The Hubble Space Telescope will mark its 32nd year in space on Sunday, April 24th, and the image that it snapped to commemorate its anniversary week is absolutely breathtaking.
Hubble captured a mesmerizing 'dance' between five distant galaxies in Hickson Compact Group (HCG) 40, a small galaxy cluster located in the Hydra constellation roughly 300 million light-years away. The quintet, composed of three spiral galaxies, one irregular galaxy, and one lenticular galaxy, are careening toward each other due to their collective gravity.
HCG 40's cosmic residents are crammed into a volume less than twice as wide as the Milky Way's spiral disk, which spans 100,000 light-years from end to end.
"Though such cozy galaxy groupings can be found in the heart of huge galaxy clusters, these galaxies are notably isolated in their own small patch of the Universe, The National Aeronautics and Space Administration said.
NASA said that HCG 40 is "one of the most densely packed" galactic clusters of its kind ever observed in modern astronomy.
That unique feature of HCG 40 made Hubble's revelation even more extraordinary.
"I remember seeing this on a sky survey and saying, 'wow look at that!'" said Paul Hickson of the University of British Columbia, Vancouver, Canada. "All that I was using at the time was a big plastic ruler and a magnifying glass while looking over sky survey prints."
NASA believes that the objects – each of which contains hundreds of billions of stars – will collide in about a billion years.
"Astronomers have studied this compact galaxy group not only in visible light, but also in radio, infrared, and X-ray wavelengths. Almost all of them have a compact radio source in their cores, which could be evidence for the presence of supermassive black holes," NASA said. "X-ray observations show that the galaxies have been gravitationally interacting due to the presence of a lot of hot gas among the galaxies. Infrared observations reveal clues to the rate of new star formation."
But researchers are unsure just how HCG 40's arrangement came into being in the first place.
An acutely high concentration of dark matter – the composition of which is one of the biggest unsolved mysteries in science – may play a role in HCG 40's unusual compactness.
"One possible explanation is that there's a lot of dark matter — an unknown and invisible form of matter — associated with these galaxies," Hubble officials wrote. "If they come close together, then the dark matter can form a big cloud within which the galaxies are orbiting. As the galaxies plow through the dark matter, they feel a resistive force due to its gravitational effects. This slows their motion and makes the galaxies lose energy, so they fall together."
Scientists maintain that studying ancient galaxies and how they behave will help foster a better understanding of how they formed and evolve.
"Studying nearby groups like HCG 40 helps astronomers learn about how galaxies formed," the Hubble team said. "Tight groups like this," Hubble officials added of HGC 40, "may have been more common in the early universe when their superheated, infalling material may have fueled very energetic black holes called quasars."
The discovery, which was announced on Twitter, is part of Hubble's SpaceSparks series.
"Each year, Hubble dedicates a small portion of its observing time to taking a special anniversary image," the Hubble team tweeted. "Watch this new episode of SpaceSparks to find out the story behind this year’s stunning look at an unusual close-knit collection of five galaxies."
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