Episodes
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In this Universe, there are a few objects that are just larger, and a few events that are just more powerful, than others. As far as size goes, the cosmic web creates some of the largest features ever discovered, with the largest galaxy filaments and the largest regions devoid of galaxies spanning as much as ~2 billion light-years. No robust, verified structure has ever been found that's larger. Meanwhile, as far as energy and power go, collisions of galaxy clusters are the most energetic events, outstripped only by the Big Bang itself.
However, nearly rivaling galaxy cluster collisions are the strongest black hole jets ever seen, capable of emitting trillions of times the energy of a Sun-like star, but also capable of sustaining those energies over timescales of a billion years or more. Astronomers have just set a new record for the longest black hole jet with the discovery of Porphyrion, which spans a whopping 24 million light-years across! How did this jet and others like it come to be, and what effects do they have on the larger Universe, and how do they get generated from such physically small objects (i.e., black holes) to begin with?
That's the subject of the latest edition of the Starts With A Bang podcast, featuring Dr. Martijn Oei: the discoverer of Porphyrion himself! We get deep into the physics and astrophysics of black holes and their jets, which have profound implications for how structures get carved and magnetized onto the scales of the cosmic web itself. Buckle up and tune in; it's a wild ride ahead!
(This illustration shows how black hole jets can be as large as the scale of the cosmic web itself, with Porphyrion, as illustrated here, setting a new cosmic record with its bipolar jets spanning 23-24 million light-years across. Credit: Erik Wernquist/Dylan Nelson (IllustrisTNG collaboration)/Martijn Oei; Design: Samuel Hermans)
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It's hard to imagine, but it was only five years ago, in 2019, that humanity feasted our collective eyes on the first direct image of a black hole's event horizon. Thanks to the technique of very long baseline interferometry and the power of arrays of radio telescopes stitched together from all across the Earth, we were able to resolve the event horizon of the black hole M87*, despite the fact that it's an impressive 55 million light-years away.
That was with radio interferometry, but historically, most telescopes have used optical light, not radio light. Does that mean that optical interferometry is possible? Not only is the answer a resounding "yes," but we've been performing it for decades. In fact, the most ambitious optical interferometry project of all-time is already under construction in New Mexico: the Magdalena Ridge Observatory Interferometer (MROI). With an array that will feature a total of ten separate telescopes all linked together, and with a maximum tunable distance of 340 meters between them, it's poised to achieve higher-resolution imagery of a suite of astronomical objects than has ever been obtained before, from the ground or from in space.There's so much mind-blowing science to learn that we had to bring two guests onto our podcast this month to explain it all: Dr. Michelle Creech-Eakman of New Mexico Tech and Dr. Chris Haniff of Cavendish Laboratory at Cambridge University. Be prepared for a fascinating look at the science of optical interferometry, what we'll be able to discover once MROI is complete, and an incredible tour of the instrumentation science that powers it. It's a fascinating episode you won't want to miss!
(The first two telescopes (of ten) that will eventually be part of the Magdalena Ridge Observatory Interferometer when its full array is complete. Credit: James Luis/MROI)
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When you think of an active galaxy, what picture comes to mind? Do you think about a monstrous supermassive black hole feasting on tremendous stores of gas and other forms of matter? Do you picture an enormous disk of accreted matter, being accelerated, heated, and eventually shot out along two jets, each perpendicular to the disk itself? This common picture of active galaxies describes many of the most prominent ones, but isn't universal to them all.
Some active galaxies aren't giant ellipticals, but just average-looking spiral galaxies. Some galaxies aren't in the process of a major merger, but seem to be powered by their own internal gas. And some of these black holes aren't ridiculously massive, with billions of solar masses inherent to them, but are rather much more modest. Some of these active galaxies actually show practically no signs of activity in visible light, but must be viewed in other wavelengths, such as with radio telescopes, to reveal their activity.
Above, you can see galaxy NGC 3227, which may appear to be just a normal spiral galaxy. However, not only is it active, but it's actively in the process of launching a "cone" of energetic material from very close to the black hole itself. Here to help us untangle its mysteries and take us on a deep dive into the physics of these objects, I'm so pleased to welcome Julia Falcone to the podcast. Julia is a PhD candidate at Georgia State University, and her very first published first-author paper is about this exact system shown here. Come join us as we explore these fascinating objects and open a window onto the Universe we're still discovering!
