13
มิ.ย.
2023

Dark Matter NASA Science for Kids

Extraordinary efforts are under way to detect and measure the properties of these unseen WIMPs, either by witnessing their impact in a laboratory detector or by observing their annihilations after they collide with each other. There is also some expectation that their presence and mass may be inferred from experiments at new particle accelerators such as the Large Hadron Collider. The closest measurement to date — carried out in 2020 at the University of Washington — involved a 52-micron separation between two test bodies. The Austrian group is hoping to eventually attain the 1-micron range predicted for the dark dimension.

  1. And those massive gravitons, traveling around the extra-dimensional loop, produce a significant gravitational influence at the point where the loop attaches to the sphere.
  2. A second possibility is for the dark matter particles to interact more weakly than neutrinos, to be less abundant, and to have a mass of order 1 keV.
  3. The mass of the clusters, however, is not affected, indicating that most of the mass consists of dark matter.
  4. The dark dimension proposal, if supported by upcoming tests, has the potential to bring us closer to understanding what dark matter is, how it is linked to both dark energy and gravity, and why gravity appears feeble compared to the other known forces.
  5. Golwala helps manage the fabrication of the detector assemblies for SuperCDMS; the detectors are being built at the SLAC National Accelerator Laboratory, which leads the SuperCDMS project.

The gravitons they had concocted were, after all, weakly interacting yet capable of mustering some gravitational heft. One merit of the idea, he noted, is that gravitons have been a part of physics for 90 years, having been first proposed as carriers of the gravitational force. (Gravitons, it should be noted, are hypothetical particles, and have not been directly detected.) To explain dark matter, “we don’t have to introduce a new particle,” he said.

But if the universe is only made of the galaxies, stars, planets, and other things that we know about, it shouldn’t be expanding. If Kepler’s laws are correct, then the obvious way to resolve this discrepancy is to conclude the mass distribution in spiral galaxies is not similar to that of the Solar System. In particular, there is a lot of non-luminous matter (dark matter) in the outskirts of the galaxy. In principle, “dark matter” means all components of the universe which are not visible but still obey ρ ∝ a−3 . In practice, the term “dark matter” is often used to mean only the non-baryonic component of dark matter, i.e., excluding “missing baryons”. Dark matter’s existence was first inferred by Swiss American astronomer Fritz Zwicky, who in 1933 discovered that the mass of all the stars in the Coma cluster of galaxies provided only about 1 percent of the mass needed to keep the galaxies from escaping the cluster’s gravitational pull.

Normally, physicists define gravitons as massless particles that travel at the speed of light and convey the gravitational force, similar to the massless photons that convey the electromagnetic force. But in this scenario, as Obied explained, these early collisions created a different type of graviton — something with mass. More than that, they produced a range of different gravitons. Because galaxy-size density fluctuations get washed out by free-streaming, hot dark matter implies the first objects that can form are huge supercluster-size pancakes, which then fragment into galaxies. Deep-field observations show instead that galaxies formed first, followed by clusters and superclusters as galaxies clump together.

The 1997 DAMA/NaI experiment and its successor DAMA/LIBRA in 2013, claimed to directly detect dark matter particles passing through the Earth, but many researchers remain skeptical, as negative results from similar experiments seem incompatible with the DAMA results. Cold dark matter offers the simplest explanation for most cosmological observations. It is dark matter composed of constituents with an FSL much smaller than a protogalaxy. This is the focus for dark matter research, as hot dark matter does not seem capable of supporting galaxy or galaxy cluster formation, and most particle candidates slowed early.

That means we may not have to wait long to see whether the hypothesis will bear up under empirical scrutiny — or be relegated to the list of tantalizing ideas that never fulfilled their original promise. Together, dark energy and dark matter make up 95% of the universe. That only leaves a small 5% for all the matter and energy we know and understand.

Velocity dispersions

But, over the years, evidence for supersymmetry has failed to materialize. Sean Carroll, research professor of physics at Caltech, and his colleagues also wrote an early paper, in 2008, on the idea that dark matter might interact just with itself. Possibilities range from large objects like MACHOs (such as black holes[135] and Preon stars[136]) or RAMBOs (such as clusters of brown dwarfs), to new particles such as WIMPs and axions. Primordial density fluctuations smaller than this length get washed out as particles spread from overdense to underdense regions, while larger fluctuations are unaffected; therefore this length sets a minimum scale for later structure formation. As an alternative to dark matter, modifications to gravity have been proposed to explain the apparent presence of “missing matter.” These modifications suggest that the attractive force exerted by ordinary matter may be enhanced in conditions that occur only on galactic scales.

