This week’s image from the Hubble Space Telescope shows an odd couple: One large spiral galaxy and its diminutive companion.
This pair of interacting galaxies is known collectively as Arp 86. The larger spiral galaxy is NCG 7753, and the smaller galaxy seen in the bottom left is NGC 7752. They are close enough together that the smaller NGC 7752 seems to be almost touching one of the spiral arms of NCG 7753 — which is why they are given one shared name, in which “Arp” stands for the Atlas of Peculiar Galaxies, a list of unusual galaxies compiled by astronomer Halton Arp in 1966.
This list of unusual galaxies includes spiral galaxies with three arms, or with just one, or with one arm heavier than the others, as well as strangely shaped amorphous galaxies, or double or multiple interacting galaxies. The full catalog is available on Caltech’s website, but for a more easily readable version of the list with example images of the different types of galaxies, you can peruse the list on Wikipedia.
As for Arp 86, as well as being peculiar, it could help astronomers to understand how stars form in cold gas environments.
“Hubble observed Arp 86 as part of a larger effort to understand the connections between young stars and the clouds of cold gas in which they form,” Hubble scientists write. “Hubble gazed into star clusters and clouds of gas and dust in a variety of environments dotted throughout nearby galaxies. Combined with measurements from ALMA [the Atacama Large Millimeter/submillimeter Array], a gigantic radio telescope perched high in the Chilean Andes, these Hubble observations provide a treasure trove of data for astronomers working to understand how stars are born.”
The Hubble scientists also write that their observations of Arp 86 will be built on by future research by the upcoming James Webb Space Telescope. Webb, which will be the world’s most powerful space telescope, will study a wide variety of subjects in its first year including looking for exoplanet atmospheres and looking back in time to study the earliest galaxies. Relevant to Arp 86 is its study of star formation, which will look at how stars are born in dusty regions of galaxies like Arp 86.
