By Prof Nial Tanvir
11th January 2019
Nial started by giving an overview of what we know of the universe with regard to distance and scale. He explained Hubble’s discovery of red shift and produced charts showing what we “see” in the spectrum and what we can detect in the blue shift to the red shift.
He explained that the primary satellite recording the gamma ray bursts it the Swift telescope, launched in 2004. Past its best but still doing sterling work recording data from the GRB’s – as many as two per week!
The data suggests that when a star dies and shrinks, the outer material is slower to move than the core. The resulting GRB is emitted before the slower material has caught up. A member questioned this and Nial was able to explain the dynamics involved. GRB’s are the brightest and most violent explosions we know of, and so can be seen to very great distances. He was able to show us slides of actual GRB’s showing the light lasting several days.
One particular topical issue, Nial explained, is the question of how the tenuous gas between the galaxies came to be ionized, which it has been since only a few hundred million years after the Big Bang. Astronomers have long suspected that UV radiation from early stars must have caused this ionization, but studies of GRB’s suggest that UV radiation would have been trapped within galaxies, so couldn’t be the cause. One of the questions arising from this is that not all the hydrogen stays within the vicinity of the collapsed star. A proportion of it wanders between galaxies and doesn’t become ionised. Those asking these questions, including myself, caused Nial to laugh as we described the non-ionised hydrogen as lazy as it just wanders the universe doing nothing. It is only the ionised hydrogen that contributes to the formation of new stars. Thus the mystery of ionization continues.
A member asked a question that had been perplexing him for over 20 years and was very pleased that Nial was able to answer it to his satisfaction. In fact as I thanked him for his talk when I saw him off, he said he was delighted with the questions as it gave him much satisfaction when giving talks.