A starburst galaxy, glowing with stars in the process of forming, devours nearby dwarf galaxies in a stunning new image from the twin Gemini North telescopes.
The bright red and pink filaments of gas and dust, as well as the bright white and blue stars seen in the image, make up the galaxy NCG 4449, also known as Caldwell 21, located about 13 million light-years from Earth in the constellation Canes Venatici. NCG 4449 is classified as a Magellanic-type irregular galaxy, reflecting its loose spiral structure and close resemblance to the Milky Way’s satellite dwarf galaxy, the Large Magellanic Cloud (LMC).
Image NCG 4449 was released to celebrate 25 years of Gemini North, which consists of an 8.1 meter optical and infrared telescope located on the dormant Maunakea volcano in Hawaii. The volcano rises about 13,825 feet (4,214 meters) into the dry, stable Pacific air, giving Gemini North a view of space that is mostly unobstructed by Earth’s atmosphere.
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Although the stars in NGC 4449 have been forming for billions of years, the galaxy is currently in the midst of an extreme star birth that astronomers call a “starburst.”
NGC 4449 stands out even for a starburst galaxy. Its star formation is widely distributed throughout the body, rather than concentrated in a central region as seen in most stellar galaxies. This widespread or “global” star birth in NGC 4449 is evidenced by the presence of the galaxy’s youngest stars both in its heart and in the gas and dust streams woven throughout the galaxy.
The global star formation of NGC 4449 means that this galaxy resembles some of the oldest galaxies in the universe, which grew by cannibalizing smaller star systems and taking their contents for themselves.
Like these oldest galaxies, NGC 4449’s extended star formation is likely the result of it eating smaller dwarf galaxies that surround it. This is possible because NGC 4449 is part of the M94 galaxy group, which lies in close proximity to several nearby dwarf galaxies, two of which this very galaxy is currently interacting with in a starburst.
One of these dwarf galaxies is extremely faint and is currently engulfed by NGC 4449. This “invisible merger” is evidenced by a diffuse stream of stars on one side of NGC 4449, but is almost undetectable in visible light due to the diffuse nature and low stellar mass of the cannibalized galaxy.
Astronomers can infer the merger due to the presence of a massive globular cluster, an ancient tightly bound conglomeration of stars embedded in the outer halo of NGC 4449. Astronomers think this globular cluster is what is left of a gas-rich satellite galaxy that is now almost completely engulfed by the NGC 4449.
As NGC 4449 absorbs smaller dwarf galaxy companions, tidal interactions send shock waves through the galaxy’s gas, compressing it. This can be seen as glowing red spots in the image of NGC 4449, indicating the presence of hot ionized hydrogen, a telltale sign of active star birth.
An abundance of hot, young blue star clusters can be seen in the galaxy, growing with the help of gas and dust supplied by the dark filaments woven through NGC 4449. This supply of raw material for star formation will not last forever. At the current rate NGC 4449 is giving birth to stars, the supply of gas that supplies this starburst period will be exhausted in about a billion years.
June 25, 2024, marked exactly 25 years since the dedication ceremony held at Maunakea, Hawaii, to unveil Gemini North, then a new world-class 8.1-meter telescope. That’s when she revealed her first pictures. In the two decades since that day, Gemini North has made significant contributions to our understanding of the universe.
Gemini North’s partner, Gemini South, is located on a mountain in the Chilean Andes called Cerro Pachón in northern Chile. Gemini South also consists of an 8.1 meter optical and infrared telescope, but is three years younger than Gemini North, first opening its eye to space in January 2002.