If the laws of physics are symmetrical as we think they are, then the Big Bang should have created matter and antimatter in the same amount.
Imagine a dust particle in a storm cloud, and you can get an idea of a neutron's insignificance compared to the magnitude of the molecule it inhabits.
But just as a dust mote might affect a cloud's track, a neutron can influence the energy of its molecule despite being less than one-millionth its size. And now physicists at MIT and elsewhere have successfully measured a neutron's tiny effect in a radioactive molecule.
The team has developed a new technique to produce and study short-lived radioactive molecules with neutron numbers they can precisely control. They hand-picked several isotopes of the same molecule, each with one more neutron than the next. When they measured each molecule's energy, they were able to detect small, nearly imperceptible changes of the nuclear size, due to the effect of a single neutron.
The fact that they were able to see such small nuclear effects suggests that scientists now have a chance to search such radioactive molecules for even subtler effects, caused by dark matter, for example, or by the effects of new sources of symmetry violations related to some of the current mysteries of the universe.
"If the laws of physics are symmetrical as we think they are, then the Big Bang should have created matter and antimatter in the same amount. The fact that most of what we see is matter, and there is only about one part per billon of antimatter, means there is a violation of the most fundamental symmetries of physics, in a way that we can't explain with all that we know," says Ronald Fernando Garcia Ruiz, assistant professor of physics at MIT.
"Now we have a chance to measure these symmetry violations, using these heavy radioactive molecules, which have extreme sensitivity to nuclear phenomena that we cannot see in other molecules in nature," he says. "That could provide answers to one of the main mysteries of how the universe was created."
Ruiz and his colleagues have published their results today in Physical Review Letters.
A special asymmetry
Most atoms in nature host a symmetrical, spherical nucleus, with neutrons and protons evenly distributed throughout. But in certain radioactive elements like radium, atomic nuclei are weirdly pear-shaped, with an uneven distribution of neutrons and protons within. Physicists hypothesize that this shape distortion can enhance the violation of symmetries that gave origin to the matter in the universe.
"Radioactive nuclei could allow us to easily see these symmetry-violating effects," says study lead author Silviu-Marian Udrescu, a graduate student in MIT's Department of Physics. "The disadvantage is, they're very unstable and live for a very short amount of time, so we need sensitive methods to produce and detect them, fast."
Rather than attempt to pin down radioactive nuclei on their own, the team placed them in a molecule that futher amplifies the sensitivity to symmetry violations. Radioactive molecules consist of at least one radioactive atom, bound to one or more other atoms. Each atom is surrounded by a cloud of electrons that together generate an extremely high electric field in the molecule that physicists believe could amplify subtle nuclear effects, such as effects of symmetry violation.
However, aside from certain astrophysical processes, such as merging neutron stars, and stellar explosions, the radioactive molecules of interest do not exist in nature and therefore must be created artificially. Garcia Ruiz and his colleagues have been refining techniques to create radioactive molecules in the lab and precisely study their properties. Last year, they reported on a method to produce molecules of radium monofluoride, or RaF, a radioactive molecule that contains one unstable radium atom and a fluoride atom.
In their new study, the team used similar techniques to produce RaF isotopes, or versions of the radioactive molecule with varying numbers of neutrons. As they did in their previous experiment, the researchers utilized the Isotope mass Separator On-Line, or ISOLDE, facility at CERN, in Geneva, Switzerland, to produce small quantities of RaF isotopes.
The facility houses a low-energy proton beam, which the team directed toward a target — a half-dollar-sized disc of uranium-carbide, onto which they also injected a carbon fluoride gas. The ensuing chemical reactions produced a zoo of molecules, including RaF, which the team separated using a precise system of lasers, electromagnetic fields, and ion traps.
The researchers measured each molecule's mass to estimate of the number of neutrons in a molecule's radium nucleus. They then sorted the molecules by isotopes, according to their neutron numbers.
In the end, they sorted out bunches of five different isotopes of RaF, each bearing more neutrons than the next. With a separate system of lasers, the team measured the quantum levels of each molecule.
"Imagine a molecule vibrating like two balls on a spring, with a certain amount of energy," explains Udrescu, who is a graduate student of MIT's Laboratory for Nuclear Science. "If you change the number of neutrons in one of these balls, the amount of energy could change. But one neutron is 10 million times smaller than a molecule, and with our current precision we didn't expect that changing one would create an energy difference, but it did. And we were able to clearly see this effect."
Udrescu compares the sensitivity of the measurements to being able to see how Mount Everest, placed on the surface of the sun, could, however minutely, change the sun's radius. By comparison, seeing certain effects of symmetry violation would be like seeing how the width of a single human hair would alter the sun's radius.
