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Best Bang Since The Big One

StarKinder, I'll warn you.  This might make your brain hurt a bit.

Illustration. Credit: NASA/CXC/M.Weiss

In September of 2006, Robert Quimby, an astronomer at the University of Texas, was looking for exploding stars.  This sounds tricky but is really pretty straightforward.  Just pick an easy to observe galaxy, point a camera (telescope) at it and wait.  Eventually a star in it will go Boom!  On September 18th, Dr. Quimby was observing a ordinary galaxy named NGC1260 when he noticed his nova - now named SN2006gy.  Dr. Quimby notified the other nova hunters around the world and they pointed bigger ground based and space based scopes at it.  40 days later, it was still getting brighter.  This was really strange.  No type of nova ever acted like that and the peak brightness of SN2006gy was at least 10 times brighter than any supernova ever recorded.  What could this thing be?

Now, we need to do a bit of refreshing.  Do you remember our discussions about how stars explode?   Go to: https://solar-center.stanford.edu/activities/jeff/ and refresh your memory.  Basically a star explodes when it uses up all its fuel and the central core collapses or one star in a binary (2 star) system steals the outer atmosphere of its companion and goes boom.  Pretty much all nova are variations on these two ideas.  SN2006gy didn't look like either of these types.

E=mc˛  Remember that?  It is an important part of the Laws of Relativity.  Energy equals mass and mass equals energy.  We can "make" particles by smashing other particles together at very nearly the speed of light and we can turn mass into energy by putting a particle and its anti-particle together (there are other ways of making the mass-energy magic but these are good examples).  You can even turn an photon - one of those particles of "light" - into real solid particles of matter.  Sometimes doing this can create a disaster.  Here's how.

If you have REAL high energy photon - more energetic than violet, or ultra-violet, or even x-rays - called a gamma ray and you tangle it up in an electromagnetic field, you can get the photon to turn into an electron and a positron both traveling in the same direction that the gamma ray was traveling.  Normally an electron-positron pair would instantly smack together and form a gamma ray again (kind of a waste of time).  Well, since we are in a electromagnetic field and electrons and positron are electrically charged, one gets bent one way and the other the other and they don't smack together.

Turns out that if you have a HUGE star, one that has about 150 times the mass of our sun, it uses up its fuel really really fast.  It turns all its core hydrogen to helium, and helium to beryllium, and beryllium to oxygen, all in just a few hundred thousand years (maybe a couple million).  Each one of those steps is hotter than the last and the star gets hotter and puffed up.  Hot gas expands - as in a hot air balloon - and the high energy photons steaming out of the core also expand the star (this is much like the solar wind we talked about a few days ago but this is WAY more powerful) by "light pressure".  It turns out that the photons that are created when the star starts "burning" oxygen have just enough energy to turn into an electron-positron pair as we discussed above.  Suddenly the outer atmosphere of our star is no longer held up by light pressure and the outer atmosphere crashes down on the star's core.  All that gravitational energy crunches the hydrogen and helium still in the atmosphere and causes lots of it to fuse and there is a big explosion.  Now this is a big explosion but not BIG BIG.  Two things happen.  The outer atmosphere gets blown off in a sphere of moderately fast expanding hot gas and the core of the star uses up lots of fuel in this "bounce".  In just a few years the oxygen starts fusing into sulfur and the core gets REALLY hot and the whole thing happens again only this time the outer atmosphere gets blown off moving very fast.  This new shell of rapidly expanding super hot gas smashes into the older, slower shell of gas from the first boom and almost all of the total energy in both shells turns into photons.  This is probably the huge explosion that Dr. Quimby found.

There is a possibility that the size of the huge star was just right that the entire core of the star blew up and left nothing but debris - no black hole, no neutron star, no white dwarf!

The reason why this is a very rare event is that stars of 150 solar masses are extremely rare.  We may not even have any in our galaxy.  When the universe was very young and there was nothing but lots of hydrogen and helium about, these kinds of huge stars were common but they ran out of fuel a blew up in just a few thousand years and the stars we see now are made from the debris left over from these titanic precursors.  This debris is made up of all the elements from hydrogen to uranium and it is very difficult to build a huge mass star out of it (there are laws of physics that make it hard to do).

When Robert Quimby found this nova, it was the record largest nova ever found.  It is quite a surprise that it no longer holds that record.  But that's another story.