ETA_CARINAE by wanghonghx


									                  ETA CARINAE

Students: Blau Lynn, O’Connell Jillian and Schmit Raphaëlle

Teacher: Daman Pascal

School:   Lycée de garçons de Luxembourg

Our presentation is about the very large and very luminous star Eta Carinae. Our goal
consists in finding out the difference between the observation of the star with the
telescopes ALMA and EELT, a telescope which will be completed in a couple of
years. Can a better telescope give more information? Why? How?

We divided our project into three parts in order to investigate these questions.
Our first part describes the history of Eta Carinae, when it was first discovered and
how it developed. Our second part is the description of the star, its characteristics and
how it will end in the future. And finally, in our third part, we will describe the
different types of telescopes such as Optical, Infrared, Radio and X-Ray telescopes.
Then, with all of this information, we will try to answer all of these questions.

Eta Carinae was first catalogued by Edmund Halley in 1677 when the star was of the
fourth magnitude. The apparent magnitude of a star, planet or other celestial body is a
measure of its apparent brightness as seen by an observer on Earth. The brighter the
object appears, the lower the numerical value of its magnitude. Its brightness has
varied a numerous times, it increased and decreased and over until 1843 when it
reached its maximal brilliance of -0.8, it outshone all the stars in the sky except for
Sirius. After this, Eta Carinae slowly faded until it became invisible in 1868. By 1900
it was of the eighth magnitude where it remained until 1941. Then it started to
brighten again and in the 1990’s reached the sixth magnitude and was again visible to
the naked eye. Around 1998 and 1999 its brightness suddenly and unexpectedly

                                           Eta Carinae is a very large and very luminous
                                           star. It is surrounded by a large bright nebula
                                           called the Eta Carinae Nebula. Its mass
                                           ranges from 100-150 times and its luminosity
                                           is about 5 times that of the sun. Eta Carinae is
                                           currently one of the most massive visible
                                           stars in the sky. Because of the star’s
                                           extremely high mass, it is unstable and it uses
                                           its fuel very quickly, compared to other stars.
                                           Such massive stars also only have a short
                                           lifetime and Eta Carinae is expected to
                                           explode as a supernova or hypernova in about
                                           1 million years or less from now.
                                           A supernova is a stellar explosion which
produces an extremely luminous object made of plasma. A hypernova is an
exceptionally large star which is many times more violent than a supernova. It
collapses at the end of its lifespan.
Because of its instability Eta Carinae sometimes has large outbursts, the reason
however is not yet known. The last of these outbursts occurred in 1841. The
instability of Eta Carinae isn’t yet fully understood. According to the current theo ry it
is caused by the fact that its high mass causes an extremely high luminosity. This
leads to a high radiation pressure at the star’s surface, which blows significant
portions of the star’s outlayers off into space, in a slow but violent eruption.


The Atacama Large Millimeter/submillimeter Array (ALMA) is an international
astronomy project that consists of an astronomical interferometer formed by an array
of radio telescopes, located at Llano de Chajnantor Observatory in the Atacama desert
in northern Chile. The telescope is expected to revolutionise modern astronomy by
providing an insight into star formation in the early universe and imaging local star
and planet formation in great detail.

The European Extre mely Large Telescope (E-ELT) is an extremely large telescope
design proposed for the next- generation European Southern Observatory optical
telescope with a mirror diameter of 42 meters.
This telescope has the aim of observing the Universe in greater detail. A mirror of
approximately 42 meters would allow the study of the atmospheres of extrasolar
planets. It could be completed by 2017.

Optical Telescope: An optical telescope is
used to gather and focus light mainly from the
visible part of the electromagnetic spectrum.
Optical telescopes increase the apparent
angular size of distant objects, as well as their
apparent brightness. Telescopes work by using
one or more optical elements like for example
lenses or mirrors, to gather light or other
electromagnetic radiation and bring it to a
focus, where the image can be observed,
photographed or studied.
The optical image of Eta Carinae was made by
the Hubble Space Telescope. Two spectacular bubbles of gas can be seen. The
bubbles are expanding in opposite directions away from a central bright region at
speeds of a million miles per hour. The inner region visible in the Chandra image has
never been resolved before, and appears to be associated with a central disk of high
velocity gas rushing out at much higher speeds perpendicular to the bipolar optical

Infrared Telescope: The Spitzer Space Telescope
is an example for an infrared telescope. Spitzer
obtains images and spectra by detecting the infrared
energy, or heat, radiated by objects in space
between wavelengths of 3 and 180 microns (1
micron is one- millionth of a meter). As most of this
infrared radiation is blocked by the Earth's
atmosphere, it cannot be observed from the ground.
This is why a telescope needs to be launched into
space and Spitzer is the largest one ever launched. It
gives us a unique view of the Universe and allows
us to peer into regions of space which cannot be
seen by optical telescopes. Many areas of space are filled with vast, dense clouds of
gas and dust which block our view, however infrared light can penetrate these clouds,
allowing us to peer into regions of star formation, the centers of galaxies, and into
newly forming planetary systems. Infrared also brings us information about smaller
stars which are too dim to be detected by their visible light, extrasolar planets, and
giant molecular clouds. Also, many molecules in space, including organic molecules,
have their unique signatures in the infrared.

Most of Eta Carinae’s energy is radiated at infrared wavelengths. It is shrouded in a
rapidly expanding cloud of dust which absorbs radiation from the central star and re-
radiates it in the infrared.

Radio telescope:

                                In order to study radio emission from stars, galaxies,
                                quasars and other astronomical objects between
                                wavelengths of about 10 meters and 1 millimeter a
                                radio telescope is used.
                                Eta Carinae’s radio image shows a bright feature at the
                                center, that’s where the star is: the emission here is
                                effectively “burnt out”. A radio outburst which Eta
                                Carinae has undergone makes it one of the brightest
                                radio stars in the sky.

On this Chandra X-Ray image of Eta Carinae a hot
inner core around this star is revealed. The X-ray
observation shows three distinct structures: an outer,
horseshoe shaped ring about two light years in
diameter, a hot inner core about 3 light months in
diameter, and a hot central source less than a light
month in diameter which may contain the star.
These three structures are thought to represent shock
waves rushing away from the star at high speed.


With help of the ALMA telescope, we get to know the center of the star better.
The E-ELT telescope on the other hand gives us more information about the inner
region and the gas rushing out of the star Eta Carinae. This telescope in combination
with the ALMA telescope could help to explain the luminosity fluctuations.

We have consulted the following websites:


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