Spiral Spectacle: Hubble Explores a Cosmic Marvel in the Virgo Cluster

The Hubble Telescope imaged NGC 4731, a vibrant barred spiral galaxy 43 million light-years away, to understand its complex structures and their role in galaxy dynamics and star formation. Credit: ESA/Hubble & NASA, D. Thilker

NGC 4731, a barred spiral galaxy in the Virgo cluster, is this week’s Hubble Picture of the Week. Featuring detailed colors and structures, the galaxy’s study may help explain how its bar and spiral arms influence star formation and matter dynamics.

This Hubble Space Telescope image features the broad and sweeping spiral galaxy NGC 4731. This galaxy lies among the galaxies of the Virgo cluster, in the constellation Virgo, and is located 43 million light-years from Earth.

This highly detailed image was generated by using six different filters. The abundance of color illustrates the galaxy’s billowing clouds of gas, dark dust bands, bright pink star-forming regions and, most obviously, the long, glowing bar with trailing arms.

Characteristics of Barred Spiral Galaxies

Barred spiral galaxies outnumber both regular spirals and elliptical galaxies put together, numbering around 60% of all galaxies. The visible bar structure is a result of orbits of stars and gas in the galaxy lining up, forming a dense region that individual stars move in and out of over time.

This is the same process that maintains a galaxy’s spiral arms, but it is somewhat more mysterious for bars: spiral galaxies seem to form bars in their centers as they mature, accounting for the large number of bars we see today, but can also lose them later on as the accumulated mass along the bar grows unstable.

The orbital patterns and the gravitational interactions within a galaxy that sustain the bar also transport matter and energy into it, fueling star formation. Indeed, the observing program studying NGC 4731 seeks to investigate this flow of matter in galaxies.

Interaction and Structure of NGC 4731

Beyond the bar, the spiral arms of NGC 4731 stretch out far past the confines of this close-in Hubble view. The galaxy’s elongated arms are thought to result from gravitational interactions with other, nearby galaxies in the Virgo cluster.