It wouldn't come as a surprise to moderns that the universe is mainly made up of non-luminous, unknown substances that we've dubbed "dark matter." Despite advances in astronomy, such as the James Webb Space Telescope, this rigorous concept remains a mystery, dominating the cosmos and curiously hidden from view. Unlike ordinary baryonic matter, which consists of a nucleus and a cloud of electrons, dark matter is a hypothetical subject that requires interdisciplinary skills in physics and astronomy. In essence, the history of the universe's evolution can be unraveled by mapping all the matter in the universe and understanding dark matter and dark energy.
What filled up the seemingly mysterious universe has been a question since Swiss astronomer Fritz Zwicky first used the term dark matter in the 1930s. His studies in galaxy revolve give insight into how the speed of clusters is measured: It correlates with the object’s weight and position; however, exaggerated measurement implies that more mass affects the object than the observable light suggested.
Until the early 1990s, one thing about the universe's expansion was quite certain. It may have enough energy density to cease its growth and collapse, or it could have so little energy density that it would never stop growing. However, gravity would undoubtedly slow it down over time. To be sure, this slowing has not been observed; rather, star motions are accelerating due to Fritz's finding; nevertheless, in theory, the cosmos must slow down. Gravity's attraction draws all matter together since it is full of matter. Then, in 1998, Hubble Space Telescope (HST) measurements of very distant supernovae revealed that the cosmos formerly expanded more slowly than it does now. So, the expansion of the Universe has not been slowing down due to gravity. It has been accelerating. No one has thought of this, no one knows how to explain it. But something was causing it.
Eventually, theorists came up with three explanations:
Maybe it's the outcome of a long-discarded version of Einstein's theory of gravity, which incorporates a so-called "cosmological constant." Or maybe there's some odd energy fluid filling the area. They then challenged Einstein's theory of gravity, claiming that it was flawed and that a new theory may contain some form of field that causes this cosmic acceleration. Theorists are still unsure about the exact explanation, but they have given the potential answer a name. It's known as dark matter and dark energy.
Dark Matter, Dark Energy
When speaking of dark matter and dark energy, there is little doubt that more is unknown than known. Roughly 68% of the universe is dark energy, and 27% is comprised of dark matter, leaving the eye-opening 5% to our Earth, the Sun, and everything we can observe, even with the most precise instrument. While this eludes many scientists in the first interference, we are now concrete as to where dark matter and dark energy play a role in the universe: bending starlight, accelerating stars, having an entire effect on the galaxies, and coincidentally, similar to that of gravity (since weight is the determining factor of object’s speed). What might explain the dark matter’s ground state and its fundamental structure as a hypothetical particle called the weakly interacting massive particle, or WIMP?
Various high-energy sources, including black holes and exploding stars emit gamma rays. However, contemporary ideas imply that they might also be caused by WIMPs, which are massive particles that do not emit or absorb light. Supersymmetry, a hypothesis that expands particle physics' very successful Standard Model, predicts such particles.
WIMPs, according to supersymmetry, function as their antimatter particles. When two WIMPs collide, they destroy and annihilate each other, generating a slew of secondary particles and gamma rays. The scientists aim to identify these high-energy signatures of dark matter in our galaxy using Gamma-ray Large Area Space Telescope, also known as GLAST. If they are successful, this finding will assist in answering one of astronomy's greatest riddles.
"If GLAST detects these signals, it will be enormously important for both particle physics and astrophysics. It will represent a huge intellectual achievement and a big leap forward in our understanding of the Universe on the largest and smallest scales simultaneously," said Lynn Cominsky of Sonoma State University in Rohnert Park, California, who heads the GLAST education and public outreach.
Signs of sights below
Tucked hidden in the mountains of western South Dakota, the little town of Lead touts itself as "picturesque" and "rugged". Visitors passing by the hair salon or the dog park may have no idea that an odd - perhaps extraterrestrial – experiment is taking place a mile below the surface.
A team of researchers, comprising professors and graduate students from the University of Maryland, is attempting to steer a hypothetical particle from outer space into the city's Sanford Underground Research Facility. The facility is housed in a historic gold mine that was active during the 1870s gold rush. The natural depth of the mine prevents interference from cosmic rays, otherwise disturbance on results.
The mine host the largest and most sensitive WIMP detector in the world. Until 2018, the record was also held by Sanford, known as the Large Underground Xenon experiment, and a late renovation succeeded in an improved LUX-ZEPLIN launched at the same site.