(This image shows galaxy NGC 3227, at left, with its neighbor NGC 3226, as viewed in optical light by the Hubble Space Telescope. Despite copious features common to spiral galaxies, including rich dust lanes, a bright central bulge, and new stars forming along its spiral arms, this galaxy is actually active, with bright features emanating from the central supermassive black hole in non-optical wavelengths of light. Credit: NASA, ESA, and H. Ford (Johns Hopkins University); Image Processing: G. Kober (NASA Goddard/Catholic University of America))
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Right now, the Large Hadron Collider (LHC) is the most powerful particle accelerator/collider ever built. Accelerating protons up to 299,792,455 m/s, just 3 m/s shy of the speed of light, they smash together at energies of 14 TeV, creating all sorts of new particles (and antiparticles) from raw energy, leveraging Einstein's famous E = mc² in an innovative way. By building detectors around the collision points, we can uncover all sorts of properties about any known particles and potentially discover new particles as well, as the LHC did for the Higgs boson back in the early 2010s.
But the LHC has a limited lifetime, and by the 2030s, will complete its data-taking runs. If we want to go beyond the LHC, we need to start planning for a new particle collider now, and there are four great options that can take us beyond the current frontier: a linear lepton collider, a circular lepton collider, a circular hadron collider, and a potentially new innovation of a circular muon collider. In this episode of the Starts With A Bang podcast, Dr. Cari Cesarotti joins us to discuss all of these options and much more, as we look ahead to the future of particle physics.
The serious question isn't whether we should build one (we definitely should), but which approach will be most fruitful in pushing our suite of knowledge beyond the known frontiers. There's an entire Universe to explore at the subatomic level, and those of us curious about the Universe want to know what's out there better than ever before!
(This image shows the expected signature of a Higgs boson decaying to bottom-quark jets around the collision point inside a muon collider. The yellow lines represent the decaying background of muons, while the red lines represent the b-quark jets. Credit: D Lucchesi et al.) -
On the largest of cosmic scales, the best description we have of our Universe is known as the ΛCDM model with an inflationary hot Big Bang: our consensus cosmology. It tells us that we have a Universe consistent with being made of about 5% normal matter, a little bit of radiation in the form of photons, around 0.1% neutrinos, and the rest made of the mysterious dark matter (~27%) and dark energy (~68%). Governed by General Relativity, this explains what we see on Solar System scales, where dark matter and dark energy are negligible, and on cosmic scales, where dark matter and dark energy are important.
But on in-between scales, we aren't quite sure that this same "consensus cosmology" leads to a very successful description. It's long been known that, on galactic scales, rotating galaxies appear to obey a different force law: MOND, for MOdified Newtonian Dynamics. In MOND, the traditional Newtonian acceleration is replaced, at very low accelerations, by a combination of the Newtonian acceleration with a fundamental new parameter, which prevents accelerations from dropping too far below a certain value: around ~10^-10 meters-per-second-squared. If this deviation is real, it should show up someplace else: in pairs of stars separated by large distances, a class of systems known as wide binaries.
Although this area of physics was widely ignored for decades, new observations with the ESA's Gaia mission have recently brought it back into the forefront, where different teams are claiming different results based on how they use and interpret the data. In this rare edition of the Starts With A Bang podcast, I sit down with astrophysicist Xavier Hernandez of UNAM in Mexico, who's one of the main players in this story and a strong advocate of MOND as an alternative to dark matter. The conversation takes many interesting turns and as a result, we've got a great episode that's nearly two hours long. (Although there is some confusion over the maximum distance that Xavier's sample goes out to in the podcast: the correct answer is not mentioned, but turns out to be ~12,000 AU, not the 6000 or 16,000 mentioned in the podcast.) Take a listen, learn some new astrophysics, but most importantly, stay open to new challenges to the conventional paradigm. If there's a crack in our consensus cosmology, this area of astrophysics might someday be the critical blow that shatters it apart!
(This photo shows the bright, naked-eye star, Albireo. To the naked eye, it appears as just a single point of light. However, a binocular or telescope view shows that it's actually two very different colored stars separated by a substantial fraction of a light year: a wide binary system. Even thousands of years after its identification, we still don't know if this is a bound system, or two stars that happen to be passing one another in close proximity. Credit: Jared Smith/Flickr)
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One of the most swiftly forgotten revolutions in all of science is our understanding of the Solar System out beyond Neptune. Although Pluto was discovered nearly a full century ago, it wasn't until the early 1990s that we even discovered the next object beyond Neptune that wasn't also part of the Plutonian system. And yet, in the 30 short years that have passed since then, we've learned so much more about the structure of the Kuiper belt and beyond, but we also face tremendous challenges in the quest to learn more thanks to an unwelcome intruder: the rise of satellite megaconstellations.
