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Events on Thursday, September 28th, 2023

Astronomy Colloquium
The Census of Supermassive Black Holes over Cosmic Time
Time: 3:30 pm - 4:30 pm
Place: 4421 Sterling Hall
Speaker: Jonathan Trump, University of Connecticut
Abstract: Supermassive black holes are a critical ingredient in our Universe. They are the most luminous persistent sources in the sky, in both photons and gravitational waves, and they play an essential role in the formation and growth of galaxies. My research seeks a comprehensive census of black holes using two complementary approaches. First, I will show how pioneering new SDSS time-domain spectroscopy enables a census of black hole mass, growth rate, and spin over most of cosmic time. I will also present the forecast for Rubin/LSST discovery of binary black holes: the electromagnetic counterparts to gravitational echoes seen in pulsar timing and (eventually) LISA. Meanwhile the first year of JWST observations has revealed a surprisingly active early Universe, with a large number of massive black holes identified in z>5 galaxies. This implies a significant population of heavy black hole seeds and suggests that accreting black hole play a significant role in reionizing the Universe. The next generation of time-domain, space-telescope, and multi-messenger experiments make it a truly bright time for understanding the dark nature of black hole astrophysics.
Host: Ke Zhang
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Graduate Program Event
Coral biomineralization vs. climate change
Time: 6:00 pm - 8:00 pm
Place: 2241 Chamberlin
Speaker: Pupa Gilbert, Physics Faculty
Abstract: Coral reefs cover only 1% of ocean floors, yet they host 25% of all known marine species. This incredible
biodiversity is sheltered by the 3D structure of coral skeletons. My group and I revealed that corals form
their skeletons by attachment of amorphous calcium carbonate (ACC) nanoparticles, then fill
interstitial spaces by ion attachment. Subsequent crystallization starts as aragonite (CaCO3)
nanocrystals, randomly oriented and termed sprinkles, which coarsen and become radially oriented
acicular crystals termed spherulites. This is Nature’s 3D printing! The resulting space-filling, solid,
isotropic structure grows slowly (0.5-5.0 cm/year) to form m-km coral reefs visible from outer space.
Corals are threatened by climate change, including ocean warming and acidification. With acidification,
the solubility of CaCO3 increases, thus, making it increasingly difficult for corals to build their skeletons,
especially because the ACC transient precursor phase is more soluble than aragonite. Different coral
species are differently sensitive to ocean acidification, indicating that mechanistic biological factors link
ocean chemistry and CaCO3 mineral growth, which we are studying. My group’s research suggests two
science-based interventions to help coral reefs. First, species selection based on resilience to acidification may allow repopulation of damaged reef ecosystems. Second, we are building electrified grids on
which corals are expected to grow faster, resist bleaching and acidification.
Presentation: Pupa's flyer-2.pdf
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