47 Tucanae: The Mysterious Afterlife of Stellar Giants

Narrator (April Hobart, CXC): Neutron stars are the ultra-dense cores left behind after a massive star reaches the end of its life and explodes. The star's outer layers are blasted away in the explosion, but material at the centre of the star collapses in on itself. This forming a tightly packed ball of material and what we end up with is the densest (meaning 'most tightly packed') object known in the entire Universe outside of a black hole: a neutron star!

This new space picture shows a group of stars called a globular cluster. These are some of the oldest objects in space - almost as old as the Universe itself! This means many of the stars within have already lived their lives. The most massive have long since exploded, leaving behind several neutron stars.

Using a neutron star within this cluster, along with several others, astronomers have worked out the relationship between the stars' mass (how much material they have) and how big they are.

The new data shows that an average neutron star, with the same mass as around one and a half of our Sun's, would be around 12 km across. That's about the size of a town! With all this material packed down into such a small space, neutron stars are unbelievably dense objects. The pressure at their centers is over ten trillion trillion times the pressure required to form diamonds inside the Earth.

Return to Podcasts

Narrator (April Hobart, CXC): HD 189733b: An exoplanet in orbit around a star about 63 light years from Earth. It has been nearly two decades since the first exoplanets – that is, planets around stars other than our Sun – were discovered. Now for the first time, X-ray observations have detected an exoplanet passing in front of its parent star. The observations, made by NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton Observatory, took advantage of the alignment of a planet and its parent star in HD 189733. This alignment enabled the observatories to observe a dip in X-ray intensity as the planet moved in front of, or transited, the star. This technique is the one used so successfully at optical wavelengths by NASA's Kepler telescope. In earlier studies using optical light, astronomers discovered that the main star in the HD 189733 system had what is known as a "hot Jupiter" around it. This means the planet is about the size of Jupiter, but in very close orbit around its star. The planet – that has been named HD 189733b -- is over 30 times closer to its star than Earth is to the Sun, and goes around the star once every 2.2 days. The new X-ray data suggest that this planet has a larger atmosphere than previously thought. This, in turn, may imply that radiation from the parent star is evaporating the atmosphere of HD 189733b more quickly than expected. The results on HD 189733 demonstrate how we need information from many different telescopes that detect different types of light to get a fuller picture of these mysterious worlds that we are now able to explore.