Let there be gamma rays

It was one of the first coughing turnovers of the cosmochemistry engine.

The NASA Swift satellite has detected the oldest known star detonation in the universe… 13 billion years old. The previous record was only about 200 million years younger, but at such an early epoch of our universe – which is itself only 13.7 billion years old – 200 million years becomes a significant amount of time. The gamma ray burst heralding this ancient star’s end occurred about 700 million years after the universe instantiated, which is just about as old as a star can be.

According to a very bad article about this discovery on CNN.com, this new oldest gamma burst erupted from a star of about 30 to 100 solar masses…. meaning it probably used to be a supergiant or hypergiant star. The CNN.com piece is a bad article because it says:

“Telescopes around the world swiveled to focus on the explosion, soon picking up infrared radiation, which travels more slowly than gamma rays. Berger waited for the visible light which he expected to come next.

I can’t believe this made it past the science editor. Oh, that’s right… there probably isn’t one. In brief, all electromagnetic radiation (which includes light) always travels at the local velocity of light at all times and everywhere. What that article tried to say was that the first bright flash that happens during a massive supernova is brightest in the gamma ray region of the electromagnetic spectrum. The gamma blast reaches a catastrophic peak of searing intensity, then proceeds to cool through the gamma and X-ray bands, then passes through a temperature range where visible light shines, then finally dims to emit infrared light for a long, long time.

Anyway, back to the oldest gamma burst. At such an early stage of the universe’s evolution, that star would have been made almost entirely of virginal hydrogen and helium, and essentially nothing else. The first stars had no stars to preceed them, and so incorporated no fusion ash of heavier elements such as carbon, oxygen, nitrogen and iron. Only after several generations of primal supergiants congealed, burned out, and detonated would the interstellar medium begin to accumulate enough heavy atoms to form particles of ice and rock.

Fortunately for planets and life, there were probably many super- and hypersuns around back then to get the job started. Such massive stars only live for a few million years – mere moments, cosmologically – then explode, forming a black hole and spewing metals into the surrounding void-ocean of primordial hydrogen, from which stars emerge and into which dead stars deposit their cooling remains. After only a few hundred million years of this, galaxies probably started to accumulate enough metals to make icy, rocky worlds… the first planets ever to exist. Ours is not one of those planets… Earth came along about 8.4 billion years later. Those first, most-primal planets are probably now long dead, circling star corpses or drifting through empty space….

… or ARE they?


~ by Planetologist on April 29, 2009.

6 Responses to “Let there be gamma rays”

  1. […] around, and found two things (which I presume are reliable) to help clarify.  First was a blog by “The Planetologist”, which quoted the CNN article with regard gamma rays and light arriving at two separate times. […]

  2. Thanks for the clarification on the absence of visible light! I am interested in the universe and have a college degree in science and was in the dark after reading the article.

  3. If there were Gama Rays then there should be light can you explain why?

  4. I caught this blunder immediately as well. When I scrolled down to look for a way to comment or reply to CNN, I found the link to your blog.

    Ray Gedaly

  5. Thanks for the clarification of the CNN article, I knew that that could not be right….In their defense, they have a link to your blog at the bottom. Can you also clear up for me what the significance is of the visible light ‘never arriving?’ It sounds from your explanation like visible should have been seen before infrared; did CNN get that backwards as well?

    • Visible light tends to get absorbed easily by the interstellar medium – that being one big reason we don’t see the Galactic core from Earth. Our Galactic core is fairly bright, but dust and gas between it and us blocks the light we can see with our chordate jelly-eyes. In other parts of the EM spectrum, though, that core light is detectable with tech instruments. Depending on what the signal from this gamma-burster had to pass through on its way to us, parts of its spectrum might be dark from out point of view. I’ll defer a more detailed description of the intensity/time spectrum of gamma-bursters to those with more expertise in the field than I have. 🙂

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