Friday, March 5, 2021

NGC 4151

NGC 4151 (also known as UGC 7166 and PGC 38739) is a spiral Seyfert galaxy, located at a distance of around 53 million light years in the constellation of Canes Venatici. It was discovered on the 17th of March 1787 by William Herschel.

This is an intermediate galaxy in terms of size and it displays a weak inner ring structure. NGC 4151 is one of the nearest galaxies to ours with a supermassive black hole that is on a growing phase.

Observations in X-rays have detected emission from NGC 4151 in an area that coincides with the position of the nucleus of the galaxy. This emission has been interpreted with two mechanisms. 

The first involves material that is falling into the black hole. Thus, as this material falls into the black hole it carries significant energy to remove electrons from atoms in the gas along its path. Eventually, these electrons recombine with the ionized atoms leading to X-ray emission.

The second mechanism suggests that responsible for the X-ray emission is material flowing into the black hole from an accretion disk. This creates an outflow of gas from the surface of the disk, which in turn heats gas along its path to superhot temperatures (i.e., million(s) of Kelvin), leading to X-ray emission.

Finally, it has  been suggested that the nucleus of NGC 4151 may host a binary black hole. The orbital period of the system is around 16 years, with the primary component having a mass of 40 million solar masses, while the secondary around 10 million solar masses.

Image 1: Composite image of NGC 4151. The image was created using data from the Chandra X-rays Observatory (blue), optical data from the 1-m. Jacobus Kapteyn Telescope in La Palma Spain (yellow), and radio data from the Very Large Array (red). Astronomers have nicknamed NGC 4151 "the Eye of Sauron", due to the resemblance of the galaxy with Sauron's Eye.

Image 2: Composite optical image of NGC 4151 taken with the Hubble Space Telescope. The image was created using broadband filters.

Image 1 Credit: X-ray: NASA/CXC/CfA/J.Wang et al.; Optical: Isaac Newton Group of Telescopes, La Palma/Jacobus Kapteyn Telescope, Radio: NSF/NRAO/VLA

Image Credit 2: NASA, ESA, and J. DePasquale (STScI)

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