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First data from XRISM space mission provides new perspective on supermassive black holes | University of Michigan News
I've often remarked on how the stark difference between their laughably childish description of the Universe in the Bible and the reality science is revealing, illustrates the scientific illiteracy of its parochial authors, and so gives the lie to claims that it was written or inspired by a creator god.
They were writing with the knowledge and understanding of Bronze Age pastoralists - which is hardly surprising, since that's exactly what they were. They only knew of the small area around the Canaanite Hills, so nothing that was more than a day or two's walk for them was included, which is why it seemed to them like a small flat planet with a dome over it, and fixed to the dome were the sun, moon and stars; stars being mere small points of light and only those that were visible to the naked eye.
So, just imagine what they would have made of the information if some time traveler from today went back and told them about black holes and the centre of a galaxy 120,000 light years across and containing a billion suns with planets orbiting them! How could they have comprehended the idea of mass bending space-time or something smaller than a grain of sand weighing the same as a million suns?
What would they have made of distances so great that it takes light 120,000 years to travel its length? To them, light was instantaneous; it mattered not whether it came from the sun or the campfire, and the sun was merely a lamp hanging from the dome over the earth. What on Earth was this nonsense about the sun being really big and Earth going round it, things weighing millions of times more than the sun or light taking more time than they thought there had been to travel from one place to another?
They knew nothing of laws of motion and how forces make things move, so they had no concept of gravity. They walked on Earth because they didn't float above it, and they couldn't fly. Only gods and supernatural beings could travel up and down at will. So, what on Earth would mass causing gravity and gravity being an attractive force mean?
Black holes would have been simply beyond their comprehension and outside their experience of the world.
So, of course, they could have included nothing of any of this stuff in the stories they invented to explain things they didn't understand. Had they done so, we might have had some cause to think something must have told them. As it was, they wrote tales that illustrated their scientific illiteracy because they had no option but to do so. They were scientifically illiterate by today's standards.
Tell me all about black holes, please* How does the discovery of an accretion disc around Sagittarius A~ fit with the current state of knowledge? Black Holes: OverviewAnd by the standards of future scientists, we too are ignorant and functionally illiterate, though nowhere near to the same degree as the Bibles authors were.
A black hole is a region in space where gravity is so intense that nothing, not even light, can escape from it. They are formed when massive stars collapse under their own gravity at the end of their life cycles. Black holes come in different sizes, ranging from stellar-mass black holes to supermassive black holes, which are found at the centers of most galaxies.
Key components of a black hole:
- Singularity: The core of the black hole where the mass is thought to be concentrated in an infinitely small point.
- Event Horizon: The boundary around the black hole beyond which nothing can return.
- Accretion Disk: A rotating disk of gas, dust, and other materials that spiral into the black hole.
Types of Black Holes:
- Stellar Black Holes: Formed from the collapse of massive stars. They typically have masses between 3 to 10 times that of the Sun.
- Intermediate Black Holes: A less understood category that fills the gap between stellar and supermassive black holes.
- Supermassive Black Holes: These exist at the centers of galaxies, including our own Milky Way, and have masses ranging from millions to billions of solar masses.
- Primordial Black Holes: Hypothetical black holes that could have formed soon after the Big Bang, though they have not been observed.
Sagittarius A* (Sgr A*)
Sagittarius A* is the supermassive black hole located at the center of the Milky Way galaxy, about 26,000 light-years from Earth. It has a mass of approximately 4 million times that of the Sun. Sgr A* is not very active compared to some other supermassive black holes found in quasars, which emit intense radiation as matter falls into them. Nonetheless, it's a key object of study for astronomers.
Accretion Disks: Essential for Understanding Black Holes
An accretion disk forms when gas, dust, and other matter spiral into a black hole. As this matter accelerates due to the gravitational pull of the black hole, it heats up and emits electromagnetic radiation, particularly in the X-ray spectrum.
Accretion disks are important because they allow astronomers to indirectly observe black holes, which themselves emit no light. By studying the light and radiation coming from the disk, scientists can infer a black hole’s properties, including its mass, spin, and the physics of matter in extreme conditions.
