Eta Carinae's Uncertain Future

A recent image of the star Eta Carinae taken at the European Southern Observatory. It shows double-lobed (bi-polar) structure and jets coming from the central star. The star has not yet blown up, but will soon. ESO

Have you ever wondered what it looks like when a star blows up? There's a good chance humans will see such a thing happen when one of the most massive stars in our galaxies goes ka-boom sometime in the near future in an event astronomers are terming a hypernova

Anatomy of a Giant Star's Death

The southern hemisphere sky has one of the most explosive and fascinating stars around: Eta Carinae. It's a star system at the heart of a huge cloud of gas and dust in the constellation Carina. The evidence we have suggests that it's about to blow up in a hugely catastrophic explosion called a hypernova, any time from the next few years to a couple of thousand years. 

What is it about Eta Carinae that makes it so fascinating? For one thing, it has more than a hundred times the mass of the Sun, and may be one of the most massive stars in our entire galaxy. Like the Sun, it consumes nuclear fuel, which helps it create light and heat. But, where the Sun will take another 5 billion years to run out of fuel, stars like Eta Carinae run through their fuel very quickly. Massive stars normally live maybe 10 million years (or less). Stars like the Sun exist for about 10 billion years. Astronomers are interested in watching what happens when such a massive star runs through its death throes and finally explodes. 

Lighting Up the Sky

When Eta Carinae does go, it will be the brightest object in the nighttime sky for quite a while. The explosion probably will not damage Earth, even though the star is "only" around 7,500 light-years away, but our planet will definitely feel some effects from it. At the point of the explosion there will be a huge flash of across the spectrum of light :gamma rays will race away and eventually impact our planet's upper magnetosphere. Cosmic rays will also come racing along, as well as neutrinos. The gamma rays and some cosmic rays will be absorbed or bounced back, but there is a possibility that our ozone layer, plus satellites and astronauts in orbit could take some damage. The neutrinos will travel through our planet, and they will be captured by neutrino detectors deep underground, which will likely give us the first indication that something has happened at Eta Carinae. 

If you look at Hubble Space Telescope images of Eta Carinae, you'll see what looks like a pair of balloons of cloudy material exploding away from the star. It turns out that this object is a very temperamental kind of star called a Luminous Blue Variable. It's very unstable and occasionally brightens up as it ejects material away from itself. The last time it did this was in the 1840s, and astronomers tracked its brightness for decades. It started to brighten up again in the 1990s, with very bright outbursts thereafter. So, astronomers are keeping close track of it, just waiting for the next outburst.

When Eta Carinae does explode, it will  blast an enormous amount of material into interstellar space. It is often rich in chemical elements such as carbon, silicon, iron, silver, gold, oxygen, and calcium. Many of these elements, particularly carbon, play a part in life. Your blood contains iron, you breathe oxygen, and your bones contain calcium — all from stars that once lived and died before our Sun formed. 

So, astronomers are interested in studying Eta Carinae not just for its explosive characteristics, but also for the cosmic recycling it will do when it finally explodes. Perhaps very soon, they'll learn even more about how giant stars end their lives in the universe.