Where it all began
Just as human beings, planets and stars are born, live their lives and die, so the Universe also lives its life in distinct stages. It began 13.75 billion years ago with the Big Bang, and in this embryonic period without the light from the stars, although in its early years the swirling hot matter would have glowed as brightly as a sun. For the first 100 million years, the conditions were far too violent for stars to form. This changed when the Universe had expanded and cooled sufficiently for the force of gravity to begin to clump the primordial dust, gas and dark matter into galaxies. With this came the dawning of the second great epoch in the life of our universe: the Stelliferous Era, the age of stars.
The Age Of Stars
The moment the first stars were born is one of the most evocative milestones in the evolution of the cosmos. It signals the end of an alien time when the Universe was without structure – a formless void. The beginning of the stelliferous Era marks the beginning of the age of light, the moment when the Universe would have become recognisable to us. The sky would have become black, punctuated with the glowing mist of the galaxies and the sharp silver of the stars. This is our universe today – a place where starlight decorates our nights and illuminates our days.
Close to the beginning of the Stelliferous Era
Our sun is one of at least two hundred billion stars in our galaxy. We live in a cosmos of countless islands of countless stars which bathe the Universe in light. Yet despite the fact that Universe is over 13 billion years old, we are still just at the beginning. Although the cosmos is awash with stars, is populated with vast nebulae and systems of planets and countless billions of worlds that we’ve yet to explore, we are living close to the beginning of the Stelliferous Era, an era of astonishing beauty and complexity. But the cosmos isn’t static and unchanging; it won’t always be this way because as the arrow of time plays out, it produces a cosmos that is as dynamic as it is beautiful.
The First Star
On 23 April 2009 at 07.55 GMT, NASA’s Swift detected one of the most distant cosmic explosions ever seen – a gamma-ray burst that lasted ten seconds. The Swift satellite was designed and built with the intention that it would aid the study of a rare type of event known as a gamma-ray burst. These events, which last only a few seconds, are the most energetic and powerful emitters of radation in the known universe. It is thought that gamma-ray bursts occur in supernova explosions as the dying act of the most massive stars as they collapse to form black holes. By 08.16 GMT, minutes after the burst had added away, the UK’s Infared Telescope (UKIRT) in Hawaii saw the glowing ember of the explosion. As the day wore on, the largest telescopes across the world focused on the event as it appeared above their horizon. The afterglow was observed for several hours, but by 28 April the event had faded completely from view.
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 blood at the centre. This blob is the fading remains of GRB 090423 – once one of the brightest stars in the Universe. The poetically names GRB 090423 was once a Wolf-Rayet star. Named after the two French astronomers who discovered the first one in 1867, Wolf-Rayed stars are 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 produce in its entire 10-billion-year lifetime.
Grb 090423 was a big, 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, its the age of it. The light from this dot has travelled a very long way across the Universe to reach us, and has travelled 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 an entire history of the Universe. GRB 090423 dies over thirteen billion years ago, just over 600 million tears after the Universe began. This is incredibly early in 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 that is slightly older than GRB 090423. 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 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.