Events

Image: Ana Carvalho

Is LIGO really observing black holes?

The observation of gravitational radiation emitted by black hole mergers is now providing direct experimental evidence of black holes. According to general relativity, the merger remnant emits “ringdown” radiation: a superposition of damped exponentials (“quasinormal modes”) with complex frequencies that depend only on the final black hole’s mass and spin. These spectral lines uniquely identify the black hole, just like the 21 cm line identifies interstellar hydrogen. In the first part of the talk I will discuss recent theoretical and experimental developments in this “black hole spectroscopy” program, including the importance of nonlinear effects and new models of the frequency-domain waveform based on the black hole’s greybody factors. In the second part of the talk I will discuss recent subsolar-mass LIGO-Virgo-KAGRA public alerts. If these events are real, it is tantalizing to conclude that they may be primordial black holes. I will argue that one should first exclude alternative explanations of astrophysical origin, such as the merger of subsolar-mass neutron stars formed in collapsar disks.

Monday, October 5, 2026 11:00 AM

Inperson
G10

Virtual
Zoom

Measuring the Acceleration-Dependent Temperature of the Minkowski Vacuum

Relativistic quantum field theory is the structure on which the Standard Model and beyond-Standard Model physics are built. One of its most striking predictions is the Unruh effect: an accelerating observer measures the Minkowski vacuum as a thermal bath at a fixed temperature. Despite decades of theoretical interest, this effect has never been directly observed. We propose to use the high acceleration gradients provided by wakefield accelerators, coupled with a forward laboratory-frequency ~THz detector array, to measure the resulting forward-beamed radiation, and outline the unique signature provided by quantum detailed balance to extract the signal from backgrounds. While challenging, such a measurement appears within reach of present-day accelerator and detector technologies.

Monday, October 5, 2026 9:30 AM

Inperson
Speaker will be in person – BHI Conference Room

Virtual
Zoom

Monday, October 12, 2026

Modeling emission from super-Eddington supermassive black holes

Tidal disruption events (TDEs) light up hidden supermassive black holes and encode information about the
properties of both these black holes and their environments. They also regularly produce super-Eddington
mass return rates, providing a local test of extreme black hole growth. The light curves and spectra of TDEs
show signatures of these super-Eddington feeding rates, including evidence of large outflows, very high
electron densities, and strongly ionizing but obscured emission. Many of these signatures are also seen in
other candidates for super-eddington accretion, including luminous fast blue optical transients, ambiguous
nuclear transients, and little red dots. However, properties of the system such as the origin, mass/energy
budget and black hole mass are often better understood in TDEs. I’ll discuss how we can use theoretical
models to connect the observed light curves and spectra to the actual source emission as well as to the
properties of the gas surrounding the black hole in these transients. More broadly I’ll discuss how we can
combine theoretical models with observations to investigate the black hole mass function, probe emission
from forming and evolving accretion disks, and study the properties of stars on size scales we cannot
observe outside our own galactic nuclei.

Monday, October 19, 2026 11:00 AM

Inperson
G10

Virtual
Zoom

The Approximate Cosmological Principle and Permanent Underdetermination in Cosmology

In this talk, I will discuss the implications of some recent work in observational cosmology and mathematical general relativity (GR) for the epistemology of spacetime. My primary aim is to articulate a non-trivial and physically relevant underdetermination thesis concerning the global, topological structure of models of GR. I will argue that my thesis is philosophically interesting for at least two reasons: (i) it affects “sensible realists,” viz., those who counsel realism only about theoretical claims that are amenable to empirical investigation (Stanford 2006); and (ii) it is “permanent” (in the sense of Pitts 2011). In order to formulate my thesis and to defend my claims, I begin by surveying cosmological research devoted to empirically determining the spatial topology of the universe (e.g., Akrami et al. 2024). This research typically assumes the Cosmological Principle (CP); however, CP is a very strong constraint on our theorizing, and its justification is fraught with difficulties. Indeed, strictly speaking, it is known not to hold, even in the observable universe. As such, it has been suggested that a more accurate reflection of our observational situation would be to assume an “approximate” CP. Drawing on recent mathematical work, I discuss one possible way of making this notion precise (Ringström 2013). Interestingly, when we pass to Ringström’s approximate CP, it appears that one cannot draw any conclusions about the topology of space. I carefully analyze why this occurs, and demonstrate that the resulting underdetermination is permanent. Time permitting, I compare my thesis to related results and sketch how my discussion can serve as a powerful starting point for anti-realist positions in the epistemology of spacetime.

Monday, October 19, 2026 9:30 AM

Inperson
Speaker will be in person – BHI Conference Room

Virtual
Zoom

Monday, October 26, 2026 11:00 AM

Inperson
G10

Virtual
Zoom

Monday, October 26, 2026 9:30 AM

Inperson
BHI Conference Room

Virtual
Zoom

Monday, November 2, 2026 11:00 AM

Inperson
G10

Virtual
Zoom

Monday, November 2, 2026 11:00 AM

Inperson
G10

Virtual
Zoom

Monday, November 16, 2026 9:30 AM

Inperson
BHI Conference Room

Virtual
Zoom

Monday, November 23, 2026 – Monday, November 30, 2026

Monday, December 7, 2026 11:00 AM

Inperson
G10

Virtual
Zoom

Monday, December 14, 2026 11:00 AM

Inperson
G10

Virtual
Zoom

Monday, December 21, 2026 – Monday, January 18, 2027