Do objects in the Universe moving towards us show a blue shift? © Getty Images

Do objects in the Universe moving towards us show a blue shift?

Whether we observe a blue- or red-shift is all to do with wavelengths of light changing due to the object’s direction of movement.

Asked by: David Kelly, Manchester 

Advertisement

The wavelength of light emitted by an object is changed by its motion relative to an observer. An object moving away from us is ‘redshifted’ – that is, its light is shifted towards the longer wavelengths at the red end of the visible spectrum. But although the Universe is expanding, not all objects are redshifted.  

Some of the nearest stars, such as Barnard’s Star, are moving towards us and hence show a ‘blueshift’ (their light is shifted towards shorter wavelengths). Even some galaxies (for example, the Andromeda Galaxy) are blueshifted. This is because, over relatively short distances, the local gravitational attraction between galaxies can overcome the general expansion of the Universe.  

The highest blueshift yet recorded is actually from a group of stars called a ‘globular cluster’ that’s whizzing towards us at 1,026km/s. But fear not – it is still millions of light-years away!

Read more:


Advertisement

Subscribe to BBC Science Focus Magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun facts.