Wonders of the Universe

STELLAR NURSERIES

Above our heads a story of life and death is being told in spectacular fashion. This tale begins in the vast stellar nurseries where new stars burst into life. These fertile areas of star formation are known as nebulae and are among the most beautiful structures in the skies. One of these, the Orion Nebula (pictured far right), is perhaps the most studied astronomical object. It is usually credited as being discovered by Nicolas-Claude Fabri de Peiresc in 1610, but there is evidence from folk tales that the Mayans knew of the faint smudge beneath the stars of Orion’s belt. It can be seen with the naked eye in a very dark clear sky, and it is this complex, ever-changing formation that has taught us most about how stars are born.

The Omega Nebula (the Horseshoe, or Swan, Nebula) is a vast interstellar cloud that is over fifteen light years across and illuminated by hundreds of bright young stars. These stars, depending on their masses, will burn for hundreds of millions or billions of years, sending a constant stream of light across the Universe until their voracious hunger depletes the hydrogen in their cores and forces them to expand and transform into giants.

As they near the end of their lives, the most massive stars are transformed into colossal giants – such as the red Mira, whose radius is 400 times that of our sun and only just clinging onto life. When the end finally comes for stars like these, the ensuing supernova explosion will leave only a faint trace of the star. For the largest stars, the supernova will leave a black hole behind – an object so dense that even light cannot escape its clutches. Slightly smaller stars will end their post-supernova days as neutron stars, which we detect by the lighthouse beam of radiowaves they emit as they spin every few seconds or less.

Stars much smaller than Mira won’t go out with a bang. Such relatively cool stars are called red dwarfs and are the most common type of star in our galaxy. Perhaps the most famous of these we have studied is Gliese 581. Just over twenty light years away from Earth, this star has been the subject of intense observation in recent years due to the discovery of at least six exoplanets orbiting around it. Most excitingly, planet Gliese 581 g is thought to orbit within the habitable zone of the star and so is considered a prime location for the search for extraterrestrial life

These fascinating ultraviolet images, taken by NASA’s Galaxy Evolution Explorer, show a star named Mira speeding across the sky and leaving behind it an enormous trail of debris. This material is in fact ‘seeds’ which will be recycled to create new stars, planets and possibly even life, as it travels through our galaxy.

NASA

Known as the Horseshoe, or Swan, Nebula, this molecular cloud is also often called the Omega Nebula, due to its similarity in shape to the Greek letter Omega. Ultraviolet light from a cluster of massive young stars buried within the nebula make the surrounding gas glow. This image was taken by the European Southern Observatory’s 3.6-metre (11.8-foot) telescope in La Silla, Chile.

NASA

Perhaps the most studied astronomical object, the Orion Nebula is also one of the most beautiful structures in the sky. On over 100 orbits of Earth between October 2004 and April 2005, NASA’s Hubble Space Telecope captured this nebula in one of the most detailed astronomical images ever produced. On a clear, dark night sky this impressive formation – which includes more than 3,000 stars of varying sizes – can be seen with the naked eye. This complex, constantly evolving formation has provided scientists with crucial insight into how stars are formed.

The Venus transits of our sun are a rare occurrence, they only happen twice in eight years and won’t be repeated for another 100 years. The last transit happened in 2004, with another due in 2012. We will have to wait until 2116 for the next one.

This is a composite image of Venus transiting the Sun on 8 June 2004. Venus can be seen from Earth as a small black disc moving across the face of the Sun.

ECKHARD SLAWIK / SCIENCE PHOTO LIBRARY