NGC 4151
A Seyfert galaxy with an actively growing supermassive black hole.
NGC 4151 is a spiral galaxy of the intermediate type, classified as a Seyfert galaxy, with a faint inner ring. It sits about 52 million light-years away in the constellation Canes Venatici. This galaxy is among the closest to us that hosts a supermassive black hole that is actively feeding. It was also one of the six galaxies featured in Carl Seyfert’s original paper that first described this class of active galaxies.
The central black hole is estimated to have a mass between 2.5 million and 30 million times that of the Sun. Some astronomers have suggested the nucleus might actually contain a pair of black holes—one of about 40 million solar masses and another of about 10 million—orbiting each other every 15.8 years, though this idea remains under debate. Because of its appearance, some observers call NGC 4151 the “Eye of Sauron.”
This galaxy belongs to a small group of nine galaxies called the NGC 4151 Group, which itself is part of the larger Ursa Major Cloud, a structure within the Virgo Supercluster.
One supernova has been recorded in NGC 4151: SN 2018aoq, a Type II-P event that reached magnitude 15.3, discovered on April 1, 2018, by the Lick Observatory Supernova Search.
X-ray emission from NGC 4151 was first detected on December 24, 1970, by the Uhuru satellite, though the observation had a large error box of 0.56 square degrees. There is some uncertainty whether Uhuru actually detected the BL Lac object 1E 1207.9+3945 instead, which lies within that error box. Later, the HEAO 1 satellite found an X-ray source at 1H 1210+393, matching the optical position of the galaxy’s nucleus and outside Uhuru’s error box.
Two main explanations have been proposed for the X-ray emission. One is that radiation from material falling onto the central black hole—which was growing much faster about 25,000 years ago—was so intense it stripped electrons from gas atoms in its path, and those electrons later recombined with the ionized atoms. The other is that energy from material flowing into the black hole via an accretion disk drove a powerful outflow of gas from the disk’s surface, heating the gas in its path to temperatures that produce X-rays.
Quick Facts
- Epoch
- J2000
- Ra
- 12 · 10 · 32.6
- Dec
- +39 · 24 · 21
- Dist Ly
- 15.8 ±
- Z
- 0.003262 / 995 ± 3 km/s
- Appmag V
- 11.5
- Constellation Name
- Canes Venatici
- Names
- UGC 7166, PGC 38739
Facts from the source article.
Lore & Background
NGC 4151 was first mentioned by William Herschel on March 17, 1787. It was one of the six galaxies described in Carl Seyfert's original paper which defined Seyfert systems. Some astronomers nickname it the 'Eye of Sauron' from its appearance.
The galaxy hosts a supermassive black hole with a mass on the order of 2.5 million to 30 million solar masses. It has been 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, though this remains a matter of active debate.
X-ray emission from NGC 4151 was apparently first detected on December 24, 1970, with the X-ray observatory satellite Uhuru, although there is controversy over whether Uhuru might have detected a different object. The later HEAO 1 detected an X-ray source coincident with the optical position of the nucleus. Two possibilities have been proposed to explain the X-ray emission: radiation from material falling onto the central black hole that stripped electrons from atoms, or energy from an accretion disk outflow directly heating gas.
Reader's Guide
NGC 4151 is significant as one of the nearest galaxies with an actively growing supermassive black hole, making it a key object for studying active galactic nuclei. Its inclusion in Carl Seyfert's original paper established it as a prototype Seyfert galaxy. The ongoing debate about a possible binary black hole system highlights its importance for understanding black hole dynamics and galaxy evolution. The detection of X-ray emission, despite early controversy, has contributed to the study of accretion processes and outflows. The observation of one supernova, SN 2018aoq (Type II-P, mag 15.3) on April 1, 2018, adds to its value as a site of transient events. As a member of the NGC 4151 Group, part of the Ursa Major Cloud and Virgo Supercluster, it also provides context for large-scale structure.
Did You Know?
- The galaxy's supermassive black hole has a mass estimated between 2.5 million and 30 million solar masses.
- One supernova, SN 2018aoq (Type II-P, mag 15.3), was observed on April 1, 2018.
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