Eta Carinae
Peculiar star Eta Carinae,
in Carina
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
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
for this image, as presented at SEDS).
Newer HST pictures (taken in September 1995)
have revealed even more detail, and significant changes with time.
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Eta Carinae materials by Augusto Damineli
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Eta Carina material collection
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Bill Arnett‘s Eta Carinae and
NGC 3372 photo page,
-
Carinae page from
The First Known Variable Stars pages
Last Modification: 2 Feb 1998, 22:00 MET