- 2885 - BLACKHOLES - pictures and theories.? 100 years ago, Albert Einstein’s theory of General Relativity predicted that blackholes should exist. In 1960 physicist John Wheeler coined the name ‘blackhole’ and the study of these mysterious objects became a cottage industry in theoretical physics and astrophysics.
--------------------------- 2885 - BLACKHOLES - pictures and theories?
- Quasars and x-ray sources had simply no other explanation for how such phenomena could generate so much energy in such an impossibly small volume of space until blackholes came along.
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- The existence of blackholes was elevated to a certainty by 1990 as studies of distant galaxies by the Hubble Space Telescope turned in so much data that clinched the idea that the cores of most if not all galaxies had a blackhole. These blackholes contained millions or even billions of times the mass of our sun.
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- General relativity is the “theory of gravity“, but it is completely couched in the language of geometry, that is called a “4-dimensional spacetime continuum“.
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- In general relativity, what we call space is just a particular feature of the gravitational field. It is a theory with some problems though. The problems stem from what happens when you collect enough mass together in a small volume of space so that the geometry of spacetime, that is the strength of gravity, becomes enormously “curved“.
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- The very first thing that happens according to the theory is that a condition in spacetime called a “Singularity” forms. Here, general relativity itself falls apart because density and gravity tend towards infinite conditions. Spacetime immediately develops a zone surrounding the Singularity called an “event horizon“.
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- For blackholes more massive than our sun, the distance in kilometers of this spherical horizon from the Singularity is just 2.9 times the mass of the blackhole in multiples of the sun’s mass.
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- For example, if the mass of a supermassive blackhole is 6.5 billion times the mass of our sun, its event horizon is at 6.5 billion x 2.9 or 19 billion kilometers. Our solar system has a radius of only 8 billion kilometers to Pluto, so this supermassive blackhole is over twice the size of our solar system!
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- Objects and even light can travel through the event horizon from outside the blackhole, but once inside they can never return to the outside universe to give a description of what happened. No light or information of any kind comes out of a blackhole.
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- Blackholes are points of intense gravitational force, and if our sun were replaced by one our Earth would not even register the event and continue its merry way in its orbit. It has never been possible to take a look at what is going on around the event horizon, until April 10, 2019.
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- Using the “radio telescope interferometer system” astronomers were able to synthesize an image of the surroundings of the supermassive blackhole in the quasar-like galaxy Messier-87 located 55 million light years from Earth.
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- They combined the data from eight radio telescopes scattered from Antarctica to the UK to create one telescope with the effective diameter of the entire Earth. With this, they were able to detect and resolve details at the center of M-87 near the location of a presumed supermassive blackhole.
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- This blackhole is surrounded by a swirling disk of magnetized matter, which ejects a powerful beam of plasma into intergalactic space. It has been intensively studied for decades and the details of this process always point to a supermassive blackhole as the cause.
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- Beginning in 2016, several petabytes of data were gathered creating the first images of the vicinity of the event horizon. Surrounding the black shadow zone containing the event horizon was a clockwise-rotating ring of billion-degree plasma traveling at nearly the speed of light.
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- When the details of this image were compared with supercomputer simulations, the mass of the supermassive blackhole could be accurately determined as well as the dynamics of the ring plasma.
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- The round shape of the event horizon was not perfect, which means that it is a rotating “Kerr-type blackhole“. The darkness of the zone indicated that the event horizon did not have a photosphere of hot matter like the surface of our sun.
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- Only the blackness of a blackhole and its compact size now remain as the most consistent explanation for what we are ‘seeing’. Over time, astronomers will watch as this ring of plasma moves from week to week.
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- Supermassive blackholes in the centers of galaxies, make themselves visible by spewing bright jets of charged particles, or by flinging away, or ripping up nearby stars. Up close, these blackholes are surrounded by glowing accretion disks of in falling material. The blackhole’s extreme gravity prevents light from escaping, the dark centers of remain entirely invisible.
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- The silhouette is of a blackhole’s event horizon, the perimeter inside is where nothing can be seen or escape from its accretion disk.
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- The project of imaging M87’s blackhole required observatories across the globe working in tandem as one virtual Earth-sized radio dish with sharper vision than any single observatory could achieve on its own.
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- Weighing 6.5 billion times the mass of our sun, this is supermassive blackhole inside M87 . But viewed from 55 million light-years away on Earth, the blackhole is only about 42 microarcseconds across on the sky.
