This new image from the NASA/ESA Hubble Space Telescope is one of the best images ever seen of Arp 4, a visual pair of galaxies in the constellation Cetus.
This Hubble image shows the Arp 4 galaxy pair. 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 Cetus, the pair was discovered by Dutch-Canadian astronomer Sidney van den Bergh in 1959.
Arp 4 is the fourth object in the Halton Arp 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,” Hubble astronomers explained in a statement.
“Unusual galaxies were selected and photographed to provide examples of strange and unusual shapes to better study how galaxies evolve into these shapes.”
During its mission, Hubble revolutionized the study of galaxies and showed us some fantastically unusual examples from the Arp Atlas.
In this catalog, the first few galaxies, such as Arp 4, are low surface brightness galaxies, a type of galaxy that is unexpectedly faint and difficult to detect.
“The large galaxy here, also cataloged as MCG-02-05-050, with its fragmented arms and dim disk fits this description well,” the astronomers said.
“Its smaller companion, MCG-02-05-050a, is a much brighter and more active spiral.”
“The tricky part 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 and smaller companion MCG-02-05-050a, 675 million light years away, is more than ten times further away!”
“Because of this, MCG-02-05-050a is likely the larger galaxy of the two, while MCG-02-05-050 is comparatively smaller.”
“Their pairing in this image is simply an unlikely visual coincidence,” they noted.
“Despite the lack of physical connection between them, our vantage point on Earth allows us to enjoy the sight of Arpa 4 as an odd couple in the sky.”
