Washington, D.C. – 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 to complete.
We can only measure the distances to a few nearby objects like the Sun, planets, and some nearby stars directly. Beyond that, astronomers need to use various indirect methods; one of the most important examines Type Ia supernovae, and this is where the NASA/ESA Hubble Space Telescope excels.
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. Type Ia supernovae are the result of a white dwarf exploding, and their peak brightness is very consistent.
This attribute allows astronomers to use Type Ia supernovae to measure distances: we know how bright a Type Ia supernova should be, so we can tell how far away it must be by how dim it appears. One snag with this method is intergalactic dust.
Because intergalactic dust blocks some of the supernova’s light, astronomers need to determine how much light the dust reduces to measure the supernova’s brightness and calculate its distance accurately. Hubble’s unique capabilities offer them a clever way of doing this.
Astronomers use Hubble to take images of the same Type Ia supernovae in ultraviolet light, which the dust almost completely blocks out, and in infrared light, which passes through dust nearly unaffected. By carefully noting how much light comes through at each wavelength, astronomers can determine how much dust lies between Hubble and the supernova, letting them confidently calibrate the relationship between a supernova’s brightness and its distance.
Hubble’s unique capability to observe in ultraviolet and infrared wavelengths of light in great detail with the same instrument makes it the perfect tool for these types of observations. Indeed, some of the data used to make this beautiful image of NGC 3810 focused on its 2022 supernova. You can see it as a point of light just below the galactic nucleus in the annotated image below.
There are many ways to measure cosmic distances, but Type Ia supernovae are one of the most useful and accurate tools because they are so bright. Astronomers must use other methods 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 about 50 million light-years from Earth.
