Direct Comparisons of Black Hole Mass Measurements

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Black holes often appear in science fiction, but they are now also science fact. These invisible objects are some of the most extreme in the universe. The black holes that live in the centers of galaxies contain as much material as millions or billions of Suns, but they are collapsed down into incredibly small sizes. This means that they have enormous amounts of gravity. While black holes are invisible because they do not give off any light, they can be detected by their effects on objects around them. Just as the wind is invisible but it clearly shakes leaves, black holes are invisible but their gravity whips around stars and glowing gas. Astronomers have developed a few different ways to use telescopes to measure the motions of stars and gas around invisible black holes. Faster motions indicate more gravity from a black hole. Black holes with more gravity contain more material that has collapsed down, and so the visible motions of stars and gas allow astronomers to “weigh” invisible black holes. The researchers have collected a small sample where they can weigh all of the black holes with both of the most widely-used methods. In Broader Impacts, the PI will work with the Girl Scouts of Greater Atlanta to develop and offer astronomy workshops that target girls in grades 4-5 and high school. The PI will engage the broader community through her ongoing commitments to facilitate and participate in a wide variety of public outreach events, with the goal of bringing science literacy and appreciation to a broad audience.Black holes are some of the most extreme objects in the universe. The black holes that are found in the centers of galaxies contain the mass of millions or billions of Suns, but they are collapsed down into infinitesimal sizes. While black holes are invisible because they do not emit any light, they can be detected by their gravitational effects on nearby stars or gas. Astronomers have thus developed a few different techniques to measure the motions of stars and gas to constrain black hole masses. But it is difficult to compare how well the different techniques agree with each other because each one requires a specific set of conditions. Nevertheless, this is an important point to check, because nearby black holes are mostly studied with one method but a completely different method is used for distant black holes. Distant celestial objects are seen as they were in the past, so large samples of nearby and distant black holes are used to understand how they were born and grow over time. Thus it is important to be sure that both techniques are calibrated to the same mass scale. The researchers have collected a small number of black holes where they can determine their masses using both of the most widely-used methods. In this program, they will apply both methods and carefully compare their results. This will allow them to determine for the first time if both techniques are giving similar answers, or if there may be previously unknown biases affecting our understanding of black holes and their galaxies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.