A new study proposes that Hawking radiation could be used to find dark matter in places like primordial black holes.
- A new paper narrowed down what type of black holes may be the best candidates for containing dark matter.
- So far, dark matter has not been directly observed.
- The research team also developed new techniques to spot Hawking radiation that potentially comes from black holes.
Predicted to account for over 80 percent of all matter in the universe, so far, no one has directly seen dark matter. This is perhaps not surprising for a substance that doesn't reflect or emit any light. Now, a new study examines the possibility of finding dark matter in primordial black holes (PBHs), structures that hypothetically formed in the early life of the universe.
The paper, authored by scientists at the University of Amsterdam and the University of California-Santa Cruz and published in Physical Review Letters, looked to narrow down the parameters PBHs would need to contain dark matter. The authors also proposed a technique that could find dark matter by looking for so-called Hawking radiation.
What is Hawking radiation?
The late Stephen Hawking proposed the existence of thermal radiation that spontaneously emanates from black holes. He hypothesized the radiation was created by quantum effects near the black hole's event horizon, the boundary beyond which no light can escape. Furthermore, Hawking believed that over time, the radiation would result in enough energy and mass being taken away from a black hole to make it evaporate completely.
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In the new paper, the researchers calculated the likely mass constraints of PBHs that could be composed of dark matter. Specifically, they concluded that PBHs similar to an asteroid in size (around 1017 grams to 1022 grams) could "make up all the dark matter" in the universe. Furthermore, the study looked at new techniques for finding dark matter, examining the possibility of using MeV (megaelectron volt) gamma-ray telescopes to detect Hawking radiation coming from the primordial black holes.
In an interview with Phys.org, researcher Adam Coogan explained why their approach could work.
"The main idea behind our work was to think about a particular way of looking for asteroid-mass PBHs," Coogan shared. "Light PBHs are expected to emit Hawking radiation consisting of a mix of photons and other light particles, such as electrons and pions. Telescopes can then search for this radiation by observing our galaxy or other galaxies."
Paving the way for future telescopes
Coogan added that the goal of their paper was to evaluate if future telescopes would be able to spot this radiation and "how much of the asteroid-mass PBH parameter space they could probe."
What the researchers discovered is that previous studies have not yet analyzed data from NASA's COMPTEL gamma-ray telescope aboard the Compton Gamma Ray Observatory (CGRO). Utilizing the telescope's data could help narrow down the PBHs that need to be examined to those just below the asteroid-mass gap (that is, below 1017 grams). These would comprise the strongest constraints found so far and could lead to further discovery.
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The scientists also refined the calculations necessary to spot the spectrum of the hypothesized Hawking radiation supposedly emitted by a primordial black hole. Specifically, they improved upon the detection of radiation produced by electrons and pions within the spectrum.
The team's calculations could help determine how much PBHs of particular masses contribute to the overall amount of dark matter in the universe. Comparing their calculations of the radiation spectrums to observed data from areas believed to contain a lot of dark matter, like the center of the Milky Way, could help scientists rule out or zero in on certain black holes as dark matter candidates.
Looking ahead, the researchers believe that the next generation of MeV gamma-ray telescopes would be able to find dark matter in primordial black holes by directly detecting Hawking evaporation.
Researchers discovered a galactic wind from a supermassive black hole that sheds light on the evolution of galaxies.
- A new study finds the oldest galactic wind yet detected, from 13.1 billion years ago.
- The research confirms the theory that black holes and galaxies evolve together.
- The galactic wind was spotted using the Atacama Large Millimeter/submillimeter Array in Chile.
An enormously powerful galactic wind generated by a supermassive black hole 13.1 billions years ago has been discovered by researchers. The scientists used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, which combines 66 radio telescopes, to make the find. The results are published in the Astrophysical Journal.
This is the earliest example of this type of wind yet spotted that underscores the role of black holes in the formation of galaxies. Research has shown that galactic winds affect redistribution of metals around the galaxy and impact start formation.
Black holes and galaxies evolve together
In previous studies, scientists have noticed an unexpected proportional relationship between the mass of a supermassive black hole at the center of a large galaxy, which can grow up to billions of times more massive than the sun, and the mass of the galaxy's central area (known as a "bulge"). The proportionality of the masses is especially unusual considering that galaxies and black holes are so different in size, with the bulge generally being orders of magnitude larger. This led the researchers to conclude that galaxies and black holes developed together through coevolution, which involved some physical interaction courtesy of the galactic wind.
