Eta Carinae is a star system about 7,500 to 8,000 light-years from the Sun. That’s an awfully long way from the “pale blue dot” we call home, but astronomers are currently paying it a lot of attention.
Eta Carinae contains at least two stars, one of which at one time had 150 times the mass of the sun. It later lost some of that mass. Around this primary star orbits a hot supergiant of approximately 30 solar masses, although a thick red interstellar cloud of dust, hydrogen, helium and other ionized gases makes it impossible to see it optically.
For the record, light travels at 186,000 miles per second. A light year is the distance that light can travel in a year, or 186,000 miles/second x 60 seconds/minute x 60 minutes/hour x 24 hours/day x 365 days/year = 5,865,696,000,000 miles/year. Eta Carinae is 5,865,696 million x 7,500 miles away! The well known comparison of frozen peas filling London’s Albert Hall comes to mind. If each pea were a galaxy, there would be some 150 billion. Our galaxy, the Milky Way, would be on one side and Eta Carinae might be somewhere in the middle.
First catalogued by astronomer Edmond Halley in 1677, over succeeding centuries Eta Carinae’s brightness increased dramatically and then faded. Some of the cloud of dust and gas that surrounds it is thought to have been released at this time. The last large outburst of activity took place in 1841, around the time of its maximum brightness. After 1843, Eta Carinae faded yet again and between about 1900 and 1940 became invisible. A sudden and unexpected doubling of brightness was observed in 1998-99 and in 2007, Eta Carinae could once again be seen with the naked eye.
The Eta Carinae system currently has a luminosity over five million times the Sun’s. Because of its mass and the stage of its life, astronomers are expecting it to explode in a supernova in the astronomically near future. When that happens, it could affect Earth. However, it is unlikely to impact terrestrial life directly, as we are protected from gamma rays by the atmosphere and from other cosmic rays by the magnetosphere. Damage would likely be restricted to the upper atmosphere, the ozone layer, satellites, and anyone who happened to be in space. But some scientists claim that radiation damage to the upper atmosphere would cause catastrophic effects on Earth as well.
This drama is taking place in an unimaginably vast void. In A Short History of Nearly Everything (2003), Bill Bryson writes:
“The most perfect vacuum ever created by humans is not as empty as the emptiness of interstellar space. And there is a great deal of this nothingness until you get to the next bit of something. Our nearest neighbour in the cosmos, Proxima Centauri… is 4.3 light years away, a sissy skip in galactic terms, but still a hundred million times further than a trip to the Moon. To reach it by spaceship would take at least twenty-five thousand years… To reach the next landmark of consequence, Sirius, would involve another 4.6 light years of travel… Just reaching the centre of our own galaxy would take far longer than we have existed as human beings.”
Instead, Eta Carinae may come to us. If it does, we may yet catch a falling star.