Supermassive black hole dust ring can cast shadows from the heart of a galaxy

Some of the most amazing views of our sky occur at sunset, when sunlight breaks through the clouds, creating a mixture of light and dark rays formed by the shadows of the clouds and the light beams scattered by the atmosphere.

Astronomers studying the nearby galaxy IC 5063 are tempted by a similar effect in images taken by NASAof The Hubble Space Telescope. In this case, a collection of narrow light rays and dark shadows are seen radiating out of the extremely bright center of the active galaxy.

A team of astronomers, led by Peter Maksym from the Center for Astrophysics | Harvard and Smithsonian (CfA), in Cambridge, Massachusetts, traced the rays to the heart of the galaxy, the location of an active supermassive black hole. A black hole is a dense, compact region of space that engulfs light and matter under the overwhelming pull of gravity. The monster object frantically feeds on infallible material, producing a powerful jet of light from nearby superheated gas.

While the researchers have developed several plausible theories for the light show, the most intriguing idea suggests that an inner tube-shaped ring, or torus, of dusty material surrounding the black hole casts its shadow into space.

According to the scenario proposed by Maksym, the dust disk around the black hole does not block all the light. Gaps in the disc allow light to diffuse, creating brilliant cone-shaped rays similar to the fingers of light sometimes seen at sunset. However, the rays in IC 5063 occur on a much larger scale, spanning at least 36,000 light years.

Some of the light hits dense areas in the ring, casting the shadow of the ring into space. These shadows appear as dark finger shapes interspersed with light rays. These beams and shadows are visible because the black hole and its ring are tilted laterally with respect to the plane of the galaxy. This alignment allows the light beams to extend far outside the galaxy.

This interplay of light and shadow offers a unique insight into the distribution of matter surrounding the black hole. In some areas, the material may look like scattered clouds. If this interpretation is correct, the observations can provide an indirect probe of the mottled structure of the disc.

“I’m very excited about the shadow of the torus idea because it’s a really cool effect that I don’t think I’ve seen in the footage before, although it has been speculated,” said Maksym. “Scientifically, it shows us something that is difficult – usually impossible – to see directly. We know this phenomenon should be happening, but in this case we can see the effects across the galaxy. Learning more about the geometry of the torus will have implications for anyone trying to understand the behavior of supermassive black holes and their environments. As a galaxy evolves, it is shaped by its central black hole. “

The study of the torus is important because it channels matter towards the black hole. If the “shadow” interpretation is correct, the dark rays provide indirect evidence that the IC 5063 disk might be very thin, which is why light escapes all around the structure.

Observations of similar black holes by NASA’s Chandra X-ray Observatory detected X-rays escaping from holes in the torus, making the structure appear like Swiss cheese. The holes can be caused by the disc tightening by internal forces, which distorts it, Maksym said. “It is possible that the warping creates spaces large enough for some of the light to pass through, and as the torus spins, beams of light could sweep the galaxy like lighthouse beams through the fog,” he added.

Citizen Science Serendipity

Although astronomers have studied the galaxy for decades, it took a non-scientist to make this startling discovery. Judy Schmidt, an artist and amateur astronomer based in Modesto, Calif., Discovered dark shadows when she reprocessed the Hubble galaxy exhibits in December 2019. Schmidt regularly plots the Hubble Archives for interesting observations that she can transform in beautiful pictures. She shares these images on her Twitter feed with her many followers, including astronomers such as Maksym.

Schmidt selected the Hubble observations of IC 5063 from the archives because she is interested in galaxies that have active nuclei. The cone-shaped shadows weren’t apparent in the original exhibits, so she was surprised to see them in her reprocessed image. “I had no idea they were there, and even after I treated him I kept blinking my eyes wondering if I was seeing what I thought I was seeing,” she says.

She immediately posted her image on her Twitter account. “It was something I had never seen before, and although I strongly suspected that it was shadow rays or ‘crepuscular rays’ as Peter dubbed them, it’s easy to leave free rein to her imagination and wishful thinking, ”she explained. . “I told myself that if I was wrong, someone would come and earth me.”

The image sparked a heated discussion on Twitter among its astronomer followers, including Maksym, who debated where the rays came from. Maksym had previously analyzed the Hubble images of the jets produced by the galaxy’s black hole. So he took the lead in studying rays and writing a scientific article. His study is based on near infrared observations made by the Wide Field Camera 3 and the Advanced Camera for the Hubble surveys in March and November 2019. Red and near infrared light pierces the dusty galaxy to reveal details that can be shrouded in dust.

This discovery would not have been possible without Hubble’s sharp vision. The galaxy is also relatively close, just 156 million light years from Earth. “Older images from ground telescopes may have shown clues of this type of structure, but the galaxy itself is such a mess you’d never guess that’s what happens without Hubble,” explained Maksym. “Hubble has crisp images, is sensitive to pale things, and has a field of view large enough to image the entire galaxy.”

Maksym hopes to continue his study of the galaxy to determine if his scenario is correct. “We will want to continue to investigate, and it will be great if other scientists also try to test our findings with new observations and new models,” he said. “It’s a project that only asks for new data because it raises more questions than it answers.”

The team’s results were published in Letters from the astrophysical journal.

Reference: “Crepuscular rays of the strongly tilted active galactic nucleus in IC 5063” by W. Peter Maksym, Judy Schmidt, William C. Keel, Giuseppina Fabbiano, Travis C. Fischer, Joss Bland-Hawthorn, Aaron J. Barth, Martin Elvis, Tom Oosterloo, Luis C. Ho, Minjin Kim, Hyunmo Hwang and Evan Mayer, October 8, 2020, Letters from the astrophysical journal.
DOI: 10.3847 / 2041-8213 / abb9b6

The Hubble Space Telescope is an international cooperation project between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland operates the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts science operations at Hubble. STScI is operated for NASA by the Association of Universities for Astronomical Research in Washington, DC