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).
Image Credit: NASA
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.
NGC 4603 is a spiral galaxy located a bit more than 100 million light years away in the constellation Centaurus. It’s a pure spiral galaxy with relatively loosely wound arms. During 1999, this galaxy was the subject of an extended study using the Hubble Space Telescope to locate Cepheid variable stars. Over 40 were found, and the measurement of their periodicities gave a net distance estimate of 108.7, +5.5,−4.9 million light years. That was consistent with the distance estimate determined through redshift measurements. As of the date of that study, NGC 4603 was the most distant galaxy for which a distance estimate had been made using Cepheid variable.
