The star RS Puppis was observed during a period of five weeks by the Hubble Space Telescope. It’s a Cepheid variable star about 6,500 light years from Earth. Because of its variability, its brightness continuously increases and decreases and these pulsations created a phenomenon known as light echo. In essence, the light emitted by the star seems to reverberate through the nebula that surrounds it, a phenomenon admired by astronomers thanks to Hubble.
RS Puppis is a yellow supergiant of spectral class F8Iab with a mass about ten times that of the Sun. It’s a star that is nearing the end of its life when mutations begin to take place. The progressive depletion of hydrogen prevents it from continuing to have a constant brightness because it starts expanding and contracting. It’s a phase that doesn’t last long so astronomers got very interested in RS Puppis.
A peculiarity of RS Puppis is that it’s be surrounded by a nebula. The observation made with the Hubble Space Telescope allowed to admire its light eco during its pulse cycle. When the star expands and becomes brighter, we can see part of the light after it’s been reflected by shell of gas that surround it increasingly distant. This creates the illusion of the gas that moves outwards and the reflected light must travel for a longer distance and time to reach the Earth.
This light echo, an effect analogous to the sound echo, gives a great show but observing RS Puppis is also very useful from the scientific point of view. The pulsation period of a Cepheid variable stars is directly connected to their intrinsic brightness, a property that allows astronomers to use them as cosmic markers.
The light echo made it possible to measure the distance to RS Puppis with the highest accuracy achieved so far for a Cepheid. The study of stars such as RS Puppis is one of those that provides us with great images and at the same time important scientific measurements to understand the scale of the universe.