Knife Edge Galaxy (NGC 5907)

The Knife Edge Galaxy (NGC 5907) is a spiral galaxy in the constellation Draco, also known as the Sliver or Knife Edge. It is located at a distance of about 50 million light-years from the Sun. In 2006, a trail of old stars, also called a star stream, was discovered near the galaxy. One theory for the origin of this trail suggests that some of the stars were ejected by the gravity of a smaller galaxy passing nearby. NGC 5907 (also known as the Knife Edge Galaxy or Splinter Galaxy) is a spiral galaxy located at a distance of about 46.5 million light-years from Earth. The galaxy was discovered by German-British astronomer William Herschel on May 5, 1788.

Features

NGC 5907 has an abnormally low metal content and a small number of giant stars, consisting almost entirely of dwarf stars. It is a member of the NGC 5866 group.

The galaxy was long considered a classic example of a warped spiral in relative isolation. However, in 2006, an international team of astronomers discovered the presence of an extended tidal stream surrounding the galaxy. This challenges the previous theory and suggests that gravitational perturbations caused by a precursor to the stream may be responsible for the warping. Recent deeper studies dispute the existence of part of these tidal streams.

An ultra-luminous X-ray source has been discovered in the galaxy. NGC 5907 and the galaxy KUG 1513+566 are mentioned together as Holm 704 in Erik Holmberg's study "A Study of Double and Multiple Galaxies Together with Inquiries into some General Metagalactic Problems", published in 1937.

The NGC 5907 group, also known as LGG 396, includes at least four members: Messier 102, NGC 5879, and UGC 9776.

Supernovae

NGC 5907 has hosted one supernova: SN 1940A (Type II-L, apparent magnitude 14.3), discovered by Joseph J. Johnson on February 16, 1940.

Research

Recent images reveal an extragalactic view of an extended stellar tidal stream that surrounds the spiral galaxy NGC 5907. These images reveal for the first time a large, complex structure of arcuate loops, providing an excellent example of how accretion of low-mass companions can produce an interlocking, rosette-like structure of debris distributed throughout the halo of a host galaxy. The existence of this structure, likely preserved for several gigayears, confirms that the halos of spiral galaxies in the local universe still contain significant amounts of galactic fossils from their hierarchical evolution.

To test the external accretion hypothesis, N-Body simulations of tidal disruption of a dwarf galaxy in a dark halo disk galaxy were performed, which showed that most of the observed tidal features in NGC 5907 can be explained by a single accretion event. Unfortunately, without kinematic data and considering only the projected flow geometry, the parameters of our model remain rather uncertain and, for now, should be considered only illustrative.

Interestingly, NGC 5907 has long been considered a classic example of a warped spiral in relative isolation. The presence of an extended tidal flow challenges this picture and suggests that gravitational perturbations caused by the flow precursor may be the cause of the warping. The discovery of an old and complex tidal stream in a nearby galaxy using relatively modest instruments points to the possibility of conducting surveys to detect extragalactic tidal substructures around spiral galaxies in the local bulk universe (less than 15 Mpc), which could lead to statistically significant data for comparison with cosmological models.