Starts With A Bang podcast

One of the most exciting possibilities for life beyond Earth doesn't require us going very far. While Mercury and the Moon have no atmosphere and Venus is an inferno-esque hellscape, Mars offers a tantalizing possibility for a new line of life, independent of Earth, here in our Solar System. With the same raw ingredients and more than a billion years of a watery, wet past, Mars could have had, or might even still have today, some form of life on its surface. Part of the reason Mars is so exciting for us is that we've been there: at least, robotically, with a series of orbiters, landers, and even rovers. We've seen and learned so much about the red planet, including some tantalizing hints of what might be biological activity. But there's so much more to learn, and we're reaching the limits of what we can accomplish without having human beings walk on the Martian surface. On this episode of the Starts With A Bang podcast, we're joined by Mars expert Dr. Tanya Harrison, who's worked on three generations of Mars Rovers and is a strong advocate for a variety of future missions to Mars. Join us for this fascinating conversation where she lays out what we know, what remains uncertain, and what we'll need to do if we want to take those next, critical steps. (And, as a bonus, she corrects one or two of my misconceptions along the way!) (This image shows the Mars Perseverance rover in one of its "selfie-mode" images, where its own tracks and the Ingenuity rover are both visible in the background. Credit: NASA/JPL-Caltech/ASU/MSSS/Seán Doran)

Back in the 1990s, observations of type Ia supernovae were the key data set that led astronomers to conclude that the Universe's expansion was accelerating, and some new form of energy, now known as dark energy, was permeating the Universe. Over the past ~25 years, those observations have gotten so good that we now have a tension within the expanding Universe, as different methods of measuring the expansion rate yield two different sets of mutually incompatible results. What's remarkable is that this result is robust even though we're still somewhat uncertain as to exactly how these type Ia supernovae occur. The original scenario, put forth by Chandrasekhar nearly a century ago, still has its adherents, but the evidence appears very strong that approaching and reaching a "mass limit" beyond which atoms are unstable can only explain a small fraction of white dwarf behavior. Instead, a new paradigm dominated by merging white dwarfs may explain nearly all type Ia supernova explosions! On this episode of the Starts With A Bang podcast, we talk to UC Berkeley astronomer Dr. Ken Shen, a theorist whose expertise lies in type Ia supernovae, and learn how just the last 20 or so years have led to a revolution in how we conceive of these "standard candles" in the Universe, and just what observations might soon lead us to know, for certain, how these cosmic events are truly triggered! (The titular illustration shows two merging white dwarfs, the preferred theoretical mechanism for the triggering of some, and perhaps most or even nearly all, type Ia supernovae. The double detonation scenario, where a "detonation" event on the surface propagates to the core and causes a detonation that leads to total destruction of the stellar remnant, it one very intriguing theoretical possibility. Credit: D. A. Howell, Nature, 2010)

When stars are born, they can come with a wide variety of masses. But there are only a few ways that stars can die, and only a few types of remnants that can be left behind: white dwarfs, neutron stars, and black holes. Neutrons stars and black holes are most frequently created from core-collapse supernova events: the deaths of massive stars. Somewhere, even though we're not sure exactly where it is, there's a dividing line between "what makes a neutron star?" and "what makes a black hole?" Somewhere out there, there's a heaviest neutron star, and someplace else a lightest black hole. But the dividing line might not be so clean, after all. It turns out that when neutron stars merge, they can form another neutron star, a black hole, or a third case: an in-between scenario. In this third case, you can temporarily form a hypermassive neutron star: a neutron star that's too massive to be stable, but that collapses in short order to a black hole, but only after persisting as a neutron star for a detectable amount of time. To help guide us through the science of hypermassive neutron stars, I'm so pleased to welcome Dr. Cecilia Chirenti to the show, a joint scientist at NASA Goddard and the University of Maryland, College Park. There's a whole lot of cutting-edge science right at (and even over) the horizon of what we know today, and you won't want to miss this information-rich episode! (This image shows the illustration of a massive neutron star, along with the distorted gravitational effects an observer might see if they had the capability of viewing this neutron star at such a close distance. Credit: Daniel Molybdenum/flickr and raphael.concorde/Wikimedia Commons)

