Starts With A Bang podcast

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/)

Since the advanced LIGO detectors first began operating in 2015, we've not only directly detected our first gravitational wave signals from merging objects in the Universe, we've observed close to 100 such systems that have emitted detectable gravitational wave signals. All of them to date, however, are the result of short-period, low-mass stellar remnants that have inspiraled and merged into one another. The most massive black holes, at least in gravitational waves, remain elusive. If all goes well, however, that won't be the case for long. At the centers of very massive galaxies, there's often not just one supermassive black holes, but multiples. Ultramassive binary black holes, in fact, send such energetic ripples through spacetime that they ought to distort, in measurable ways, the arriving radio signals from pulsars distributed all throughout the Milky Way. By monitoring these pulsars extensively through a series of timing arrays, we just might be able to extract information about the longest-wavelength gravitational waves that fill the Universe. Here to walk us through what we're looking for, how we're conducting this science, what we've seen so far, and what the prospects are for gravitational wave direct detection in an entirely new regime is Dr. Caitlin Witt, who I'm so pleased to welcome to the Starts With A Bang podcast. We've got a 100 minute spectacular for this episode, and you won't want to miss a single moment of it! Image: This illustration show how the Earth, itself embedded withing spacetime, sees the arriving signals from various pulsars delayed and distorted by the background of cosmic gravitational waves that propagate all throughout the Universe. The combined effects of these waves alters the timing of each and every pulsar, and a long-timescale, sufficiently sensitive monitoring of these pulsars can reveal the gravitational signals. (Credit: Tonia Klein/NANOGrav)

It's now been nearly a full six months since the JWST was launched, and we're on the cusp of getting our first science data and images back from some 1.5 million kilometers away. There are all sorts of things we're bound to learn, from discovering the farthest galaxies of all to examining details in faint, small objects to searching for black holes in dusty galaxies and a whole lot more. But what's perhaps most exciting are the things we're going to find that we aren't expecting, simply because we've never looked in this particular fashion before. I'm so pleased to welcome two guests to the show: Research Professors Dr. Stacey Alberts and Dr. Christina Williams both join me this month, and we have a far-ranging conversation about infrared astronomy and all that we're poised to learn from exploring the Universe in the infrared as never before. If you're already excited about JWST and what we're going to learn from it, wait until you listen to this episode! (Image: Although Spitzer (launched 2003) was earlier than WISE (launched 2009), it had a larger mirror and a narrower field-of-view. Even the very first JWST image at comparable wavelengths, shown alongside them, can resolve the same features in the same region to an unprecedented precision. This is a preview of the science we'll get. Credit: NASA and WISE/SSC/IRAC/STScI, compiled by Andras Gaspar)

When we look out at the Universe, what we see is typically what we think of: the points of light. Depending on the scales we're looking at, this can come in the form of stars, galaxies, or even clusters of galaxies, but it's almost always information that comes to us in some form of electromagnetic radiation, or light. But sometimes, light can be just as informative for what either isn't there or how it's been affected by the various media that it's passed through! In the case of our own cosmic backyard, a new study from earlier this year, 2022, revealed something spectacular and entirely unexpected: that the Sun sits at the center of a ~1000 light-year wide structure known as the Local Bubble, itself just about 15 million years old but containing all of the nearest young star clusters to us. In fact, the star Aldebaran, one of the brightest in the sky, helped "blow" this bubble in the interstellar medium! It's the very first episode of the Starts With A Bang podcast ever to feature multiple guests, and I'm so pleased to welcome Drs. Catherine Zucker, Alyssa Goodman, and João Alves to the podcast, all three of whom helped make this knowledge possible! I hope you enjoy the listen, and it's a 90 minute spectacular you won't regret spending your time on! Links: Discovery paper: https://www.nature.com/articles/s41586-021-04286-5 Press release: https://www.cfa.harvard.edu/news/1000-light-year-wide-bubble-surrounding-earth-source-all-nearby-young-stars Video: https://sites.google.com/cfa.harvard.edu/local-bubble-star-formation Interactive visualization: https://faun.rc.fas.harvard.edu/czucker/Paper_Figures/Interactive_Figure1.html (This visualization shows the Sun's location at the center of a structure about 1000 light-years across known as the Local Bubble. Recent episodes of star-formation have led to a series of new star clusters, shown in the illustration, which have formed a bubble and pushed it out. The Sun has only entered this region recently, and just happens to be at the center now, when we're looking. Credit: Leah Hustak/STScI)

