Measuring the distance to truly remote objects like galaxies, quasars and galaxy clusters is a crucial task in astrophysics, particularly
when it comes to studying the early Universe, but it’s a difficult one.
Only in the case of a few nearby objects like the Sun, planets
and some nearby stars can we measure their distances directly. Beyond
that, various indirect methods need to be used; one of the most
important is by examining Type Ia supernovae, and this is where the
NASA/ESA Hubble Space Telescope comes in.
NGC 3810, the galaxy featured in this image, was the host of a Type Ia supernova
in 2022. In early 2023 Hubble focused on this and a number of other
galaxies to closely examine recent Type Ia supernovae. This kind of
supernova results from a white dwarf
exploding, and they all have a very consistent brightness. That allows
them to be used to measure distances: we know how bright a Type Ia
supernova should be, so we can tell how far away it must be from how dim
it appears. One uncertainty in this method is that intergalactic dust
in between Earth and a supernova blocks some of its light. How do you
know how much of the reduction in light is caused by distance, and how
much by dust? With the help of Hubble, there’s a clever workaround: take
images of the same Type Ia supernovae in ultraviolet light, which is
almost completely blocked by dust, and in infrared light, which passes
through dust almost unaffected. By carefully noting how much light comes
through at each wavelength, the relationship between supernova
brightness and distance can be calibrated to account for dust. Hubble
can observe both these wavelengths of light in great detail with the
same instrument. That makes it the perfect tool for this experiment, and
indeed, some of the data used to make this beautiful image of NGC 3810
were focused on its 2022 supernova. You can see it as a point of light
just below the galactic nucleus, or in the annotated image here.
There are many ways to measure cosmic distances; because Type Ia
supernovae are so bright, they are one of the most useful and accurate
tools, when they’re spotted. Many other methods must be used as well,
either as an independent check against other distance measurements or to
measure at much closer or farther distances. One such method that also
works for galaxies is comparing their rotation speed to their
brightness; based on that method, NGC 3810 is found to be 50 million
light-years from Earth.
