NGC 2623
A late-stage galaxy merger with bright tidal tails and intense star formation.
NGC 2623, also cataloged as ARP 243, is an interacting galaxy roughly 263 million light-years from Earth in the constellation Cancer. French astronomer Édouard Jean-Marie Stephan first spotted it on January 19, 1885. Its bizarre, twisted shape comes from a violent collision and ongoing merger between two galaxies, putting it in a late stage of that process.
The crash compressed gas clouds, sparking intense star formation. This activity shows up as bright blue speckles clustered in the galaxy’s center and along two sweeping tidal tails, which stretch about 50,000 light-years from end to end. At least 170 bright star clusters have been identified within NGC 2623, many of them young and hot. The galaxy’s core is packed with newborn stars, but it does not host an active galactic nucleus.
One supernova has been recorded here: SN 1999gd, a Type Ia event reaching magnitude 17.8, discovered on November 24, 1999.
The galaxy’s infrared luminosity is 3.3×10¹¹ times that of the Sun, and its distance modulus is 34.50. Despite its bright core, NGC 2623 is classified as a Seyfert galaxy—a type that makes up only about 2 percent of spiral galaxies. Seyfert galaxies have very bright nuclei and properties similar to quasars, both containing active supermassive black holes that emit high levels of energy, though they give off relatively little visible light.
Star formation is concentrated mostly in the nucleus, which accounts for over 99 percent of it. Still, the tidal tails also host many young stars and bright clusters. The lower tail is especially rich, with 100 star clusters found there. These may have formed from a loop of stretched material linked to the northern tail, or from debris falling back toward the nucleus. Both tails contain very young stars in early evolutionary stages.
The tidal tails—long strips of bright star clusters—are strong signs of a galactic merger. They formed as the two original galaxies pulled gas and stars from each other, eventually merging their centers into one nucleus. Similar tails appear in other merging systems, like the Antennae Galaxies, and help astronomers study how galaxies evolve. It’s thought that the Milky Way will look something like NGC 2623 when it collides with the Andromeda Galaxy in about four billion years.
Quick Facts
- Epoch
- J2000
- Constellation Name
- Cancer
- Ra
- 08 · 38 · 24.10
- Dec
- +25 · 45 · 01.00
- Z
- 0.01847
- Dist Ly
- 263 Mly (80.91 Mpc)
- Appmag V
- 13.36
- Notes
- Late stage of collision/merging
- Names
- NGC 2623, PGC 24288, MCG+04-21-009, UGC 4509, Arp 243
Facts from the source article.
Lore & Background
NGC 2623 gained its shape from a violent collision and merger of two galaxies, which compressed and stirred up gas clouds, triggering a sharp spike of star formation. This active star formation is marked by speckled patches of bright blue clustered both in the center and along the galaxy's sweeping tidal tails, which extend roughly 50,000 light-years from end to end. Many young, hot, newborn stars form in bright stellar clusters, with at least 170 such clusters known to exist within the galaxy.
The prominent lower tail is richly populated with bright star clusters—100 have been found in these observations. These clusters may have formed as part of a loop of stretched material associated with the northern tail, or from debris falling back onto the nucleus. Both galactic arms harbor very young stars in the early stages of their evolutionary journey. The nucleus is filled with many young stars, and despite the many clusters in the tails, the center still accounts for more than 99 percent of the star formation occurring.
NGC 2623 does not have an active galactic nucleus. It is thought that the Milky Way will eventually resemble NGC 2623 when it collides with the Andromeda Galaxy in four billion years time.
Reader's Guide
NGC 2623 serves as a key example of a late-stage galaxy merger, offering astronomers a nearby laboratory to study the processes that shape massive galaxies. Its tidal tails—long strips of bright star clusters—are strong indicators that a merger has taken place, and similar structures are seen in other merging systems like the Antennae galaxy. The galaxy's high infrared luminosity, 3.3×10^11 L☉, is comparable to that of Seyfert galaxies, though NGC 2623 lacks an active nucleus. The intense star formation, concentrated in the nucleus and along the tails, demonstrates how gravitational interactions can compress gas and trigger bursts of stellar birth. The presence of at least 170 star clusters, many in the tails, provides insight into how star formation proceeds in extreme environments. Observations from space telescopes such as HST and GALEX have revealed recent star formation within the galaxy. NGC 2623 also helps predict the future of the Milky Way, as it is thought to resemble what our own galaxy will look like after its collision with the Andromeda Galaxy in four billion years.
Did You Know?
- NGC 2623 was discovered on 19 January 1885 by French astronomer Édouard Jean-Marie Stephan.
- One supernova, SN 1999gd (Type Ia, mag. 17.8), was observed in NGC 2623 on 24 November 1999.
- At least 170 star clusters are known to exist within NGC 2623.
More in NGC Objects, Part 4 1-24
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