page_title: Homunculus Nebula
section_title: Shape
hierarchical_section_title: Homunculus Nebula / Shape
caption_attribution_description: English: If you're looking for something to print with that new 3D printer, try out a copy of the Homunculus Nebula. The dusty, bipolar cosmic cloud is around 1 light-year across but is slightly scaled down for printing to about 1/4 light-nanosecond or 80 millimeters. The full scale Homunculus surrounds Eta Carinae, famously unstable massive stars in a binary system embedded in the extensive Carina Nebula about 7,500 light-years distant. Between 1838 and 1845, Eta Carinae underwent the Great Eruption becoming the second brightest star in planet Earth's night sky and ejecting the Homunculus Nebula. The new 3D model of the still expanding Homunculus was created by exploring the nebula with the European Southern Observatory's VLT/X-Shooter. That instrument is capable of mapping the velocity of molecular hydrogen gas through the nebula's dust at a fine resolution. It reveals trenches, divots and protrusions, even in the dust obscured regions that face away from Earth. Eta Carinae itself still undergoes violent outbursts, a candidate to explode in a spectacular supernova in the next few million years.
context_page_description: The Homunculus Nebula is a bipolar emission and reflection nebula surrounding the massive star system Eta Carinae, about 7,500 light-years from Earth. The nebula is embedded within the much larger Carina Nebula, a large star-forming H II region. From the Latin homunculus meaning Little Man, the nebula consists of gas which was ejected from Eta Carinae in 1841. It also contains dust which absorbs much of the light from the extremely luminous central stellar system and re-radiates it as infra-red. It is the brightest object in the sky at mid-IR wavelengths.
  Within the Homunculus is a smaller Little Homunculus, and within that a shell of shocked material from stellar winds that has been called Baby Homunculus.
context_section_description: The Homunculus consists of two lobes, referred to as northwest (NW) and southeast (SE) based on their orientation as seen from Earth. Each is approximately 7″ wide by 5″ long.  There is also a ragged equatorial skirt of material which can be seen faintly in deep images at certain wavelengths.  The lobes are mostly hollow with the material strongly concentrated towards the poles.
  The equatorial skirt appears to contain material of the same age and younger than the lobes.  It contains a much smaller mass of material than the lobes, shining mainly by reflected light which escapes most easily at equatorial latitudes.  There is less dust and little molecular hydrogen compared to the lobes.
  The bipolar nebula is angled so that the NW lobe is further away from Earth than the SE lobe is.  The whole nebula is expanding so that the SE lobe is blue-shifted and the NW lobe is red-shifted, relative to the central source.  The lobes contain the majority of the material in the Homunculus Nebula, in relatively thin shells concentrated towards the poles.  The shells consist of two components, an inner warm region and a more massive outer cool skin.  The shells are smooth and thin suggesting they were ejected in as little as five years, but there are streaks of thicker dust detectable within the shells.
  Each lobe has polar "hole" although it is not known whether it is an actual gap in the shell of the lobe or just a deep indentation. Surrounding each polar hole is a "trench".  The trenches are visible as approximate semicircles centred on the axis of the lobes but may form complete circles.  There are other smaller irregular indentations and protrusions to the lobes, which are symmetrical with the same features appearing on each lobe.  These include flattened protrusions at about 10° latitude, one on each lobe, with other smaller protrusions near the equatorial skirt.
  The mass of the nebula cannot be determined directly.  However, the amount of dust can be measured fairly accurately and estimates of the gas to dust ratio used to calculate the total mass.  The total dust mass is calculated at 0.4 M☉, leading to estimates that up to 40 M☉ of gas are contained in the Homunculus itself.  Nearly as much material is detected within outer ejecta, which formed earlier, but within the last thousand years.  Older calculations had produce consensus estimates of 10-15 M☉
caption: A 3D model of the Homunculus Nebula.
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