Latest news with #Hawkingradiation
Yahoo
4 days ago
- Science
- Yahoo
What if we've been thinking about dark matter all wrong, scientist wonders
When you buy through links on our articles, Future and its syndication partners may earn a commission. Dark matter could be made from tiny black holes formed when so-called "dark baryons" collapse, scientists suggest. Or, alternatively, dark matter could be a type of particle created by a form of Hawking radiation on the cosmic horizon. Here's what all that means. Dark matter is the substance that appears to make up about 27% of our universe, compared to the 5% of our universe composed of "normal" matter. Scientists certainly know dark matter exists due to some peculiar effects observed in the cosmos that normal matter can't account for. However, nobody knows what dark matter is made of. For decades, the leading candidate has been WIMPs, or Weakly Interacting Massive Particles. But as the search for WIMPs begins to falter with experiments continuing to turn up empty handed, new theories of dark matter are starting to surface. Among them are two new models developed by Stefano Profumo, who is a professor of theoretical physics at the University of California, San Diego — and his ideas take a very different view of the dark-matter problem. "My attitude is that we've tried very hard to think about dark matter as a particle, but it hasn't worked out so far," Profumo told "I think it's natural to take a break and look at the whole thing from a distance, and wonder whether we are fundamentally thinking about this in the wrong way." In one paper, Profumo considers whether the "dark sector" could be what gives birth to dark matter. By dark sector, he isn't referring to how our universe is governed by dark matter and dark energy. Instead, he's referring to a kind of "mirror world" of particles that interact via forces that our world's kind of matter does not experience. Profumo says the concept is not as strange as it may sound. For example, he highlights how the quarks inside protons and neutrons are bound together by the strong nuclear force. "But then take electrons, which are absolutely blind to the strong force. They don't feel it at all. For them the strong force is a dark sector," said Profumo. "It's common in the Standard Model." Dark baryons would be the equivalent of protons or neutrons in this dark sector, except that they could contain more than three quarks, Profumo says, and therefore be more massive. The next step in the researcher's theory was inspired by his teenage son asking whether a sufficiently massive particle could collapse under its own gravity to form a mini black hole. The dark baryons in the dark sector, if it so exists, could be massive enough to do just that — and these tiny black holes could then be rife in the universe and collectively form what we call dark matter. "I've worked with people who have thought very deeply about a dark-sector equivalent to the strong force, but they've never really pushed all the way to the black hole frontier," said Profumo. "But I really think it is a possibility that we need to take into consideration." Black holes, large or small, are surrounded by an invisible boundary called the event horizon, inside which gravity is so strong that not even light can escape. However, the event horizon is 'hot' – particles created at the boundary by quantum effects can radiate away as what we call Hawking radiation (named for famous physicist Stephen Hawking, who is credited with the idea). Over time, Hawking radiation removes mass and energy from a black hole, causing it to gradually evaporate. For supermassive black holes, this would take an unimaginably long time — 10^100 years at least. However, black holes on the smallest scales — what we call the Planck scale —- can evaporate in an amount of time less than the age of the universe. However, if we make certain assumptions about the nature of these black holes formed by the collapse of dark baryons, then their Hawking radiation could become suppressed, preventing them from evaporating and enabling them to act as dark matter. Meanwhile, Profumo's other idea plays on the concept of Hawking radiation as well, but in a completely novel way. We live in a universe that is expanding at an accelerating rate, taking regions of the cosmos so far away that their light will never reach us. This leads to a boundary, or a cosmic horizon, which defines the edge of the visible universe. There could be much more of the universe beyond this horizon, but we will never see it. Now, let's go back in time to the moment of the Big Bang. The universe began with a burst of expansionist energy known as inflation. This inflationary period lasted a tiny fraction of a second. However, some models also posit that there was a second brief burst of expansionary energy that followed inflation. "It is basically a period of mini-inflation," said Profumo. "It could be associated with inflation and how it ends, or it could be driven by a similar set-up to inflation." This second expansionary period created cosmic horizons like the cosmic horizon that borders the visible universe today. However, the visible universe today is 93 billion light-years across, with Earth at its center (the concept of a "visible" universe is very observer dependent — observers in different parts of the cosmos will see a different volume of observable universe centered around themselves). The vast size of the visible universe means the temperature at the cosmic horizon is very low because space itself has become so spread out. However, during the second burst of inflation, the universe was still incredibly compact and the temperature at the horizon was extremely hot. Profumo realized these early cosmic horizons could act like event horizons; indeed, the concept is a bit like a black hole but turned inside-out because everything beyond the cosmic horizon is forever disconnected from us, just like everything inside a black hole's event horizon is separated from us. And just as Hawking radiation is emitted from a black hole's event horizon, Profumo suggests the cosmic horizon could also experience Hawking radiation in the same manner, and that the energy of this radiation could transform into some kind of dark matter particle. "Maybe [dark matter] is as simple as that," said Profumo. "Early on, the universe behaved like a black hole, and there was stuff sprinkled into the universe because the universe was evaporating in the same way that a black hole evaporates." This might seem somewhat arbitrary, because the location of the cosmic horizon depends upon the location of the observer. However, because the universe is homogenous (the