Tuesday, 16 June 2009

Nova Orionis

From the SF short story Planet Killer:

“Like Nova Orionis?” Kevin asked. The death of the star formerly known as Betelgeuse had been a spectacular learning experience for two generations of human astronomers, and the radiation pulse was still fifteen light-years from the Solar System.
6500 Light Years away lies the Crab Nebula.
Recent analysis of historical records have found that the supernova that created the Crab Nebula probably appeared in April or early May, rising to its maximum brightness of between apparent magnitude −7 and −4.5 (brighter than everything in the night sky except the Moon) by July. The supernova was visible to the naked eye for about two years after its first observation. Thanks to the recorded observations of Far Eastern and Middle Eastern astronomers of 1054, Crab Nebula became the first astronomical object recognized as being connected to a supernova explosion.

Rather closer, at about 600 Light Years away lies the star Betelgeuse (α Orionis), which according to current theory, is an incipient Type II Supernova, just like SN 1024. One day, it's going to blow. And that day might be rather sooner than we thought.

Once the massive star builds up an iron core and begins to run out of fuel in the outer shells, it is doomed. Its death is accelerated by the fact that at the increasingly high core temperatures set up by successive stages of fusion processes, neutrino emission increases. Neutrinos flood out of the core unobstructed by the higher layers, robbing the star of energy.

The end comes quickly. The star collapses in on itself, producing nuclear fusion and fission reactions that absorb energy and accelerate the collapse, quickly compressing the stellar core to incredible densities. The core collapse is announced by a huge burst of neutrino emission. The core is squeezed so heavily that it forms into a tiny but ultradense "neutron star". The biggest stars form an infinitely tiny and dense "singularity" that wraps spacetime around itself, becoming a "black hole" in space.

A neutron star or black hole cannot be compressed further, and following the burst of neutrino emission, the infalling matter "rebounds" in a "core bounce", resulting in a tremendous explosion that tears the star apart. This is a Type II supernova, and it can be as bright as a billion Suns for a few weeks, emitting heavily in the ultraviolet.
The first sign of such an event would be a giant star shrinking, collapsing in on itself. Such a contraction could be quite rapid, over a few decades or less. And guess what?
Nobel Laureate Charles Townes announced evidence that 15 consecutive years of stellar contraction has now observed to be occuring by UC Berkeley's Infrared Spatial Interferometer (ISI) atop Mt. Wilson Observatory in Southern California. Reported on June 9, 2009, the star has shrunk 15% since 1993 with an increasing rate. The average speed at which the radius of the star is shrinking over the last 15 years is approximately 470-490 miles per hour.

According to the university, Betelgeuse's radius is about 5.5 A.U.s, and the star's radius has shrunk by a distance equal to half an astronomical unit, or about the orbit of Venus. Some theorists have speculated that this behavior is expected for a star at the beginning of the gravitational collapse at the end of its life. The mass of Betelgeuse puts it in range to become a neutron star or possibly a black hole.
The trouble is... until we observe such a thing, we can't be sure if our models are correct. It could be that the star will start to pulse, in a series of cycles of expansion and contraction of increasing amplitude, until it finally goes over the edge. Or it may be as inexorable as falling off a cliff, the process accelerating rapidly in one titanic high-energy event.

If we had highly directional neutrino detectors, we could observe what's happening and make some accurate predictions. Unfortunately, a highly directional neutrino detector would require the ability to move small planets or large moons around to narrow the field of view. A bit beyond our current engineering abilities.

Still, it could be that some time between 10 and 100 years from now, we'll have a star easily visible in daytime, and brighter than a full moon for several months, fading but still a brilliant pinpoint for a couple of years afterwards.

The direction of the axis of spin is nowhere near us, so there's no possibility of the gamma rays from the initial explosion being focussed our way. 600 Light Years is none to far away to be if that was the case. Anyway, the only effect on the biosphere would be a minor disruption of nocturnal creatures' routines. Dark Nights will only happen when it's overcast.


.:dyssonance:. said...

hey, dang it -- get on Facebook and add me, silly, LOL

Anonymous said...

Oooooooooh shiny!


Lloyd Flack said...

Long Gamma-ray bursts appear to originate in a type of supernova. However it appears that the type of star that produces these bursts is not present in the Galaxy. Earth may have been hit by short Gamma-ray bursts but these appear to have a different origin.