News that Will Turn Your World…or Your Star…Inside Out
What astronomers see out in space is often a reflection of what might happen in our own corner of the universe. Asteroids collide with one another, stars collapse, etc. Observing these phenomena reveal much about even own space in the galaxy and therefore when the supernova Cassiopeia A occurred, astronomers took notice. What they found was unusual.
When astronomers observed Cassiopeia A, they noticed that the supernova was turned inside out and that the iron, which normally forms in the center of the supernova remnant, was on the outside instead.
Cas A is 11,000 light years away from Earth and exploded 330 years ago. As with other stars, Cas A was fueled by hydrogen until all this was spent and the core began to collapse as it heated up. The increased temperature allows the star to fuse other materials, and depending on the size of the star, heavier materials can be fused. Layers of materials fuse, continually cooling and expanding as the core collapses, until all that is left is a core of iron because the iron requires too much energy to fuse. The lack of outward pressure following the fusion forces the star to collapse, as the subatomic particles of the core are crushed towards one another, turning protons and electrons into neutrons and neutrinos. Neutrinos ‘bounce’ out layers and parts of the star as it collapses providing enough energy to even fuse heavier elements such as gold, silver, platinum, or uranium. By studying the light emitted from this supernova, scientists can determine the supernova remnants and its composition. Cas A is anywhere from 15 to 25 times the mass of the sun that exploded prior on its path and therefore it would be expected that it would collapse as the other one did. However, the experts were startled to see what occurred.
Using data recorded by NASA’s Chandra X-ray Observatory, Una Hwang of the Goddard Space Flight Centre, Maryland and J Martin Laming of the Naval Research Laboratory, Washington, studied the distribution of elements across the remnants. They found the amount of iron that they had expected, but surprisingly the iron was “on the outside, with apparently nothing in the center”. This observation has shed some light on a fairly rare occurrence—a neutron star kick. A neutron star kick is the recoil a neutron star experiences following supernovae explosions. Hwang and Laming suspect that this kick is caused by instability in the core of the supernova, reasoning that if momentum is conserved, then the ejecta of the collapsing supernova would move in the away from the neutron star, as seen in Cas A. Subsequently the iron should have moved in the opposite direction as well—but it didn’t. For now, astronomers are still unsure why.
Truth be told, the answer to many of these questions about neutron stark kicks are largely unknown. Other approaches to interpreting this data such as observing the movement of titanium-44 in the supernova, have been used but still the data can be deemed “noisy and inconclusive”. The best chance of astronomers understanding this phenomenon is through data that will be collected by NuSTAR, the first high energy X-ray observatory set to launch this year. Hopefully, this will provide better data, but until then our understanding of these astrological phenomena remains incomplete.
Alex Kumar is a freshman from Baker College at Rice University.