same at every point on large scales) and isotropic (the same in all directions) — two truisms that we call the Cosmological Principle —- then any two observers should see the exact same amount of dark matter, wherever they are. Profumo isn't necessarily saying dark matter has to be one of these two possibilities; indeed, the fact that he has developed two theories implies that he's reluctant to nail his colors to any particular mast. "The aim of the game is to understand the breadth and scope of what dark matter could be, and to cast the net as wide as possible," said Profumo. RELATED STORIES — What is dark matter? — 'Dark matter is more valuable than gold': Wobbly galaxies help shine a light on the universe's strangest stuff — Captured dark matter may transform some 'failed stars' into 'dark dwarfs' All we know for sure about dark matter is that it interacts via gravity, and yet despite its mystery it is utterly dominant in how matter in the universe assembles itself into galaxies. Almost a century since Fritz Zwicky first suggested the existence of dark matter, and about half a century since Vera Rubin confirmed the need for dark matter in our universe, we still don't know anything more about it. Experiments can narrow down dark matter's properties, so the more ideas we have on the table, the more likely it is that we will be able to match one of them up to the observed properties of dark matter. Profumo's dark sector–black hole hypothesis was published on May 9 in Physical Review D, and his cosmic horizon model was published in the same journal on July 8. Solve the daily Crossword
South China Morning Post
11-08-2025
- Science
- South China Morning Post
Good vibrations: the music of black holes
If mature black holes had personalities, they would be extremely introverted. They don't let anything out – not light, not particles, and certainly not music. Hawking radiation is a fascinating exception to this rule, but for astrophysical black holes, it is a tiny effect. But before they settle down, during their brief but wild youth, newly formed black holes ring out a strange, pure music. It would be beautiful to experience, and soon we will be able to do it. When a new black hole is formed, say by collapse of a star or by fusion of other objects such as neutron stars or smaller black holes, the material that produced it gets swallowed up. Once that material passes beyond the newly formed event horizon, no trace of it remains perceptible. The baby black hole itself, as a distortion of space-time, quickly settles into a stable shape, sculpted by its own gravity. The same force that makes stars and planets very nearly into round balls – or, if they're spinning, smooth ellipsoids – works even more powerfully to mould black holes. Precisely because they swallow all signs of their origin and squash any outer lumpiness, black holes reach a level of mathematical perfection that is unique among macroscopic objects. Given only a black hole's mass and angular momentum, the equations of general relativity predict with utter precision the distortion of space-time it embodies.
CBS News
13-05-2025
- Science
- CBS News
Universe will die "much sooner than expected," researchers say
Could dark energy cause the universe to collapse? The universe is poised to die much faster than previously thought, according to new research by Dutch scientists. But there's no great need to panic. We still have 10 to the power of 78 years before it happens — that's a one with 78 zeroes. However, that is a major revision from the previous estimate of 10 to the power of 1,100 years, notes the research paper from Radboud University, published in the Journal of Cosmology and Astroparticle Physics. "The final end of the universe is coming much sooner than expected but fortunately it still takes a very long time," said lead author Heino Falcke. A trio of scientists at Radboud set out to calculate when the most "durable" celestial bodies — white dwarf stars — would eventually die out. They based their calculations on Hawking radiation, named after celebrated British physicist Stephen Hawking. Hawking postulated in the mid-1970s that black holes leak radiation, slowly dissolving like aspirin in a glass of water -- giving them a finite lifetime. The Radboud scientists extended this to other objects in the universe, calculating that the "evaporation time" depends on density. This enabled them to calculate the theoretical dissolution of the longest-lasting body, the white dwarf. "By asking these kinds of questions and looking at extreme cases, we want to better understand the theory, and perhaps one day, we can unravel the mystery of Hawking radiation," said co-author Walter van Suijlekom. Humankind needn't worry too much about the end of the universe. Unless we escape planet Earth, we'll be long gone. Scientists think that our sun will be too hot for life in about a billion years, boiling our oceans. In about eight billion years, our star will eventually expand towards the Earth, finally gobbling up our by-then barren and lifeless planet and condemning it to a fiery death. Shedding light on dark energy The research comes just weeks after scientists released new findings that may also shed light on the fate of the universe. Researchers in March said new data shows dark energy — a mysterious force that makes up nearly 70% of the universe — may actually be weakening. If dark energy is constant, an idea first introduced by Albert Einstein in his theory of relativity, scientists say our universe may continue to expand forever, growing ever colder, lonelier and still. If dark energy ebbs with time, the universe could one day stop expanding and then eventually collapse on itself in what's called the "Big Crunch." "Now, there is the possibility that everything comes to an end," said cosmologist and study collaborator Mustapha Ishak-Boushaki of the University of Texas at Dallas. "Would we consider that a good or bad thing? I don't know." This image provided by NSF's NOIRLab shows the trails of stars above Kitt Peak National Observatory, where a telescope is mapping the universe to study a mysterious force called dark energy. NSF's NoirLab via AP Other efforts around the globe have an eye on dark energy and aim to release their own data in the coming years, including the European Space Agency's Euclid mission and the Vera C. Rubin Observatory in Chile. Launched in 2023, the ESA's $1.5 billion Euclid space telescope is equipped with a near-perfect 3-feet 11-inch-wide primary mirror and two instruments: a 600 megapixel visible light camera and a 64-megapixel infrared imaging spectrometer. The telescope's field of view is roughly twice the size of the full moon.