As a result, its density perturbations are washed out and unable to condense into structure.[81] If there were only ordinary matter in the universe, there would not have been enough time for density perturbations to grow into the galaxies and clusters currently seen. Although both dark matter and ordinary matter are matter, they do not behave in the same way. In particular, in the early universe, ordinary matter was ionized and interacted strongly with radiation via Thomson scattering. Dark matter does not interact directly with radiation, but it does affect the cosmic microwave background (CMB) by its gravitational potential (mainly on large scales) and by its effects on the density and velocity of ordinary matter. Ordinary and dark matter perturbations, therefore, evolve differently with time and leave different imprints on the CMB.

Detection of dark matter particles

So how does one go about finding a hypothetical particle less massive than a proton? Zurek and others have proposed tabletop-size experiments much smaller than other dark matter experiments, which can weigh on the order of tons. Although hidden-sector particles are thought to only rarely and weakly interact with normal matter, when they do, they cause disturbances that could, in theory, be detected. In 2006, Zurek and colleagues proposed the idea that dark matter could be part of a hidden sector, with its own dynamics, independent of normal matter like photons, electrons, quarks, and other particles that fall under the Standard Model. Unlike normal matter, the hidden-sector particles would live in a dark universe of their own. Somewhat like a school of fish who swim only with their own kind, these particles would interact strongly with one another but might occasionally bump softly into normal particles via a hypothetical messenger particle.

The Dark Tower

At Caltech, hidden-sector ideas are in full bloom, with several scientists cultivating new theories and experiments. One particle is normal, while the other is a particle of anti-matter. And, since all this matter is bound together, should the particles destroy each other, ALL MATTER GOES. Dark matter and dark energy raise some of the biggest questions in the study of space and physics.

More about space!

In the 1970s, Vera Rubin and Kent Ford, while based at the Carnegie Institution for Science, measured the rotation speeds of individual galaxies and found evidence that, like Zwicky’s galaxy cluster, dark matter was keeping the galaxies from flying apart. Other evidence throughout the years has confirmed the existence of dark matter and shown how abundant it is in the universe. In fact, dark matter is about five times more common than normal matter. Every second, millions to trillions of particles of dark matter flow through your body without even a whisper or trace. This ghostly fact is sometimes cited by scientists when they describe dark matter, an invisible substance that accounts for about 85 percent of all matter in the universe. Unlike so-called normal matter, which includes everything from electrons to people to planets, dark matter does not absorb, reflect, or shine with any light.

Dark matter makes up 30.1 percent of the matter-energy composition of the universe. The rest is dark energy (69.4 percent) and “ordinary” visible matter (0.5 percent). As gravitons leak into the dark dimension, the waves they produce can have different frequencies, each corresponding to different energy levels. And those massive gravitons, traveling around the extra-dimensional loop, produce a significant gravitational influence at the point where the loop attaches to the sphere. For example, an extraordinarily small lambda, as has been observed, should be accompanied by much lighter, weakly interacting particles with masses directly linked to lambda’s value. When it comes to understanding the fabric of the universe, most of what scientists think exists is consigned to a dark, murky domain.

Lots of scientists are using observations and math to figure out what these are. This will help us understand more about our amazing universe, where there is always more to discover and more to learn. Those searches for dark matter were made with data collected by the Compact Muon Solenoid instrument. Golwala helps manage the fabrication of the detector assemblies for SuperCDMS; the detectors are being built at the SLAC National Accelerator Laboratory, which leads the SuperCDMS project.

Recently, Hopkins and his students have refined this simple simulation to include hidden-sector physics. He says his research serves as a bridge between that of Zurek and Golwala, in that Zurek comes up with the theories, Hopkins tests them in computers to help refine the physics, and Golwala looks for the actual particles. In the galaxy simulations, the hidden sector dark matter is “harder to squish” because of its self-interacting properties, explains Hopkins, and this trait ultimately systems development life cycle affects the properties of galaxies. The team’s computer creations allow them to make predictions about the structure of galaxies on fine scales, which next-generation telescopes, such as the upcoming Vera C. Rubin Observatory, scheduled to begin operations in Chile in 2022, should be able to resolve. In addition, a theory known as supersymmetry (which states that every particle has a partner with a complementary spin) predicts partner particles, one of which could be a WIMP.

This is not observed.[62] Instead, the galaxy rotation curve remains flat as distance from the center increases. Now, Peña is developing quantum-sensing experiments to detect dark matter. The state-of-the-art sensors he is using are being developed as part of a quantum internet project involving INQNET in collaboration with Fermilab, JPL, and the National Institute of Standards and Technology, https://traderoom.info/ among others. INQNET was founded in 2017 with AT&T and is led by Maria Spiropulu, Caltech’s Shang-Yi Ch’en Professor of Physics. A research thrust of this program focuses on building quantum-internet prototypes including both fiber-optic quantum links and optical communication through the air, between sites at Caltech and JPL as well as other quantum network test beds at Fermilab.

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