The Hubble Space Telescope has encountered the appendages of 12 interacting galaxies and revealed them to be adorned with the gleaming jewels of youthful stellar clusters — researchers liken the occurrence to celestial "strands of pearls."
When spiral galaxies engage, whether through direct collision or close proximity, their spiral appendages unfurl. The gravitational influence exerted by a galaxy is immense, so when two galaxies draw near, the gravitational forces generated pull on those spiral appendages, elongating them to form extensive "tails" that can span many tens of thousands of light-years.
As spiral appendages harbor gas and particles, when they are stretched out to create a so-called tidal tail, that gas and particles become agitated. This, in turn, can spark a flurry of star birth. Consequently, tidal tails can evolve into the most concentrated regions of star formation within a galaxy. Presently, astronomers led by Michael Rodruck of Randolph-Macon College in Virginia, U.S. have utilized Hubble imagery of 12 interacting galaxies dispersed across seven distinct interacting systems to discern 425 youthful, yet substantial, star clusters adorning those galaxies' tidal tails. Each cluster comprises approximately a million youthful, azure stars that emit copious amounts of ultraviolet radiation. By referencing archived ultraviolet observations of the galaxies, furnished by NASA's Galaxy Evolution Explorer (a mission that operated from 2003 to 2012) and the Swift mission, Rodruck's team managed to ascertain the galaxies' rates of star formation.
Combined with the observation that these clusters exhibit pronounced emission lines in their spectra, indicative of hydrogen gas being ionized by the deluge of ultraviolet radiation, Rodruck's team could then estimate the age of the clusters. Detrimental feedback from the youthful stars, in the guise of stellar winds and radiation, ultimately disperses the gas from the cluster; for it to still be present, as evidenced by the emission lines, implies that the clusters must all still be under 10 million years old. "It's remarkable to observe numerous youthful entities in the tails," remarked Rodruck in a statement. "It provides substantial insights into the efficiency of cluster formation. Through tidal tails, you can foster new generations of stars that might otherwise not have come into existence."
These tidal-tail clusters possess considerable mass compared to youthful star clusters in our galaxy, resembling more closely the ancient and dense globular clusters discovered in the halo of the Milky Way. Could Hubble be witnessing occurrences akin to the formation of globular clusters in bygone eras, or will these modern youthful clusters eventually disperse?
Cosmology
Galaxy
Modern Physics