Studying the Universe

Multimessenger Astronomy

Every day light reaches us, some of it having traveled from across the solar system, some of it having traveled across the Milky Way. Every once in a while, a "new star" is visible to humans on earth, signaling a massive astrophysical change. It has only been recently that humans have seen the effects of such a massive event both in light, and gravitational waves in GW170817. This represents the first observation of a binary neutron star merger (at least, that we've been able to identify as such). It's possible people long ago saw such an event in our own galaxy and wondered what the cause was As humans improve our ability to see the sky, our view of these changes in the universe will improve as well. I aim to help people across the world better understand the way the sky changes, and what it tells us about everything else in the universe.

One of the remarkable things that we can learn from studying neutron stars is the properties of the matter inside of them. This matter is extremely dense, about a million billion times denser than water. A teaspoon of it would weigh as much as a mountain. The properties of this matter are in principle determined by the standard model of particle physics, but solving the equations of motion of this matter is impossible with modern computational techniques (and likely will be for a long time). Noneththeless, the large scale structure of neutron stars is determined by the properties of this matter, so by observing neutron stars, we can test theories of how this matter behaves; if neutron stars look one way, then it must be the case that the matter inside is compatible with them looking that way. We are still only in the infancy of these studies, and many more promising neutron star observations promise to reveal much more about what is going on. One of the most powerful tools to learn about this matter, is via multimessenger observations of neutron stars.

How do we know what to look for

Numerical Relativity and Hydrodynamics

The history of theoretical science is long. The earliest astronomers tended to misestimate the configuration of the Universe and place the Earth in a distinguished place, inventing new rules to explain why the planets moved they did. It turns out the Earth has an orbit that is quite generic, around the sun! Most people tend to agree that among competing explanations for something, the explanation that makes the fewest assumptions, while still producing correct results is the best, or perhaps, most useful. General Relativity is in some sense the most "generic" theory in history. Giving no special significance to any frame of reference, any observer, any prior geometry of our cosmos. It also has yet to make an incorrect prediction. Some day it almost certainly will, but until then we find that using the equations Einstein wrote down to make predictions about the way the universe works is remarkably effective. Today, computers are leveraged to model the complex physics that results from merging compact objects (a unique feature of General Relativity). Black holes are themselves simple, being described by only a few numbers, while neutron stars contain matter and are much more complicated. Correctly simulating the physics inside of mergers of binary neutron stars is a major problem we face. Nonetheless, with the advent of supercomputers, we now have an opportunity to model these mergers with fewer and fewer simplifying assumptions, which will be crucial for understanding how the observations we make of merging neutron stars meshes with our understadnign of fundamental physics and the standard model of particle physics.