During the semester, while taking an astrophysics class with Professor Penprase, a transient astronomical event occurred: a star exploded some 41 million light years away.

The Type Ia: A candle in the dark

Very shortly after the explosion is discovered, an astronomer took a spectrum of the object and found it to be a Type Ia supernova—basically an explosion that results from a merger of at least two stellar objects. One of these objects have to be a white dwarf, a stellar corpse really, that is made up of an agglomeration of degenerate atoms, densely packed together. A white dwarf, left on its own, can live on for trillions of years, but when it interacts with another astronomical body, it may acrete matter from its companion to a point it becomes unstable. The mass limit for a white dwarf to lose its stability is at around 1.4 solar masses, known as the “Chandrasekhar mass limit” after the renown Indian physicist Subrahmanyan Chandrasekhar. Once a white dwarf’s mass exceeds the Chandrasekhar mass limit, the binary system becomes one powerful, titanic explosion—so powerful that it shines more brightly than its host galaxy.

What’s really interesting about the limit is that it gives us an idea of how bright a Type Ia supernova really is when it goes off. This allows us to calibrate vast astronomical distances, using these explosions as a “standard candle”. In fact, the 2011 Nobel Prize in Physics to Adam Riess, Saul Perlmutter, and Brian P. Schmidt was awarded for their work providing evidence for an expanding universe, through the extensive use of Type Ia supernovae to measure distance in the cosmological scale.

What so special about SN 2017cbv then?

The supernova that I was working on has a rather unsexy code name: SN 2017cbv (it’s just a naming convention for transients in the “cbv” part, and SN stands for supernova). While there are hundreds of well-studied Type Ia supernovae, SN 2017cbv stands out for its proximity to us—at just around 41 million light years away. Other Type Ia usually go in the scale of 200 million to 1 billion light years away. SN 2017cbv proximities allow us to use multiple distance calculation techniques available in an astronomer’s tool book, more notably: the TRGB method and the use of Cepheid variables. It’s akin to finding the Rosetta Stone for the cosmic distance ladder in astronomy—not too shabby, is it?

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