Hubble’s 32nd Anniversary Celebration by the Galaxy Group.

NASA and ESA’s Hubble Space Telescope is celebrating its 32nd birthday with a stunning image of an unusual collection of five closely related galaxies dubbed the Hixson Compact Group 40. This photo captures a special moment in their lives when they come together before merging.

This collection includes three spiral galaxies, one elliptical galaxy and one lenticular galaxy. Somehow these different galaxies intersected to form an exceptionally populated and eclectic collection of galaxies.

Caught in a leisurely gravitational dance, the entire group was so tightly packed together that it could fit into a region of space less than twice the diameter of the stellar disk of our Milky Way.

Although such galaxy clusters can be found at the center of huge galaxy clusters, these galaxies are surprisingly isolated in their own small section of the Universe, towards the constellation Hydra.

One possibility is that these galaxies have a lot of dark matter (an invisible and little-known form of matter) associated with them. If they come close to each other, dark matter can form a large cloud within which galaxies orbit. As galaxies pass through dark matter, they experience a frictional force resulting from its gravitational pull. This slows them down and causes the galaxies to lose energy, so they fall together. Therefore, this image captures galaxies at a special moment in their lives. In about a billion years, they will eventually collide and merge, forming one giant elliptical galaxy.

Astronomers have studied this group of compact galaxies not only in visible light, but also in radio, infrared and X-ray wavelengths. Almost all galaxies have a compact radio source at their core, which may indicate the presence of a supermassive black hole. X-ray observations show that the galaxies interacted gravitationally, as evidenced by the presence of large amounts of hot gas between them. Infrared observations provide insight into the rate of new star formation.

Although more than 100 of these compact galaxy groups are cataloged, Hickson Compact Group 40 is one of the densest, according to sky surveys conducted decades ago. Observations suggest that these compact blobs may have been more abundant in the early Universe, and they provided the fuel needed to power black holes known as quasars, whose light from ballooning superheated material is projected through space. Studying the details of galaxies in such close groups helps astronomers determine when and where galaxies formed and what they are made of.

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The Hubble Space Telescope is an international collaboration between ESA and NASA.

As Hubble celebrates its 32nd year of operation, here are some interesting facts about the achievements and impact of the famous observatory:

• Launched on April 24, 1990, the NASA/ESA Hubble Space Telescope has made more than 1.5 million observations of approximately 50,000 celestial objects.

• Astronomers using Hubble data have published more than 19,000 scientific papers, including more than 1,000 in 2021.

• Every three years, about 100,000 references attributed to Hubble accumulate. On average, each article based on Hubble data has about 54 citations.

The observations were carried out as part of the Hubble Observing Program 16848 (PI: K. Britt).

Image credit: NASA, ESA and STScI.

https://esahubble.org/news/heic2205