Hubble Telescope Captures Hybrid Galaxy NGC 2775, Puzzling Astronomers

The Hubble Space Telescope, a collaborative endeavor between NASA and ESA, has delivered stunningly detailed imagery of the galaxy NGC 2775. This celestial object’s unique morphology continues to spark considerable debate among the astronomical community. Also cataloged as Caldwell 48, NGC 2775 resides within the constellation Cancer, situated approximately 67 million light-years away from our planet.

The core mystery surrounding NGC 2775 lies in its distinctly dual nature. Its central region features a smooth, gas-depleted nucleus, a characteristic typically associated with elliptical galaxies. Conversely, the outer regions are encircled by a dusty ring interspersed with scattered clusters of nascent stars, features more commonly seen in spiral systems. The majority of researchers assign NGC 2775 the classification of a flocculent spiral galaxy, denoted as SA(r)ab. This designation implies a spiral structure lacking a central bar but possessing a pronounced ring architecture. Nevertheless, a contingent of astronomers posits that NGC 2775 might belong to the rarer category of lenticular galaxies—a transitional type that blends attributes of both spiral and elliptical forms.

The galaxy’s core, which spans an angular radius of about 0.4 arcminutes, appears dormant and largely devoid of gas. This scarcity severely restricts ongoing star formation within that area. Such a condition could be the consequence of numerous past supernova explosions that effectively ejected gas into the galaxy's periphery. Significant evidence strongly suggests that this peculiar morphology is the result of prior galactic interactions, potentially involving mergers. Supporting this hypothesis is the detection of a faint hydrogen tail extending nearly 100,000 light-years around NGC 2775. This gaseous plume is likely the remnant material from one or more satellite galaxies that were absorbed over cosmic time.

Adding weight to the interaction theory, the nearby irregular galaxy NGC 2777 also exhibits a tidal hydrogen tail pointing toward NGC 2775, suggesting a gravitational connection between the two. NGC 2775 stands as the dominant member of the small NGC 2775 Group, which also encompasses UGC 4781 and NGC 2777. This small group, in turn, is situated within the larger Antlia-Hydra Cluster, itself a component of the vast Virgo Supercluster. Historically, this galaxy was first documented by William Herschel on December 19, 1783.

The latest image captured by Hubble incorporated observations utilizing red light from hydrogen. This addition allowed for a more precise mapping of the active star-forming regions located in the outer ring, which manifest in the new picture as delicate, pale-pink structures. Despite this ongoing star birth in the outer perimeter, the galaxy itself does not currently display signs of a major starburst event. NGC 2775 presents observable dimensions of roughly 4.3 by 3.3 arcminutes and boasts a visual magnitude of 10.4. Furthermore, archival databases confirm the observation of a single supernova event, SN 1993Z (a Type Ia), which was discovered on September 23, 1993.