Eta Carinae: humanity’s death sentence?

Drawing of a massive star collapsing to form a...
Drawing of a massive star collapsing to form a black hole. Energy released as jets along the axis of rotation forms a gamma ray burst that lasts from a few milliseconds to minutes. Such an event within several thousand light years of Earth could disrupt the biosphere by wiping out half of the ozone layer, creating nitrogen dioxide and potentially cause a mass extinction. (Photo credit: Wikipedia)

Probably not, thankfully. But this super massive star system, some 7,500 light years from earth (i.e., very roughly about 500 million times further away from us than the Sun) could really be some sort of threat.

New discoveries in astronomy suggest we could find out quite soon – any day now (and for next few thousand years) – just how dangerous it is. Indeed, for reasons I discuss below, sooner might be better than later.

At the core of Eta Carinae is a very massive star, perhaps the biggest in our galaxy, at about 30 solar masses. Stars of this size burn their basic nuclear fuel so quickly that they cannot generate enough internal pressure for very long to stave off gravity. A time comes when they start to collapse under their own weight – a process which, like a stone in free fall, accelerates. But as it does, it also drives up the star’s core temperature to ever higher values burning up elements in a fusion ‘reactor’ and indeed every element on Earth heavier than iron was generated in this way – before eventually triggering a supernova.

Such a supernova would see the star shed mass and emit more radiation than the rest of the galaxy combined. But even that would not stop the star’s collapse, which would continue at an ever accelerating rate and lead to an emission of the most deadly form of radiation known – a gamma ray burst – as the remnant heads towards becoming a black hole.

If such a burst hit the Earth then the consequences could be absolutely devastating – damaging our atmosphere as well as potentially exposing any one on the side of the planet facing the burst to huge quantities of ionising radiation (how much we do not know, as this has not happened, at least in human timescales).

Gamma ray bursts are believed to be emitted in the direction of the polar axes of rotation of the collapsing star and so if Eta Carinae were to blow tonight (or rather this night, 7,500 years ago) we would almost certainly be okay, given that we do not think those currently point anywhere near us.

The exploding star would, though, turn night into day for perhaps a few weeks or months. But the unknown factor is how the Eta Carinae system might change over time:  it is a binary system and the energy released as the star’s collapse began could upset the apple cart.

So why bring all this up now? Well, as reported in this week’s New Scientist, astronomers have confirmed that a star in a distant (67 million light years away) galaxy which recently was seen to go supernova exploded just three years after a so-called “supernova imposter” event when it shed a small but significant proportion of its mass. This is just the second time such a phenomenon has been observed by professional astronomers.

Eta Carinae was seen to flare up not two years ago but in the 1840s. Perhaps we are now 170 years overdue on the biggest fireworks display ever seen?

Not all astronomers agree. Some suggest Eta Carinae still has some many thousands of years to go before it starts to run out of fuel and so begins its final collapse. The truth is, we just do not know.