Homunculus Nebula
Encyclopedia
The Homunculus Nebula is an emission nebula
surrounding the massive star system Eta Carinae. The nebula is embedded within a much larger ionized hydrogen (H II) region
, the Eta Carinae Nebula
.
The Homunculus
(from the Latin
meaning Little Man) is believed to have been ejected in an enormous outburst from Eta Carinae seen from Earth in 1841, a brightening event visible from Earth at the time. In the event, Eta Carinae became the second-brightest star in the sky after Sirius
; but the ejected gas and dust has since obscured much of its light. The massive —near supernova— explosion produced two polar lobes and a large thin equatorial disk, all moving outward at 670 km/s. Future eruptions remain a distinct possibility.
Though Eta Carinae is some 7,500 light-years away, its luminosity is so great that 'small' structures only 10 billion miles across —about the diameter of our solar system— can be distinguished. Dust lanes, tiny condensations, and strange radial streaks all appear with unprecedented clarity. The outer ejecta blobs are much fainter than the brilliant central star (by about 100,000 times). Excess violet light escapes along the equatorial plane between the bipolar lobes. Apparently there is relatively little dust-debris between the lobes as most of the blue light is able to escape. On the other hand, the lobes contain large amounts of dust which preferentially absorb blue light, causing the lobes to appear reddish.
The Homunculus-Eta Carinae system is currently one of the most massive that can be studied in great detail. Until recently, this system was thought to contain the most massive single star known, but Eta Carinae was recently demoted to a binary system. Instead, the most massive star in the Eta Carinae multiple star system has less than 100 times the mass of the Sun. Other known massive stars are more luminous and more massive.
Emission nebula
An emission nebula is a cloud of ionized gas emitting light of various colors. The most common source of ionization is high-energy photons emitted from a nearby hot star...
surrounding the massive star system Eta Carinae. The nebula is embedded within a much larger ionized hydrogen (H II) region
H II region
An H II region is a large, low-density cloud of partially ionized gas in which star formation has recently taken place. The short-lived, blue stars forged in these regions emit copious amounts of ultraviolet light, ionizing the surrounding gas...
, the Eta Carinae Nebula
Eta Carinae Nebula
The Carina Nebula is a large bright nebula that surrounds several open clusters of stars. Eta Carinae and HD 93129A, two of the most massive and luminous stars in our Milky Way galaxy, are among them. The nebula lies at an estimated distance between 6,500 and 10,000 light years from Earth...
.
The Homunculus
Homunculus
Homunculus is a term used, generally, in various fields of study to refer to any representation of a human being. Historically, it referred specifically to the concept of a miniature though fully formed human body, for example, in the studies of alchemy and preformationism...
(from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
meaning Little Man) is believed to have been ejected in an enormous outburst from Eta Carinae seen from Earth in 1841, a brightening event visible from Earth at the time. In the event, Eta Carinae became the second-brightest star in the sky after Sirius
Sirius
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...
; but the ejected gas and dust has since obscured much of its light. The massive —near supernova— explosion produced two polar lobes and a large thin equatorial disk, all moving outward at 670 km/s. Future eruptions remain a distinct possibility.
Though Eta Carinae is some 7,500 light-years away, its luminosity is so great that 'small' structures only 10 billion miles across —about the diameter of our solar system— can be distinguished. Dust lanes, tiny condensations, and strange radial streaks all appear with unprecedented clarity. The outer ejecta blobs are much fainter than the brilliant central star (by about 100,000 times). Excess violet light escapes along the equatorial plane between the bipolar lobes. Apparently there is relatively little dust-debris between the lobes as most of the blue light is able to escape. On the other hand, the lobes contain large amounts of dust which preferentially absorb blue light, causing the lobes to appear reddish.
Shape
Some astrophysicists theorize the unusual shape of the Homunculus nebula is attributed to a "peanut" shape of the star —or binary star system, see below. It is believed that interacting blast waves from the 1841 brightening event(s) have created a standing wave at the intersection of the two sides of the wave, gravitationally grouping the ejecta into a plane. It is possible that due to the solar-system-size nodes of the cloud that some other mechanism is being witnessed. One theory holds that two small black holes may be at the center of each lobe, one of which is consuming Eta Carinae (or a binary star). The "skirt" of ejecta in this case is due to a tangential release of the restraining gravity fields at the collision point.The Homunculus-Eta Carinae system is currently one of the most massive that can be studied in great detail. Until recently, this system was thought to contain the most massive single star known, but Eta Carinae was recently demoted to a binary system. Instead, the most massive star in the Eta Carinae multiple star system has less than 100 times the mass of the Sun. Other known massive stars are more luminous and more massive.