The Massive Tidal Forces of Galaxy NGC 4013

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This gorgeous,  oddly shaped galaxy is nearly 50 million light-years away in the constellation Ursa Major, Seen edge-on, this spiral galaxy is known for its flattened disk and central bulge of stars, cut by silhouetted dust lanes.

A recent deep color image of NGC 4013 below revealed a looping tidal stream of stars extending over 80 thousand light-years from the galactic core. This structure is thought to be the remnants of a smaller galaxy that was torn apart by tidal forces as it collided with NGC 4013. Supernova SN 1989Z was discovered on December 30, 1989 at apparent magnitude 12.


The discovery of a giant, low surface-brightness loop-like stellar structure around the galaxy  was independently confirmed in three separate datasets from three different telescopes.The significantly redder colour of the stream material compared to the outer parts of the disk of NGC4013 suggests that this loop did not originate from the disk itself, but rather is the tidal stream of a dwarf galaxy being destroyed in NGC4013's gravitational potential.

Although its true three-dimensional geometry is unknown, the projected tidal loop displays a very good overall match with the external edge-on perspective of the Monoceros tidal stream in the Milky Way predicted by recent N-body simulations.

NGC4013, previously considered a prototypical isolated disk galaxy, is in fact undergoing a tidal encounter with a low-mass satellite. NGC 4013\could be a Rosetta Stone for understanding disks that appear almost pristine in the optical but warped in Hi maps and may provide key insights into the formation of warps.

Viewed face-on, it would look like a nearly circular pinwheel, but NGC 4013 happens to be seen edge-on from our vantage point. Even at 55 million light-years, the galaxy is larger than Hubble's field of view, and the image shows only a little more than half of the object.

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Image Credit: NASA/ESA and The Hubble Heritage Team STScI/AURA

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