Physics Professor Anwar Bhattu stands from the group, with his experience and early attempts from 2005 to 2013, the sight of WIMP is closer than ever. Unlike experiments carried out by particle smashers like the Large Hadron Collider (LHC) in Switzerland, where Bhatti used to trail for clues, the Sanford lab focuses on directly observing rather than manufacturing, dark matter.
Since July 2022, the Team led by Professor Carter Hall has been looking for sights of the undiscovered particles. Their next set of data would derive further clues and answer unknowns about the universe, possibly creating new ones.
"Here, on the surface of the Earth, we're constantly being bathed in cosmic particles that are raining down upon us. Some of them have come from across the galaxy and some of them have come across the universe," Hall explained. "Our experiment is about a mile underground, and that mile of rock absorbs almost all of those conventional cosmic rays. That means that we can look for some exotic component which doesn't interact very much and would not be absorbed by the rock."
Under isolated ground, the experiment is carried out by generating bursts of light produced by particle collisions. Using the characteristics of this light, their team is able to work backward and determine the type of particle. The research team calibrates the apparatus that drives the LUZ experiment by preparing and injecting tritium, a radioactive form of hydrogen, into a liquefied form of xenon, an incredibly dense gas. The radioactive mixture is then circulated throughout the device, where particle collisions may be seen.
Observation above
An alternative for finding the perplexing dark matter is tracing faints of radiation traveling among stars and specks of dust; seeing where the path leads and where all the matter ended up. In a study carried out by the University of Chicago, scientists are combining two different methods of observing the universe. "It functions like a cross-check, so it becomes a much more robust measurement than if you just used one or the other," said UChicago astrophysicist Chihway Chang. Currently, data are combined from The Dark Energy Survey from a mountain in Chile, which surveys possible signs of Dark matter, and the South Pole Telescope spotting the origins of hovering radiations.
In both cases, the observation backed the phenomenon called gravitational lensing. Matter bends starlight in a significant way, unlikely credited by gravity itself. Thus, the method catches both regular matter and dark matter -- the prevalent matter unknown which has only been detected due to its effects on regular matter -- because both regular and dark matter exerts gravity.
In attempts, scientists are drawing a map to which all the matters end up. While being more precise than ever, it narrows down the possibilities for where this matter fetches up.
The bulk of the findings is consistent with the best hypothesis of the universe now in use. However, there are hints of a crack, which has already been revealed by similar research.
"It seems like there are slightly fewer fluctuations in the current universe than we would predict assuming our standard cosmological model anchored to the early universe," stated analysis coauthor and University of Hawaii astrophysicist Eric Baxter, suggesting that contemporary models deviate from the fact that the universe is more clustered than spread out, again, likely caused by exertions of dark matter.
The analysis, however, is significant since it derived relevant information from two quite distinct telescope surveys. As additional huge telescopes come online in the next decades, this is a much-anticipated approach for the future of astrophysics. Mappings of all matters cast a better understanding of the nature of the universe, posing a step forward in the field of dark matter.
Edwin Valentijn, a scientist of new research shows that to understand dark matter, systematic measurements of the galaxies are required. He helps formulates the future of peeking at the dark matter: "As observational astronomers, we have reached the point where we are able to measure the extra gravity around galaxies more precisely than we can measure the amount of visible matter. The counterintuitive conclusion is that we must first measure the presence of ordinary matter in the form of hot gas around galaxies before future telescopes such as Euclid can finally solve the mystery of dark matter."
Whether dark matter research has reached a breakthrough in the gold mine of South Dakota, or mappings of matters trace trails left by bent starlight, even if research returns back to the ground state with finding clues from visible matter, the mystery of the universe would come apart, starting from unwinding--the dark matter.
Reference
X, Science. “Is Dark Matter Real, or Have We Misunderstood Gravity?” Phys.org, Phys.org, 22 June 2021, https://phys.org/news/2021-06-dark-real-misunderstood-gravity.html.
“Scientists Release Newly Accurate Map of All the Matter in the Universe.” ScienceDaily, ScienceDaily, 31 Jan. 2023, https://www.sciencedaily.com/releases/2023/01/230131130943.htm.
Nunez, Emily C. “Deep in a South Dakota Gold Mine, Physicists Prospect for Dark Matter.” Phys.org, Phys.org, 3 Feb. 2023, https://phys.org/news/2023-02-deep-south-dakota-gold-physicists.html.
Dunbar, Brian. “Dark Matter.” NASA, NASA, https://www.nasa.gov/mission_pages/GLAST/science/dark_matter.html.