🔭 This cosmic image, taken by Hubble, is an illusion

Arp 4 is a galactic duo immortalized by the Hubble Space Telescope. In the image, a small bright spiral appears to be orbiting around a larger, darker companion. However, this apparent proximity is simply the result of an optical effect.

This pair gets its name from the Atlas of Peculiar Galaxies, a catalogue compiled by astronomer Halton Arp in the 1960s. This collection groups galaxies with unusual shapes, selected for their strange structures to help scientists trace galactic evolution. Arp 4 is classified among low surface brightness galaxies, objects that emit little light and are often difficult to observe.


The most imposing galaxy in the image, named MCG-02-05-050, illustrates this category well. Its spiral arms appear fragmented and its disk appears diffuse, explaining its low luminosity despite its significant size. Conversely, its neighbor, MCG-02-05-050a, stands out for its compactness, brightness, and sustained star formation activity, giving it a much more dynamic appearance.

The measured distances between these two galaxies remove all ambiguity. MCG-02-05-050 is located about 65 million light-years from Earth, while MCG-02-05-050a is nearly 675 million light-years away, more than ten times farther. This considerable gap confirms that their alignment in our line of sight is purely coincidental, with no real interaction between them.

These detailed observations are made possible by powerful instruments like the Hubble Space Telescope. They highlight how perspective can create spectacular but deceptive images, reminding us of the usefulness of precise methods for establishing distances in the cosmos.