Echoes from Great Eruption Reach Astronomers

According to researchers 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. 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. 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. 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. Surprisingly, their observations suggest the Great Eruption is different from so-called “supernova impostors,” events that resemble the explosive supernova deaths of stars but are thought to be eruptions from bright blue variables. According to study co-author Jose Prieto, now at Princeton University this star’s Giant Eruption has been considered a prototype for all supernova imposters in external galaxies. But this research indicates that it is actually a rather unique event. These new findings mean that researchers still do not know what caused the Great Eruption. The scientists now plan to look for more light echoes from the Great Eruption, to see how Eta Carinae altered over time, and that will further help in constraining what the eruption mechanism is.