As ALMA's press release explains, a galactic wind starts coming into existence when a supermassive black hole gobbles up giant quantities of matter. It is then moved at such a high speed by the black hole's gravity that it radiates intense energy, which in turn, pushes surrounding matter away, creating the galactic wind.
Takuma Izumi, the paper's lead author and a researcher at the National Astronomical Observatory of Japan (NAOJ), says an important question is: "When did galactic winds come into existence in the universe?" Finding this out can lead to understanding how galaxies and supermassive black holes coevolved.
Finding an ancient galactic wind
The researchers used NAOJ's Subaru Telescope to locate over 100 galaxies that existed more than 13 billion years ago that featured supermassive black holes. They then used the high sensitivity of ALMA to analyze the gas motion in these galaxies, finding that the dust and carbon of one of them (dubbed J1243+0100) emitted radio waves. This allowed the scientists to detect the presence of an intense galactic wind that rushes forth from the supermassive black hole at about 1,118,468 miles per hour (500 km/second). The energy of the wind, the oldest found so far, is so strong that it pushes away stellar materials, preventing stars from forming.
Interestingly, the mass of the bulge in J1243+0100 was found to be about 30 billion times larger than that of the sun, while the mass of the galaxy's supermassive black hole was estimated to be about 1 percent of that. This ratio is essentially the same as the mass ratio of black holes to galaxies in today's universe. To the scientists, this demonstrates how essential black holes are in affecting the growth of galaxies, supporting the notion of coevolution from the early period of the universe.
"Our observations support recent high-precision computer simulations which have predicted that coevolutionary relationships were in place even at about 13 billion years ago," explained Izumi.
The scientists are planning to observe a large pool of space objects in the future, with the goal of clarifying "whether or not the primordial coevolution seen in this object is an accurate picture of the general universe at that time," further commented Izumi.
Researchers discover black holes that violate the uniqueness theorem and have "gravitational hair."
- Scientists discover that some extreme black holes may violate the "no hair" theorem.
- These black holes feature properties outside of the three classical black hole traits of mass, spin, and charge.
- The researchers ran sophisticated simulations to discover these space oddities.
Black holes are wonderfully weird, sparking the imagination with the many mysteries surrounding their formation and functions in our universe. Now scientists found a new kind of extreme black hole, one that breaks the so-called "ho hair" theorem. In other words, this black hole has "hair."
The idea of the "no hair" or "black hole uniqueness" theorem was encapsulated by the American theoretical physicist John Wheeler who claimed: "Black holes have no hair." What he meant is that black hole solutions to Einstein's field equations of general relativity can be completely characterized by only three physical quantities: mass, spin, and charge. There aren't supposed to be any other "hairy" traits that can make one black hole different from another. Black holes with the same mass, spin, and charge should be identical, explains the press release from Theiss Research, which was behind the new discovery.
The team involved Dr. Lior Burko of Theiss Research, Professor Gaurav Khanna of the University of Massachusetts Dartmouth and the University of Rhode Island, as well as his former student Dr. Subir Sabharwal.
They found there's an extremal black hole that may violate the "no hair" theorem. This type of black hole is "saturated" with the maximum charge or spin it can potentially carry. The researchers discovered that there exists a conserved quantity or property that can be constructed from the spacetime curvature at such a black hole's horizon. It may be measurable from Earth by gravitational wave observatories like LIGO and LISA. Since this property is dependent on how the black hole was formed, it breaks the black hole uniqueness theorem and is considered "gravitational hair."
"This new result is surprising because the black hole uniqueness theorems are well established, and in particular their extension to extreme black holes," shared Dr. Burko. "There has to be an assumption of the theorems that is not satisfied, to explain how the theorems do not apply in this case."
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For their findings, the researchers employed elaborate numerical simulations running on dozens of the top Nvidia graphics-processing-units (GPUs) that had over 5,000 cores each, working in parallel. "Each of these GPUs can perform as many as 7 trillion calculations per second; however, even with such computational capacity the simulations look [sic] many weeks to complete," shared Khanna.
Another type of black hole "hair" was proposed by Stephen Hawking who predicted that quantum particles would leak out of black holes, in a phenomenon dubbed "Hawking radiation." This claim was possibly proven correct by a 2020 study that found evidence of "quantum fuzz" and gravitational wave "echoes" beyond black hole event horizons.
Check out the new study published in Physical Review D.
Baby universes led to black holes and dark matter, proposes a new study.
- Researchers recently used a huge telescope in Hawaii to study primordial black holes.
- These black holes might have formed in the early days from baby universes and may be responsible for dark matter.
- The study also raises the possibility that our own universe may look like a black hole to outside observers.
