The Heaviest Couple in the Milky Way
One of the brightest and most spectacular objects in the night sky, eta Carinae, actually consists of two stars. This makes it the most massive binary star system ever discovered. Since eta Carinae attracted the attention of astronomers with a supernova in 1843 and became the second brightest star in the firmament, the interest of experts in the celestial body has not diminished, because eta Carinae survived the explosion. Today the star - or as it has now become known: the pair of stars - emits about five million times as much radiant energy as our sun, which remains a mystery to physicists and astronomers.
Augusto Damineli from the University of Sao Paulo and Peter Conti from the University of Colorado have calculated that the two stars each weigh about 70 times as much as our sun. They orbit each other on an elongated ellipse, the diameter of which is larger than the distance between the Sun and Saturn. Every 5.5 years, when the stars are closest, spectral changes can be observed from Earth. These include fading emission lines from elements such as helium and argon, and aberrations in the flux of X-rays and radio waves.
"The key to the mystery is that these changes are as predictable as a clock," says Conti. “We cannot predict the behavior of an individual with the accuracy of a clock. The only explanation for the precise timing of the spectral changes we observe at eta Carinae lies in the mechanical orbit of a companion star.”
Astronomers determined the elliptical orbits of the two stars from sudden changes in velocity that could be measured using the Doppler effect. "The star is turning at high speed at the top of its orbit," explains Damineli."When we see such turns, we know we are observing stars in elliptical orbits."
The stars pass each other at a distance twice the distance from the Sun to the Earth. Nevertheless, they cannot be separated visually. At maximum approach, solar winds from eta Carinae collide with those of its companion, increasing X-ray emission and causing gas emissions to become jumbled from the observer's perspective.
According to Damineli's ideas, the supernova could have been caused by gravitational waves on the surfaces of the stars more than 150 years ago. At that time, eta Carinae's diameter increased tenfold, pushing the smaller companion into the large star's atmosphere. That may have triggered the explosion of eta Carinae, as evidenced today by the twin wings and equatorial disk seen in images of the binary star.
The astronomers, together with Otmar Stahl and Andreas Kaufer from the University of Heidelberg, presented their results on January 7, 1998 at the meeting of the American Astronomical Society.
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