One of the great advances of 20th and 21st century science has been, for the first time to show us two things: how the Universe began and what the Universe looks like today. The modern frontier is all about the in-between stages: how did the Universe grow up? How did it go from particles to atoms to the first stars and galaxies to the modern Milky Way, Local Group, and Universe-at-large? It's a question that, the more deeply we answer it, the greater the number of details that emerge, requiring us to make a special effort to pin each one down. For this episode, I'm so pleased to welcome Dr. Ivanna Escala to the podcast: an expert in how stars and stellar properties within the Local Group can reveal not only its stellar history, but its history of galactic assembly. While the Milky Way has had a few major mergers, its most recent was a whopping ~10 billion years ago. Andromeda, our Local Group's other large galaxy, has a remarkably different story: with a major merger that occurred only 2-4 billion years ago! Have a listen and enjoy, and thanks to Avenues Online for being our sponsor! (This image, assembled from very long wavelengths of light of the neighboring Andromeda Galaxy, shows features within Andromeda's galactic disk as well as the gas clouds of neutral hydrogen found in Andromeda's galactic halo. By examining these features, as well as streams and stars in and around Andromeda, we can reconstruct precisely how this galaxy came to be the way it is today. Credit: NRAO/AUI/NSF, WSRT)

For life on Earth, there's no more important source of energy than the Sun; without it, it's doubtful that life would have arisen on Earth, and it certainly wouldn't have evolved to give rise to the wild diversity of biological organisms seen today. But the Sun is more than just a constant source of heat and light; it also emits particles, and there's a darker side to that activity: flares, coronal mass ejections, and the threats this space weather poses to living planets like our own. It turns out that for technologically advanced civilizations like our own, the threats that arise from the Sun are far greater and more dangerous than at any time prior in Earth's history, and despite the knowledge we have of what the Sun can do to the Earth, we're woefully unprepared for the inevitable. Thankfully, there are not only people studying it, but many of them are also fighting and advocating for solutions and planetary protection, including Sierra Solter, a plasma physicist specializing in solar plasmas, who joins us on this edition of the Starts With A Bang podcast. Welcome to a glorious 2023, and may we learn the needed lessons for what must be done before we're left with the sad alternative of simply picking up the pieces! (This illustration shows a massive space weather event, larger than a typical solar flare, known as a surface mass ejection. Although SMEs have the capacity to entirely destroy a planet, they're thankfully limited to occurring on red supergiants, a class of star that will never include our Sun or anything it will evolve into. Credit: NASA, ESA, Elizabeth Wheatley (STScI))

For a cosmologist like me, "cosmic dust" is a thing that's in the way, confounding our data about the pristine Universe, and it's a thing to be understood so that it can be properly subtracted out. But the old saying, that "one astronomer's noise is another astronomer's data," proves to be more true than ever with cosmic dust, as how it's produced, where it came from, and how it comes together to form planets, molecules, and eventually creatures like us, are some of the most essential elements necessary for us to exist within this Universe. In visible light, cosmic dust is normally just a starlight blocker, but in other wavelengths of light, its composition, distribution, density, grain size, polarization, and many other kinetic and thermal features can be revealed. Here to guide us through the ins-and-outs of cosmic dust, with a special view towards millimeter, submillimeter, and radio wavelengths, I'm so pleased to welcome PhD candidate Carla Arce-Tord to the show. Enjoy this far-ranging tour of cosmic dust, and perhaps by the end you'll walk away inspired about all there is to know as well as the remarkable people making it happen! (The image shows the magnetic field lines imprinted by the galaxy on the cosmic dust in the interstellar medium, as revealed by the Planck CMB experiment. These field lines are of microgauss strength and can be coherent over hundreds or even thousands of light-years. Credit: ESA/Planck Collaboration. Acknowledgement: M.-A. Miville-Deschênes)

The supermassive black holes at the centers of galaxies is a tremendously interesting area of research, advancing rapidly over the past few years. While most of these observations focus on either high-energy or radio emissions from them, there's a recent push to see what these objects are doing in other wavelengths of light, as well as how they vary in time. Once, it was thought that supermassive black holes would become "activated" at a certain point in time, would remain on for hundreds of thousands or even millions of years, and would then turn-off. But our observations have shown us that there are remarkable variations in what types of light and energy these objects emit over time, and with new studies being conducted at the South Pole and other places studying the Universe in millimeter-wavelength light, we're about to get an unprecedented amount of high-quality data. Here to guide us through what we've learned so far about these active galaxies and where this research might take us in the future is Dr. John Hood, a postdoctoral research associate at the University of Chicago. It's a wild ride here at the frontiers of science, and I hope you enjoy every minute of it! (In this artistic rendering, a blazar is accelerating protons that produce pions, which produce neutrinos and gamma rays when they decay. Lower-energy photons are also produced, allowing blazars, a form of Active Galactic Nucleus (AGN) to be seen all across the electromagnetic spectrum. In recent years, we’ve advanced to the point where we’re detecting neutrinos from billions of light-years away, beginning with blazar TXS 0506+056. Credit: IceCube collaboration/NASA)