Although the original team of Mike Brown and Konstantin Batygin continue to advocate for a novel, massive, undiscovered world located at hundreds of times the Earth-Sun distance, they're largely alone, as other scientists have weighed in and see no evidence for this hypothetical world. Nevertheless, more science must be conducted to know for sure, and in the meantime, the rise of satellite megaconstellations such as Starlink now poses an existential threat to all sorts of endeavors, including planetary astronomy.
Here to guide us through the current status of the hunt for Planet Nine, as well as the new obstacles that astronomers are contending with, I'm so pleased to welcome Prof. Sam Lawler to the show. Sam is a professor at the University of Regina in Saskatchewan, Canada, and is also known for her advocacy work in favor of dark and quiet skies for all of humanity to enjoy and benefit from. It's a fascinating discussion that took me to some unexpected places, and I think you'll enjoy it a whole lot!
(This image shows an illustration of the hypothetical Planet Nine: a planet theorized to be more massive than Earth but hundreds of times farther away from the Sun than our own world. Credit: Tobias Roetsch/Future Publishing)
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Every January, I head to the American Astronomical Society's big annual meeting with an ulterior motive in mind. Beyond merely uncovering new scientific findings, gathering information for potential stories, and connecting with friends and colleagues, I also look to meet emerging junior researchers who are swiftly becoming not only experts, but leaders, in their particular sub-field of astronomy.
One of the most popular research topics in astrophysics today is the connection between the dark Universe, including the only indirectly-observed dark matter and dark energy, and the observable components that astronomers routinely see: stars, galaxies, gas, plasma, and other forms of light-emitting and light-absorbing matter. The dark Universe, to date, is best revealed by looking at the luminous, electromagnetic signals that are imprinted onto the visible components of our cosmos.
To better understand what scientists are investigating, I'm so pleased to welcome KeShawn Ivory to the podcast. KeShawn is a PhD candidate at Vanderbilt University and researches the connection between dark matter, the non-luminous, gravitationally interacting "stuff" that holds the Universe together (as best as it can), and the luminous, observable galaxies that populate the visible Universe in numbers that rise into the trillions. It's a fascinating topic and a great addition to your May listening, right here on Starts With A Bang!
(The SIBELIUS project, which simulates galaxies and structures beyond the local Universe, is part of the Virgo Consortium that attempts to use cosmological simulations to reproduce features of galaxies, groups, and clusters that are seen all across the Universe. By using a mix of theory, observations, and simulations, astrophysicists can better understand the nature of dark matter in our cosmos. Credit: Virgo Consortium/SIBELIUS project)
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Have you ever wondered what the full story with the galactic center is? Sure, we have stars, gas, and an all-important supermassive black hole, but for hundreds of light-years around the center, there's a remarkable story going on that's traced out in a variety of elements at a whole slew of different temperatures. Imprinted in that material is a remarkable set of features that reveals the magnetic fields generated in our galaxy's core, with some of them spanning much greater distances than have ever been seen elsewhere.
It's a testament to the power of multiwavelength astronomy, and in particular to the long wavelengths like the far-infrared, the microwave, and the radio portions of the spectrum that shows us these features of the Universe that simply can't be revealed in any other way. To help bring this story to all of you, I'm so pleased to welcome Dr. Natalie Butterfield, a scientist at the National Radio Astronomy Observatory (NRAO), to join us on this episode of the Starts With A Bang podcast.
Natalie is the discoverer of a giant magnetized ring some 30 light-years in diameter located in the galactic center, and is one of the leaders of the FIREPLACE survey: the Far-Infrared Polarimetric Large-Area CMZ Exploration survey that used the (sadly, now-defunct) SOFIA telescope to image the galactic center as never before. Strap in and have a listen, because you just might never think about the core of the Milky Way in the same way again!
(This image shows the magnetized galactic center, with various features highlighted, as imaged by the SOFIA/HAWC+ FIREPLACE survey team. The giant bubble at the left of the image is some 30 light-years wide, several times larger than any other supernova-blown bubble ever discovered. Credit: D. Paré et al., arXiv:2401.05317v2, 2024)
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All throughout the Universe, galaxies exist in a great variety of shapes, ages, and states. Today's galaxies come in spirals, ellipticals, irregulars, and rings, all ranging in size from behemoths hundreds or even thousands of times larger than the Milky Way to dwarf galaxies with fewer than 0.1% of the stars present here in our cosmic home. But at the centers of practically all galaxies, particularly the large ones, lie supermassive black holes.
