Starts With A Bang podcast

Starts With A Bang #131 - The Baryon Life Cycle

In order for stars to form, you need the right ingredients to make it happen: gravity, mass, time, and of course the right type of matter in the form of baryons. Shortly after the Big Bang, the Universe had plenty of them, but they were all very simple: protons, deuterons, helium-3 and helium-4 nuclei, and a tiny bit of lithium-7. These nuclei, made out of protons and neutrons, were all that the Universe gave us to work with prior to the formation of stars. But, in clumps of material small and large, from individual star clusters to enormous galaxy cluster scales and everything in between, these baryons went to work and, across the Universe over the past 13.8 billion years, created sextillions of stars within the observable Universe.In a very real way, the story of how we ourselves came to be is the story of how baryons evolved, matured, and wound up deducing our own cosmic history. Yet so many mysteries about that process still remain, from the baryon life cycles within galaxies to identifying the right conditions to trigger star-formation in the vastly different environments where they formed throughout cosmic history. Yet, it's by examining so many different environments where stars do and don't form, in galaxies of all different masses and metallicities, and in the modern, nearby Universe as well as far back in ancient cosmic history, that we can begin to piece the full story together.Here to guide us through this topic, and starring in this episode of the Starts With A Bang podcast, I'm so pleased to welcome newly-minted Dr. Ava Polzin to the show. Ava got her Ph.D. from the University of Chicago and is about to begin a postdoc at the University of Toronto, and has a whirlwind tour of information in store for us all on this episode of the podcast. Plus, at the end, there are a few bonuses she was eager to highlight, and you can find the links to two fabulous papers she's written for the good of the world below. Make sure you tune in; this is one episode you won't want to miss!Astronomy as a Field: https://arxiv.org/abs/2312.04041Picture an Astronomer: https://arxiv.org/abs/2512.24465(This image shows a composite of Hubble and JWST data for gas-rich spiral galaxy NGC 7496, which highlights not only the starlight you're used to seeing in optical images, but heated dust that shines brilliantly in JWST imagery, showcasing the locations of near-future episodes of star-formation yet to come. Credit: NASA / ESA / CSA / Judy Schmidt)

Starts With A Bang #130 - the initial mass function of stars

One of the most foundational questions we know how to ask in astronomy is simply this: given a cloud of gas of a given mass, what types of stars will form? How many stars of a given mass will you wind up with, and what factors does that depend on? The answer to this question, if we can give an answer, is known as the "initial mass function," and is generally very difficult to measure except in the most nearby of places: within our own Milky Way.It's possible that every time we form stars, we have a different initial mass function to reckon with. It's possible that in a different environment, perhaps with less dust, fewer heavy elements, or earlier in the Universe (when the background temperature was hotter), things behaved very differently from how they do in the here-and-now. Yet because of the extreme difference in brightness between high-mass and low-mass stars, we can only measure both high and low mass stars together nearby. It's as though we're only measuring the tip of the cosmic iceberg as far as stars go, where we're compelled to use what we know to draw conclusions about the rest of the Universe.In a very exciting new development, University of Missouri professor Charles Steinhardt, along with his undergraduate students Carter Meyerhoff and Alexander Luening, just put out a paper (link here: arxiv.org/abs/2603.23594) that could wind up revolutionizing what we think about star-formation across the Universe. Astronomers have long considered a top-heavy mass function as a possibility, but early on, perhaps "bottom-light" is a better answer. Have a listen and a good think for yourself in this truly remarkable episode of the Starts With A Bang podcast!(This image shows the Eagle Nebula, Messier 16, in a three-color composite that closely approximates the colors a very sensitive human eye would be able to see. Although the gas and dust makes prominent features, those are transient; they will be blown away in only a few million years. Although the new stars inside have formed across all different masses, the majority of the new starlight is dominated by massive, bright, blue, short-lived stars. Credit: ESO.)

Starts With A Bang #129 - Triton and the outer solar system

We often think about the Solar System as being our own cosmic backyard, and in many ways, it is: these are the closest objects to us in all the Universe, and our only opportunity to study lunar and planetary systems in situ. However, when it comes to the objects beyond Saturn, including the Uranian and Neptunian systems, as well as everything that lies in the Kuiper belt and beyond, the only probes we've ever sent their way are Voyager 2, which flew by Uranus and Neptune in the late 1980s, and New Horizons, which flew past Pluto in 2015.That means, unlike Jupiter and Saturn, we've never had a dedicated orbiter, lander, or atmospheric probe around the outermost planets or lunar systems even in our own backyard. Moreover, there are no such planned missions that are funded and slated to fly, which is really too bad, as there's so much to learn about these planets and worlds that are so well-represented in exoplanet analogues all across the galaxy and Universe. In particular, one moon stands out as the largest body with a solid surface: Triton, the 7th largest moon in the Solar System and which represents more than 98% of the mass of all the moons that orbit Neptune.Here to guide us through the far reaches of our Solar System, I'm so pleased to welcome PhD candidate Lana Tilke to the program. There's a whole lot of ground that we cover, and the conversation left me inspired with the questions that we're asking today, and brimming with hope that we take the steps we needed to answer them. If you'd like to know where we are and where we're headed next, you just might love this episode too!(This image shows a composite of Neptune's giant moon Triton, assembled from Voyager 2 imagery at the highest possible resolution. The dark streaks come from cryovolcanic geysers, also known as black smokers, from Triton's south polar region. Credit: NASA/JPL)

