Description of November 19th Radio Show: Supernovae and Gamma-Ray Bursts

Long available here, below (finally) is the description of the November 19th episode of this radio show, devoted to supernovae and Gamma-Ray Bursts (GRBs). On this program I discussed:

• News: SHIMMER spacecraft observes second season of Polar Mesospheric Clouds, the highest clouds on Earth (link); Chandrayaan-1 Lunar Spacecraft reaches final orbit around the Moon, successfully impacts lunar surface with probe (link); Martian dust storm cuts energy supply on NASA's Mars Rover Spirit (link), but it is still communicating with the Earth (link); recent European conference discussed how life formed on Earth and maybe could have formed on Mars (link); Cassini discovers new, weird aurorae on Saturn (link); Hubble Space Telescope directly images planet around another star - first time ever done! (link), another extra solar planetary system similarly imaged using Keck Observatory (link); International Space Station celebrates 10th anniversary, receives payload of spiders and butterflies (link), a camera to observe crops in the Great Plains and Rockies, and a device to recycle human liquid waste (link); NASA design for new Ares rocket passes review, receives hardware for upcoming test flight of rocket's first stage; NASA restores historic picture of Earth rising above the Moon, available here; NASA tests new Lunar Rover concepts in Hawaii; rocket launched to study effect of Northern Lights on radio communications (link); NASA's Orbiting Carbon Observatory arrives at launch site; 'sun shield" designed for James Webb Space Telescope, NASA's successor to Hubble (link); first "pico satellites" (very small satellites) beign designed and built at University of Florida (link); ESA ministers meet to determine their objectives for upcoming years; Czech Republic becomes 18th member state of ESA; Doug Cooke appointed next NASA Associate Administrator for Exploration Systems; ESA sponsors development of "Health Early Warning System" in Africa; NASA introduces Endeavor Science Teaching Certificate program (link).
• Calendar of upcoming Science / Astronomy events in the greater Poughkeepsie / New York City area.
• Supernovae and Gamma-Ray Bursts: As massive stars age, they run out of lighter elements like Hydrogen and Helium to fuse together to produce energy, and end up with a core full of Iron. Since energy is not released when Iron fuses together, there is no energy source to prevent the core from collapse under its own gravity, so it collapses. As it does so, it releases a lot of energy (much much more energy than the Sun will release in its lifetime), creating a shock wave that moves through the outer part of the star - heating it up and eventually causing it to explode. Light from the hot gas behind this shock is trapped until the shock wave leaves the star, causing a flash of light called "shock breakout." This flash was observed for the first time from a supernova SN2008d (link 1, link 2), an important confirmation for how astronomers think massive stars explode. Analysis of archival data indicated that shock breakout was observed from another supernova (article, link). After this shock exits the star, the star explodes. The stellar material is initially so hot and dense that it forms heavy nuclei, like Nickel 56, whose radioactive decay powers optical light for days - months after the explosion. The spectrum of this light, and the way its brightness (luminosity) changes with time, provides pretty much the only available information on the type of star that exploded and how it did so. Thanks to dust clouds reflecting this light - through a process called "light echos", this emission has been seen from the supernova which created the Cas A supernova remnant (SNR) - confirmed that this explosion was from the core-collapse of a massive star (article, link), and maybe reflection emission from the shock breakout of this explosion has also been detected (link). Light echos from past supernova explosions have detected from many supernova remnants in the Large Magellanic Cloud (link), where they are actually easier to see than in the Milky Way due to the lack of dust in that dwarf galaxy. As I mentioned before, the light from these explosion is powered by the radioactive decay of Nickel-56, which scientists have made in the lab for the first time recently (link). Two clusters of Red Supergiant Stars, likely to produce lots of supernovae in the "near" future, discovered in the Galactic Bar of the Milky Way (link). By looking at "before" and "after" pictures of nearby galaxies which have supernovae, it is possible to identify the star that exploded. This was done for a supernova in NGC 6946, and the exploding star had a mass close to the minimum mass believed to be required for a core-collapse supernova, about 10 times that of the Sun. Stars can also explode if they come to close to a black hole, whose gravity will literally rip the star apart and cause it to explode (link). Similar to NGC 6946, an exploding star was identified in nearby galaxy NGC 2397, which also had a "low" mass for this type of event (link). A supernova similar to SN 1987a which occurred in the Large Magellanic Cloud and is, by far, the best observed supernova ever, is identified (SN 1996cr, link). It has been suggestsed that supernovae whose energy output is much higher than "normal" might produce an ultra-dense object called a "quark star" instead of a neutron star (link). By studying the spectrum of the optical light produced in these explosions, astronomers have found evidence that the explosions are not symmetric. It has also been speculated that SN 2008d, the supernova with the shock breakout, might be a gamma-ray burst (GRB) - a rare class of supernova which produced a narrow beam of gamma-rays - where the gamma-rays were not pointed towards the Earth, though this is highly controversial (article, link). One of these GRBs, GRB 080319B, produced a flash of visible light so bright it could be seen with the naked eye, believed to be the result of this jet of gamma-rays pointed directly towards the Earth (link). Integral satellite detects low-power GRBs. Current satellites are able to see GRBs from the time the first stars formed after the Big Bang, but don't, suggesting these stars when they exploded did not produce GRBs. The galaxies which host long GRBs (the ones produced by exploding stars) tend to be low mass, contain a relatively small amount of metals, while the host galaxies of short GRBs aren't as specific - suggesting two different of objects create these two different classes of GRBs. The properties of the stars that produce long GRBs can be estimated from the X-ray emission observed during and after these explosions (article). Origin of short GRBs still unknown, though there are several suspects.

Thank you very much for listening, and your patience, and hope you enjoyed this show. As always, please email or post below any comments, questions, or concerns you might have.