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Ancient Cosmic Explosions Ancient Cosmic Explosions Background Science Author: Haley Gomez Background Science - Faulkes Telescope Project Ancient Cosmic Explosions Background Science Supernovae Supernovae are the violent explosions of stars occurring at the end of their lives. On average, one supernova goes off every 50 years or so in our Galaxy. There are two main types of supernovae - Type Ia and II. Type II are the explosions of very massive stars with mass greater than 8 times the mass of the Sun. Type Ia are the explosions of stars similar in mass to the Sun, which have a binary companion and become unstable. Type II -These stars 'live fast - die young', using up all of their Hydrogen and Helium fuel in only a few million years, thousands of times faster than the Sun burns its fuel. When the fuel supply is exhausted the star must burn heavier and heavier elements until, finally, when it can do no more to keep itself alive, the inner parts of the star collapse to form a neutron star or black hole, and the outer parts are flung off in an explosion we call a supernova. Ancient Cosmic Explosions Type Ia - A star similar in mass to the Sun reaches the end of its life as a white dwarf star, which is a hot, dense core (see the Lifecycle of Stars programme). If this hot core has a companion star (so the two stars are orbiting around a common centre of mass - known as a binary system), the white dwarf will pull matter from the companion star onto its surface, until it becomes unstable. The enormous explosion from these stars ejects material into the surroundings at very high velocities, sweeping up the surrounding gas into a shell or a giant bubble. This is known as a supernova remnant. The ejected material and the swept-up compressed gas are very hot. The shell (or bubble) shines at different wavelengths, mainly in the Xray, optical and radio. Supernovae release more energy in a single instant than the Sun will produce in its whole lifetime! If the nearest massive star, Betelgeuse, in the constellation Orion, were to go supernova it would (for a short time) be brighter than the full moon. Below are some images of supernovae captured with the Hubble Space Telescope and the Chandra X-ray Observatory. Credit: Dr CBurrows, ESA/STScI and NASA; NASA/CXC/ASU/J Hester et al.; NASA/CXC/SAO. Page 2 of 5 Background Science - Faulkes Telescope Project Multi-wavelength Supernovae Supernova remnants are studied at many different wavelengths from optical light to Xrays. Different things are happening in different wavelengths; when we observe in, say the X-ray, we are looking at the parts of the shell that are much hotter than the areas shining in the optical. The X-rays come from the extremely hot material at around 10 million degrees Kelvin. These high energy rays are emitted from the chemical elements in the gas, for example, from silicon, iron, magnesium, calcium etc. At such high temperatures, the electrons in these elements are ripped out of the atoms and emit X-rays. Using X-ray images of these objects, we can find out about the distribution of the different elements and how much of these elements are present. This tells us important things about the material in the explosion. The optical emission comes from the interaction between the outwardly moving shell and the material that surrounds the supernova. The material is compressed and heated to 10 thousand Kelvin. At optical wavelengths we are looking at the shocks caused by the expanding material as the ejected material sweeps outwards at high velocities. Ancient Cosmic Explosions Radio emission is a different story. Radio waves in a supernova remnant come from high energy electrons which are heated up by the energy released in the explosion and whiz about in the strong magnetic field of the remnant. In this project you will either use observations of one supernova remnant already studied by Faulkes or you can also make your own observations from a list of three remnants (see the list below). However, be warned, these objects are very faint and require long exposure times! Information about the three supernova remnants chosen for this project are listed below. The X-ray pictures are from the Chandra Observatory, optical from the Hubble Space Telescope and radio from the Very Large Telescope (VLT) and Australian Telescope Compact Array (ATCA) telescopes. Name Type Constellation Cas A Distance (light years) 10,200 II Cassiopeia Kepler 15,000 II or Ia? Ophiuchus N49 160,000 II Dorado, in the Large Magellanic Cloud Note: 1 light year is 9.5 x 1015 m. Page 3 of 5 Background Science - Faulkes Telescope Project Cassiopeia A (Cas A) Cassiopiea A is the brightest radio object in the sky so it is very well studied (and very beautiful)! The massive star at the centre exploded about 300 years ago into a Type II supernova. It is around 11,000 light years away and measures about 8 arcmin across. Credit: NASA/CXC/MIT/UMass Amherst/M D Stage et al; NRAO/AUI/NSF; NASA/ESA/Hubble Heritage The X-ray image shows red for low intensity X-rays, Green for medium intensity and blue for high intensity X-rays. These show the X-rays from hot iron and silicon, which gives us information about the chemical elements in the explosion. Ancient Cosmic Explosions Kepler Kepler’s remnant was discovered by the astronomer Johannes Kepler 400 years ago. It is 15,000 light years away and is 5 arcmin across in the sky. The Sun is very small in comparison to this remnant. You would need 1, 000, 000, 000, 000 Suns placed side by side to stretch out the whole length of our Galaxy but you would only need 6000 Kepler supernova remnants placed side by side! We do not know whether Kepler is a Type Ia or Type II supernova, as there is evidence that supports both! Credit: NASA/CXC/NCSU/S Reynolds et al; VLA; NASA/ESA/ R Sankrit and W Blair Notice how Kepler’s optical image is very faint (this is because it is not as energetic as Cas A’s explosion was). You can already see some differences between Kepler and Cas A. In the X-ray, radio and optical the remnants look very different, even though the same process is thought to have formed them! Page 4 of 5 Background Science - Faulkes Telescope Project N49 N49 is seen in our nearest neighbour galaxy, the Large Magellanic Cloud, about 160, 000 light years away. It is the brightest supernova in this galaxy and is believed to be more than 5000 years old! The shell is 1 arcmin across, and looks incomplete. Credit: ATCA/I. Ill/J. Dicket et al; NASA/STScI/UIUC/Y.H.Chu & R.Williams et al; NASA/CXC/Caltech/S.Kulkarni et al. Ancient Cosmic Explosions N49 has a strange, lop-sided filamentary structure. It was a Type II Supernova which formed this remnant. Page 5 of 5