A new paper takes a deep dive into primordial black holes that were formed as a part of the early universe when there were still no stars or galaxies. Such black holes could account for strange cosmic possibilities, including baby universes and major features of the current state of the cosmos like dark matter.
To study the exotic primordial black holes (PBHs), physicists employed the Hyper Suprime-Cam (HSC) of the huge 8.2m Subaru Telescope operating near the 4,200 meter summit of Mt. Mauna Kea in Hawaii. This enormous digital camera can produce images of the entire Andromeda galaxy every few minutes, helping scientists observe one hundred million stars in one go.
In their study, the scientists considered a number of scenarios, especially linked to the period of inflation. That is the time of quick expansion following the Big Bang, when the universe we know today came into existence with all its structures.
The researchers calculated that in the process of inflation, the climate was ripe for creating primordial black holes of various masses. And some of them reflect the characteristics predicted for dark matter.
Another way PBHs could have been created during inflation is from "baby universes" – small universes that branched off from the main one.
Hyper Suprime-Cam (HSC) is a gigantic digital camera on the Subaru Telescope
Credit: HSC project / NAOJ
A baby or "daughter" universe would ultimately collapse but the tremendous release of energy would lead to the formation of a black hole, explains the press release from the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) in Japan, one of the institutions participating in this study.
What's also fascinating, some of the bigger baby universes might not have gone so quietly. Above a certain critical size, the theory of gravity developed by Albert Einstein permits that such a universe may be perceived differently by observers. If you were inside it, you'd see an expanding universe, while if you were outside, this baby universe would look like a black hole. A conjecture that leads to wondering – are we potentially on the inside or outside of such a universe ourselves?
If you follow this multiverse logic, it also may be possible that while primordial black holes would appear to us as black holes, their true structural natures could be concealed by their "event horizons" – the boundaries surrounding black holes from which not even light can escape.
It should be noted, while strange or counter-intuitive, this is not the first go-around for these types of ideas. A study earlier in 2020 found that so-called "charged" black holes may include within them endlessly-repeating fractal universes of various sizes, including miniature, that can be stretched and deformed in all directions.
To solidify their theories and to find a primordial black hole, the researchers will continue using the Subaru Telescope, with some promising PBH candidates already emerging.
The international team of particle physicists working on the research came from the University of California, Los Angeles and the Kavli Institute. The group included cosmologists and astronomers Alexander Kusenko, Misao Sasaki, Sunao Sugiyama, Masahiro Takada and Volodymyr Takhistov.
Check out their new paper "Exploring Primordial Black Holes from the Multiverse with Optical Telescopes" in Physical Review Letters.
A new study shows our planet is much closer to the supermassive black hole at the galaxy's center than previously estimated.
If you think Earthly matters haven't been going well already, it also turns out that our planet is much closer to the supermassive black hole at the center of the galaxy than we imagined. New observation data allowed researchers to improve the modeling of the Milky Way Galaxy, showing Earth is moving 7 km/s (~16,000 mph) faster and is 2,000 light years closer to the supermassive black hole Sagittarius A*.
The more precise information came from 15 years worth of data collected by the Japanese radio astronomy project VERA, which is a collection of acronyms standing for VLBI Exploration of Radio Astrometry (with "VLBI" meaning Very Long Baseline Interferometry). The project started in 2000 and has the goal of mapping the Milky Way's three-dimensional velocity and spatial structures.
VERA employs interferometry to pull together and combine data from radio telescopes all over the Japanese archipelago. This technique allows the project to get astounding resolution, as good as a telescope with a 2300 km diameter. The measurement is so accurate at this precise resolution of 10 micro-arcseconds, that it would be sufficiently sharp to pick out a U.S. penny if it was somehow left on the Moon's surface.
The VERA Astrometry Catalog and observations made recently by other researchers allowed the astronomers to put together a position and velocity map with a new center for the Galaxy. It's a point around which everything in the Galaxy revolves.
Arrows on this map show position and velocity data for the 224 objects utilized to model the Milky Way Galaxy. The solid black lines point to the positions of the spiral arms of the Galaxy. Colors reflect groups of objects that are part of the same arm, while the background is a simulation image.
The new map claims this center, along with the supermassive black hole it contains, is about 25,800 light-years away from Earth. Notably, this is closer than the distance of 27,700 light years established as the official value in 1985 by the International Astronomical Union.
The new map's velocity component also differentiated the velocity of the planet, showing that it's traveling at 227 km/s in its orbit around the Galactic Center. That's 7 km/s faster than the previously "official" speed of 220 km/s.
VERA next turns its attention to other objects, especially those close to the supermassive black hole at the galaxy's center.