Eta Carinae - Future Prospects

Future Prospects

Because of their disproportionately high luminosities, very large stars such as Eta Carinae use up their fuel very quickly. Eta Carinae is expected to explode as a supernova or hypernova some time within the next million years or so. As its current age and evolutionary path are uncertain, however, it could explode within the next several millennia or even in the next few years. LBVs such as Eta Carinae may be a stage in the evolution of the most massive stars; the prevailing theory now holds that they will exhibit extreme mass loss and become Wolf-Rayet stars before they go supernova, if they are unable to hold their mass to explode as a hypernova.

More recently, another possible Eta Carinae analogue was observed: SN 2006jc, some 77 million light years away in UGC 4904, in the constellation of Lynx. Its brightened appearance was noted on 20 October 2004, and was reported by amateur astronomer Koichi Itagaki as a supernova. However, although it had indeed exploded, hurling 0.01 solar masses (~20 Jupiters) of material into space, it had survived, before finally exploding nearly two years later as a Mag 13.8 type Ib supernova, seen on 9 October 2006. Its earlier brightening was a supernova impostor event.

The similarity between Eta Carinae and SN 2006jc has led Stefan Immler of NASA's Goddard Space Flight Center to suggest that Eta Carinae could explode in our lifetime, or even in the next few years. However, Stanford Woosley of the University of California in Santa Cruz disagrees with Immler’s suggestion, and says it is likely that Eta Carinae is at an earlier stage of evolution, and that there are still several stages of nuclear burning to go before the star runs out of fuel.

In NGC 1260, a spiral galaxy in the constellation of Perseus some 238 million light years from earth, another analogue star explosion, supernova SN 2006gy, was observed on September 18, 2006. A number of astronomers modelling supernova events have suggested that the explosion mechanism for SN 2006gy may be very similar to the fate that awaits Eta Carinae.

It is possible that the Eta Carinae hypernova or supernova, when it occurs, could affect Earth, about 7,500 light years away. It is unlikely, however, to affect terrestrial lifeforms directly, as they will be protected from gamma rays by the atmosphere, and from some other cosmic rays by the magnetosphere. The damage would likely be restricted to the upper atmosphere, the ozone layer, spacecraft, including satellites, and any astronauts in space, although a certain few claim that radiation damage to the upper atmosphere would have catastrophic effects as well. At least one scientist has claimed that when the star explodes, "it would be so bright that you would see it during the day, and you could even read a book by its light at night". A supernova or hypernova produced by Eta Carinae would probably eject a gamma ray burst (GRB) out from both polar areas of its rotational axis. Calculations show that the deposited energy of such a GRB striking the Earth's atmosphere would be equivalent to one kiloton of TNT per square kilometer over the entire hemisphere facing the star, with ionizing radiation depositing ten times the lethal whole body dose to the surface. This catastrophic burst would probably not hit Earth, though, because the rotation axis does not currently point towards our solar system. If Eta Carinae is a binary system, this may affect the future intensity and orientation of the supernova explosion that it produces, depending on the circumstances.