Most of the mass in the universe is invisible. We call it "Dark Matter", and the only reason we know it's there is because we can see how it gravitationally interacts with regular matter. For example, in our own galaxy, Dark Matter comprises most of the mass, in a large spherical "halo" that binds the smaller spiral of gas and stars that we can see. As all our stars orbit the Milky Way, they are passing through a sea of dark matter, and this should create observable consequences that allow us to test theories about the nature of dark matter itself. Dr. Gurtina Besla develops large-scale computer simulations of the Milky Way to compute these observational signatures, allowing us to put our theories of dark matter to the test inside our own galaxy.

What's the deal with black holes?

How did our solar system form? More generally, how does any solar system form? We get some of our answers to these questions by looking at newly-forming planetary systems in the first million years of their lives. But getting a complete picture also requires a lot of theoretical work, understanding each stage of solar system formation, which often entails big computational models of the early solar system. Dr. Kaitlin Kratter is a leader in the practice of building these big models and using them to improve our understanding of how the planets first formed.

A white dwarf star is the compact, dense remnant of a once-thriving solar system. Long after the original star has died and turned into a white dwarf, it can still interact with its solar system. We can even see white dwarfs eating up the rocky debris that once made up their solar system, and apparently making sense of all of this requires a detailed understanding of how convection works in these dead stellar remnants.

How did the planets form? What was going on in the first few brief million years of our solar system? And how did it impact what we see in our solar system today? Dr. Merel van 't Hoff takes us on a journey through astrochemistry to understand the planetary wombs that house solar systems in their prenatal years.

What kinds of things do neutron stars do? They can smash into each other, producing bright flashes of radiation and strong ripples in spacetime that can be detected across the universe! Or, a neutron star can just be sitting there, and its magnetic field might suddenly shift and produce a dramatic burst of radio waves! But mainly, neutron stars are super-dense and super-complicated, giving us a probe of fundamental physics in its most extreme limits. Dr. Wen-Fai Fong tells us all about how we can learn more!

Just how big can black holes get? Well, they can get super-massive! That is, millions to billions of times as massive as the sun. How do we know this? We've detected these supermassive black holes at the centers of galaxies in a number of ways, and Dr. Daniel D'Orazio has been leading the way in figuring out new ways we can detect more, especially if it's not one but two black holes orbiting one another in a binary system.

In this week's episode, Dr. Abigail Polin joins us to answer your questions from the internet, on a variety of topics tangentially related to astrophysics! Questions range from the basic and fundamental to the obscure and weird. Answers are totally unprepared and rambling. Our guests this week are Dr. Abigail Polin, PLUS an extra-special mystery guest!