Credit: NASA & ESA
Acknowledgement: A. Riess (STScI)
This
NASA/ESA Hubble Space Telescope image shows the spiral galaxy NGC 3021
which lies about 100 million light-years away in the constellation of
Leo Minor (The Little Lion).
Among many other types of stars, this galaxy contains
Cepheid variable stars, which can be used work out the distance to the
galaxy. These stars pulsate at a rate that is closely related to their
intrinsic brightness, so measurements of their rate of pulsation and
their observed brightness give astronomers enough information to
calculate the distance to the galaxy itself.
Cepheids are also used to calibrate an even brighter distance marker,
that can be used over greater distances: Type Ia supernovae. One of
these bright exploding stars was observed in NGC 3021, back in 1995.
In addition, the supernova in NGC 3021 was also used to refine the
measurement of what is known as the Hubble constant. The value of this
constant defines how fast the Universe is expanding and the more
accurately we know it the more we can understand about the evolution of
the Universe in the past as well as in the future. So, there is much
more to this galaxy than just a pretty spiral.
