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Ergosphere – what?

Regarding recent posts about black holes, here’s another YouTube video by The Science Asylum on the topic (published February 16, 2019): “Black Holes can SPIN?!?”

Most sources talk about Schwarzschild black holes, but those don’t spin. Most are what we call Kerr black holes, or rotating black holes, surrounded by a region called an ergosphere. The spacetime around them is not only stretched, but also twisted, leading to some strange phenomena.

I’ve previously highlighted The Science Asylum as a science communicator. This latest video is an interesting overview of black holes: non-spinning vs. spinning, the math vs. reality inside and outside event horizon(s), the ergosphere, frame dragging.

And here’s a YouTube video on the ehtelescope channel “Zoom into M87 Explaining Formation of the Supermassive Black Hole Image” (published on Apr 15, 2019) which visualizes a black hole which has been much in the news lately.

This artist’s impression based on real black hole accretion simulations delves into the surroundings of a black hole, showing an accretion disc of superheated plasma and a relativistic jet. It also shows the paths of photons in the vicinity of a black hole, as they curve close to the event horizon due to strong gravity. The gravitational bending and capture of light by the event horizon is the cause of the black hole shadow captured by the Event Horizon Telescope in the galaxy M87.
Credit: Nicolle R. Fuller / NSF Scientific Advisory, Simulations, Final Image: EHT Collaboration

2 thoughts on “Ergosphere – what?

  1. The ergosphere is related to the event horizon of a black hole. This Space.com article discusses the upcoming reveal of the first-ever photo of a black hole (one of many teasers for this event): “The Event Horizon Telescope Is Trying to Take the First-Ever Photo of a Black Hole.”

    Astronomers orchestrated radio dish telescopes across the world into an Earth-size virtual camera for a bold new experiment attempting to deliver the first-ever image of a black hole. The telescope collaboration is set to make a big announcement of results this week [week of April 8, 2019], and members also described their research approach at a talk in March.

    The astronomers’ idea is to photograph the circular opaque silhouette of a black hole cast on a bright background. The shadow’s edge is the event horizon, a black hole’s point of no return.

    Article contains good overview video.

    Wiki: Event Horizon Telescope

  2. And today (April 9, 2019) Space.com published another article on black holes” “What Exactly Is a Black Hole Event Horizon (and What Happens There)?

    “The event horizon is the ultimate prison wall — one can get in but never get out,” Avi Loeb, chair of astronomy at Harvard University, told Space.com.

    “The event horizon protects us from the unknown physics near a singularity,” Loeb said.

    The size of an event horizon depends on the black hole’s mass. If Earth were compressed until it became a black hole, it would have a diameter of about 0.69 inches (17.4 millimeters), a little smaller than a dime; if the sun were converted to a black hole, it would be about 3.62 miles (5.84 kilometers) wide, about the size of a village or town. The supermassive black holes that the Event Horizon Telescope is observing are far larger; Sagittarius A*, at the center of the Milky Way, is about 4.3 million times the mass of our sun and has a diameter of about 7.9 million miles (12.7 million km), while M87 at the heart of the Virgo A galaxy is about 6 billion solar masses and 11 billion miles (17.7 billion km) wide.

    Good recap of non-rotating vs. rotating black holes.

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