Dating not so close to the galactic kind

Hubble Space Telescope image showing the galaxies NGC 4496A and NGC 4496B. Credit: ESA/Hubble & NASA, T. Boeker, B. Holwerda, Dark Energy Survey, DOE, FNAL/DECam, CTIO/NOIRLab/NSF/AURA, SDSS, Acknowledgment: R. Colombari

The twin galaxies NGC 4496A and NGC 4496B dominate the frame of this image of the " data-gt-translate-attributes="[{" attribute="">Nasa/ESA The Hubble Space Telescope. Both galaxies are in the constellation Virgo, but although they appear side by side in this image, they are at very different distances from Earth and from each other. NGC 4496A is 47 million light years from Earth while NGC 4496B is 212 million light years away. The huge distances between the two galaxies mean that the two cannot interact, and they only seem to overlap due to a fortuitous alignment.

Random galactic alignments like this offer astronomers the opportunity to delve into the distribution of dust in these galaxies. Galactic dust adds to the beauty of astronomical images – it can be seen in this image as dark tendrils traversing both NGC 4496A and NGC 4496B – but it also complicates observations for astronomers. The dust absorbs starlight, making the stars dimmer and shifting their light to longer wavelengths, a process astronomers call “blushing” (not the same as redshift). By carefully measuring how starlight from background galaxies is affected by dust in intervening galaxies, astronomers can determine where the dust is in the spiral arms of the foreground galaxy. The resulting “dust maps” help astronomers calibrate measurements of everything from cosmological distances to the types of stars populating galaxies.

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