Eta Carinae

Right Ascension	10 : 45.1 (h : m)
Declination	-59 : 41 (deg : m)
Distance	10.0 (kly)
Visual Brightness	6.21 (mag) [-0.8 .. 7.9, var]
Apparent Dimension	?? (arc min)

Eta Carinae is one of the most remarkable stars in the heavens. It is one of the most massive stars in the universe, with probably more than 100 solar masses (Jeff Hester of the ASU, who made this HST image, has estimated 150 times the mass of our sun). It is about 4 million times brighter than our local star, making it also one of the most luminous stars known. Eta Carinae radiates 99 % of its luminosity in the infrared part of the spectrum, where it is the brightest object in the sky at 10-20 microns wavelength.

As such massive stars have a comparatively short expected lifetime of roughly 1 million years, Eta Carinae must have formed recently in the cosmic timescale; it is actually situated in the heavily star forming nebula NGC 3372, called the Eta Carinae Nebula. It will probably end its life in a supernova explosion within the next few 100,000 years (some astronomers speculate that this will occur even sooner).

Because of its high mass, Eta Carinae is highly unstable, and prone to violent outbursts. The last of these occurred in 1841, when despite its distance (over 10,000 light years away) Eta Carinae briefly became the second brightest star in the sky.

According to the current theory of stellar structure and evolution, this instability is caused by the fact that its high mass causes an extremely high luminosity. This leads to a high radiation presure at the star's "surface", which blows significant portions of the star's outlayers off into space, in a slow but violent eruption. Our image shows the nebula formed by the ejected material.

The picture is a combination of three different images taken in red, green, and blue light. The ghostly red outer glow surrounding the star is composed of the very fastest moving of the material which was ejected during the last century's outburst. This material, much of which is moving more than two million miles per hour, is largely composed of nitrogen and other elements formed in the interior of the massive star, and subsequently ejected into interstellar space.

The bright blue-white nebulosity closer in to the star also consists of ejected stellar material. Unlike the outer nebulosity, this material is very dusty and reflects starlight. The new data show that this structure consists of two lobes of material, one of which (lower left) is moving toward us and the other of which (upper right) is moving away. The knots of ejected material have sizes comparable to that of our solar system.

Previous models of such bipolar flows predict a dense disk surrounding the star which funnels the ejected material out of the poles of the system. In Eta Carinae, however, high velocity material is spraying out in the same plane as the hypothetical disk, which is supposed to be channeling the flow.

The rapidly moving ejected gas shows up in spectra of Eta Carinae by peculiarly shifted spectral lines, forming the so-called P Cygni profiles (named after the only other known star of same type in the Milky Way, P Cygni).

Our image is one of the first taken with the refurbished Hubble Space Telescope (HST) in January, 1994, with the new Wide Field Planetary Camera (WFPC) 2, which had been mounted by the crew of the STS-61 Space Shuttle mission (look at the press release for this image, as presented at SEDS). Newer HST pictures (taken in September 1995) have revealed even more detail, and significant changes with time.

• Eta Carinae materials by Augusto Damineli
• Chris Kronberg's Munich Astro Archive's Eta Carina material collection
• Bill Arnett's Eta Carinae and NGC 3372 photo page, info page
• Eta Carinae page from The First Known Variable Stars pages

Last Modification: 2 Feb 1998, 22:00 MET