Q&A WITH A GALAXY EVOLUTION EXPERT

Fresh evidence shows supernovae aren't the trusty yardsticks we thought, putting the standard model of an accelerating, expanding Universe in doubt

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How do astronomers currently think the Universe is expanding?

Astronomers have long believed the Universe is expanding at an accelerating rate, driven by what we call ‘dark energy’. This led to a model known as Lambda cold dark matter (ACDM), in which the density of dark energy doesn't vary with time. Then, 27 years ago, a group of scientists observed distant supernovae – specifically Type Ia supernovae – and found they were dimmer than expected. This fitted the predictions of ACDM very well, which is how we got the model of the Universe we have today.

What did your team discover instead?

Type Ia supernovae were used to test ACDM because they were thought to explode with an almost identical intrinsic brightness, making them good reference objects. Instead, we found that the brightness of Type Ia supernovae is strongly affected by the age of the stars they come from.