Have you ever wondered how it is that we know all we do about galaxies? How they formed, what they're made of, how we can be certain they contain dark matter, and how they grew up in the context of the expanding Universe? In any scientific discipline, we have the things we know and can be quite confident in, the things that we think we've figured out but more data is required to be certain, and the things that remain undecided given the current evidence: things over the horizon of the present frontiers. Fortunately, we have the ability to scrupulously identify which aspects of galaxy formation and evolution fall into each category, and to walk right up to the edge of our knowledge and peer over that ever-expanding horizon. Joining me for this episode of the Starts With A Bang podcast is scientist Arianna Long, Ph.D. candidate at the University of California at Irvine and soon-to-be Hubble Fellow at the University of Texas at Austin. With the advent of ALMA and the James Webb Space Telescope, in particular, we're poised to seriously push back the frontiers of the unknown, and you can get the insider's view of exactly what we'll be looking for and how. This is one episode you certainly won't want to miss! Image: This view of a portion of the DREaM simulated galaxy catalog provides a snippet of sky that might correspond, statistically, with what James Webb expects to see. This particular snippet showcases an incredibly rich region of relative nearby galaxies clustered together, which could provide Webb with an unprecedented view of galaxies magnified by strong and weak gravitational lensing. (Credit: Nicole Drakos, Bruno Villasenor, Brant Robertson, Ryan Hausen, Mark Dickinson, Henry Ferguson, Steven Furlanetto, Jenny Greene, Piero Madau, Alice Shapley, Daniel Stark, Risa Wechsler)

Every time we've figured out a different way to look at the Universe, going beyond the capabilities of our own meagre senses, we've opened up an opportunity to learn something new about what's out there. Although optical astronomy and near-infrared astronomy are arguably the most popular ways to view the Universe, with James Webb soon to bring the mid-infrared Universe into view as never before, we shouldn't forget about the value of other, more distant wavelengths of light. One of the most fascinating sets of data that we can collect is in the far-infrared, where gas heated to just a few tens of Kelvin shines, but where much hotter, even ionized gas can emit very special hyperfine transitions. Mapping out these regions of space helps us understand what's going on beyond mere star-formation or other violent events, and a series of remarkably specific observational techinques are, quite arguably, how we're obtaining the most valuable information of all in this part of the electromagnetic spectrum. Joining the Starts With A Bang podcast to help guide us through the topic of far-infrared astronomy is Dr. Jessica Sutter, an astronomer at NASA Ames who's part of the USRA and who works with the SOFIA telescope, a one-of-a-kind far-infrared observatory that can do what no ground-based nor space-based observatory can. Have a listen, and I hope you wind up learning as much as I did! (The featured image shows galaxy NGC 7331 along with other members of its galactic group, including the prominent galaxies NGC 7335, 7336, 7337, and 7340. Credit: Vicent Peris/c.c.-by-2.0)

When you start looking at the Universe, you realize that there are more signals out there than are simply generated by stars. On the one hand, you have astrophysical objects like gas, dust, plasma, as well as stellar corpses and their remnants. But there are also failed stars that didn't quite make it to the nuclear fusion stage that defines our Sun and the other stars like it: brown dwarfs. Beyond that, there may also be signatures of planets like Earth out there: planets inhabited by an intelligent civilization. It's of paramount importance, when asking the biggest questions, to make sure that we aren't fooling ourselves, but that's where projects like SETI and Breakthrough Listen come in: to help us extract legitimate science where "wishful thinking" has the potential to lead us in precisely the most dangerous direction: the possibility of fooling ourselves. I'm so pleased to welcome Ph.D. Candidate Macy Huston to the podcast, as we explore the less commonly seen side of the Universe: from exoplanets to brown dwarfs to the search for extraterrestrial intelligence. With the advent of the James Webb Space Telescope, we really are going to see a tremendous change in what we know!