Stefan Quintet (HCG 92)

Stephan's Quintet (HCG 92) is a unique group of five galaxies that form a compact system in the constellation Cygnus. The group was named after the astronomer Pierre Stephan, who first noticed the group in 1877. Four of these galaxies are so close to each other that they interact gravitationally, which affects their structure and evolution.

Structure and Evolution

The group's components include five galaxies that are located at a relatively small spatial distance. Four of them, bound by gravity, will merge into a single larger galaxy within a few million years. The fifth galaxy, visible in the image, is only visually close to the group, but is actually 39 million light-years away from Earth, significantly closer than the other four galaxies, which are between 260 and 340 million light-years away.

Interactions and Effects

The Stephan's Quintet group is of interest to astronomers because it is the best-studied compact galaxy group. One of its features is the brightness of the galaxy NGC 7320, which is the brightest in the group and is notable for its active star-forming regions called H II regions (red regions in the image).

X-ray and infrared studies

X-ray observations using the Chandra telescope have shown that when the galaxy NGC 7318B collides with the gas between the galaxies, a shock wave is created that heats the gas to temperatures of millions of degrees, causing it to emit X-rays. This shock wave propagates through intergalactic space, creating giant changes in the gas clouds surrounding the galaxies.

Infrared observations with the Spitzer Space Telescope have revealed powerful emission from molecular hydrogen produced by collisions between galaxies. This emission is among the most powerful ever observed from such molecular hydrogen formations, and is found at the center of the shock wave region.

Radio Emissions and Light Emissions

Radio observations in the early 1970s detected an elongated region of emission between the galaxies in the group. This same region was also detected as a faint glow of ionized atoms in the visible spectrum, forming a green arc.

Additional Data

The redshifts of the galaxies in the group vary: NGC 7320 has a low redshift (790 km/s), while the other four galaxies have significantly higher values ​​(around 6600 km/s). This suggests that NGC 7320 is actually a foreground galaxy located at a distance of about 39 million light years, compared to the other four galaxies, which are located between 210 and 340 million light years.

Space Telescope Observations

Stephan's Quintet was chosen as one of the targets for observation by the James Webb Space Telescope, confirming its importance for studying galactic evolution and interactions.

Conclusion

Stephan's Quintet (HCG 92) is an important target for studying galaxy interactions. Its study helps scientists better understand the processes of galaxy mergers and evolution, and also allows them to study the dynamics of intergalactic gas, star formation, and the occurrence of shock waves in such complexes.