Largest Black Hole in the Universe

 Discovery of 'The biggest black hole' ever seen by Scientists

Astronomers have discovered what could be the largest black hole ever detected. With a mass of 36 billion times that of our Sun, its gravity is so powerful that it bends the light of an entire galaxy behind it into a near-perfect circle called an Einstein ring, effectively reducing a realm with trillions of stars of its own into an astrophysical fashion accessory. It's 10,000 times as heavy as our Milky Way's own central black hole, and is nigh unto breaking the universe's theoretical upper limit. If anything ever warranted being called a cosmic monster, it's this. This is amongst the top 10 most massive black holes ever discovered, and quite possibly the most massive. A bright yellow blob surrounded by a warped blueish line in the shape of a horseshoe. This blue horseshoe is a distant galaxy magnified and distorted by the strong gravitational pull of the massive foreground Luminous Red Galaxy. Together, these galaxies create the Cosmic Horseshoe system. About 5 billion light-years away from where you're sitting, in one of the most massive galaxies on record, there exists an astonishing black hole. It was only just measured by scientists who managed to peer through the fabric of warped space-time, and it appears to hold a mass equivalent to that of 36 billion suns.

"This is amongst the top ten most massive black holes ever discovered, and quite possibly the most massive," Thomas Collett, a professor of astrophysics at the University of Portsmouth and coauthor of a new study about the giant said about the work. Other detections of similar sized objects, Collett noted, have generally come with uncertainties too large to be definitive. This not-super but ultramassive black hole lurks in the centre of the famous Cosmic Horseshoe galaxy, which itself ranks among the most massive ever spotted. The galaxy is considered a fossil group, which formed from other large galaxies, and their constituent supermassive black holes, collapsing together. "So we're seeing the end state of galaxy formation and the end state of black hole formation," Collet said. It's no exaggeration to say, then, that we're literally witnessing a black hole's final form. More specifically, the black hole is found in one of two galaxies which make up the Cosmic Horseshoe system and is what's known as a "dormant" black hole. This means it's a relatively quiet black hole; it isn't actively chomping on matter in its surroundings, as opposed to an active black hole that is accreting matter from a disk which circles it, known as an accretion disk. The black hole at the centre of our Milky Way galaxy, Sagittarius A*, is also a dormant black hole, but, for context, it only holds the mass of about 4.15 million suns.

Located some five billion light years away, the Cosmic Horseshoe is so named due to its gravitational lensing effect, a phenomenon in which the light of a background galaxy is warped by the gravity of a foreground one. Lensing is common throughout the cosmos, and it can be a fortuitous tool for astronomers, acting like a magnifying glass which allows them to observe distant objects whose light would otherwise be too faint to examine. But in this case, the huge foreground galaxy and its companion in the background happen to be in almost perfect alignment with our Earthly perspective, bending the light into an incomplete ring. The fact that the Cosmic Horseshoe black hole is found in such a massive galaxy and that Sagittarius A* is found in our more modestly sized Milky Way is probably not a coincidence. In fact, the team behind the new measurement is hoping to learn more about the apparent size connection between supermassive black holes and their parent galaxies. "We think the size of both is intimately linked," Collett said, "because when galaxies grow they can funnel matter down onto the central black hole. Some of this matter grows the black hole, but lots of it shines away in an incredibly bright source called a quasar. These quasars dump huge amounts of energy into their host galaxies, which stops gas clouds condensing into new stars."

Astronomers have long suspected that there was a black hole at the heart of the Cosmic Horseshoe, but have never been able to spot it. One of the reasons why is its extreme distance, at billions of light years away. But the even more impressive hurdle that's been overcome is that it's a "dormant" black hole that's no longer accreting matter, according to Carlos Melo, lead author from the Universidade Federal do Rio Grande do Sul in Brazil. "Typically, for such remote systems, black hole mass measurements are only possible when the black hole is active," Melo said. "But those accretion-based estimates often come with significant uncertainties." When a black hole devours significant amounts of matter, the infalling material gets heated up and radiates huge amounts of energy and light, forming what's known as an active galactic nucleus. (The brightest of these are called quasars.) But this detection "relied purely on [the black hole's] immense gravitational pull and the effect it has on its surroundings," Melo said. Their method involved a combination of lensing and what's known as stellar kinematics, which allows astronomers to infer a black hole's mass by studying the velocity of stars trapped in the surrounding galaxy. "What is particularly exciting is that this method allows us to detect and measure the mass of these hidden ultramassive black holes across the universe, even when they are completely silent," Melo said.

