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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!

A black hole is so dense, its gravitational field prevents anything from escaping, including light. You would think that would make them the "blackest" things in the universe; how in the world do we know they are there? Dr. Andrea Derdzinski tells us about how we detect black holes, either due to the gravitational waves they produce, or due to their interaction with material orbiting around them, which paradoxically can make them some of the brightest objects in the universe.

Up in Orion's shoulder sits Betelgeuse, a supergiant star near the end of its life. The surface of Betelgeuse has been roiling and pulsing for centuries, as long as humans have recorded its modulated luminosity. Dr. Jared Goldberg is a postdoctoral research fellow at the Center for Computational Astrophysics in the Flatiron Institute in New York City. Dr. Golberg has been developing computer models for Betelgeuse to help understand and interpret its oscillations over time.

What happens when a black hole eats up a star? Apparently a lot of things happen, and if you wait around awhile and look in the radio, even more things happen! Dr. Yvette Cendes tells us what it's like to be a radio astronomer and about her latest research into tidal disruption events (TDE's), when a black hole shreds up a star and eats it, producing a dramatic light show across the electromagnetic spectrum.

Some things happen out in the universe that are too powerful to make in a lab. Other phenomena are so coherent and well-ordered, we can't figure out how they can be made without a lab! Fast radio bursts are an incomprehensible combination of both; they are extremely powerful, highly coherent, and very rapid bursts of radio emission. Dr. Maxim Lyutikov spends a lot of his time pondering how these bursts could possibly be made, and all the data seems to point to the most extreme physics imaginable: neutron stars at the highest densities we can imagine, with extremely strong gravity and with a magnetic field a quadrillion times stronger than the Earth's magnetic field.

How do we know so much about supernovae, when all we see is this little point of light getting brighter and then dimmer over time? Given this minimal data, we can often say what type of star exploded, and even some details about how the explosion took place. Supernova astronomers are a lot like forensic scientists dusting for fingerprints and getting DNA samples at the scene of a crime. But instead of a typical crime scene, they are investigating the death of an entire solar system. Dr. Lindsey Kwok is a CIERA fellow at Northwestern University and an expert at using JWST to perform state-of-the-art forensic supernova science.

How big a computer do you need to simulate a supernova? Or a planet being formed? Or a black hole swallowing gas? Many astrophysicists spend their time developing computational models to simulate these systems and learn how they evolve. We discuss these computer simulations with Purdue Professor Dr. Paul Duffell. In this first episode of season 2, Dr. Abigail Polin takes over as host.

What do black holes like to eat? Sometimes a steady diet of interstellar gas just isn't enough and a black hole needs to snack on a whole star. No judgment, we all get that way sometimes. But it can lead to some extremely energetic outflows, visible from across the universe. Dr. Brenna Mockler tells us all about these events, called "Tidal Disruption Events", and what we can learn from observing them.