Discovery of an Accretion Disk Around Sagittarius A*
The discovery of an accretion disk around Sagittarius A* was significant for several reasons:
- Verification of Theories: It provided direct evidence for long-standing theoretical models of how supermassive black holes behave. Astrophysicists had predicted that black holes, even relatively quiet ones like Sgr A*, would be surrounded by accretion disks.
- Understanding Black Hole Activity: Although Sgr A* is relatively "dormant" compared to other active galactic nuclei (AGN), the presence of an accretion disk suggests that it occasionally consumes material from its surroundings. The dynamics of this disk provide insights into why the black hole is not as luminous or active as those in quasars or other AGNs.
- Testing General Relativity: Black holes like Sgr A* offer excellent natural laboratories for testing Einstein's theory of general relativity, particularly near the event horizon. Observations of the behavior of matter in the accretion disk allow scientists to examine the effects of extreme gravity.
- Imaging the Black Hole: In 2019, the Event Horizon Telescope (EHT) collaboration captured the first image of a black hole (M87*), and scientists are working toward obtaining an image of the shadow of Sagittarius A*. Observing the accretion disk around Sgr A* helps refine models for imaging its event horizon.
- Astrophysical Implications: The discovery sheds light on how supermassive black holes grow and interact with their environments. The process by which gas flows into the accretion disk and is either consumed or expelled could help explain galaxy formation and evolution.
Current State of Knowledge and Future Research
The discovery fits into the broader understanding of how black holes grow and evolve. In recent years, technologies like the EHT have advanced our ability to observe black holes directly, turning theoretical predictions into observable phenomena. Researchers are keen on further studying accretion disk mechanics, magnetic fields, and how black holes influence galaxy formation through feedback mechanisms such as jets—streams of high-energy particles ejected along the poles of the black hole.
The accretion disk around Sagittarius A* presents a less active, yet highly intriguing, environment compared to other more energetic black holes, and future studies will likely provide deeper insights into how such systems operate over cosmic time scales.
On a technical point, there should be a point at which a collapsing black hole passes from the domain of Relativity into the domain of Quantum Physics, so the laws of Relativity break down. What happens as this boundary is crossed?
You're absolutely right: the collapse of a black hole reaches a point where the laws of general relativity (which govern large-scale structures like stars and planets) intersect with the laws of quantum mechanics (which govern very small-scale phenomena, like particles). This intersection occurs at incredibly small scales and extreme conditions, such as at the singularity within a black hole, where current physical theories break down.
Let's break it down:
General Relativity vs. Quantum Mechanics
- General Relativity (GR): Describes how matter and energy shape the curvature of spacetime. It works extremely well for large-scale objects like stars, galaxies, and the universe as a whole. It predicts that when a star collapses into a black hole, all its mass is concentrated into a single point called a singularity where spacetime curvature becomes infinite.
- Quantum Mechanics (QM): Describes the behavior of matter and energy at extremely small scales (like atoms and subatomic particles). At these scales, the universe behaves very differently, governed by probabilities rather than certainties. It includes quantum field theory, which describes the fundamental forces of nature except gravity.
The problem is that general relativity and quantum mechanics are mathematically incompatible. Relativity does not account for quantum effects, and quantum mechanics doesn’t explain gravity. The singularity predicted by general relativity inside a black hole is where these two realms collide, and we need a new theory—one that unites both.
The Planck Scale: The Boundary Between GR and QM
The boundary between general relativity and quantum physics is typically thought to occur at the Planck scale, which is defined by fundamental physical constants.
- Planck Length: About \(\small 1.6 \times 10^{-35}\) meters. This is the scale at which quantum gravitational effects become significant.
- Planck Time: The time it takes light to travel one Planck length, about \(\small 5.4 \times 10^{-44}\) seconds.
- Planck Mass: Around \(\small 2.2 \times 10^{-8}\) kilograms.
When you approach the Planck scale near the center of a black hole, gravity becomes so strong and spacetime so curved that quantum effects must dominate. Unfortunately, our current theories can't adequately describe what happens in this regime.
What Happens at the Boundary?
