Protostellar Disk

It all began when Edwin Hubble published A Relation Between Distance and Radial Velocity Among Extra-Galactic Nebulae, which detailed that the recently discovered “extra-galactic nebulae,” other galaxies, were expanding outward—that the universe wasn’t static. It was a foundational discovery that really led to the birth of cosmology. This, along with Henrietta Leavitt, who, in 1912, discovered a relationship between the varying brightness of “Cepheid Variable stars” and their brightnesses, led to the understanding of what we use today. The method using type Ia supernovae was largely, and still is, calibrated using the relationship between period and luminosity that Henrietta Leavitt found, known as Leavitt’s law. Throughout the rest of the 20th century, work to understand the universe progressed, supported by Einstein’s theories of general and special relativity. This led to one of the most important discoveries in history: the universe wasn’t just expanding, the expansion was happening faster and faster. In 1998, Adam Riess, among others, used type Ia supernovae to determine that the universe is expanding at an increasing rate, the rate that is now being contested by cosmologists. The paper was the first evidence that dark energy, the name we gave to whatever is causing the acceleration, existed. The discovery won the Nobel Prize in 2011, just two years before the two values for the acceleration statistically disagreed. Today, the field is taking advantage of telescopes including Hubble, James Webb, DESI, VLT, and more to understand what we are observing. Adam Riess’ work on the cosmological crisis is invaluable to the field and will be integral for me as it provided a foundation for what is one of the foremost areas of science today. 

A supernova is the violent end to a star’s life. Derived from latin, “super” means beyond or above, and “nova” means new. Before we knew that supernovae were actually the violent deaths of stars, we believed that these bright appearances were the births of stars, shining the cosmos in new light. There are a few types of supernovae. Generally, they can be classified into two groups: core collapse supernovae, and type Ia supernovae. Core collapse supernovae are what people typically think of when thinking of a supernovae. When a massive star eventually runs out of fuel for the nuclear fusion that keeps the star up, gravity wins out, the star collapses, and explodes in what is one of the most energetic events in the entire universe. In contrast, Type Ia supernovae (SNe Ia) occur in binary systems of a red or orange giant star, not unlike what our sun will become in a few billion years, and the compact core of a dead star that was not massive enough to go supernova itself. Most stars are part of a binary system in the universe, and these systems usually birth both stars at about the same time. When one of the orange or red giant stars dies, it sheds its outer layers, not large enough to go through a core collapse supernova. These dense cores that remain, typically white dwarf or neutron stars, syphon mass from their large companion star that is still left. Over time, until reaching 1.4 solar masses, the Chandrasekhar limit, the small core gains mass and eventually explodes as a Type Ia supernova. These are the types of supernovae I am looking at in my research because they have a very special quality. These type Ia supernovae are referred to in astronomy as standard candles or standardizable candles. Their significance comes from the fact that every type Ia supernovae explodes in a similar way. They all brighten to the same intrinsic luminosity at the peak. Just like a regular explosion, there is always a moment that is the hottest, brightest, and most violent. During these violent explosions, the brightest moment is always the same for every one of these binary supernovae. Over the last century, we have been able to quantify that luminosity as about -19.4 magnitude, which I will explain later. This was largely possible because of the Leavitt law that I described earlier. Astronomers determine the distances to the supernovae using other methods and, with the apparent magnitude, they can extrapolate the intrinsic luminosity. Think about it like a car headlight. We know that every car’s headlight is about the same brightness. Therefore, if it looks really bright, it’s probably really close, and if it looks really dim, it’s probably really far. The same can be applied to SNe Ia at their peak. Since we know they always peak at the same brightness, if we measure how bright they “look” at their peak, we can find out how far they are. A relatively simple distance-luminosity relationship, guided by the inverse square of the distance, can be used to find the distances to SNe Ia. 

This is how it’s possible for me to determine the distance by building a curve throughout several different data points. Keep in mind, due to the scale of these explosions, it takes weeks and months for the whole thing to play out simply due to how large the scale is compared to the speed of light which caps the speed at which these processes can occur. While I am not entirely sure how I am going to fully analyze my light curves, there is one source that I may or may not rely heavily on. The source provides a large amount of data points that form a “master curve.”