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- That is smaller than an orange on the moon would appear to someone on Earth. Still, besides the blackhole at the center of our own galaxy, Sagittarius A* or Sgr A* this image of M87’s blackhole is the largest blackhole silhouette on the sky.
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- Only a telescope with unprecedented resolution could pick out something so tiny. For comparison, the Hubble Space Telescope can distinguish objects only about as small as 50,000 microarcseconds and this is 42 microarcseconds.
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- A telescope’s resolution depends on its diameter: The bigger the dish, the clearer the view, and getting a crisp image of a supermassive blackhole would require a planet-sized radio dish.
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- A “very long baseline interferometry” combines radio waves seen by many telescopes at once, so that the telescopes effectively work together like one giant dish. The diameter of that virtual dish is equal to the length of the longest distance, or baseline, between two telescopes in the network.
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- These eight radio telescope observatories teamed up in 2017 to work together as a global telescope, called “the Event Horizon Telescope network‘. Their mission was to image a supermassive blackhole for the first time.
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- Data from seven were used to create a picture of the blackhole inside the galaxy M87; since M87 appears in the northern sky, the South Pole observatory, number eight, couldn’t see it.
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- M87’s supermassive blackhole spits out bright jets of charged subatomic particles that extend thousands of light-years. The ideal array has as many baselines of different lengths and orientations as possible. Telescope pairs that are farther apart can see finer details, because there’s a bigger difference between the pathways that radio waves take from the blackhole to each telescope.
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- The telescope pairs with both north-south and east-west orientations, which change relative to the blackhole as Earth rotates. In order to braid together the observations from each observatory, researchers need to record times for their data with exquisite precision.
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- For that, they use hydrogen maser atomic clocks, which lose about one second every 100 million years. There was a lot of data recorded at a rate of 64 gigabits per second, which is about 1,000 times faster than your home internet connection.
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- These data are then transferred to MIT Haystack Observatory and the Max Planck Institute for Radio Astronomy in Bonn, Germany, for processing in a special kind of supercomputer called a correlator.
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- Each telescope station amasses hundreds of terabytes of information during a single observing campaign which is far too much to send over the internet. So the researchers had to mail their data.
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- Combining the data still isn’t enough to render a vivid picture of a supermassive blackhole. The reason we can reconstruct images, even though we don’t have 100 percent of the information, is because we know what images look like in general.
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- Imaging a blackhole with the Event Horizon Telescope is like listening to a song played on a piano with a bunch of broken keys. There are mathematical rules about how much randomness any given picture can contain, how bright it should be and how likely it is that neighboring pixels will look similar. Those basic guidelines can inform how software decides which potential images, or data interpretations, make the most sense.
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- Blackholes are some of the strangest and most fascinating objects in outer space. They're extremely dense, with such strong gravitational attraction that even light cannot escape their grasp if it comes near enough.
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- After decades of blackholes being known only as theoretical objects, the first physical blackhole ever discovered was spotted in 1971.
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- Then, in 2019 the Event Horizon Telescope collaboration released the first image ever recorded of a blackhole. They saw the blackhole in the center of galaxy M87.
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- Astronomers have identified three types of blackholes: stellar blackholes, supermassive blackholes and intermediate blackholes.
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- When a star burns through the last of its fuel, the object may collapse, or fall into itself. For smaller stars, those up to about three times the sun's mass, the new core will become a neutron star or a white dwarf. But when a larger star collapses, it continues to compress and creates a stellar blackhole.
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- Blackholes formed by the collapse of individual stars are relatively small, but incredibly dense. One of these objects packs more than three times the mass of the sun into the diameter of a city.
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- This leads to a crazy amount of gravitational force pulling on objects around the object. Stellar blackholes then consume the dust and gas from their surrounding galaxies, which keeps them growing in size.
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- Small blackholes populate the universe, but their cousins, supermassive blackholes, dominate. These enormous blackholes are millions or even billions of times as massive as the sun, but are about the same size in diameter. Such blackholes are thought to lie at the center of pretty much every galaxy, including the Milky Way.
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- Scientists are not certain how such large blackholes spawn. Once these giants have formed, they gather mass from the dust and gas around them, material that is plentiful in the center of galaxies, allowing them to grow to even more enormous sizes.
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- Supermassive blackholes may be the result of hundreds or thousands of tiny blackholes that merge together. Large gas clouds could also be responsible, collapsing together and rapidly accreting mass.
