Readers ask about photon loops and more

Sept. 24, 2022 Hardcover

Rings and rainbows

A team of scientists claims to have detected a thin ring of light called the photon ring around the first black hole to capture its image, the supermassive black hole in the galaxy M87. But the skeptics are not convinced. Emily Conover mentioned inPhysicists question the photon loop claim(SN: 9/24/22, p. 8).

Assuming the Earth and the photon ring are on the same plane, reader James P. Rice I wondered why we see light as a circle instead of a straight line.

“The photon ring is a bit like a rainbow,” a physics writer said James R. Reardon Says. “It’s a visual effect, not a physical episode.” Rainbows are caused by the way raindrops affect the paths of light. A person can see a rainbow in the rain in front of him as long as the sun is behind him. But where the rainbow appears to the observer changes depending on where that person is standing in relation to the sun.

In a similar way, the photon loop occurs due to the influence of the black hole on the paths of light, Reardon Says. The photon ring will appear as a circular ring around the black hole no matter which direction you look at the black hole from. “You can’t be any more level with the photon ring than you can walk to the end of the rainbow,” he says.

I just wonder

Science news Readers often ask questions that have nothing to do with our journalism but are fascinating nonetheless. We indulge our distinct impulses to try to answer these questions.

reader Mark Sapir He was asked if light from the early solar system could be bent back to us during space travel so that one day we could see past Earth events.

“Everything bends a little bit,” he says. Sam Grala, a physicist at the University of Arizona in Tucson. But in order for the light to come back to us all the way, it has to bend a lot.

Our sun, for example, “bends light a little less than one-thousandth of a degree, so it won’t help us see into our past,” Jarala Says. In theory, if the sun collapsed into a black hole of the same mass, “then it could bend light all the way, which would be cool,” he says. “But only a very small part of the light emitted is bent so strongly, so we have to have amazing telescopes to see it.” Even if we had such telescopes, humans and other life on Earth would not survive without sunlight. Jarala Says. Unfortunately, our sun is destined to become a red giant when it dies, not a black hole.

Some light from our early solar system could also have reached Sagittarius A*, the black hole at the center of the Milky Way. “Sgr A* can bend light a lot,” Jarala Says. “But unless light is emitted near it, only a small part is actually bent.” For light from our solar system to return to us, it must approach Sgr A* in exactly the right direction, he says. “The proverbial needle in a haystack.”

“However, it is amusing to think that aliens near black holes might be looking at themselves in the ‘black hole mirror’ at this very moment,” Jarala Says.

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