When matter falls in towards these black holes, it doesn't just get swallowed, but accelerates and heats up, leading to phenomena like accretion disks, jets, and emitted radiation all across the electromagnetic spectrum. When these conditions exist, we know we have what's called an active galaxy, and it isn't just the rest of the galaxy that's impacted by that central activity, but far larger structures in the Universe beyond.
Here to help us explore these objects and their impact this month is Skylar Grayson, a PhD candidate at the School of Earth and Space Exploration at Arizona State University. Skylar works at the intersection of theory and computational astrophysics, and helps simulate the Universe while focusing on the inclusion and modeling of this type of galactic activity, and is one of the people helping uncover just how profound of a role these galaxies play in shaping the Universe around them. Buckle up for another exciting 90 minute episode; you won't want to miss it!
The powerful radio galaxy Hercules A, shown above, is a stunning example of how central activity from the galaxy's active black hole influences not only the host galaxy, but a large region of space extending far outside the galaxy itself, as visible from the extent of the radio lobes highlighted visually. (Credit: NASA, ESA, S. Baum and C. O'Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA))
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Up until the early 1990s, we didn't know what sorts of planets lived around stars other than our Sun. Were they like our own Solar System, with inner, rocky planets close to our star and large, giant worlds farther away? It turned out that exoplanetary systems come in a great variety of configurations: with planets of all sizes, masses, and distances from their parent stars. But some configurations are more common than others.
There are lots of hot Earth-sized planets and lots of hot Jupiter-sized planets, but precious few "hot Neptune" worlds out there. Furthermore, there appear to be lots of Earth-sized and super-Earth-sized worlds at greater distances, as well as many Neptune-sized and mini-Neptune-sized worlds. However, there's a gap there, too: between the large super-Earths and the small mini-Neptunes. Where are these missing exoplanets? Or, rather, why are these classes of exoplanets so uncommon?
That's what we're exploring on this episode of the Starts With a Bang podcast, featuring Ph.D. candidate Dakotah Tyler as our guest this month. By looking at how a hot (but low-mass) Jupiter-sized planet is being photoevaporated by its parent star, we can learn so much about not only the classes of objects we see out there, but even the ones we don't!
(Around the star WASP-69, a "hot Jupiter" exoplanet has its outer layers of atmosphere photoevaporated away, creating a comet-like tail whose extent and mass were recently measured for the first time. Credit: W. M. Keck Observatory/Adam Makarenko)
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Happy new year, everyone, and with a new year comes a spectacular new podcast! We normally cover an intricate and underappreciated aspect of astrophysics on the podcast, but I had the opportunity to bring on a true expert in the field of quantum computing and just couldn't pass it up.
You've likely heard a lot of noise about quantum computers and the benefits that they're poised to bring, with buzzwords like "P=NP," "quantum supremacy," and "quantum advantage" tossed around, but a lot of what you're likely to hear is hype, not actual science. Good thing I was able to get Dr. Riccardo Manenti as a guest for our podcast!
Riccardo is the author of a state-of-the-art textbook on quantum computers, has his PhD from Oxford in Quantum Computing, and has been working for Quantum Computing startup Rigetti for several years now. Join us as he helps demystify some of the recent progress and problems right here on the cutting edge of this promising new arena of physics, right here on the Starts With A Bang podcast!
(This illustration show's Rigetti's widely-available quantum computer, Novera, with 9 superconducting physical cubits within it. The great hope is that by scaling up to greater numbers of physical qubits, quantum advantage will be an achievable milestone in the relatively near future. Credit: Rigetti/Novera)
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It's hard to believe, but it was only back just a year and a half ago, in mid-2022, that we had yet to encounter the very first science images released by JWST. In the time that's passed since, we've gotten a revolutionary glimpse of our Universe, replete with tremendous new discoveries: the farthest black hole, the most distant galaxy, the farthest red supergiant star, and many other cosmic record-breakers.
What is it like to be on the cutting edge of these discoveries, and what are some of the most profound ways that our prior understanding of the Universe has been challenged by these observations? I'm so pleased to welcome Dr. Jeyhan Kartaltepe to the program, who's not onlya member of the CEERS (Cosmic Evolution Early Release Science) collaboration, but who has spearheaded a number of novel discoveries that have been made with JWST.