When a black hole collapses to a point near the singularity, general relativity predicts an infinite curvature of spacetime (a singularity), where densities become infinite. However, quantum mechanics suggests that such infinities should not exist because quantum uncertainty prevents particles from occupying a definite, infinitely small space. Here's a closer look at the possibilities:
- Quantum Gravity: A yet-to-be-discovered theory of quantum gravity would explain how gravity works on quantum scales. Leading candidates include string theory and loop quantum gravity, but neither has been fully validated by experimental data. These theories suggest that spacetime is not continuous but "quantized," and at the Planck scale, the fabric of spacetime itself could be discrete, avoiding the formation of a true singularity.
- Hawking Radiation: Quantum effects at the event horizon (the boundary of the black hole) give rise to Hawking radiation, a form of radiation that causes black holes to slowly lose mass and potentially evaporate. This is an important quantum mechanical prediction for black holes, but it doesn't fully explain what happens at the singularity.
- he Firewall Paradox: There’s a theoretical puzzle in quantum physics called the black hole information paradox. General relativity suggests that information is lost when something falls into a black hole, but quantum mechanics insists that information is conserved. This has led to speculative ideas like the firewall paradox, which proposes that an observer falling into a black hole would encounter a "firewall" of high-energy particles at the event horizon.
- Planck Star Hypothesis: An alternative idea to a singularity is the Planck star, a theoretical object that forms at the core of a black hole. This hypothesis suggests that instead of a singularity, collapsing matter reaches a Planck-scale object where quantum gravity effects halt the collapse, potentially allowing the black hole to "bounce" and release energy, which might be observed as gamma-ray bursts.
Crossing the Boundary: Known and Unknown
- Classical Collapse (GR): As a star collapses, its core contracts under its own gravity. When it passes a critical threshold, its density and spacetime curvature grow without bound. General relativity holds sway during most of this process.
- Quantum Region: Near the singularity, spacetime reaches the Planck scale. Here, quantum mechanics begins to dominate, but because we lack a complete theory of quantum gravity, we don’t know what happens. Some theories suggest spacetime becomes “foamy” or even experiences quantum fluctuations.
- Quantum Foam & Wormholes?: Some quantum gravity theories predict that spacetime could have a foamy structure at the Planck scale, with tiny wormholes popping in and out of existence. Others suggest black holes might connect to other regions of the universe through "wormholes," though this is still highly speculative.
- End of Collapse: In the absence of a unifying theory, it's unclear whether the collapse ever truly reaches a point where general relativity predicts a singularity. Quantum gravity may prevent this, but we don’t yet know how.
Possible Solutions and Future Directions
- Theory of Quantum Gravity: The development of a quantum theory of gravity is crucial to understanding what happens as a black hole collapses. If we discover a theory that unites quantum mechanics and general relativity (sometimes called a "Theory of Everything"), it may provide the answers to what happens at the Planck scale.
- Experimental Evidence: Observations of black hole mergers, made possible by gravitational wave detectors (like LIGO and Virgo), and further exploration of phenomena like Hawking radiation might provide clues to what happens inside black holes. However, directly probing the singularity will be difficult because it's hidden behind the event horizon.
In summary, as a black hole collapses and reaches the Planck scale, the laws of general relativity begin to break down, and quantum mechanics takes over. However, without a unified theory of quantum gravity, we can't fully describe what happens at the singularity or the extreme conditions within a black hole's core. The next big step in theoretical physics is to bridge this gap between relativity and quantum mechanics.
The plain fact is that knowledge builds on knowledge. Scientists like the team led by Professor Jon Miller of the University of Michigan, are discovering more about black holes than that they are so massive that even light can't escape the pull of their gravity when it crosses and event horizon beyond which nothing can escape. They have just announced the discovery of accretion discs around a black hole. They did this using tools that have been developed to provide data in much greater detail and much greater accuracy then anything previously used, so we can expect further discoveries.
The team have just published their findings, open access, in The Astrophysical Journal Letters and announced them in a University of Michigan news release:
First data from XRISM space mission provides new perspective on supermassive black holes
Some of the first data from an international space mission is confirming decades worth of speculation about the galactic neighborhoods of supermassive black holes.
