NGC 4151

NGC 4151
300px Image of NGC 4151 from the 0.8m Schulman Telescope at the Mount Lemmon SkyCenter
Observation data (J2000 epoch)
Constellation	Canes Venatici
Right ascension	12h 10m 32.6s
Declination	+39° 24′ 21″
Redshift	0.003262 995 ± 3 km/s
Distance	19 Mpc (62×10^6 ly)
Type	(R')SAB(rs)ab, Sy1
Apparent dimensions (V)	6′.4 × 5′.5
Apparent magnitude (V)	11.5
Other designations
UGC 7166, PGC 38739

NGC 4151 is an intermediate spiral Seyfert galaxy located 19 megaparsecs (62 million light-years) from Earth in the constellation Canes Venatici. The galaxy was first mentioned by William Herschel on March 17, 1787; it was one of the two Seyfert galaxies described in the paper which defined the term. It is one of the nearest galaxies to Earth to contain an actively growing supermassive black hole; it was speculated that the nucleus may host a binary black hole, with about 40 million and about 10 million solar masses respectively, orbiting with a 15.8-year period. This is, however, still a matter of active debate.

Some astronomers nickname it the "Eye of Sauron" from its appearance.

X-ray source

File:NGC 4151.jpg

NGC 4151. X-rays (blue), optical data (yellow), radio observation (red)

File:X-ray 'Echoes' Probe Habitat of Monster Black Hole.ogv

Astronomers using data from the European Space Agency’s XMM-Newton satellite have found a long-sought X-ray signal from NGC 4151. When the black hole’s X-ray source flares, its accretion disk reflects the emission about half an hour later.

X-ray emission from NGC 4151 was apparently first detected on December 24, 1970, with the X-ray observatory satellite Uhuru, although the observation spanned an error-box of 0.56 square degrees and there is some controversy as to whether UHURU might not have detected the BL Lac object 1E 1207.9 +3945, which is inside their error box - the later HEAO 1 detected an X-ray source of NGC 4151 at 1H 1210+393, coincident with the optical position of the nucleus and outside the error box of.

To explain the X-ray emission two different possibilities have been proposed:

• radiation of material falling onto the central black hole (which was growing much more quickly about 25,000 years ago) was so bright that it stripped electrons away from the atoms in the gas in its path, and then electrons recombined with these ionized atoms
• the energy released by material flowing into the black hole in an accretion disk created a vigorous outflow of gas from the surface of the disk, which directly heated gas in its path to X-ray emitting temperatures

See also

• X-ray astronomy

External links

• Hubble site news center: Fireworks Near a Black Hole in the Core of Seyfert Galaxy NGC 4151