This brings us to another key aspect of the team's findings: the way this black hole was measured to begin with. The research team was able to utilize a unique approach that doesn't rely on the black hole being an actively accreting one. Without active feeding, black holes can kind of hide behind the veil of the cosmos. It is the accretion itself that usually gives these objects away. Such commotion produces lots of emissions, like X-rays, which scientists here on Earth can detect. Naturally, it's also far easier to measure the precise masses of black holes via such emissions. However, there is one characteristic of black holes which even dormant ones can't suppress: their immense gravitational pull. And the greater the gravitational pull, the greater the warp in space-time, as predicted by Albert Einstein's general relativity theory. And its size is no coincidence. There's a reason, the astronomers argue, that we're finding this ultra massive rarity in one of the heaviest galaxies on record, and not in one of relatively unremarkable size like our Milky Way, which hosts a comparatively puny black hole of 4.3 million solar masses. "We think the size of both is intimately linked," Collet said, "because when galaxies grow, they can funnel matter down onto the central black hole." In a nutshell, Albert Einstein's famous theory of general relativity explains the true nature of gravity. It suggests that gravity isn't quite an intrinsic, elusive property of an object which pulls things down. In other words, Earth itself isn't really pulling us down to the ground. Rather, general relativity states that objects with mass (all objects, including you and me) warp the four-dimensional fabric of space-time, and these warps influence the motion of other objects caught up in the folds.

It may seem like an obvious conclusion to draw, but how supermassive black holes attain their enormous sizes remains one of the great mysteries of cosmology. Some have been spotted so early on in the universe's history that they physically shouldn't exist, not having enough time to accrete the mass they possess. If it formed from galactic mergers, it provides a strong clue of at least one mechanism which can spawn these colossal objects. For instance, imagine a trampoline on which you place a ball. That ball would warp the trampoline inward. Now, imagine placing a smaller ball on the trampoline. That smaller ball would fall inward as well, along the warped trampoline's fabric and sit right next to the original ball. The trampoline in this case is space-time, the original ball is Earth and the smaller ball is you. The big caveat in this analogy, however, is that this trampoline exists in three dimensions. We'd need to scale this up to the four-dimensional universe for it to start representing reality more accurately, but our brains have a hard time comprehending that dimension visually. Importantly for the team's new measurements, something which arises from warped space-time (in the fourth dimension, remember) is that physical matter isn't the only thing affected by the warps. Light gets affected, too — and that includes light emanating from galaxies, such as the other galaxy in the Cosmic Horseshoe. This is the effect the study team managed to take advantage of when spotting the newly confirmed black hole. Light from the Cosmic Horseshoe system's background galaxy was warped as it travelled past the foreground galaxy that contains black hole. The Cosmic Horseshoe system is actually an iconic example of this effect, which is called gravitational lensing. Not only does this system have a strong version of this effect, but each galaxy involved happens to be perfectly aligned such that the light-warped background galaxy appears as almost a perfect ring around the foreground galaxy. When this happens, it's called an "Einstein Ring." So, we're seeing an "almost" Einstein ring in this case. 

There are quite a few ways to move forward on this work, one of which is to reveal the link between galaxy size and supermassive black hole size, but another could be to zero in on the Cosmic Horseshoe black hole alone and learn how it became so utterly gigantic. The Cosmic Horseshoe is what's known as a "fossil group," which refers to the end stage of the "most massive gravitationally bound structures in the universe, arising when they have collapsed down to a single extremely massive galaxy, with no bright companions," according to the statement. The Milky Way and Andromeda galaxies will likely become a fossil group someday, seeing as they're likely on a path to colliding somewhere in the far future. That crash has recently been brought into question, but it's still a possibility. Nonetheless, the Cosmic Horseshoe could very well be a peek into our realm's final era.