New standard candle, new astronomy


Any student who has ever taken an Astronomy course should remember how important standard candles are to Astronomy. We can only directly measure the distance to a star if it’s within a few 10’s of lightyears from us. Further out than that and geometric calculations (parallax) stop being measurable.

So we use standard candles – which are objects where we know how intrinsically bright they are. Using simple geometry, if we know how bright something is in an absolute way, we can calculate how bright it will appear at any distance.

When we find a standard candle that’s really really bright, like a Cephid variable star, or a class of supernovas, we can use that to plot a map of the Universe. Cephids proved that we live in a galaxy surrounded by other much more distant galaxies. It was Hubble’s (the original, not the telescope’s) greatest contribution to Cosmology. Using Supernovas we discovered that the Universe is accelerating in its expansion.

Darach Watson at the Dark Cosmology Centre of the University of Copenhagen in Denmark, et al, have figured out a way to measure the brightness of the core of a galaxy in such a way that we can use it as a standard candle.

“[…] Watson and co have used this technique to measure the distance to 38 active galactic nuclei at distances of up to z=4. That’s significantly further than is possible with type 1a supernova, whose distance cannot be accurately measured beyond z=1.7.”

More here.

Their measurements line up well with existing measurements, meaning this is a good tool.

And it’s an awesome tool because this has the potential of extending our distance measurements all the way back to about 750 million years after the Big Bang.

Galaxies, supermassive blackholes, dark energy have all been discovered using standard candles as a fundamental tool. Let’s see what’s next shall we?

The Author

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