic Table. One of the hallmarks of science is the ability to alter and modify what we know as new information comes to light. Of course, this is much to the chagrin of the man on the street, who likes his science bit-sized, tweet-able, and unchanging…

Now, one of the most fundamental tools in cosmology may need calibration. Recently, studies using NASA’s Spitzer space telescope have discovered that Delta Cephei, that most famous and prototype for Cepheid variable stars, looses mass and shrinks throughout its life span. Could this model for the “standard candle” need adjustment?

Cepheids are an essential component for measuring cosmic distances. First analyzed and decoded by Henrietta Leavitt in 1912, these pulsating variables oscillate in a fashion that is in direct relationship to their luminosity. We know to a high degree the parallax measurements to nearby Cepheids in our own galaxy (Polaris, the North Star is another famous example). If an extragalactic Cepheid can be pinpointed in another galaxy, its distance can be measured via the inverse square law. Edwin Hubble did this to measure the distance to the Andromeda galaxy in 1926.

If, however, the scale is off, the measurements will become more inaccurate as distances increase. One caveat: I know what some cosmology detractors are thinking: does this mean that the Big Bang NEVER HAPPENED? Not at all. Keep in mind, this was ONE study of ONE Cepheid; the period-luminosity relationship is pretty well documented and established.  Likewise for the Big Bang; supernova luminosity, red-shift, the age of globular clusters and white dwarfs and the cosmic microwave background all dove-tail nicely with a 13.7 billion year old universe; would be nay sayers and basement cosmologists have their work cut out against such a bulwark. Of course, that may not stop commenters with long and convoluted explanations as to why the Big Bang theory just isn’t so… just remember the idea behind Occam’s razor stating the simplest and most elegant solution is likely to be right.

The take away idea from the Spitzer discoveries is that a refinement in the Cepheid variable yardstick may be do a for a modification, but certainly isn’t to be thrown out all together.  “When using Cepheids as standard candles we must be extra careful because, much like actual candles, they are consumed as they burn.” States astronomer Massimo Marengo of Iowa State University at NASA Ames.

In the end, these yardsticks may be due an overhaul, but still serve as ingenious and reliable tools to measure cosmic distances. And isn’t that ultimately the hallmark of good science, the ability to change and adapt to reality as new information presents itself?


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