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Black hole systems – communicating the cosmos

[Communicating science series]

Today my post celebrates another science communicator, Fraser Cain, and his YouTube channel by the same name. This week, I noticed his video “Two Supermassive Black Holes Orbiting Each Other. Stephen Hawking Was Right!” (May 11, 2020). Well-done visualization.

The Moon orbits around the Earth. The Earth orbits around the Sun. And out in the distant Universe, astronomers have found a system that takes this logical progression to its most extreme. There’s a system where a supermassive black hole with millions of times the mass of the Sun orbits another black hole with billions of times the mass of the Sun.

How astronomers discovered this incredible interaction took careful observations, imagination, and the hard work of the Spitzer Space Telescope, taken during its final years of operation.

His channel description says:

Space and astronomy news from Fraser Cain, publisher of Universe Today and co-host of Astronomy Cast.

If you’re a fan of space, sci-fi and pop culture, you’ll love our Guide to Space. These short videos come out every Monday and Thursday and answer a burning question that astronomy fans want to know. We talk about black holes, galaxies, the Universe, and the search for aliens.

Cain teamed up with a science teacher for the book The Universe Today Ultimate Guide to Viewing the Cosmos: Everything You Need to Know to Become an Amateur Astronomer (published October 23, 2018), a resource for viewing the Night Sky.

David Dickinson is an Earth science teacher, freelance science writer, retired USAF veteran and backyard astronomer. He currently writes and ponders the universe as he travels the world with his wife.

Fraser Cain is the publisher of Universe Today. He’s also the co-host of Astronomy Cast with Dr. Pamela Gay. He lives in Courtenay, British Columbia.

Wiki: Binary black hole (BBH).

And here’re some more questions about black hole systems.

So, most, if not all, black holes spin; and around them are spinning accretion disks of matter which feed those black holes. How fast is the spin in each case?

Or, how fast can matter fall into a black hole? That’s the question addressed in this article (below). The geometric alignment of a black hole system is important.

Royal Astronomical Society > “Matter falling into a black hole at 30 percent of the speed of light” (2018).

A UK team of astronomers report the first detection of matter falling into a black hole at 30% of the speed of light, located in the centre of the billion-light year distant galaxy PG211+143. The team, led by Professor Ken Pounds of the University of Leicester, used data from the European Space Agency’s X-ray observatory XMM-Newton to observe the black hole. Their results appear in a new paper in Monthly Notices of the Royal Astronomical Society.

Until now it has been unclear how misaligned rotation might affect the in-fall of gas. This is particularly relevant to the feeding of supermassive black holes since matter (interstellar gas clouds or even isolated stars) can fall in from any direction.

YouTube > Uni of Leicester > “Computer simulation predicts matter plunging into a black hole at extreme velocity” (Sep 17, 2018).

Computer simulation predicts matter plunging into a black hole at extreme velocity.

X-rays are so cool, eh.

5 thoughts on “Black hole systems – communicating the cosmos

  1. A “hydrodynamical backflow model” explains the “double boomerang” shape of a galaxy containing an active supermassive black hole.

    Live Science > “The sky is full of weird X-shaped galaxies. Here’s why.” by Brandon Specktor – Senior Writer (May 13, 2020).

    PKS 2014−55 is an X-shaped radio galaxy (XRG), an unusual type of galaxy that looks like an enormous X in the night sky when imaged in radio wavelengths.

    According to William Cotton, an astronomer at the National Radio Astronomy Observatory (NRAO) in Virginia who studies XRGs, fewer than 10% of known cosmic radio sources take on a distinct X shape like this one.

    “It’s actually a ‘double boomerang’ shape,” Cotton said. “That means something in the galaxy is diverting the flow into these secondary wings.”

    In a new study posted May 7 on the pre-print server arXiv and accepted for publication in the journal Monthly Notices of the Royal Astronomical Society, researchers with the NRAO and South African Radio Astronomy Observatory (SARAO) used the massive MeerKAT radio telescope in South Africa’s Karoo desert to capture the most detailed image of an XRG ever.

    First, the galaxy’s central black hole gobbles up matter for millions of years, … The black hole belches twin jets of matter into space, each traveling in opposite directions at incredible speed.

    Eventually (tens of thousands of years later), those jets blast through the galaxy’s gassy halo, traveling onward into intergalactic space. Pressure slowly builds up in the jets as they travel farther and farther out of the galaxy, ultimately forcing some material in each jet to flip around and flow back toward the center again.

    Backflow is common in active galaxies, Cotton said, but usually all that returning material bulges up in the middle of the galaxy, rather than bouncing off to the side. In PKS 2014−55, the galaxy’s hot halo of dust and gas is angled in such a way that the backflow is actually “deflected” back out of the galaxy, giving each jet a boomerang-like appearance.

  2. Light can escape from a black hole’s accretion disk, but the dynamics of such disks is complex. More clues from X-ray astronomy.

    Live Science > “Black hole bends escaping light ‘like a boomerang’” by Mindy Weisberger – Senior Writer (April 24, 2020).

