This month we are reprising a popular segment of The Astronomer’s Universe that talks about the giant star Eta Carinae. This stellar behemoth is a supermassive star that will go supernova soon.
Astronomers have been studying the region of the sky in the Southern Hemisphere constellation Carina with great interest since the 1840s. That’s Eta Carinae — a supermassive star embedded in a nebula there brightened up considerably, making it one of the brightest stars in the sky. Over time, it dimmed down again. Today, we know that Eta Carinae is a massive stellar giant, called a luminous blue variable, is paired with a white dwarf. We also know that Eta Carinae is going to explode as a type of supernova called a hypernova. It will be an incredibly bright event, something that could brighten that region of the sky again when it finally occurs.
Eta Carinae is part of the vast Carina Nebula, a cloud of gas and dust and bright stars that lies about 7,500 light-years from Earth. The star itself has about 100 times the mass of the Sun, making it one of the most massive stars known. If this star could be placed in our solar system where the Sun is now, its atmosphere would reach all the way out past the orbit of Jupiter.
Eta Carinae is a million times brighter than the Sun, and it may only be a few million years old. That makes it a newborn in comparison to stars like the Sun, which is around 6 billion years old. Stars as massive as Eta Carinae live fast and die young. This one has entered its final stage of life and is very unstable. It’s losing mass through giant outbursts, and the material it’s puffing off is creating a double-lobed cloud around the star. Astronomers are zeroing in on that cloud to understand the process that is causing the star to emit such prodigious quantities of material. Is this a part of the death of all supermassive stars? When will this star ultimately explode? Those are questions astronomers are still working to answer through continuing observations of Eta Carinae.
In a paper to appear in the Monthly Notices of the Royal Astronomical Society, available online now here, astronomer Nathan Smith of UC Berkeley, concludes that dust grains “composed of corundum or similar species that condense at high temperatures” are responsible for the infrared (IR) spectral energy densities (SED) that are noted in conjunction with the nebulosity called Eta Carinae. This study highlights the importance of our understanding of the interstellar medium and cosmic dust in particular.
Yesterday, the European Space Agency (ESA) released new images of some of the largest and hottest stars ever, utilizing the Hubble Space Telescope (HST). These stars, WR 25 and Tr16-244 are in the region of the Carina Nebula. Why is it of interest to study these massive stars, some 7500 light years distant? Because large, massive, hot blue stars such as these will not last long on the main sequence (fusing hydrogen into helium in their cores) and are candidates to go supernova in an astronomically short period of time (perhaps less than a million years). Although you and I won’t be around, it is amusing to ponder the consequences of a relatively nearby supernova. This is actually outlined in a book I reviewed on this blog by Philip Plait called “Death from the Skies!” If you want to see what he says about such a fate, see his comments about another blue supergiant in the Carina Nebula region, specifically Eta Carinae in his fourth chapter. If you want to see WR 25 and Tr16-244 check out http://www.esa.int/esaSC/SEMWHR5DHNF_index_0.html