The bright star RS Puppis at the center of this image is surrounded by a cocoon of reflective dust. The super star is ten times more massive than the Sun, 200 times larger, and averages over 15,000 times brighter than the Sun. Averages? Yes, it is one of the most luminous Cepheid variable stars, and its brightness varies rhythmically over a six-week period.
The surrounding nebula flickers in brightness as pulses of light from the Cepheid propagate outwards. By tracking the fluctuation of light in RS Puppis itself and recording the faint reflections of light pulses moving across the nebula, astronomers are able to measure these light echoes and compute the distance to the star with about one percent uncertainty. The distance to RS Puppis is just about 6,500 light-years.
This Hubble Space Telescope image resembles a holiday wreath full of sparkling lights. The bright star RS Puppis is at the center of the image and is wrapped in a cocoon of reflective dust lit by the star. RS Puppis is huge, ten times more massive than our sun and 200 times larger. It’s one of the most luminous stars in the class of known as Cepheid variables and brightens and dims over a six-week cycle. Its average intrinsic brightness is 15,000 times greater than our Sun’s.
The surrounding nebula flickers in brightness as pulses of light from the Cepheid move outwards. Hubble has taken a series of photos of light flashes rippling across the nebula in a phenomenon known as a “light echo.” Several can be seen in this picture, most easily the ones moving toward seven o’clock. Even though light travels at around 300,000 km/s, the nebula is so large that reflected light can actually be photographed traversing the nebula. Using these reflections, astronomers are able to measure these light echoes and accurately compute the distance to RS Puppis—6,500 light-years (with a margin of error of only one percent).