Standard Candle upgrade

Almost every measurement in cosmology ultimately depends on using a “standard candle” to determine distance, which in turn is used to determine every other observable quantity – age, mass, speed, etc.

A standard candle is just what it sounds like. A light source with a known brilliance. A cosmological standard candle is, ideally, a luminous object that can be seen over great distances, is somewhat common, and is, well, standard. In other words each object either has the same brilliance at a given distance, or there exists an algorithm for figuring out it out as a function of mass or size or something else.

For a long time astronomers searched for such an object that would be bright enough close up that it could be seen all the way across the universe. (Which is not all trivial – galaxies aren’t generally that bright…) A couple of decades ago scientists finally realized that a specific sort of super nova (Type Ia) were all created by the same mechanism – the explosion of a white dwarf that has exceeded the Chandrasekhar limit of 1.4 solar masses. (No degenerate object can grow larger than that mass – the electroweak forces can’t sustain the pressures beyond that.) Which means we can calculate exactly how much energy is present in the explosive event. Which means we know how bright it is…

Which means determining distance is merely then a matter of measuring how bright the explosion is when it’s observed from Earth and then using the inverse square law to figure out how far away it is.

Voila! Standard Candle distance! Just what we need! And because the object is a super-nova, it’s so intrinsically brilliant that it can be seen across the Universe.

That’s why this news is a big deal:

“The new brightness-ratio correction appears to hold no matter what the supernova’s age or metallicity (mix of elements), its type of host galaxy, or how much it has been dimmed by intervening dust.

Using classic methods, which are based on a supernova’s color and the shape of its light curve – the time it takes to reach maximum brightness and then fade away – the distance to Type Ia supernovae can be measured with a typical uncertainty of 8 to 10 percent. But obtaining a light curve takes up to two months of high-precision observations. The new method provides better correction with a single night’s full spectrum, which can be scheduled based on a much less precise light curve.”

Read the full article here.

So, we can much more efficiently grab the data, and ultimately get much more accurate numbers out of it.

It was the data from these super-novas that led to the discovery that the Universe’s expansion was, to everyone’s massive surprise, accelerating rather than slowing down. Which we guess is being caused by the mysterious Dark Energy. Which we don’t understand really at all. But which has to be there because of the observations based on these standard candle measurements.

Which is why this could be so important. Maybe we’ll get a few more important clues about the explosive acceleration that goes against everything we thought we knew about gravity. Which means maybe we’ll understand gravity better. Which means we’ll be able to do some new cool things eventually.

Which should lead to new discoveries as exciting as this one.

Which is why science is such a blast!

(Pun sort of intended…)

Author: Nick Knisely

Episcopal bishop, dad, astronomer, erstwhile dancer...