SGR 0418+5729: A Flare for the Dramatic

Narrator (April Hobart, CXC): Never let it be said that stars don't have style: when a massive star comes to the end of its life it doesn't quietly burn out like a dying candle. Instead, it goes out with a bang, or rather an explosion that outshines almost everything else in the Universe! This explosion is called a supernova, and when this happens, the star is torn apart, throwing material into space. But something is left behind - a 'neutron star' - the remaining core of a massive star once it has exploded.

This picture might look like a jawbreaker that's been dipped in dental floss, but it actually shows an artist's impression of a very exotic type of neutron star called a "magnetar".

Magnetars are some of the most extreme objects known in the Universe. They are a very small and ultra-compact type of neutron star that erupt randomly with bursts of powerful high-energy flares. These stars were given their name because they are very strong magnets. You've probably played with magnets in school. Each magnets is surrounded by an invisible force field, called a "magnetic field".

Magnetars have notoriously strong magnetic fields - the strongest in the entire Universe, in fact! Well, except for this one. This picture shows "SGR 0418", a magnetar that doesn't fit the mould. It has a much weaker magnetic field on its surface than any other star of its kind. What makes this really puzzling is that it raises the question: where does the energy come from to power its dramatic high-energy flares? It is thought to come from the strong magnetic field. But this theory doesn't work for SGR 0418! SGR 0418 appears to be an oddity amongst oddities! Astronomers are puzzled but think that there is a much stronger magnetic field underneath the surface of SGR 0418.

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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.

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