Wonders of the Universe - Brian Cox [95]
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When these stars run out of nuclear fuel…they die in a dramatic fashion, collapsing in an instant and releasing more energy in one second than our sun will produce in its entire 10-billion-year lifetime.
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The picture shown here merges data from two of Swift’s telescopes, and the important feature of this composite image is the rather unremarkable-looking red blob at the centre. This blob is the fading remains of GRB 090423 – once one of the brightest stars in the Universe. The poetically named GRB 090423 was once a Wolf-Rayet star. Named after the two French astronomers who discovered the first one in 1867, Wolf-Rayet stars are massive – over twenty times the mass of our sun – and because they are so massive, and burn so brightly, they are also extremely short-lived. When these stars run out of nuclear fuel after only a few hundred thousand years, they die in a dramatic fashion, collapsing in an instant and releasing more energy in one second than our sun will produce in its entire 10-billion-year lifetime.
GRB 090423 was a big Wolf-Rayet star – perhaps 40 or 50 times the mass of the Sun – however, this is not the only thing that is interesting about it. It’s not just the story of the death of this star, revealed by the brief appearance of the pale red dot, that has captivated astronomers, it’s the age of it. The light from this dot has travelled a very long way across the Universe to reach us, and has taken a very long time to do it. When we look at the afterglow of this explosion, we are looking at an event that happened a long time ago, in a galaxy far, far away. In fact, this light has been travelling towards us for almost the entire history of the Universe. GRB 090423 died over thirteen billion years ago, just over 600 million years after the Universe began. This is incredibly early in the Universe’s history. At the time of filming Wonders of the Universe, in autumn 2010, GRB 090423 was the oldest single object ever seen, although just after filming a galaxy was discovered in the Hubble Space Telescope’s Ultra Deep Field Image (see Chapter 3) that is slightly older than GRB 090423. Even more poetically named UDFy-38135539, this galaxy currently holds the distance and age record with a light travel time of slightly over 13 billion years. Allowing for the expansion of the Universe, the (so-called co-moving) distance of UDFy-38135539 is currently 30 billion light years away from Earth.
However, it is the discovery of GRB 090423, this ghostly pale red dot, and the sight of the explosive death of one of the first stars in the Universe, that gives us a glimpse of the grandest timescale of them all
THE DESTINY OF STARS
The arrow of time has been playing out in every corner of the Universe since the beginning of time. It dictates the destiny of everything; our civilisation, our planet, the Solar System, and all that lies beyond. The entropic march is inevitable and relentless. Nothing can resist the arrow of time, nothing can last forever, no star can shine without end and no planet can continue to turn. The Universe, bound by the laws of nature, must decay towards a radically different tomorrow.
We take for granted the sight of the Sun rising and setting on our horizon, but we now know its presence is not eternal.
Today, 13.7 billion years after the Universe began, we are living through the most productive era that our universe will ever know. The Stelliferous Era is a time of life and death, with the constant