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- A third option is the collapse of a stellar cluster, a group of stars all falling together.
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- Fourth option, supermassive blackholes could arise from large clusters of dark matter. This is a substance that we can observe through its gravitational effect on other objects; however, we don't know what dark matter is composed of because it does not emit light and cannot be directly observed.
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- Scientists once thought that blackholes came in only small and large sizes, but recent research has revealed the possibility that midsize, or intermediate, blackholes could exist. Such bodies could form when stars in a cluster collide in a chain reaction. Several of these blackholes forming in the same region could then eventually fall together in the center of a galaxy and create a supermassive blackhole.
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- In 2014, astronomers found what appeared to be an intermediate-mass blackhole in the arm of a spiral galaxy.
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- Blackholes are strange regions where gravity is strong enough to bend light, warp space and distort time. Blackholes have three "layers": the outer and inner event horizon, and the singularity.
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- The event horizon of a blackhole is the boundary around the mouth of the blackhole, past which light cannot escape. Once a particle crosses the event horizon, it cannot leave. Gravity is constant across the event horizon.
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- The inner region of a blackhole, where the object's mass lies, is its “singularity“, the single point in space-time where the mass of the blackhole is concentrated.
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- Scientists can't see blackholes the way they can see stars and other objects in space. Instead, astronomers must rely on detecting the radiation blackholes emit as dust and gas are drawn into the dense creatures.
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- Supermassive blackholes, lying in the center of a galaxy, may become shrouded by the thick dust and gas around them, which can block the telltale emissions.
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- Sometimes, as matter is drawn toward a blackhole, it ricochets off the event horizon and is hurled outward, rather than being tugged into the center. Bright jets of material traveling at near-relativistic speeds are created. Although the blackhole remains unseen, these powerful jets can be viewed from great distances.
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- The next target is likely Sagittarius A*, which is the blackhole in the center of our own Milky Way galaxy. Sagittarius A* is intriguing because it is quieter than expected, which may be due to magnetic fields smothering its activity, a 2019 study reported.
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- Another study in 2019 showed that a cool gas halo surrounds Sagittarius A*, which gives unprecedented insight into what the environment around a blackhole looks like.
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- In 2015, astronomers using the “Laser Interferometer Gravitational-Wave Observatory’ (LIGO) detected gravitational waves from merging stellar blackholes. LIGO's observations also provide insights about the direction a blackhole spins. As two blackholes spiral around one another, they can spin in the same direction or in the opposite direction.
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- There are two theories on how binary blackholes form. The first suggests that the two blackholes in a binary form at about the same time, from two stars that were born together and died explosively at about the same time. The companion stars would have had the same spin orientation as one another, so the two blackholes left behind would as well.
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- In the second model, blackholes in a stellar cluster sink to the center of the cluster and pair up. These companions would have random spin orientations compared to one another. LIGO's observations of companion blackholes with different spin orientations provide stronger evidence for this formation theory.
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- If you fell into a blackhole, theory has long suggested that gravity would stretch you out like spaghetti, though your death would come before you reached the singularity. But a 2012 theory suggested that quantum effects would cause the event horizon to act much like a wall of fire, which would instantly burn you to death.
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- Astronomers estimate that the Milky Way has anywhere from 10 million to 1 billion stellar blackholes, with masses roughly three times that of the sun.
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- The conventional model states that once a massive star has reached its limit for continued thermonuclear fusion, which for even the most massive stars stops at the element iron, then there is no longer sufficient energy radiating outward to counter-balance the inward gravitational force of the star. The star thus undergoes gravitational collapse forming a stellar remnant in the form of a white dwarf, neutron star or blackhole.
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- It used to be assumed that all elements heavier than iron are formed during the supernova explosion resulting from core collapse of the massive stars, but calculations have shown this not to be a viable scenario. Primordial Blackholes, not resulting from stellar gravitational collapse, have been implicated in the formation of elements heavier than iron.
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- Returning to the terminal processes “ending” the life of our massive star, once the outward radiative pressure is gone, the star begins to collapse. If the star exceeds the “Tolman-Oppenheimer-Volkoff limit “(TOV limit), its mass will be so great that the core collapses into a singularity, infinitely curving spacetime, forming a blackhole while the outer layers of the star compress into a final thermonuclear fusion event that releases the energy equivalent of billions of stars, known as a supernova.
