Astronomy Night

 The third Astronomy Open Night of the semester showcased on Friday a new method of calculating interstellar distances.  Cloudy weather prevented telescope viewing, but dozens of people arrived at the Earth and Space Sciences building to learn about supernova models and ask questions.

Alan Calder, an associate professor in the astronomy department, hosted the event.  In addition to answering questions about dark energy and black holes, he described a novel method for interpreting observations of supernovae, giant explosions of stars.  A graduate student in the astronomy program at SBU, Brendan Krueger, has developed a model that relates the brightness of some supernovae to the amount of a nickel isotope contained in the stars.  He and other researchers at Stony Brook and other American universities have submitted their findings to the Astrophysical Journal.

Supernovae are explosions of stars that throw off enormous amounts of energy. The brightness of the explosion lets astronomers gauge how far away the star was when it exploded.  One kind of supernova, Type 1a, has a very predictable brightness that allows it to be used as a “standard candle,” a light source of known intensity.  Brightness varies with the inverse of the distance squared, so a supernova twice as far away would be one quarter as bright.

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“By understanding how these things work and what makes one brighter than another,” Calder said, “then we begin to get a handle on how good they are as standard candles.”

However, some explosions are brighter or dimmer than one would expect based on distance alone.  The researchers suggest that a significant part of the variation depends on a subatomic process going on in the stars.  Some supernovae combine electrons and protons into neutrons in greater numbers than other supernovae do.  Neutrons tend to make atoms of a given element more stable, and stable atoms do not give off as much light as unstable atoms.

Stars that pack fewer neutrons into nickel atoms are brighter when they explode, the researchers found.

“The seemingly innocuous reaction of electron capture doesn’t really change the explosion dynamics,” Calder said.  “But it turns off the light curve if you don’t get to [a nickel isotope with 28 neutrons], and that’s the whole thing.  The devil is in the details of the nuclear physics.”

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The rate of the electron capture can be determined through measuring other characteristics of the supernova, so the variation in brightness can be calculated and corrected for.  Distances can then be calculated from the brightness.

Accurate knowledge of interstellar distances allows researchers to better understand the mechanics behind the age, size and growth of the universe.

Sophomore Davin Fernandez said that he wanted to learn about standard candles beyond what his astronomy class had covered, as well as the extra credit promised to those attending the lecture.

Ferid Kamoua, 13, attended the event with his family, and he expressed his appreciation for the animated simulations of exploding stars.

Science Open Night lectures are held every Friday night and are available to the public.  The next Astronomy Open Night is April 27.

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