In the quest to understand not only what our Universe is and how we fit into that cosmic story, but also the story of how the Universe evolved and grew up to be the way it is today, these are some of the most important questions, concepts, and ideas to consider. It's our 100th episode, and I promise: it's one you won't want to miss!
(This image shows a portion of the CEERS survey's area, viewed with JWST and with NIRCam imagery. Within this field of view lies a galaxy with an active supermassive black hole: CEERS 1019, which weighs in at 9 million solar masses at a time from when the Universe was less than 600 million years old. It was the earliest black hole ever discovered, until that record was broken yet again in November of 2023. Credit: NASA, ESA, CSA, Steve Finkelstein (UT Austin), Micaela Bagley (UT Austin), Rebecca Larson (UT Austin))
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You might not think about it very often, but when it comes to the question of "how old is a star that we're observing," there are some very simple approximations that we make: measure its mass, radius, temperature, and luminosity (and maybe metallicity, too, for an extra layer of accuracy), and we'll tell you the age of this star, including how far along it is and how long we have to go until it meets its demise.
This also operates under a simple but not-always-accurate assumption: that all stars of a given mass and composition have the same age-radius and radius-temperature-luminosity relationships. That simply isn't true! Stars vary, both over time as they evolve and also from star-to-star dependent on their rotation and magnetism. It's a funny situation, because just a few years ago, people had declared stellar evolution as a basically "solved" field, and now it turns out that we might have to rethink how we've been thinking about the most common classes of stars of all!
To help us explore this topic, I'm so pleased to welcome Dr. Lyra Cao (pronounced "Tsao" and not "Cow" in case you were interested) to the program, where she helps walk us through what we're only now learning about stars: particularly young stars, low-mass stars, and rapidly rotating stars. If you know nothing about stellar evolution, this will be a treat for you, as you won't have to un-learn a massive amount of information to make sense of the Universe!
(This image shows a temperature profile of star HD 12545, which unlike our Sun, doesn't just have a small number of tiny sunspots on it, but is dominated by a massive, star-spanning starspot that covers approximately 25% of its surface. Many stars, including low-mass, young, and rapidly rotating stars, have enormous sunspots that can play a major role in the habitability of their systems. Credit: K.Strassmeier, Vienna, NOIRLab/NSF/AURA)
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Out there in the Universe, there's a whole lot more than simply what we find in our own Solar System. Here at home, the largest, most massive object is the Sun: a bright, hot, luminous star, while the second most massive object is Jupiter: a mere gas giant planet, exhibiting a small amount of self-compression due to the force of gravity.
But elsewhere in the Milky Way and beyond, numerous classes of objects exist in that murky "in-between" space. There are stars less luminous and lower in mass: the K-type stars as well as the most numerous star of all: the red dwarf. At even lower masses, there are brown dwarf stars, possessing various temperatures ranging from a little over ~1000 K all the way down to just ~250 K at the ultra-cool end.
These "in-between" objects, not massive enough to be a star but too massive to be a planet, have their own atmospheres, weather, and a variety of other properties. The thing that limits our knowledge of them, at present, is merely our own instruments. That's why, on this edition of the Starts With A Bang podcast, I'm so pleased to welcome Dr. Brittany Miles, an expert on ultra-cool brown dwarfs and a specialist in instrumentation technology. If you were ever curious about these "in between" objects, you won't want to miss this journey to the frontiers of modern astronomical science!
(This graphic compares a Sun-like star with a red dwarf, a typical brown dwarf, an ultra-cool brown dwarf, and a planet like Jupiter. While brown dwarfs are neither star nor planet, they're fascinating objects in their own right, and very much part of the cosmic story uniting us all. Credit: MPIA/V. Joergens)
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When we look at our nearby Universe, it's easy to recognize our own galaxy and the other large, massive ones that are nearby: Andromeda, the major galaxies in nearby groups like Bode's Galaxy, the group of galaxies in Leo, and the huge galaxies at the cores of the Virgo and Coma Clusters, among others. But these are not most of the galaxies in the Universe at all; the overwhelming majority of galaxies are small, low-mass dwarf galaxies, and if we want to understand how we formed and where we came from, it's these objects that we need to be studying more intensely.
So what is it that we already know about them? What has recent research revealed about these tiny galaxies in the nearby Universe, both inside and beyond our Local Group, and what else can we look forward to learning in the relatively near future? Join me for a fascinating discussion with Prof. Mia de los Reyes of Amherst College, as we dive into the science of the tiniest galaxies of all, and what they can teach us about our cosmic history as a whole!
