“Galactic Onion” warps space-time and distorts light

The new image obtained from the Dark Energy Camera project shows a “galactic onion” – a shell galaxy with several layers that spread out at a distance of 150 thousand light-years. The Galaxy NGC 3923 is about twice the size of the Milky Way, but even larger is the neighboring galaxy cluster, which has such a large mass that it warps spacetime, causing light from distant galaxies behind it to bend like a magnifying glass, in a process called gravitational lensing.

Symmetrical, onion-like layers of the shell galaxy NGC 3923 are shown in this galaxy-rich image. The image of a massive galaxy cluster nearby also demonstrates a phenomenon known as gravitational lensing. Authorship: DESI Legacy Imaging Surveys/LBNL/DOE & KPNO/CTIO/NOIRLab/NSF/AURA

The Dark Energy Camera is a ground-based instrument located on the 4-meter Víctor Blanco Telescope. It was originally built to observe many galaxies as part of a project called “Dark Energy Research”. Now it is also used for other observations, such as the image of dwarf galaxies, merging galaxies, etc.

The main feature of this image is a shell galaxy, which is a type of elliptical galaxy in which the stars are not evenly distributed, but instead organized into shell structures. Spiral galaxies, such as the Milky Way, do not have such an arrangement of stars, but it is believed that about a tenth of elliptical galaxies have a similar arrangement, and such a structure is formed when two galaxies merge and a larger galaxy absorbs a smaller companion.

As NOIRLab explains, two galaxies have merged here. As they merged, the gravitational field of the larger galaxy slowly peeled the stars away from the disk of the smaller galaxy. These stars began to gradually mix with the outer halo of the larger galaxy, forming concentric bands, or shells. A simple analogy is to add a drop of food coloring to a bowl of dough that you slowly stir. The drop is stretched in a spiral that remains visible for a long time before completely mixing.

Another important feature of this image is harder to notice, but it is located in the upper center. A massive cluster of galaxies called PLCK G287.0+32.9 bends space-time and deforms the light coming from distant galaxies, which makes them seem stretched.

Earlier we reported on how the Dark Energy Camera captured the prelude to the merger of galaxies.

According to noirlab.edu

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