- 3531 - BLACKHOLES - so much left to discover? Not only do we have more to learn about supermassive blackholes, but the variations in their ravenous hunger are a demonstration that our Universe is a far more dynamic place than one would expect looking at the static night time sky.
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--------------------- 3531 - BLACKHOLES - so much left to discover?
- Some of the James Webb Space Telescope's first science investigations will probe the role that bright objects called “quasars” played in early galaxy evolution. Quasars are distant objects powered by blackholes typically a billion times as massive as our sun. They emit energies that can climb to trillions of electron volts, exceeding the total output of all the stars in a typical galaxy.
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- Webb's telescope perch in deep space, coupled with its extreme sensitivity to low levels of light and high resolution, will make the most detailed set of observations yet possible of these elusive objects, which have only been known to science over the last 50 years.
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- This summer, 2022, Webb will look at six of the most distant and luminous quasars to situate these objects in the timeline of galactic evolution. Quasars will also be used to look at gas distribution between galaxies.
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- Scientists hope to learn about a period known as the “epoch of deionization“. This epoch happened 13 billion years ago, or less than a billion years after the universe was formed. Galaxies of the era were largely opaque to energetic light and those objects are difficult to observe.
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- The astronomers will use quasars as background light sources to study the gas between us and the quasar. That gas absorbs the quasar's light at specific wavelengths. Through a technique called “imaging spectroscopy“, astronomers look for absorption lines in the intervening gas.
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- Distant, ancient galaxies could help scientists understand how the universe turned back into plasma. Webb's ability to observe in infrared light will especially be useful because the most distant quasars' light were severely stretched by expansion of space. This phenomenon, known as “cosmological redshift“, moves light waves to the red or infrared area of the spectrum, where Webb is optimized to make observations.
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- Webb should see enough light from the quasars to look for elements heavier than hydrogen or helium, elements that are called "metals" by astronomers. These elements were formed in the first stars and the first galaxies and expelled by galactic outflows.
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- Outflows will be used to better understand how gas accreted by a supermassive blackhole embedded in a galaxy pushes and heats up surrounding gas. The outflows can become so strong that they create chaos in the host galaxy and greatly affect the galaxy's evolution.
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- The supermassive blackholes in active galaxies can produce narrow particle jets and wider streams of gas known as ultra-fast outflows, which are powerful enough to regulate both star formation in the wider galaxy and the growth of the blackhole.
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- Scientists know that gas removed from a galaxy will slow the rate of star formation, since stars depend on gas to form and grow. In some cases, outflows will rob the galaxy of so much gas that star formation will cease completely.
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- Outflows are the main mechanism by which gas, dust and elements are redistributed over large distances within the galaxy, or can even be expelled into the space between galaxies, called the “intergalactic medium“.
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- Astronomers don’t know for certain what happens inside a blackhole and even the formation of supermassive blackholes in the early universe is still being worked out. The nature of dark matter, and how primordial supermassive blackholes could grow so fast in such a short amount of time are two pressing open questions in physics and astrophysics.
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- Physicists developed a model that describes one possible solution using the idea of dark matter as being ultralight, with a mass that is 28 orders of magnitude lighter than the proton but possibly spanning light years per particle.
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- If dark matter is ultralight, then that could be the key to explain the formation of primordial supermassive blackholes. The conditions needed for matter to collapse and form a blackhole of supermassive size were just right, a few days after the Big Bang when the Universe had a temperature close to that of the Sun’s core. This would be 15 million Kelvins, or 27 million degrees Fahrenheit.
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- These high temperatures would be needed for this particular type of matter to exist. Once the temperature of the Universe reached the right level, the pressure could have dropped to a very low level, allowing matter to collapse due to gravity. This would not happen with known particles, thus the idea of ultralight dark matter.
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- This collapsing of matter would cause gravitational waves. These waves have a characteristic shape. When next-generation pulsar timing arrays that are more sensitive come online they may be able to detect those waves and provide validation for the theory that dark matter is or may have been ultralight.
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- Binary blackholes can unlock another of Einstein’ predictions The structure of a blackhole is pretty simple. All you need to know is its mass, electric charge, and rotation, and you know what the structure of space and time around the blackhole must be.
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- But if you have two blackholes orbiting each other, then things get really complicated. Unlike a single blackhole, for which there is an exact solution to Einstein’s equations, there is no exact solution for two blackholes.
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- It’s similar to the three-body problem in Newtonian gravity. Although Einstein’s equations don’t have an exact solution for a binary blackhole system, there are aspects of binary blackholes that the equations can predict.
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- One of these is known as “spin-orbit resonance“. When a blackhole rotates, the structure of space around it is twisted in the direction of rotation, known as “frame dragging“.
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- When two blackholes orbit each other closely, the frame-dragging of each blackhole affects the rotation of the other. As a result, the two blackholes will tend to enter a resonance, where the rotations either align in the same way (parallel) or opposite (anti-parallel). If spin-orbit resonance is real, then binary pairs should tend to have one of these orientations.
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- One of the challenges to measuring blackhole spin is that the signal is weak. The gravitational waves we measure from distant blackhole mergers are so faint that it’s easy to get lost in the noise.
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- Observatories such as LIGO and Virgo need to make extremely sensitive measurements, and their data must be filtered through computer models. Its the combination of data processing and computer simulation that makes the mergers detectable. Adding spin to the mix makes things even more difficult.
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- These researchers found that the signal for spin resonance is strongest when they are just about ready to merge. That makes sense since that’s when they are closest together and when frame-dragging is strongest. But currently, the rotation information for binary blackholes is found by looking at gravitational waves while they are still orbiting each other.
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- Gravitational-wave astronomy is still a new field, and astronomers are still learning how to capture and analyze the data. As these new studies show, gravitational waves hold a great deal of information, and with a bit of digging there’s plenty more we can uncover.
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- Primordial blackholes could explain dark matter and the growth of supermassive blackholes at the same time. Blackholes have long been proposed as the source of dark matter. In many ways, they are the perfect candidate because they only interact with light and matter gravitationally. But stellar-mass blackholes have been ruled out observationally. There simply aren’t enough of them to account for the total dark matter mass.
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- “Primordial” blackholes are a possible solution. Unlike stellar blackholes that would have a mass larger than the Sun, primordial blackholes could have the mass of a mere planet or less. A planet-mass blackhole would be smaller than an apple, and an asteroid-mass blackhole could be smaller than a grain of sand.
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- These are known as primordial blackholes because they are thought to have formed during the early moments of the universe. The James Webb telescope could discover evidence of primordial black holes in the near future.
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- In the center of most galaxies lies a “super massive” blackhole. Some of these are actively feeding on the gas and dust around them, expelling excess energy as powerful jets that are seen as “quasars” across the entire observable Universe. With their extreme gravitational pull, they are able to engulf vast amounts of gas, dust, and perhaps even stars that wander into their vicinity.
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- This material tends to form a disk as it is drawn towards the blackhole in a phenomenon called "accretion. Now these accretion disks have velocities approaching the speed of light, and temperatures far in excess of the surface of our Sun.
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- This heat produces radiation which we see as light, but the conversion of heat to light is so efficient, about 30 times more efficient than nuclear fusion, that physicists don't quite understand how. Astronomers have more to learn!
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April 3, 2022 BLACKHOLES - so much left to discover? 3527
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