The results demonstrate that radioactive molecules such as RaF are ultrasensitive to nuclear effects and that their sensitivity may likely reveal more subtle, never-before-seen effects, such as tiny symmetry-violating nuclear properties, that could help to explain the universe's matter-antimmater asymmetry.
"These very heavy radioactive molecules are special and have sensitivity to nuclear phenomena that we cannot see in other molecules in nature," Udrescu says. "This shows that, when we start to search for symmetry-violating effects, we have a high chance of seeing them in these molecules."
This research was supported, in part, by the Office of Nuclear Physics, U.S. Department of Energy; the MISTI Global Seed Funds; the European Research Council; the Belgian FWO Vlaanderen and BriX IAP Research Program; the German Research Foundation; the UK Science and Technology Facilities Council, and the Ernest Rutherford Fellowship Grant.
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.
Hawking Radiation www.youtube.com
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.
Two ways dark energy could destroy the universe | Katie Mack | Big Think www.youtube.com
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.
The controversy over the universe's expansion rate continues with a new, faster estimate.
- A new estimate of the expansion rate of the universe puts it at 73.3 km/sec/Mpc.
- This is faster than the previous estimate of expansion in the early universe.
- The discrepancy may mean fundamental theories need rethinking.
How fast is our universe is expanding? Scientists zeroed in on a new estimate of the local expansion rate and found that it doesn't square up with previously-predicted rates of expansion in the early universe, right after the Big Bang 13.8 billion years ago.
This is significant because the expansion rate is fundamental to figuring out the universe's evolution as well as the mysterious dark energy, which is believed to make up about 68 percent of the universe and impacts how fast it's growing.
Scientists made a new estimate using the surface brightness fluctuation (SBF) technique for measuring cosmic distances. They hoped this approach could achieve more precision. The method used average stellar brightness of 63 giant elliptical galaxies to come up with the calculated rate of 73.3 kilometers per second per megaparsec (km/sec/Mpc) for the universe's expansion. That implies that every megaparsec (or 3.3 million light years from Earth), the universe expands an additional 73.3 kilometers per second.
The paper's co-author, cosmologist and University of California, Berkeley professor Chung-Pei Ma, stated that this method holds much promise.
"For measuring distances to galaxies out to 100 megaparsecs, this is a fantastic method," said Ma, "This is the first paper that assembles a large, homogeneous set of data, on 63 galaxies, for the goal of studying H-naught [Hubble constant] using the SBF method."
Ma also leads the MASSIVE survey of local galaxies, which provided data for 43 of the galaxies in this analysis.
What's controversial is that if you calculate this rate using measurements of fluctuations in the cosmic microwave background or density variation data for normal matter in the early universe, you'd get a different result of 67.4 km/sec/Mpc.
The science of expansion: Andromeda, gravity, and the ‘Big Rip’
How is the difference in estimates possible, and what do the nonmatching answers suggest? The central difficulty lies in establishing certainty for the locations and relative distances of objects in space. Astronomers believe the discrepancies in calculations may point to the fact that current cosmological theories are either not fully realized or even dead wrong.
The paper's first author, John Blakeslee, an astronomer with the National Science Foundation's NOIRLab, thinks the implications of this type of research are enormous.
"The whole story of astronomy is, in a sense, the effort to understand the absolute scale of the universe, which then tells us about the physics," Blakeslee stated in a press release, "The SBF method is more broadly applicable to the general population of evolved galaxies in the local universe, and certainly if we get enough galaxies with the James Webb Space Telescope, this method has the potential to give the best local measurement of the Hubble constant."
The ultra-powerful James Webb Telescope is on track to be launched in October 2021.
"The James Webb telescope has the potential to really decrease the error bars for SBF," Ma agreed.
Other authors of the study included Jenny Greene of Princeton University, leader of the MASSIVE team, Peter Milne of the University of Arizona in Tucson, and Joseph Jensen of Utah Valley University.
Check out their new paper published in The Astrophysical Journal.
Identifying primordial ripples would be key to understanding the conditions of the early universe.
In the moments immediately following the Big Bang, the very first gravitational waves rang out.
The product of quantum fluctuations in the new soup of primordial matter, these earliest ripples through the fabric of space-time were quickly amplified by inflationary processes that drove the universe to explosively expand.
Primordial gravitational waves, produced nearly 13.8 billion years ago, still echo through the universe today. But they are drowned out by the crackle of gravitational waves produced by more recent events, such as colliding black holes and neutron stars.
Now a team led by an MIT graduate student has developed a method to tease out the very faint signals of primordial ripples from gravitational-wave data. Their results were published in December 2020 in Physical Review Letters.
Gravitational waves are being detected on an almost daily basis by LIGO and other gravitational-wave detectors, but primordial gravitational signals are several orders of magnitude fainter than what these detectors can register. It's expected that the next generation of detectors will be sensitive enough to pick up these earliest ripples.