More exciting than the data, though, is the fact that the long-awaited satellite behind it—the X-Ray Imaging and Spectroscopy Mission or XRISM—is just getting started providing such unparalleled insights.
We have found the right tool for developing an accurate picture of the unexplored orders of magnitude around supermassive black holes. We’re beginning to see clues of what that environment really looks like.
Professor Jon Miller, co-author
Professor of astronomy
Department of Astronomy
University of Michigan, Mi USA.
The Japanese Aerospace Exploration Agency, or JAXA, which teamed up with NASA and the European Space Agency to create and launch XRISM, announced the new results Sept. 20.
The results were published Sept. 19 in two peer-reviewed studies, with Miller being the lead author of one accepted to The Astrophysical Journal Letters. He and more than 100 co-authors from around the world investigated what’s called an active galactic nucleus, which includes a supermassive black hole and its extreme surroundings.
To do this, they relied on XRISM’s unparalleled ability to gather and measure spectra of X-rays emitted by cosmic phenomena.
It is truly exciting that we are able to gather X-ray spectra with such unprecedented high resolution, particularly for the hottest plasmas in the universe. Spectra are so rich with information, we will surely be working to fully interpret the first datasets for many years to come.
Lia Corrales, co-author
Assistant professor of astronomy
Department of Astronomy
University of Michigan, Mi USA.
Accretion disks with a twist
Space exploration enthusiasts may know that the Chandra X-ray Observatory—what NASA calls its flagship X-ray telescope—recently celebrated its 25th anniversary of operating in space.
What’s less well known is that, over the past 25 years, an international cohort of scientists, engineers and space agency officials have been attempting to launch similarly sophisticated, but different X-ray missions.
The goal of these attempts was to provide high-quality, complementary data to better understand what Chandra and other telescopes were seeing. XRISM is now delivering that data.
With their data set, Miller, Corrales and their colleagues have solidified a hypothesis about structures called accretion disks near supermassive black holes in active galactic nuclei.
These disks can be thought of like vinyl records made of gas and other loose particles from a galaxy being spun by the spectacular gravity of the black holes at their centers. By studying accretion disks, researchers can better understand what’s happening around the black hole and how it impacts the lifecycle of its host galaxy.
By probing the center of a galaxy called NGC 4151, more than 50 million light years away, the XRISM collaboration confirmed that the disk’s shape isn’t as simple as once thought.
What we’re seeing is that the record isn’t flat. It has a twist or a warp. It also appears to get thicker toward the outside.
We had hints, but somebody in forensics would say that we couldn’t have convicted anyone with what we had.
Professor Jon Miller
Although suggestions of this more complex geometry have emerged in other data over the past two and a half decades, the XRISM results are the strongest direct evidence for it.
The team also found that the accretion disk appears to be losing a lot of its gas. Again, scientists have theories about what happens to this material, but Miller said XRISM will enable researchers to find more definitive answers.
It has been very hard to say what the fate of that gas is. Actually finding the direct evidence is the hard work that XRISM can do.
Professor Jon Miller
And XRISM isn’t just allowing researchers to think about existing theories in new ways. It’s enabling them to investigate parts of space that were invisible to them before.
The missing link
For all the talk of their gravitational pull being so strong that not even light can escape it, black holes are still responsible for creating a whole lot of electromagnetic radiation that we can detect.
For instance, the Event Horizon Telescope—a network of instruments on Earth sensitive to radiation emitted as radio waves—has enabled astronomers to zoom in and see the very edge of two different black holes.
There are other instruments on Earth and in space that detect different bands of radiation, including X-rays and infrared light, to provide larger, galaxy-scale views of the environs of black holes.
But scientists have lacked high-resolution tools to determine what was going on between those two scales, from right next to the black hole up to the size of its host galaxy. And that space between is where accretion disks and other interesting celestial structures exist.
If you were to divide the scale of the zoomed-out view of a black hole by that of its close-up, you’d get a number close to 100,000. To a physicist, each zero is an order of magnitude, meaning the gap in coverage spanned five orders of magnitude.
When it comes to understanding how gas gets into a black hole, how some of that gas is lost and how the black hole impacts its host galaxy, it’s those orders of magnitude that really matter.
