Against an inky black background, the blue swirls of spiral galaxy NGC 6956 stand out brilliantly. NGC 6956 is a barred spiral galaxy, a common type of spiral galaxy with a barred structure of stars at its center. This galaxy exists 214 million light-years away in the constellation Delphinus.
Scientists used NASA’s Hubble Space Telescope to image NGC 6956 to study its Cepheid variable stars, which are stars that brighten and dim at regular periods. Because the period of Cepheid variable stars is a function of their brightness, scientists can measure how bright these stars appear from Earth and compare that to their actual brightness to calculate their distance. As a result, these stars are extremely useful in determining the distance of cosmic objects, which is one of the most difficult pieces of information to measure for extragalactic objects.
This galaxy also contains a Type Ia supernova, which is the explosion of a white dwarf that gradually added mass from its companion star. Similar to Cepheid variable stars, the brightness of these types of supernovae and the rate at which they dim over time allow scientists to calculate their distance. Scientists can use measurements obtained from Cepheid variable stars and Type Ia supernovae to refine our understanding of the universe’s expansion rate, also known as the Hubble constant.
