Charles E. Kaufman Foundation

2019 New Initiative Grant

Sarah Shandera, Ph.D. (PI) Associate Professor of Physics, Pennsylvania State University

Donghui Jeong, Ph.D. (co-investigator) Assistant Professor in Astronomy & Astrophysics, Pennsylvania State University

Chad Hanna, Ph.D. (co-investigator) Associate Professor of Physics, Pennsylvania State University

Sub-solar mass black holes as a gravitational wave probe of the hidden universe


For nearly one hundred years, observations of the motions of distant stars and galaxies have suggested that a new form of matter known as dark matter is abundant in the cosmos. Indeed, precise cosmological and astrophysical measurements today find that about 85% of the matter in the Universe is made up of something other than the familiar, light-emitting matter foundational to our own physics and chemistry. Cosmological data on the history of the Universe reveals that understanding dark matter is essential for understanding the origin and formation of galaxies like the Milky Way. Despite its immense importance, we know very little about dark matter. Decades of laboratory experiments designed to detect dark matter have come up empty and we are slowly ruling out the notion that dark matter is made of just one new weakly interacting particle. In this proposal, we explore a transformative idea. What if dark matter is more complex? In fact, what if the complexity of dark matter rivals the complexity of our own visible matter? What sort of dark matter structures might form? The only surefire way to detect dark matter is through gravity and the one class of objects that are expected to be common to both dark and visible matter are black holes. The mass of the proton restricts black holes formed from visible matter to be heavier than our Sun, but we know of no such restriction for dark matter. A detection of a sub-solar mass black hole would reveal the existence of a new type of astrophysical object, new particles and new physical laws, and would provide information about the masses and interaction strengths of the dark matter particles. Even if no sub-solar-mass black holes are detected, their nonexistence can provide unique constraints on the nature of dark matter. We propose to address these questions by building on the recent successes of the LIGO and Virgo gravitational wave detectors. We will use the data collected by the upgraded LIGO instruments in the next few years to search for merging black holes with masses below the mass of the sun. Our proposed project uses gravitational signals alone to test the nature of dark matter structures with masses 11 orders of magnitude below what can be seen in typical cosmological data sets. It will provide particle physicists and cosmologists with information inaccessible via other astrophysical surveys or from laboratory searches for dark matter particles. Our team of three faculty combines expertise in particle physics, cosmology, astrophysics, and gravitational waves to carry out this work, and we are committed to training both graduate and undergraduate students who will conduct the analysis.

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