Supermassive Black Hole Powers ‘Beautiful’ Jets in ‘Hercules A’ Galaxy

RIT professors Stefi Baum and Chris O’Dea use Hubble Space Telescope

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Something spectacular is happening 2 billion light years away in the constellation Hercules.

A composite image of the elliptical radio galaxy Hercules A, captured in the optical and radio wavelengths, shows two jets of cosmic rays—subatomic particles—and magnetic fields streaming from a supermassive black hole into the interstellar and intercluster media, or the space between stars and galaxies.

The resulting image of radio galaxy Hercules A was released Nov. 29 by the Space Telescope Science Institute, which operates the Hubble Space Telescope, and the National Radio Astronomy Observatory, which runs the Karl G. Jansky Very Large Array radio telescope.

“It’s both beautiful and fascinating to look at,” says Stefi Baum, director and professor, the Chester F. Carlson Center for Imaging Science at Rochester Institute of Technology.

Baum and Chris O’Dea, professor in the School of Physics and Astronomy at RIT, collaborated with Rick Perley and William Cotton at the National Radio Astronomy Observatory on the multiwavelength study. Their technique gleans information from more than one wavelength along the electromagnetic spectrum and gives them more data about Hercules A, or 3C 348, one of the brightest known extragalactic objects emitting at radio wavelengths.

“This has always been an interesting galaxy from the radio perspective because the two sides of the source look very different,” Baum says. “It’s a source for which there have been many theories proposed as to why the radio morphology is this way. Our data will provide more information, but not solve the problem completely. This is the nature of astrophysics research, each new observation sheds light on the physics at work and slowly a coherent model and picture emerges.”

Prior to this study, Baum and O’Dea had used the Hubble to take “snapshots” of the elliptical galaxy and noted unusual dust wisps. They recently used the telescope’s Wide Field Camera 3 to re-capture the elliptical galaxy in much greater sensitivity and detail. The team combined the data with a deep image of the same source captured by the newly upgraded Very Large Array radio telescope.

The superimposed images revealed a discrepancy the team had not predicted: The dust morphology on the two sides of galaxy appears differently in the optical and radio wavelengths.

“One side has dusty filaments of cold gas that lie along the edges of the radio jet, suggesting they have been dragged along, or entrained, by the outflowing radio plasma; but the other side of the source shows dusty filaments which resemble two bubbles,” Baum says of the Hubble data.

The radio data reveals the reverse. “The side that has the dust bubbles is the side with the normal looking collimated jet and the side with what looks like more entrained dust is the side that has the very unusual bubbles in the radio,” she adds. “We’re perplexed so far.”

The differences in the structure of the radio jets on the two sides might be due to the way the outflows are generated by the supermassive black hole or how they interact with their environments as they travel outward away from the galaxy, O’Dea says.

“If the Hubble data showed that the morphology of the cold gas and dust mimicked that of the radio jet on the same side, that would be consistent with the idea that the differences were established on small scales,” O’Dea adds. “However, the fact that the cold gas and dust has a different morphology than the radio emission on the same side supports the idea that the differences in radio properties are established on larger scales as the jets interact with their environments.”

The multiwavelength image was released prior to the complete analysis of the radio data. Additional analysis will likely provide information that constrains and refines the astronomical models predicting the radio morphology in the galaxy.

Baum and O’Dea are members of the Laboratory for Multiwavelength Astronomy in RIT’s College of Science. The laboratory consolidates related research by likeminded faculty, staff and students who participate in RIT’s Astrophysical Sciences and Technology Ph.D. program.