October 15, 2022:
"A New Surprise in the Accelerating Expansion of the Universe"
with Dr. Alex Filippenko
We expected the attractive force of gravity to slow down the rate at which the Universe is expanding. But in 1998, two essentially independent research teams made a Nobel-worthy discovery: since distant supernovae appear fainter than predicted, the expansion of the Universe must be speeding up with time, rather than decelerating. Over the largest distances, the Universe seems to be dominated by a mysterious, repulsive “dark energy” that stretches space itself faster and faster. Yet the physical origin and nature of dark energy, which makes up about 70% of the contents of the Universe, is not understood. Our most recent surprise is that the current expansion rate we measure with supernovae is faster than that predicted from observations of the young Universe, even taking into account the previously discovered acceleration. This suggests the possibility of exciting new physics beyond the standard model of cosmology.
September 24, 2022:
"How to Make Stars on Computers"
with Dr. Mike Grudić
The formation of stars is a process that is fundamental to the formation of the planets they host and the galaxies that they compose. But many aspects of star formation remain deeply mysterious to astrophysicists. It remains a difficult physics problem because it involves a multitude of physical processes acting simultaneously over a wide range of length- and time-scales. The equations can only be solved with numerical simulations, and I will outline the basic procedure for taking these equations and translating them into a form that can be stepped forward in time on a supercomputer. I will then introduce the STARFORGE simulations, a new generation of high-resolution, multi-physics star formation simulations, and discuss some key insights on the nature of star formation that we have gained. I will conclude by highlighting some new interesting puzzles we've run into as we push STARFORGE to the smaller scales of protoplanetary disks, and to the larger scales of the galactic environment. The frontier for making stars on computers involves linking the large range of scales together while accounting for yet more physical processes.
August 27, 2022:
"The Era of Exoplanets: Towards an Exoplanets Demographics Ladder"
with Dr. Jessie Christiansen
The NASA Kepler mission has provided its final planet candidate catalogue, the K2 mission has contributed another four years’ worth of data, and the NASA TESS mission has been churning out new planet discoveries at a rapid pace. The demographics of the exoplanet systems probed by these transiting exoplanet missions are complemented by the demographics probed by other techniques, including radial velocity, microlensing, and direct imaging, and we are approaching a time when we may be able to recreate the full census of exoplanets. I will walk through the progress of the Kepler occurrence rate calculations, including some of the outstanding issues that are being tackled. I will present our new results from K2, and outline how K2 and TESS will able to push the stellar parameter space in which we can explore occurrence rates beyond that examined by Kepler. Finally, I will highlight some of the pieces of the larger demographics puzzle - occurrence rate results from the other techniques that probe different stellar and exoplanet regimes - and progress to be made working to join those pieces together.
July 23, 2022:
"The Most Extreme Variable Stars (and Webb Update)"
with Dr. Michelle Thaller
Want to take observing variable stars to its most extreme? While we’ve known about pulsars since the late 1960s, a recent NASA mission is proving them to be more exciting and mysterious than we ever expected. NICER, the Neutron Star Interior Composition Explorer, is one of the smaller NASA missions, as far as size and budget, but the discoveries pouring out of this dishwasher-sized instrument on the ISS are blowing the minds of both observational and theoretical astronomers. What do the jets coming off a pulsar really look like? How do the jets change? Have we discovered a “quark star?” We’ll talk about all this and, sure, do an update about the Webb telescope too.
June 25, 2022:
"All-Sky Automated Survey for Supernovae: Big Science with Small Telescopes"
with Dr. Krzysztof Stanek
Until the present day, only human eyes monitored the entire night sky. There was no optical survey that frequently searched the entire celestial sphere, seeking out the transient, variable, and sometimes violent, events that mark the evolution and transformation of our Universe. We changed that with our "All-Sky Automated Survey for Supernovae’’ (ASAS-SN), which automatically surveys the entire visible sky every night, for the first time in human history.
