The twin galaxies NGC 4496A and NGC 4496B dominate the frame in this image. The image has been captured by NASA/ESA Hubble Space Telescope. Both galaxies lie in the constellation Virgo. But despite appearing side-by-side in this image, they are at vastly different distances from both Earth and one another. NGC 4496A is 47 million light-years from Earth. NGC 4496B is 212 million light-years away from Earth. The enormous distances between the two galaxies mean that the two are not interacting. They only appear to overlap because of a chance alignment.
Chance galactic alignments like this provide astronomers with the opportunity to delve into the distribution of dust in these galaxies. Galactic dust which is the dark tendrils threading through both NGC 4496A and NGC 4496B, adds to the beauty of astronomical images. Though it also complicates astronomers’ observations.
Dust in the universe tends to scatter and absorb blue light. It makes stars seem dimmer and redder in a process called “reddening.” Reddening due to dust is different from redshift. It is due to the expansion of space itself. Scientists carefully measured how dust in the foreground galaxy affects starlight from the background galaxy. They were able to map the dust in the foreground galaxy’s spiral arms.
The resulting “dust maps” will help astronomers calibrate measurements of everything from cosmological distances to the types of stars populating these galaxies.