A starburst galaxy, teeming with forming stars, devours surrounding dwarf galaxies in a stunning new image from the twin telescopes Gemini North.
Bright red and pink wisps of gas and dust and 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 an irregular Magellanic-type galaxy, reflecting its loose spiral structure and close similarity to the Milky Way’s satellite dwarf galaxy, the Large Magellanic Cloud (GMC).
The image of NCG 4449 was released to celebrate Gemini North’s 25th anniversary. The image consists of an 8.1 meter diameter optical and infrared telescope located on the dormant Maunakea volcano in Hawaii. The volcano rises about 4,214 meters high in the dry and stable air of the Pacific Ocean, giving Gemini North a view of the cosmos that is largely unobstructed by Earth’s atmosphere.
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Although stars have been forming in NGC 4449 for billions of years, the galaxy is currently in the midst of a period of extreme star birth, which astronomers call a “starburst.”
NGC 4449 even stands out for a starburst galaxy. Star formation is widely distributed over the entire body and not concentrated in a central region, as seen in most starburst galaxies. This widespread, or “global” star birth in NGC 4449 is evidenced by the presence of the galaxy’s youngest stars, both at its heart and in the streams of gas and dust that flow through the galaxy.
NGC 4449’s global star formation means this galaxy is similar to some of the earliest galaxies in the cosmos, which grew by cannibalizing smaller galaxies and taking their contents for themselves.
Like these earliest galaxies, it is likely that NGC 4449’s widespread star formation is due to the devouring of smaller dwarf galaxies around it. This is possible because NGC 4449 is part of the M94 group of galaxies, which lie in close proximity to some surrounding dwarf galaxies, two of which this starburst galaxy is currently interacting with.
One of these dwarf galaxies is extremely faint and is currently being absorbed by NGC 4449. This stealth merger is evident from a diffuse stream of stars on one side of NGC 4449, but is virtually undetectable in visible light due to its diffuse nature and low stellar mass of the galaxy being cannibalized.
Astronomers can infer the merger thanks to the presence of a massive globular cluster, an ancient, closely linked conglomeration of stars embedded in the outer halo of NGC 4449. Astronomers think this globular cluster is the remnant of a gas-rich satellite galaxy that is now nearly gone. completely devoured by NGC 4449.
As NGC 4449 absorbs smaller dwarf galaxy companions, tidal interactions send shock waves through the galaxies’ gas, compressing it. This is 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.
Scattered throughout the Milky Way, an abundance of hot, young blue star clusters can be seen growing with the help of gas and dust supplied by dark filaments running through NGC 4449. This supply of raw materials for star formation will not last forever. At its current rate, NGC is producing 4,449 stars, and the gas supply fueling this starburst period will run out in about a billion years.
June 25, 2024 marked exactly 25 years since a dedication ceremony was held on Maunakea, Hawaii, to unveil Gemini North, then a new world-class 8.1-meter telescope. This is when it revealed its first images. In the twenty years since that day, Gemini North has made enormous 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 optical and infrared telescope with a diameter of 8.1 meters, but is three years younger than Gemini North and first opened its eyes to the cosmos in January 2002.