NGC 4253 is a barred spiral galaxy located in the constellation Coma Berenices. It is located at a distance of about 185 million light years from Earth, which, given its apparent dimensions, means that NGC 4253 is about 65,000 light years across.[1] It was discovered by William Herschel on February 3, 1788.[2] It is a Seyfert galaxy.[1]
Characteristics
The NGC 4253 is a barred galaxy with thick bar, while the arms form a ring. Marquez et al. suggested that the galaxy has a secondary bar perpendicular to the main bar,[3] although that could be an artifact due to the presence of strong dust lanes and no inner bar is visible in images by WFPC2 F606W of the Hubble Space Telescope.[4] There is evidence of star formation along the dust lanes in the leading egde of the bar, especially at the east half.[5]
The nucleus of NGC 4253 has been found to be active and it has been categorised as a narrow line type I Seyfert galaxy.[6] The most accepted theory for the energy source of active galactic nuclei is the presence of an accretion disk around a supermassive black hole. The mass of the black hole in the centre of NGC 5506 is estimated to be 1–13 × 106M☉ based on reverberation mapping of the hydrogen lines,[7]1.6+1.4 −1.2×106M☉ based on time lag spectra,[8] and 1.26+1.00 −0.77×106M☉ based on X-ray variations.[9]
The nucleus emits X-rays. The X-rays have been found to vary in intensity, exhibiting quasi-periodic oscillation, although this phenomenon appears to be transient.[10] The variability was found by ROSAT X-ray satellite.[11] The intensity varied by a factor of 3 every 6,450 seconds (about 1.8 hours) based on observations by XMM-Newton in 2005,[10] while in 2000 that period was estimated to be 4,200 seconds.[12] It has been suggested that the source of the oscillation lies at the inner part of the accretion disk.[10]
The galaxy has been found to host a maser and is a compact source in radiowaves.[13]
