Hubble Captures Puzzling Galaxy
The latest image captured by the NASA/ESA Hubble Space Telescope showcases the intriguing galaxy NGC 2775, located 67 million light-years away in the constellation Cancer. This galaxy presents a perplexing classification challenge due to its unique features. At first glance, NGC 2775 appears to embody characteristics of both elliptical and spiral galaxies: its smooth, featureless center, resembling that of an elliptical galaxy, contrasts sharply with its outer dusty ring, which is dotted with star clusters akin to those found in spiral galaxies. This duality raises the question among astronomers: is NGC 2775 a spiral, an elliptical, or perhaps something entirely different?
To complicate matters further, astronomers are divided in their classifications of NGC 2775. Some lean towards categorizing it as a spiral galaxy, primarily due to its feathery ring of stars and dust, while others propose it fits the definition of a lenticular galaxy—a hybrid with traits of both spirals and ellipticals. The formation of lenticular galaxies remains an area of active research, with theories suggesting they may evolve from spirals that have merged with other galaxies or depleted their star-forming gas, leading to a loss of their defining spiral arms. Alternatively, they might originate from elliptical galaxies that have acquired gas, forming a disk. Evidence supporting NGC 2775’s complex history includes a tail of hydrogen gas extending nearly 100,000 light-years from the galaxy, suggesting it may have previously absorbed remnants of other galaxies.
Recent observations have further illuminated NGC 2775’s characteristics. A new Hubble image enhances previous findings by capturing specific wavelengths of red light emitted by clouds of hydrogen gas surrounding massive young stars, which appear as bright pinkish clumps in the image. This additional data helps astronomers pinpoint regions of ongoing star formation within the galaxy, providing deeper insights into its structure and evolution. While most astronomers currently classify NGC 2775 as a flocculent spiral galaxy—characterized by poorly defined, feathery arms—the ongoing research and debate surrounding its classification reflect the complexities of galaxy formation and evolution in our universe. As we continue to explore these celestial wonders, NGC 2775 serves as a fascinating case study in the diverse tapestry of galactic structures.
This NASA/ESA Hubble Space Telescope image features a galaxy, NGC 2775, that’s hard to categorize.
ESA/Hubble & NASA, F. Belfiore, J. Lee and the PHANGS-HST Team
This NASA/ESA
Hubble Space Telescope
image features a galaxy that’s hard to categorize. The galaxy in question is NGC 2775, which lies 67 million light-years away in the constellation Cancer (the Crab). NGC 2775 sports a smooth, featureless center that is devoid of gas, resembling an elliptical galaxy. It also has a dusty ring with patchy star clusters, like a spiral galaxy. Which is it: spiral or elliptical — or neither?
Because we can only view NGC 2775 from one angle, it’s difficult to say for sure. Some researchers classify NGC 2775 as a spiral galaxy because of its feathery ring of stars and dust, while others classify it as a lenticular galaxy. Lenticular galaxies have features common to both spiral and elliptical galaxies.
Astronomers aren’t certain of exactly how lenticular galaxies come to be, and they might form in a variety of ways. Lenticular galaxies might be spiral galaxies that merged with other galaxies, or that have mostly run out of star-forming gas and lost their prominent spiral arms. They also might have started out more like elliptical galaxies, then collected gas into a disk around them.
Some evidence suggests that NGC 2775 merged with other galaxies in the past. Invisible in this Hubble image, NGC 2775 has a tail of hydrogen gas that stretches almost 100,000 light-years around the galaxy. This faint tail could be the remnant of one or more galaxies that wandered too close to NGC 2775 before being stretched apart and absorbed. If NGC 2775 merged with other galaxies in the past, it could explain the galaxy’s strange appearance today.
Most astronomers classify NGC 2775 as a flocculent spiral galaxy. Flocculent spirals have poorly defined, discontinuous arms that are often described as “feathery” or as “tufts” of stars that loosely form spiral arms.
Hubble previously released an image of NGC 2775 in
2020
. This new version adds observations of a specific wavelength of red light emitted by clouds of hydrogen gas surrounding massive young stars, visible as bright, pinkish clumps in the image. This additional wavelength of light helps astronomers better define where new stars are forming in the galaxy.
