An explosion in space first seen in the 19th century was apparently colder than before thought, throwing a new mystery into what may have triggered it, researchers say.
Skip to next paragraph This is a three-dimensional trip into a giant "mountain" of cool hydrogen and dust in the Carina Nebula, a vast star-forming region in our Milky Way Galaxy. The nebula is too far away for Hubble Space Telescope to see in true three dimensions. But this visualization creates foreground and background elements based on an approximation of how the region might be distributed in a 3-D volume. A virtual camera flies through this synthesized space to create a 3-D effect.The cosmic eruption came from?Eta Carinae, a star about 7,500 light-years away from Earth that is one of the most massive stars in our Milky Way galaxy. It blazed into ultra-brightness in 1838, becoming the second-brightest star in the sky for 10 years in a rare celestial outburst later dubbed the "Great Eruption." The star later dimmed, and is now not even in the top 100 list of brightest stars.
"Eta Carinae is probably the most studied object in our galaxy," said ?Armin Rest, an astrophysicist at the Space Telescope Science Institute in Baltimore and the study's lead author.
Scientists have found that Eta Carinae is a kind of star known as a luminous blue variable, meaning it goes through episodes of dimness and brightness. These rises and falls in luminosity are caused by mounting instability within the star followed by a dramatic loss of mass. The?Great Eruption of Eta Carinae?was an especially catastrophic event, where the star — once about 140 times the mass of the sun — lost mass equal to about 20 times that of the sun.
Scientists believed this rare kind of eruption was caused by a stellar wind blowing off the stars. Still, much remained uncertain, since a key detail about the Great Eruption was missing — its pattern of light. This spectrum would help yield details such as the temperature, composition and velocity of matter from the eruption. [Amazing Photos of Star Explosions]
For instance, "cool objects emit redder light than hot objects," Rest explained. "Look at an ember — if it is relatively cool, it is dark red, and the hotter it gets, the bluer, whiter it gets. So overall the color of the spectra gives you already a good idea how hot or cold the star is."
Now, using the Magellan and du Pont telescopes at Las Campanas Observatories in Chile, Rest and his colleagues have discovered spectra from the Great Eruption, by looking for light from the explosion that bounced or echoed off interstellar dust tens of light-years from the star.
"The missing piece, the big gap, has been that there were no spectra of the Great Eruption," Rest said. "Now we have it, and it gives us the chance to better understand how this eruption happened and what caused it."
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