    Researchers found this odd behavior while reviewing archival X-ray observations of a black hole that’s approximately 10 times as massive as our sun. Located about 17,000 light-years from Earth, the black hole siphons material from a partner star; together, the black hole and star are known as XTE J1550-564.

    Light in a black hole’s accretion disk — a spiraling, flattened cloud of dust and gas that circles the edges of a black hole — can sometimes escape into space. But the departing light from the XTE J1550-564 black hole didn’t follow the predictable path. Instead of escaping directly from the disk, the light was instead pulled back toward the black hole and then reflected off the disk and away from the black hole “like a boomerang,” researchers reported in a new study.

    Normally, the team studies light “coming from that corona [gas] and hitting the disk, bouncing off, and then arriving at our telescopes.”

    This time, however, some of the light bouncing off the black hole’s disk appeared to originate in the disk itself rather than in the corona; it was then dragged back toward the black hole before bouncing away.

    This discovery could help scientists confirm other elusive aspects of black holes, such as how fast they spin. Researchers already understand how an accretion disk around a black hole behaves. By adding this boomeranging light to their computer models, astrophysicists can then calculate a black hole’s rotation speed based on how much of the light is bending and bouncing back, Connors explained. [Riley Connors is a postdoctoral researcher in physics at the California Institute of Technology‘s Cahill Center for Astronomy and Astrophysics in Pasadena, California.]

    “It’s perhaps a more reliable way for us to measure how fast the black holes are spinning,” he said.

  3. Regarding how fast black holes spin, I was reminded of this 2019 Forbes article by Ethan Siegel.

    Forbes > “This Is Why Black Holes Must Spin At Almost The Speed Of Light” (August 1, 2019).

    Siegel discusses a model of collapse which conserves angular momentum as the star explosively contracts to a remnant of its original size. He illustrates the physics using the typical example of a figure skater pulling their arms in to increase spin speed. (Trying this in my swivel chair also demonstrates the principle, but makes me sick. As well as reducing rotational rate by starting with my arms in and then stretching out.)

    Making that assumption provides a ready solution for how fast a black hole spins. Such an assumption makes sense in that we’re talking about gravitational collapse – radially directed collapse (even if not exactly symmetric). No explosions (ejections) act like spin dampening thrusters on a spacecraft.

    Regardless, a simple model of conservation of angular momentum matches our observations of pulse periods of pulsars and radiation speeds from accretion flows around black holes.

    Yet if you remember that most of the stars in our Universe also have enormous volumes, you’ll realize that they contain an enormous amount of angular momentum.

    If you compress that volume down to be very small, those objects have no choice. If angular momentum has to be conserved, all they can do is spin up their rotational speeds until they almost reach the speed of light. … Perhaps someday, we’ll be able to measure that directly.

  4. Here’s another interesting article which discusses the dynamics of accretion disks.

    Live Science > “How close can you get to a black hole?” by Paul Sutter (May 27, 2020).

    A team of astronomers recently published an article in the journal Monthly Notices of the Royal Astronomical Society, which also was uploaded to the preprint journal arXiv, describing how to take advantage of that dying light to study the ISCO [innermost stable circular orbit]. Their technique relies on an astronomical trick known as reverberation mapping, which takes advantage of the fact that different regions around the black hole light up in different ways.

  5. A natural question about black holes: What happens to matter that falls into the center of the hole?

    In excerpts from his latest book [1], Carlo Rovelli is honest about the mystery – not knowing the answer (per se), but nevertheless posits an answer.

    I find his (imagined) characterization interesting because it offers continuity in fluid dynamics (including shock waves) rather than a spin into higher dimensions. It retains an effective reality with a scale beyond our everyday notion of time.

    • New Scientist > “Where does the stuff that falls into a black hole go?” by Carlo Rovelli (28 October 2020) – What happens to matter in a black hole? The question has spawned many paradoxes, and in an extract from his latest book, physics superstar Carlo Rovelli proposes an answer.


    What happens to matter that falls into the centre of the hole? We don’t know.

    In the research group I work with in Marseille, together with colleagues at Grenoble and at Nijmegen in the Netherlands, we are exploring a possibility that seems to us both simpler and more plausible: matter slows down and stops before it reaches the centre. When it is most extremely concentrated, a tremendous pressure develops that prevents its ultimate collapse. This is similar to the “pressure” that prevents electrons from falling into atoms: it is a quantum phenomenon. Matter stops falling and forms a kind of extremely small and extremely dense star: a “Planck star“. Then something happens that always happens to matter in such cases: it rebounds.

    But an extremely long time is not an infinite time, and, if we waited for long enough, we would see the matter come out. A black hole is ultimately perhaps no more than a star that collapses and then rebounds – in extreme slow motion when seen from outside.

    Imagine it: the whole of the sun contained within the volume of a foothill. … The entire mass of the star is concentrated into the space of a molecule. Here the repulsive quantum force kicks in, and the star immediately rebounds and begins to explode. For the star, only a few hundredths of a second have elapsed. But the dilation of time caused by the enormous gravitational field is so extremely strong that when the matter begins to re-emerge, in the rest of the universe, tens of billions of years have passed.


    [1] There Are Places In The World Where Rules Are Less Important Than Kindness (November 5, 2020).

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