September 13, 2008 | David F. Coppedge

Star Death Amazing – but Puzzling

Twinkle, twinkle, little stBOOM!  The explosions of some dying stars are so powerful yet so rapid, mere measurements seem inadequate to describe them.  Two death-star events were reported in recent articles.  Despite the bravado of textbook orthodoxy, the articles both mentioned that astronomers really don’t understand what’s going on all that well.
    Eta Carina is one of the most intriguing stars in the southern sky.  Its twin-lobed, bloated bubble blown out by the eruption of 1843 has given it the name the Homunculus Nebula (see dazzling photograph on Astronomy Picture of the Day for June 17).  The 1843 bubble, and another estimated to be a thousand years old, have been well known.  Astronomers recently detected, however, a newer, more powerful eruption that is catching up to the bubble.  National Geographic News reported that this material is moving outward at 1.5 million miles per hour.  It is so energetic it borders on the power of a supernova – the explosion that usually ends a large star’s life.  Is this a supernova imposter?  Team lead Nathan Smith (UC Berkeley) commented, “It means, essentially, that we still don’t fully understand what is going on in the deep interiors of massive stars shortly before they die.”
    If you think that boom was big, wait till you hear about the latest gamma-ray burst that was seen March 19.  Gamma-ray bursts are the most powerful explosions in the universe.  They were only discovered in the late 1960s.  EurekAlert said this one, numbered GRB 080319B, was aimed directly at earth.  Good thing it was 7.5 billion light-years away.  Its jets were blasting material our direction at 99.99995 percent the speed of light, the article claims.  Within 15 seconds of detection by the orbiting Swift satellite, it had become bright enough to be seen with the naked eye – even from that astronomical distance.  That’s powerful.
    Red dwarf stars, like soldiers, slowly fade away.  Larger stars shed their outer envelopes fairly calmly before retiring as white dwarfs.  Supernovas explode, growing to maximum brightness over a few days or weeks, and then dimming for months as they form neutron stars, pulsars or black holes.  Gamma-ray bursts are the flashbulbs of the cosmos.  Most appear for 10 seconds or less.  Some can flash as brief as a few thousandths of a second.  That’s why it took so long to discover them; you have to be looking at the right place at the right time.  Moreover, astronomers did not realize anything could be so energetic.
    Do astronomers understand these colossal explosions?  They certainly have models.  National Geographic explained, though, that “As a star’s core collapses, it creates a black hole or neutron star that, through processes not fully understood, drive powerful gas jets outward.”  When the jets impact gas previously ejected in earlier explosions, they heat the gas, which astronomers detect as afterglows.  Some astronomers still find it so hard to believe that explosions this bright can be seen from billions of light-years away.  They have argued that they must be nearby objects.  It’s almost unfathomable that any process could produce so much energy so quickly.
    The narrow beams of the burst are emitted from the poles of the spinning star or black hole.  Astronomers believe an ultra-fast component of the beam from GRB 080319B beam was just 0.4 degree across.  Because this rare “jackpot” burst was aimed right along our line of sight, it is providing astronomers with new data – and more questions – as they seek to understand these astonishing explosions.

Data on scientific objects is always incomplete.  The explanations about them, therefore, are also necessarily incomplete.  If star death, which can be observed in a flash, is poorly understood, how about star birth which, because theory says it takes millions of years, cannot be observed from start to finish?
    Astronomers piece together stages of star birth from actual stars presumed to be at different stages.  The charts and explanations sound convincing.  One must ask, though, whether this approach assumes what needs to be proved.  Deciding that stars evolve, and then putting them into an evolutionary sequence, is circular reasoning.  We can see stars age.  We can see them die.  But we can only theorize from laws of gravity, diffusion, viscosity, nuclear physics, quantum mechanics and other principles what a gas cloud would do, given millions of years.
    Stars are not irreducibly complex structures like those in biology.  They do not contain information.  It seems reasonable to trust models of star birth from well-known laws that have been amply confirmed in the lab.  There are many examples in the history of science, though, when plausible models turned out to be wrong.  Usually, the real world proves more complex than the models.  If we struggle with modeling processes that can be observed in a flash, we should at least retain a certain level of humility about scientific models of unobservable processes, and hold them in a tentative way.

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Categories: Amazing Facts, Astronomy

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