Rodolfo Smiljanic on long-ago hypernova

Astronomers have identified the telltale sign of a possible hypernova – a huge stellar explosion – in one of our galaxy’s oldest stars.

Rodolfo Smiljanic: So far this is a unique star. There is no other star like this that’s known.

Rodolfo Smiljanic is an astronomer at the University of São Paulo in Brazil. He’s talking about an old halo star called HD 106038. He and his colleagues found an overabundance of a rare element called beryllium in this star.

Rodolfo Smiljanic: Beryllium is a very special element. It is not produced in the Big Bang, such as hydrogen and helium. And it’s not produced by normal stellar nucleosynthesis, like all the heavier elements in the periodic table.

So the question was, how did this star come to have so much beryllium?

Rodolfo Smiljanic: Beryllium is only produced by cosmic-ray spallation in the interstellar medium.

In other words, cosmic rays are produced in stellar explosions. And as the cosmic rays move through space, they can create beryllium. So the original source of the beryllium in HD106038 might have been a stellar explosion – but it would have had to be a really big explosion – not an ordinary supernova – but a hypernova – from a star up to 150 times more massive than our sun.

By the way, beryllium is a light element with atomic number four. In the universe, it’s rarer than platinum.

Our thanks to:
Rodolfo Smiljanic
University of São Paulo, Brazil

April 9, 2008

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