Bucknell professor instrumental in the discovery of the black hole | Training

Lewisburg, Pa. – Bucknell Professor Jack Gallimore, physics and astronomy, is the leader of an international team of astronomers and students who discovered magnetic loops around a supermassive black hole.

Although the galaxy in which the hole is located is well-studied, the hole itself has largely remained a mystery due to the huge clouds of dust and gas that have accumulated around it.

The team, which includes Bucknell physics student Virginia Hostetter ’25, studied NGC 1068, the Squid Galaxy, which lies 45 to 50 million light-years away—relatively close as galaxies go—and has a supermassive black hole at its center.

The research had two goals: an astrometric mapping of the Squid Galaxy’s radio continuum and measurements of the polarization of its water masers (water vapor that amplifies microwave radiation). Water masers observed at a frequency of 22 GHz are particularly useful because they can shine through dust and gas that block the view of a black hole.

Using the High Sensitivity Array (HSA) – a multi-facility network supported by the US National Science Foundation’s National Radio Astronomy Observatory (NRAO) – the team was the first to find evidence of magnetic filaments in the accretion disk around the Black Hole observed.

The discovery was announced by the NRAO on Wednesday, December 11th. An article on this topic was also published in The Astrophysical Journal Letters.

By measuring the polarization of the Squid Galaxy’s water masers and the continuum of radio emissions, the team created a map showing the compact radio source called NGC 1068*. The project also revealed extensive structures with weaker emissions, which they dubbed “The Foxtail.”

“What these new observations really found is that these filaments of burl spots are strung like beads on a string,” Gallimore said.

The team was amazed to see that there was a clear offset – a shift angle – between the radio continuum showing the structures in the galaxy’s core and the locations of the masers.

Gallimore continued: “The configuration is unstable, so we are likely observing the source of a magnetically triggered outflow.”

HSA measurements of the polarization of the water masers gave impressive evidence of the existence of magnetic fields.

“No one has ever seen polarization in water masers outside our galaxy,” Gallimore explained. “If you look at the filaments and see that the polarization vectors are perpendicular to them, that is the key to confirming that they are magnetically driven structures. It’s exactly what you would expect.”

The polarization pattern of the water masers clearly shows that magnetic fields are an integral part of their positioning, similar to the loop-shaped filaments that form on the surface of the Sun.

Previous studies of the galaxy have suggested patterns normally associated with magnetic fields, but the technology to confirm the presence of the fields did not exist until recently.

“Only the HSA has the required combination of resolution and sensitivity to image magnetic fields with polarized light,” says Gallimore.

Their results reveal evidence of a compact central radio source (the black hole), clear water maser polarization indicating structure within NGC 1068’s magnetic fields, and spectacular extended features across the continuum of radio frequencies. Taken together, these results suggest that magnetic fields are the underlying drivers of these phenomena.

The radio emissions from the Squid Galaxy are still a mystery, particularly the Foxtail, which extends northward from the central region.

“When we set out to do this, we said, ‘Let’s see if we can really push the limits and get good continuum and polarization data. And both goals were successful,” says Gallimore. “Using the NSF NRAO High Sensitivity Array, we detected water megamaser polarization for the first time and also created a truly amazing continuum map that we are still thinking about.”

Special thanks to the NRAO and author Jessi Almstead for the use of her story.

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