Practically perfect in every way: Hubble shows galaxy with amazing symmetry

hubble spiral galaxy symmetry a beautiful whorl
This Hubble Picture of the Week shows spiral galaxy NGC 2985 in the constellation of Ursa Major (The Great Bear). ESA/Hubble & NASA, L. Ho

This week’s Hubble image shows the spiral galaxy NGC 2985, located over 70 million light-years away in the constellation of Ursa Major (The Great Bear). It is an archetypal spiral galaxy, like our Milky Way, meaning it has arms of stars reaching out from its center. The galaxy is about 95,000 light-years across with a supermassive black hole at its center that is 160 million times the mass of our Sun.

Hubble scientists describe NGC 2985 as having “near-perfect symmetry,” showing tightly wound spiral arms which converge in the center of the galaxy as its brightest point. As the spiral arms reach out into space, they gradually fade and dissipate.

The outer spiral arm is so large that it encircles the galaxy, forming a “pseudo ring” around it. The outer part of the galaxy is relatively stable, unlike the center where collisions are common and instability is high. It is theorized that the instability of the center portion is due to the presence of molecular clouds, also known as stellar nurseries. These regions are opaque clouds with a higher density of hydrogen and other gases and dust. This dust forms into clumps, which are the very first stages of star formation.

The molecular clouds are more dense than the interstellar medium in which they float, and within the clouds the dust blocks out light. So the interior of the clouds are very cold and dark. This means that deep within the cloud, instabilities can occur because of the low temperature and density. Scientist are still trying to understand how these conditions lead to the formation of unusual particles like hydroisocyanic acid (HNC), which normally converts to the more stable hydrocyanic acid (HCN).

This color image was created by combining a number of different images taken in different spectrums. Hubble’s Advanced Camera for Surveys (ACS) took a number of separate exposures showing wavelengths in the visible and near-infrared portions of the spectrum. The colors were determined by assigning different hues to the monochromatic images, with individual filters applied. The bright blue dots in the image represent regions of busy activity and star formation.

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