Starts With A Bang podcast

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!  

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!

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!

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!