ASAS-SN is discovering large numbers of bright supernovae, quasar flares, tidal disruption events, Galactic novae, and variable stars that, in turn, trigger additional observations across the electromagnetic spectrum and beyond. Because ASAS-SN transients are bright, they are easily studied in detail and frequently become the best-studied examples of any transient class and the templates for understanding fainter, less easily studied examples.
I will discuss some of the most interesting recent ASAS-SN discoveries. I will also discuss the various ways in which we make our data public. The scientific value and public utility of ASAS-SN data are growing rapidly, and I will discuss our plans for that to continue in the future.
May 28, 2022:
"Surprises from the Expansion of the Universe"
with Dr. Adam Riess
The Hubble constant remains one of the most important parameters in the cosmological model, setting the size and age scales of the Universe. Present uncertainties in the cosmological model including the nature of dark energy, the properties of neutrinos and the scale of departures from flat geometry can be constrained by measurements of the Hubble constant made to higher precision than was possible with the first generations of Hubble Telescope instruments. A streamlined distance ladder constructed from infrared observations of Cepheids and type Ia supernovae with ruthless attention paid to systematics now provide 1.4% precision and offer the means to do much better. By steadily improving the precision and accuracy of the Hubble constant, we now see evidence for 5 sigma deviations from the standard model, referred to as LambdaCDM, and thus the exciting chance, if true, of discovering new fundamental physics such as exotic dark energy, a new relativistic particle, or a small curvature to name a few possibilities. I will review recent and expected progress, most recently based on measurements by the SH0ES Team from the Hubble Space Telescope and Gaia EDR3.
April 23, 2022:
"The discovery of pulsars – a graduate student’s tale"
with Dr. Jocelyn Bell Burnell
I will describe how pulsars were accidentally discovered and relate some instances where they were 'nearly' discovered.
March 26, 2022:
"The Last Stargazers"
with Dr. Emily Levesque
A bird that mimicked a black hole. The astronomer that discovered microwave ovens. A telescope that got shot. The science of astronomy is filled with true stories (and tall tales) of the adventures and misadventures that accompany our exploration of the universe. Join Dr. Emily Levesque, author of the critically-acclaimed popular science book The Last Stargazers, to take a behind-the-scenes tour of life as a professional astronomer. We'll learn about some of the most powerful telescopes in the world, meet the people who run them, and explore the crucial role of human curiosity in the past, present, and future of scientific discovery.
February 26, 2022:
"Variable Stars and Interacting Binary Systems in High Definition"
with Dr. Margarita Karovska
Multiwavelength sub-arcsecond resolution imaging offers extraordinary opportunities for detailed studies of many astronomical sources. These include evolved stars and interacting binaries that show significant variations of physical characteristics on time scales ranging from days to many years, even centuries (as shown for example by the AAVSO long-term monitoring of its light curves).
I will highlight results from multimission imaging with high-spatial resolution of several nearby supergiants, giants, and symbiotic interacting binaries. The high definition images are key to understanding the structure and mass transfer processes, especially of progenitors of planetary nebulae, supernovae, and including supernovae type Ia (key cosmological distance indicators). AAVSO long-term observing/monitoring has facilitated these discoveries and is crucial for planning future observations of variable stars and interacting binary systems. .
I will conclude by discussing the potential of future ultra-high angular resolution imaging, with resolution over 100 times higher than that of the HST (e.g., Stellar Imager with <0.1 milliarcsecond resolution imaging in UV-Optical), which will open unprecedented possibilities for spectral and spatial studies of a wide range of currently unresolvable astronomical sources in the Universe.
January 22, 2022:
"Star Tickling and the AAVSO"
with Dr. Jill Tarter
In 2008, Learned, Kudritzki, Pakvasa, and Zee1 suggested that an advanced technological civilization might phase modulate Cepheids and other regularly variable stars in order to create a type of Morse code that could transmit information across the galaxy. Several attempts have been made to find such modulations, but the AAVSO would appear to be the ideal organization to conduct a systematic exploration of observational records stretching over a century.