NGC 6240: I Can See Your Halo

Narrator (April Hobart, CXC): The Universe is enormous and full of empty space. Light from the nearest star outside our solar system has to travel through empty black space for 4.2 years before it reaches our eyes, even though light moves faster than anything else in the Universe and we live in a very densely populated region of space! Yet somehow, despite all this empty space, galaxies crashing into each other is a fairly common sight. One such collision has been caught in this cosmic picture; which shows the enormous cloud of hot gas surrounding two large colliding galaxies called NGC 6240.

The two large spiral galaxies seen in this picture are similar in size and shape to our home galaxy, the Milky Way. Both galaxies are believed to be harbouring supermassive black holes at their centres, which are spiralling towards each other as we speak. It's likely that they will eventually merge together to form an even bigger black hole!

Another consequence of this pile up is the birth of millions of new stars in a 'stellarbaby boom' that has lasted over 200 million years! This was caused by the violent collision, which stirred up the gases in each galaxy. The baby boom resulted in the birth of many stars much more massive than the Sun. These then ended their lives in powerful supernova explosions, pumping material into the enormous gas cloud: a 'halo' of hot gas, which can be seen in this picture. And it contains enough material to make 10 billion Suns!

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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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