In the next decade, as more sensitive instruments come online, the new method could be applied to dig up hidden signals of the universe's first gravitational waves. The pattern and properties of these primordial waves could then reveal clues about the early universe, such as the conditions that drove inflation.
"If the strength of the primordial signal is within the range of what next-generation detectors can detect, which it might be, then it would be a matter of more or less just turning the crank on the data, using this method we've developed," says Sylvia Biscoveanu, a graduate student in MIT's Kavli Institute for Astrophysics and Space Research. "These primordial gravitational waves can then tell us about processes in the early universe that are otherwise impossible to probe."
Biscoveanu's co-authors are Colm Talbot of Caltech, and Eric Thrane and Rory Smith of Monash University.
A concert hum
The hunt for primordial gravitational waves has concentrated mainly on the cosmic microwave background, or CMB, which is thought to be radiation that is leftover from the Big Bang. Today this radiation permeates the universe as energy that is most visible in the microwave band of the electromagnetic spectrum. Scientists believe that when primordial gravitational waves rippled out, they left an imprint on the CMB, in the form of B-modes, a type of subtle polarization pattern.
Physicists have looked for signs of B-modes, most famously with the BICEP Array, a series of experiments including BICEP2, which in 2014 scientists believed had detected B-modes. The signal turned out to be due to galactic dust, however.
As scientists continue to look for primordial gravitational waves in the CMB, others are hunting the ripples directly in gravitational-wave data. The general idea has been to try and subtract away the "astrophysical foreground" — any gravitational-wave signal that arises from an astrophysical source, such as colliding black holes, neutron stars, and exploding supernovae. Only after subtracting this astrophysical foreground can physicists get an estimate of the quieter, nonastrophysical signals that may contain primordial waves.
The problem with these methods, Biscoveanu says, is that the astrophysical foreground contains weaker signals, for instance from farther-off mergers, that are too faint to discern and difficult to estimate in the final subtraction.
"The analogy I like to make is, if you're at a rock concert, the primordial background is like the hum of the lights on stage, and the astrophysical foreground is like all the conversations of all the people around you," Biscoveanu explains. "You can subtract out the individual conversations up to a certain distance, but then the ones that are really far away or really faint are still happening, but you can't distinguish them. When you go to measure how loud the stagelights are humming, you'll get this contamination from these extra conversations that you can't get rid of because you can't actually tease them out."
A primordial injection
For their new approach, the researchers relied on a model to describe the more obvious "conversations" of the astrophysical foreground. The model predicts the pattern of gravitational wave signals that would be produced by the merging of astrophysical objects of different masses and spins. The team used this model to create simulated data of gravitational wave patterns, of both strong and weak astrophysical sources such as merging black holes.
The team then tried to characterize every astrophysical signal lurking in these simulated data, for instance to identify the masses and spins of binary black holes. As is, these parameters are easier to identify for louder signals, and only weakly constrained for the softest signals. While previous methods only use a "best guess" for the parameters of each signal in order to subtract it out of the data, the new method accounts for the uncertainty in each pattern characterization, and is thus able to discern the presence of the weakest signals, even if they are not well-characterized. Biscoveanu says this ability to quantify uncertainty helps the researchers to avoid any bias in their measurement of the primordial background.
Once they identified such distinct, nonrandom patterns in gravitational-wave data, they were left with more random primordial gravitational-wave signals and instrumental noise specific to each detector.
Primordial gravitational waves are believed to permeate the universe as a diffuse, persistent hum, which the researchers hypothesized should look the same, and thus be correlated, in any two detectors.
In contrast, the rest of the random noise received in a detector should be specific to that detector, and uncorrelated with other detectors. For instance, noise generated from nearby traffic should be different depending on the location of a given detector. By comparing the data in two detectors after accounting for the model-dependent astrophysical sources, the parameters of the primordial background could be teased out.
The researchers tested the new method by first simulating 400 seconds of gravitational-wave data, which they scattered with wave patterns representing astrophysical sources such as merging black holes. They also injected a signal throughout the data, similar to the persistent hum of a primordial gravitational wave.
They then split this data into four-second segments and applied their method to each segment, to see if they could accurately identify any black hole mergers as well as the pattern of the wave that they injected. After analyzing each segment of data over many simulation runs, and under varying initial conditions, they were successful in extracting the buried, primordial background.
"We were able to fit both the foreground and the background at the same time, so the background signal we get isn't contaminated by the residual foreground," Biscoveanu says.
She hopes that once more sensitive, next-generation detectors come online, the new method can be used to cross-correlate and analyze data from two different detectors, to sift out the primordial signal. Then, scientists may have a useful thread they can trace back to the conditions of the early universe.
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.