(This image shows a map of stars in the outer regions of the Milky Way, from the northern celestial hemisphere, with several galactic streams visible. The color-coding indicates the distance to the stars, and the brightness indicates the density of stars in that patch of sky. In the white circles are faint companions of the Milky Way discovered by the SDSS: only two are globular clusters, the rest are all dwarf galaxies. Credit: V. Belokurov and the Sloan Digital Sky Survey)
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We all knew, if Einstein's General Theory of Relativity were in fact the correct theory of gravity, that it would only be a matter of time before we detected one of its unmistakable predictions: that all throughout spacetime, a symphony (or cacophony) of gravitational waves would be rippling, creating a cosmic "hum" as all of the moving, accelerating masses generated gravitational waves. The intricate monitoring of the Universe's greatest natural clocks, millisecond pulsars, would be one potential way to reveal this cosmic gravitational wave background.
But not many expected that here in 2023, we'd be announcing the first robust evidence for it already, and that future studies will reveal precisely what generates it and where it comes from. Yet here we are, with pulsar timing taking center stage as the second unique method to directly detect gravitational waves in our Universe!
For this edition of the Starts With A Bang podcast, I'm so pleased to welcome Dr. Thankful Cromartie to the show, where she guides us through the gravitational wave background, the science of pulsar timing arrays, and the underlying astrophysics of the objects that we monitor with them: millisecond pulsars. It's a fascinating story and one that's more accessible than ever with this latest podcast, and I hope you learn as much as I did listening to it!(The illustration shown here maps out how merging black holes from all across the Universe generate ripples in spacetime, and as those ripples pass across the lines-of-sight from a millisecond pulsar to us, those signals create timing variations across this natural array. For the first time, in 2023, we've detected strong evidence indicating the presence of this cosmic gravitational wave background. Credit: Daniëlle Futselaar (artsource.nl) / Max Planck Institute for Radio Astronomy)
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Sometimes, it's hard to believe we've come as far as we have, scientifically, in such a short period of time. We only began accumulating the first very strong evidence for supermassive black holes during the 1990s, and yet here we are, less than 30 years later, studying them, their effects, and their environments all across the Universe: from the present day to less than 1 billion years after the Big Bang.
We now believe that nearly every galaxy out there in the Universe not only produces black holes from the corpses of the most massive stars within them, but also supermassive ones that resides at the centers of these cosmic objects. Every once in a while, these supermassive black holes accrete matter and devour some of it, becoming active in a spectacular display. Just as we're learning all about how the Universe grows up in terms of stars, atoms, and gas, we're starting to learn how these supermassive black holes evolve and grow up, too.
Here to guide us through the latest and greatest scientific discoveries, I'm so pleased to welcome Dr. Allison Kirkpatrick onto our show. Allison is a professor at the University of Kansas and specializes in supermassive black holes, from X-ray to radio observations and well beyond. Join us on this exciting journey to the heart of one of our greatest cosmic mysteries, and see what it's like at the frontiers of science here on Starts With A Bang!
(This image is the first mid-infrared image of Stephan's Quintet ever taken by the James Webb Space Telescope. The galaxy at the topmost-right of the image displays a brilliant spikey pattern: evidence of a supermassive black hole that had never been revealed prior. Credit: NASA, ESA, CSA, STScI)
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We have a pretty good idea of both what's in our Universe and how it grew up. But it's only because we have several different, completely independent lines of evidence that point to the same consensus picture that we actually believe that our Universe is 13.8 billion years old and composed of a mix of normal matter and radiation, but is dominated by dark matter and dark energy on the largest of cosmic scales.
In particular, we form large, cosmically bound structures on the scales of galaxies and galaxy clusters, but on larger scales, dark energy and the expanding Universe dominate, working to drive everything apart. The story of how we've come to know this information about the Universe and how we're using both old and new techniques to push the our understanding further is the subject of this edition of our podcast. It features PhD candidate Karolina Garcia, who's kind enough to walk us through a variety of types of research that all serve the same end: to reveal the story of the Universe and how it grew up to be the way it is today. Take a listen; you won't regret it!
(This image shows a series of structure-formation simulations: at low resolution, medium resolution, and superior/high resolution, for both cold dark matter and fuzzy dark matter models. If we can measure the Universe precisely and accurately enough, we can distinguish between these types of models, contingent on whether we simulate it to great enough precision. Credit: M. Sipp et al., MNRAS (submitted), 2023)
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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)
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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)
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