11 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.

   (Excerpts)

   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.

   Notes

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

6. Research continues not only on more detailed imaging of black holes but also the physics of warped light around event horizons.

   A recent simulation modeled looping of light around black holes and confirmed the mathematics for the repetitive distance of successive (and flatter) images to the edge of the black hole – “opening up potential new ways to test Einstein’s theory of general relativity.”

   • Space.com > “Black holes warp the universe into a grotesque hall of mirrors” by Paul Sutter (July 28, 2021)

   (quote) … if you were to place a galaxy behind the black hole … [its light] can … hit the black hole at an angle that allows it to make one (or many) loops before eventually escaping.

   Looking at the edge of the black hole, your eyes would see one image of the background galaxy from its deflected light. Then, you would see a second image of the galaxy from light rays that managed to make a single orbit before escaping — and then again from light rays that made two orbits, …

7. More research on the supermassive black hole M87.

   • Newsweek > “Mystery of Black Hole’s Powerful Near-Light-Speed Jets May Be Solved” by Robert Lea (11/05/2021)

   (quote) An international team of researchers has modeled the region around the black hole in high detail, using state-of-the-art three-dimensional supercomputer simulations.

   “Our theoretical model of the electromagnetic emission and of the jet morphology of M87 matches surprisingly well with the observations in the radio, optical and infrared spectra,” Institute of Theoretical Physics of Goethe University Frankfurt researcher and the paper’s lead author, Dr. Alejandro Cruz-Osorio, said. “This tells us that the supermassive black hole M87 is probably highly rotating and that the plasma is strongly magnetized in the jet, accelerating particles out to scales of thousands of light-years.”

   To build these models, the supercomputer used a staggering million CPU hours per simulation. It had to simultaneously solve the equations of the greatest minds in physics, including the field equations of general relativity, devised by Albert Einstein, the equations of electromagnetism by James Maxwell, and the equations of fluid dynamics by Leonhard Euler.

8. A particularly dramatic example of galactic plasma dynamics.

   • Space.com > “Astronomers have detected one of the biggest black hole jets in the sky” by Western Sydney University: Luke Barnes, Miroslav Filipovic, Ray Norris, Velibor Velović (August 30, 2022)

   At a mere 93 million light-years away, the galaxy NGC2663 … Looking at its starlight with an ordinary telescope, we see the familiar oval shape of a “typical” elliptical galaxy, … Typical, that is, until we observed NGC2663 with CSIRO’s Australian Square Kilometre Array Pathfinder (ASKAP) [radio telescope] in Western Australia … The radio waves reveal a jet of matter, shot out of the galaxy by a central black hole. This high-powered stream of material is about 50 times larger than the galaxy …

   Article’s image caption: Black hole jets from NGC2663 compared to a jet engine [a pattern of regular bright spots due to expansion and contraction]. Top image: observations from the ASKAP radio telescope. Bottom: a methane rocket successfully being tested in the Mojave Desert.

   
   Credit: Black hole as plasma jet engine by John Healy from Wiki

9. Regarding the dynamics of accretion disks …

   Here’s an article about research published October 11 in The Astrophysical Journal. An international team used multi-wavelength radio and visible light astronomy to study a black hole event. After an unusually a long delay, a black hole ejected prior ingested material at about half the speed of light!

   • Space.com > “Black hole is ‘burping out’ a ‘spaghettified’ star it devoured years ago” by Robert Lea (October 14, 2022)

   “It’s as if this black hole has started abruptly burping out a bunch of material from the star it ate years ago.” – Astronomer Yvette Cendes, Harvard & Smithsonian Center for Astrophysics

   In October 2018, the black hole — located in a galaxy 665 million light-years from Earth — was observed tearing up a star that had wandered too close. The event [AT2018hyz] itself wasn’t surprising to astronomers, who often observe these violent encounters [so-called tidal disruption events] between stars and greedy black holes.

   “… in AT2018hyz there was radio silence for the first three years, and now it’s dramatically lit up to become one of the most radio-luminous TDEs ever observed.” – Astronomer Edo Berger, professor at Harvard University

   

10. Where black holes tango, there be gravitational waves (cf. “There be dragons”) …

    As noted in my original 2020 post (Fraser Cain’s video), this finding was made years ago: Research on a far, far away dot – OJ 287, a supermassive quasar – concluded it’s actually two, two black holes in one galactic heart (cf. “Two, two, two mints in one!“).

    This article (below) discusses results from a 2021/2022 astronomical observational campaign which obtained direct evidence of the secondary black hole’s dynamics.

    • Space.com > “Brilliant gamma-ray flare 100 times brighter than our entire galaxy reveals 1 monster black hole is actually 2” by Robert Lea (June 12, 2023) – The second supermassive black hole is causing blasts of energy as it dives through a disk of blisteringly hot gas.

    The new research accurately predicts the timing of the second black hole’s dives through the accretion disk, thus allowing astronomers to model both the flattened, oblong orbit of the second black hole and the timing of the accretion-disk flares it creates.

    When the secondary black hole dove through the accretion disk of its larger partner, it also created a powerful burst of gamma-rays — the largest seen from this system in six years — that was observed by the Fermi Gamma-ray Space Telescope. The gamma-ray blast was created by a jet of material from the secondary black hole hitting the gas in the main accretion disk. This was confirmed when the scientists looked back through archival data and saw a similar gamma-ray burst in 2013 — the last time the smaller black hole dropped through the accretion disk.

    
    Artistic illustration of OJ 287 as a binary black hole system. (Image credit: AAS 2018)

11. 

    Black hole mergers produce detectible gravitational-wave “chirps.”

    Here’s an interesting overview of formation of black holes, detection of collisions (mergers), and modeling the expansion of the universe.

    • Space.com > “Gravitational waves show black holes prefer certain masses before they collide” by Keith Cooper published (August 14, 2023) – A preference for “universal masses” 9 and 16 times the mass of our Sun have been identified in the gravitational-wave events detected so far.

    A larger sample of gravitational-wave events may be coming soon. A new observing run involving LIGO, Virgo and KAGRA that will last 20 months has recently begun, and the aim is to discover another 300 events. We will know soon enough whether the new results enhance the peaks in the distribution around the universal masses and the gap between them.

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