A starburst galaxy, glowing with stars in the process of forming, is devouring surrounding 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, which is 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 resemblance to the Milky Way’s dwarf satellite galaxy, the Large Magellanic Cloud (LMC).
The image of NCG 4449 was released to celebrate the 25th anniversary of Gemini North, which consists of an 8.1 meter diameter 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, still Pacific air, 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 also stands out as a galaxy with stars. Its star formation is widely distributed throughout its body rather than 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 in its heart and in the streams of gas and dust threaded throughout the galaxy.
The global star formation of NGC 4449 means that this galaxy resembles some of the earliest galaxies in the cosmos, which grew by cannibalizing smaller star systems and taking their contents for themselves.
Like these earliest galaxies, it is likely that the diffuse star of NGC 4449 is the result of the ingestion of smaller surrounding dwarf galaxies. This is possible because NGC 4449 is part of the M94 galaxy cluster, which is located in the vicinity of several nearby dwarf galaxies, two of which this star galaxy is currently interacting with.
One of these dwarf galaxies is extremely faint and is currently being absorbed by NGC 4449. This “secret merger” is evidenced by a diffuse stream of stars to one side of NGC 4449, but is nearly 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 conglomerate of tightly bound stars embedded within the outer halo of NGC 4449. Astronomers think this globular cluster is what remains of a rich satellite galaxy. gas that is now almost completely engulfed by NGC 4449.
As NGC 4449 absorbs smaller dwarf galaxy companions, tidal interactions send shock waves through the galactic gas and compress it. This is seen as bright red spots in the image of NGC 4449, which indicate the presence of hot ionized hydrogen, a telltale sign of active star birth.
An abundance of hot, young blue star clusters can be seen scattered across the galaxy as they grow using gas and dust supplied by dark filaments threaded throughout NGC 4449. This supply of raw material for star formation will not to last forever. At the current rate NGC 4449 is forming stars, the supply of gas 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 in Maunakea, Hawaii, to unveil Gemini North, a new world-class 8.1-meter telescope at the time. This is when it discovered its first light images. In the two decades since that day, Gemini North has made a massive contribution 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 peering into space in January 2002.