This new image from the NASA/ESA Hubble Space Telescope is one of the best ever views of Arp 4, a visual pair of galaxies in the constellation of Cetus.
This Hubble image shows the galaxy pair Arp 4. Image credit: NASA / ESA / Hubble / J. Dalcanton, Dark Energy Survey / DOE / FNAL / DECam / CTIO / NOIRLab / NSF / AURA.
Arp 4 consists of the small, bright spiral galaxy MCG-02-05-050a and the much larger spiral galaxy MCG-02-05-050.
Located in the constellation of Cetus, the pair was discovered by the Dutch-Canadian astronomer Sidney van den Bergh in 1959.
Arp 4 is the fourth object in Halton Arp’s Atlas of Peculiar Galaxies, and one of six Arp objects in the ‘low surface brightness galaxies’ section.
“The designation Arp 4 comes from the Atlas of Peculiar Galaxies, compiled in the 1960s by astronomer Halton Arp,” the Hubble astronomers explained in a statement.
“‘Unusual galaxies’ were selected and photographed to provide examples of weird and non-standard shapes, the better to study how galaxies evolve into these forms.”
Throughout its mission, Hubble has revolutionized the study of galaxies and shown us some fantastically unusual examples from Arp’s Atlas.
In this catalogue, the first few galaxies like Arp 4 are low surface brightness galaxies, a type of galaxy that is unexpectedly faint and hard to detect.
“The large galaxy here — also catalogued as MCG-02-05-050 — fits this description well, with its fragmentary arms and dim disk,” the astronomers said.
“Its smaller companion, MCG-02-05-050a, is a much more bright and active spiral.”
“The trick is that these galaxies are not actually very close,” they said.
“The large blue galaxy MCG-02-05-050 is located 65 million light-years from Earth.”
“Its brighter smaller companion MCG-02-05-050a, at 675 million light-years away, is over ten times the distance!”
“Owing to this, MCG-02-05-050a is likely the larger galaxy of the two, and MCG-02-05-050 comparatively small.”
“Their pairing in this image is simply an unlikely visual coincidence,” they noted.
“Despite this lack of a physical relation between them, our point of view on Earth allows us to enjoy the sight of Arp 4 as an odd couple in the sky.”