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- The supernova sends shockwaves of plasma which may trigger gravitational condensation in nebulae, birthing more stars, while the core that has collapsed to a singularity is masked behind a light-like boundary known as the ‘event horizon“.
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- If blackholes are formed from stellar collapse, then how can supermassive blackholes be present when the first stars were just beginning to form?
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- The answer is simple, blackholes form first, during the early epochs of the universe when energy densities were extremely large, and they then act as the nucleating centers guiding star and galaxy formation.
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- Immediately following the Big Bang energy densities would be so great that blackholes will be produced in vast quantities. Calculations show that the size of the blackhole is determined by the time-evolution following the Big Bang, which is to say that blackholes smaller than a stellar mass could have formed in the earliest stages, primordial Blackholes.
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- So, at a Planck time after the Big Bang, which is 10^-43 seconds, blackholes of the Planck mass (10^-5 grams) would form.
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- At one second after the Big Bang, blackholes of a 100 thousand solar masses would form. In the span between the Planck second and 1 second, an enormous range of blackhole masses would have formed.
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- Proton-sized blackholes will appear to “freeze” due to time dilation, and would appear stable to outside frames of reference, that is all those that do not include the event horizon or traveling at light speed, for periods longer than the current age of the universe.
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- Could protons be primordial blackholes? Could supermassive blackholes have formed in a short period following the Big Bang, where they would then be present during the first star formation, known as population III stars?
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- These “anomalous” blackholes, detected using the laser interferometry gravitational-wave observatory were above the expected mass range of 10 to 20 solar masses (which have raised the possibility that so-called dark matter could be primordial blackholes).
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- A prominent recent observation that is throwing the current model into question is the observation of quasars at the edge of the visible universe, with one residing 13.04 billion light years from Earth (meaning it formed earlier than 690 million years after the Big Bang) and housing a blackhole close to a billion solar masses.
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- These young galaxies are extremely luminescent due to the activity of a supermassive blackhole at their center. They are called “active galactic nuclei” .
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- The key concept is that blackholes are at the center of all galaxies, where they act as the nucleating centers for galaxy accretion, determine the number of stars that are formed, and exert an overall considerable influence on the architecture of galactic systems.
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- The Sloan Digital Sky Survey studies have found a quasar that existed 690 million years after the “big bang”. It is estimated that for a quasar to be visible at such great distances the mass of the central supermassive blackhole should be around 1 billion solar masses.
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- Based on the conventional theories of blackhole formation and growth via stellar death this far exceeds that of the expected mass, to be only a few hundred solar masses.
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- This predicted mass for the first blackholes is based on the assumption that these “seed” blackholes are remnants of the first stars, known as Pop III stars, which were formed as a result of the primordial gas cooling when the Universe was approximately 200 million old.
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- The conventional cosmological model suggests that because these original blackholes would be forming in close proximity they would eventually merge to form more massive blackholes of several thousand solar masses. However, they are still not massive enough to account for the predicted masses of quasar stellar blackholes that we see today.
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- So, how did these behemoths blackholes arise so early?
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- One possibility is that the first blackholes underwent some unpredicted extraordinary period of growth. The optimal feeding rate of a blackhole is based on the “Eddington limit“, which describes the maximum rate of growth. Under the Eddington limit, with exponential growth a 10-solar mass blackhole could grow to a billion-solar mass blackhole in about one billion years
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- The first blackhole seeds could have formed without stellar deaths. They could have formed directly from gas. Such objects would have formed within a few hundred million years after the big bang with masses of 10-100 thousand solar masses.
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- Large gas disks would usually cool and fragment instigating stellar growth and galaxy formation. However, under this model large gas agglomerates are posited to collapse into dense clumps that directly form seed blackholes of 10,000 to 1 million solar masses.
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- This could happen if normal cooling processes were halted, that is if molecular hydrogen formation, which aids disk cooling, was stopped such that the disk remains hot. The disk would then be too hot to form stars and as well would be dynamically unstable resulting in contraction until eventual collapse forming a blackhole.
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- As these “seed blackholes” grow they would briefly reach a point where their mass is greater than all the stars in their parent galaxy.
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- The mass of all the stars in a galaxy is typically 1,000 times greater than the central blackhole, so this galaxy would have a unique spectral signal, particularly in the infrared wavelength of the spectrum.
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- The model of early formation of blackholes and their importance to the evolution and development of our universe is still a mystery. The more you learn the less you seem to know.
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- November 1, 2020 2885
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