Starts With A Bang #128 - Planet formation and proto-protoplanets

Whenever a new star forms, several processes appear to be nearly universal. A cloud of cold molecular gas contracts, fragments, and rapidly collapses in certain places. The densest, coldest clumps of gas contract first, drawing in larger and larger amounts of matter onto them. A large, massive enough clump will heat up and have a random shape: collapsing along the shortest axis first, forming a protostar at the center surrounded by a disk of material. That's where the story of planet formation begins.Assuming the conditions in the disk are sufficient, clumps will begin to form, and over hundreds of thousands to millions of years, the first protoplanets and then full-fledged planets will arise: a relatively rapid cosmic process, that's usually all complete within a mere 10 million years: a blink of a cosmic eye in the history of our own 4.5 billion year old Solar System. However, by looking at the youngest stellar and planetary systems, we can uncover many details that are common to planetary systems in general, and in turn, we can learn how our own Solar System grew up.This fantastic episode of the Starts With A Bang podcast features observational astrochemist Dr. Charles Law, and takes us inside one of the most remarkable young stellar systems ever found: the edge-on system known as Gomez's Hamburger, complete with a first-of-its-kind exoplanet known as GoHam b. Come find out the incredible science behind planet formation, and meet our first-ever proto-protoplanet in the process!(This JWST NIRCam image shows many never-before-revealed details in the dusty disk of the edge-on protoplanetary system known as Gomez's Hamburger, with a massive, unique exoplanet within the disk known as GoHam b. Credit: NASA/ESA/CSA JWST; Francois Menard et al.)

Starts With A Bang #127 - Satellites and space pollution

When most of us were children, and we went to a rural area with clear skies overhead at night, we were all greeted by the same familiar sight: a dark night sky, glittering with many hundreds or even thousands of stars. Depending on how dark your sky was, you could spot up to 6000 stars at once, as well as deep-sky objects, the plane of the Milky Way, and only the rare, occasional satellite streak. As time went on, more and more satellites were launched, bringing us up to around 2000 active satellites as of 2019.And then we entered the era of satellite megaconstellations, beginning with the launch of the first Starlink satellites. Now, nearly 7 full years later, there are over 17,000 active and defunct satellite payloads in orbit, with approximately 100 times as many satellites proposed in the coming years. From satellite communications to direct-to-phone links to the proposition of AI data centers in space, the number of proposed use cases has exploded. However, as the environment around Earth becomes more crowded, the risks, the harms, and the potential for disaster all grow evermore severe, with woefully insufficient (or, sometimes, no) mitigation measures in place.Is this a cause for despair? Or could this be our finest hour in terms of combatting these new forms of pollution. I've brought expert Dr. Meredith Rawls onto the podcast this episode to discuss satellites and space pollution, and the conversation ranges from thoughtful to passionate to pessimistic to hopeful many times over. Have a listen; you don't want to be underinformed about this one!Helpful links:IAU's center for the protection of dark and quiet skies: https://cps.iau.org/NRAO/VLA's paper on radio telescope operations coordinating with satellite providers: https://arxiv.org/abs/2502.15068v1Vera C. Rubin's public alerts stream: https://rubinobservatory.org/news/first-alertsAn article on Rocket plumes: https://www.nature.com/articles/s43247-025-03154-8Meredith's Nature News and Views piece regarding streaks in space telescopes: https://www.nature.com/articles/d41586-025-03725-x The latest on the CRASH clock: https://outerspaceinstitute.ca/crashclock/Astronomers argue for astronomy on the ground and in space: https://spacenews.com/the-future-of-astronomy-is-both-on-earth-and-in-space/ and Yvette Cendes's previous appearance on the SWAB podcast: https://soundcloud.com/ethan-siegel-172073460/starts-with-a-bang-77-stellar-destruction and https://open.spotify.com/episode/4xnBB0Ma4SzHk8ulziOidk(The illustration shows all tracked objects in space as of 2025, as shown by the European Space Agency. The size of the objects, including intact satellites as well as space debris, is greatly exaggerated, but the number of objects shown is actually far less than the number of objects in space now in 2026, just one year later. Credit: European Space Agency)