Professor Jon Miller
XRISM now gives researchers access to those scales by looking for X-rays emitted by iron around black holes and relying on the “S” in its acronym: spectroscopy.
Rather than using X-ray light to construct an image, XRISM’s spectroscopy instrument detects the energy of individual X-rays, or photons. Researchers can then see how many photons were detected with a particular energy across a range, or spectrum, of energies.
By collecting, studying and comparing spectra from different parts of the regions near a black hole, researchers are able to learn more about the processes afoot.
We joke that spectra put the ‘physics’ in ‘astrophysics
Professor Jon Miller
Although there are other operational X-ray spectroscopy tools, XRISM’s is the most advanced and relies on a microcalorimeter, dubbed “Resolve.” This turns the incident X-ray energy into heat rather than, say, a more conventional electrical signal.
Resolve is allowing us to characterize the multi-structured and multi-temperature environment of supermassive black holes in a way that was not possible before.
Lia Corrales.
XRISM provides researchers with 10 times better energy resolution compared with what they’ve had before, Miller said. Scientists have been waiting for an instrument like this for 25 years.
AbstractThe technical details of this research are hard enough to understand even for someone like me with a basic understanding of physics and some knowledge I've gleaned from various articles I've read. Imagine what it would be like for a Bronze Age pastoralist who could probably not even read, write or do anything more mathematical than counting cattle!
We present an analysis of the first two XRISM/Resolve spectra of the well-known Seyfert-1.5 active galactic nucleus (AGN) in NGC 4151, obtained in 2023 December. Our work focuses on the nature of the narrow Fe Kα emission line at 6.4 keV, the strongest and most common X-ray line observed in AGN. The total line is found to consist of three components. Even the narrowest component of the line is resolved with evident Fe Kα,1 (6.404 keV) and Kα,2 (6.391 keV) contributions in a 2:1 flux ratio, fully consistent with neutral gas with negligible bulk velocity. Subject to the limitations of our models, the narrowest and intermediate-width components are consistent with emission from optically thin gas, suggesting that they arise in a disk atmosphere and/or wind. Modeling the three line components in terms of Keplerian broadening, they are readily associated with (1) the inner wall of the "torus," (2) the innermost optical "broad-line region" (or "X-ray BLR"), and (3) a region with a radius of r ≃ 100 GM/c2 that may signal a warp in the accretion disk. Viable alternative explanations of the broadest component include a fast-wind component and/or scattering; however, we find evidence of variability in the narrow Fe Kα line complex on timescales consistent with small radii. The best-fit models are statistically superior to simple Voigt functions, but when fit with Voigt profiles the time-averaged lines are consistent with a projected velocity broadening of FWHM \(\,=\,{1600}_{-200}^{+400}\,\mathrm{km}\,{{\rm{s}}}^{-1}\). Overall, the resolution and sensitivity of XRISM show that the narrow Fe K line in AGN is an effective probe of all key parts of the accretion flow, as it is currently understood. We discuss the implications of these findings for our understanding of AGN accretion, future studies with XRISM, and X-ray-based black hole mass measurements.
XRISM Collaboration; Audard, Marc; Awaki, Hisamitsu; Ballhausen, Ralf, et al.
XRISM Spectroscopy of the Fe Kα Emission Line in the Seyfert Active Galactic Nucleus NGC 4151 Reveals the Disk, Broad-line Region, and Torus
The Astrophysical Journal Letters 1 973; DOI: 10.3847/2041-8213/ad7397
Copyright: © 2024 The authors.
Published by IOP Publishing. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
And it's clear from the section of the AI panel that deals with the interface between the macro domain of Relativity and the micro domain of Quantum Mechanics inside the black hole at the level of a singularity, then even the most advanced cosmologists don't yet understand what happens at that small scale because we don't have a good theory for quantum gravity, so there is still much to learn in that respect.
That doesn't mean that a best guess to fill that gap in our knowledge and understanding, especially one which includes a magic supernatural deity just because someone wants it to be involved somewhere, should be regarded as the final word and placed beyond scientific scrutiny because someone with a vested interest declares it to be true as they did with the best guesses of scientifically illiterate Bronze Age pastoralists from the fearful infancy of our species.
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