Sometimes NASA Hubble puts out an image release about an image that has already been out for a while but may not have gotten the attention its science deserved.

On September 30, NASA directed our attention at a lonely spiral galaxy cataloged as UGC 9391. Most recently released in December 2021, this system has been under regular surveillance by the Hubble Space Telescope since 2003 when supernova 2003du was spotted in its disk.

Located just 130 million light-years away, this system is one of the few where researchers have been able to observe both a type 1a supernova and the presence of cepheid variable stars. This convergence of objects allows researchers to work on calibrating these two different ways of measuring distance. 

We’ve known for around a century that cepheid variable stars vary in direct relation to their luminosity. This means that if we look at how bright a Cepheid appears on average, and we measure how fast it changes in brightness, we can calculate its distance. These distances have been calibrated using parallax measurements to the nearest cepheids in our galaxy. Type 1a supernovae also vary, admittedly just once in a known way, and also have a consistent luminosity. No type 1a supernovae have been found in our galaxy, so we have to use cepheids in other galaxies to calibrate type 1a distances.

And UGC 9391 is one of those few galaxies.

And here it is shining without any apparent nearby companions, allowing us to calibrate our measurements to galaxies that only contain supernovae.

More Information

NASA image release