All throughout the Universe, we see stars and galaxies everywhere we look. But as we look to greater and greater distances, we're only seeing the light that's the easiest to see: the ones from the brightest, most visible objects. But the most numerous objects of all are exactly the opposite: less luminous, smaller, and lower in mass. How can we hope to find and catalogue them all if they're the hardest ones to find? The answer lies in measuring the closest stars to us. If we can measure the stars that persist in our own backyard, cataloguing them and taking as complete a census as possible, we can then combine what else we know about stars and starlight and the environments in which new stars form to reconstruct precisely what we believe is out there: not just here-and-now, but elsewhere and all throughout cosmic time. Here to bring us up to speed on how this attempt to catalogue and categorize the stars in the Universe, I'm so pleased to welcome PhD candidate at Georgia State University Eliot Vrijmoet to the show, who takes us on a fascinating journey to the edge of our knowledge, and from there we'll peer over the horizon to what just might come next. Enjoy the latest episode of the Starts With A Bang podcast! Star density maps of the Gaia Catalogue of Nearby Stars. The Sun is located at the centre of both maps. The regions with higher density of stars are shown; these correspond with known star clusters (Hyades and Coma Berenices) and moving groups. Each dotted line represents a distance of 20 parsecs: about 65 light-years. (Credit: ESA/Gaia/DPAC - CC BY-SA 3.0 IGO)

Although it seems like a long time ago, it was as recent as the early 1990s that we had no idea whether planets in the Universe were universal, common, uncommon, or even exceedingly rare. While certain data sets once seemed to indicate that practically every star in the Universe had planets around it, we now know that isn't true at all. Many stars, perhaps even most of them, have planets, but plenty of others don't. In addition, the number and types of planets that exist, including planets without parent stars at all, are still under investigation, and the field of planet formation has become extremely active. With new data coming in from infrared and radio observatories, including JWST and ALMA, we're learning so much about the planets that form in the Universe, including what conditions they form under and what the various important, dominant considerations are. Here as our latest guest on the Starts With A Bang podcast, to help us disentangle what's known from what remains a curiosity, is Dr. Kamber Schwarz, postdoctoral research associate at MPIA Heidelberg. There's still so much to learn, but wow, how much we know today compared to the early 1990s is astounding. Enjoy this look at the frontiers of what we know about how planets are made, and I hope it leaves you wondering about what else we'll learn in the very near future! [This two-toned image shows an illustration of the protoplanetary disk around the young star FU Orionis, which was imaged multiple times by the Hubble Space Telescope but years apart. The disk has changed, indicating that it's entering a more advanced stage of evolution, as planets form and the material available for forming and growing them evaporates, sublimates, and is otherwise blown away. (Credit: NASA/JPL-Caltech)]

From the earliest stages of the hot Big Bang up through and including the present day, one cosmic picture is sufficient to describe practically everything we observe: the Lambda-Cold Dark Matter (ΛCDM) cosmological model. With a mix of dark matter, dark energy, normal matter, photons, and neutrinos, we can not only model, but can simulate the Universe from the earliest times and the smallest scales up through to the present and the full scale of the observable Universe. In most cases, theory and observation match, and spectacularly so. But there are a few current points of tension: cosmological mysteries, that range from the expansion rate of the Universe to small-scale structure formation to the link between the pre-Big Bang Universe and our current dark-energy-caused accelerated expansion. Where are we, how far have we come, and how far do we still have to go? I'm so pleased to welcome Dr. Santiago Casas, who specializes in many of the same sub-areas of cosmological physics I specialized in about a decade earlier, to our podcast. In this nearly 90-minute long episode, we cover a slew of fascinating topics in more depth and detail than normal, and I hope you enjoy the extra-deep dive into some of the weediest areas of modern cosmology! This image shows a 15 million light-year long structure that arises from a detailed simulation of the cosmic web and how galaxies, galaxy clusters, and cosmic filaments form on the largest scales of all. Although this theoretical simulation, like many aspects of our standard cosmological models, largely agrees with our observations, there are points of tension that must not, despite the successes, be ignored. (Credit: Jeremy Blaizot, SPHINX project, https://sphinx.univ-lyon1.fr/)