A new study found the possible reason why some dwarf galaxies appear to not have dark matter.
- A new paper presents a possible reason for why some dwarf galaxies appear to be missing dark matter.
- The researchers at the University of California, Riverside ran cosmological simulations to find the answers.
- They discovered some galaxies were stripped of dark matter through extreme tidal loss.
Astronomers discovered that extreme tidal loss may be a possible explanation for why some galaxies seem to have no dark matter, a mystery type of matter that's supposed to take up to 27 percent of the universe, according to NASA. Dark energy takes up another 68 percent, creating a repulsive force that speeds up the universe's expansion. Neither has been directly seen so far but rather inferred through their effects on space.
The team from the University of California, Riverside, found anomalies in some smaller galaxies, known as "dwarf galaxies" (containing up to a billion stars, compared to the Milky Way's 200-400 billion). Some appear to have no dark matter at all. This is despite the fact that they were formed in galaxies that were teeming with dark matter previously. What is the explanation for this phenomenon, which muddies our understanding of dark matter?
The scientists used a cosmological simulation called Illustris on dark-matter-free galaxies DF2 and DF4. They wanted to understand how similar space objects would evolve and what might have happened that led them to lose dark matter. The simulation could create galaxies, with evolving stars, supernovas, and growing and merging black holes. Within the simulation, the researchers found "dwarf galaxies" similar to DF2 and DF4 which lost over 90 percent of their dark matter through the process of tidal stripping, in which material is stripped from the galaxy by galactic tidal forces.
The study's first author was the physics and astronomy graduate student Jessica Doppel, while the co-author Laura Sales, an associate professor of physics and astronomy, was Doppel's graduate advisor.
"Interestingly, the same mechanism of tidal stripping is able to explain other properties of dwarfs like DF2 and DF4 — for example, the fact that they are 'ultradiffuse' galaxies," said Sales. "Our simulations suggest a combined solution to both the structure of these dwarfs and their low dark matter content. Possibly, extreme tidal mass loss in otherwise normal dwarf galaxies is how ultradiffuse objects are formed."
Besides Sales and Doppel, the study involved Julio F. Navarro from the University of Victoria in Canada, Mario G. Abadi and Felipe Ramos-Almendares of the National University of Córdoba in Argentina, Eric W. Peng of Peking University in China, and Elisa Toloba of the University of the Pacific in California.
Laura Sales (seated, left) and her research group of students, including Jessica Doppel (seated, right).
Credit: UCR/Stan Lim
Sales's team is currently collaborating with the Max Planck Institute for Astrophysics in Germany to improve the simulations with more advanced physics and a resolution that's 16 times better than the Illustris they used on this study.
Check out the new paper, published in the Monthly Notices of the Royal Astronomical Society.
Dr. Katie Mack explains what dark energy is and two ways it could one day destroy the universe.
- The universe is expanding faster and faster. Whether this acceleration will end in a Big Rip or will reverse and contract into a Big Crunch is not yet understood, and neither is the invisible force causing that expansion: dark energy.
- Physicist Dr. Katie Mack explains the difference between dark matter, dark energy, and phantom dark energy, and shares what scientists think the mysterious force is, its effect on space, and how, billions of years from now, it could cause peak cosmic destruction.
- The Big Rip seems more probable than a Big Crunch at this point in time, but scientists still have much to learn before they can determine the ultimate fate of the universe. "If we figure out what [dark energy is] doing, if we figure out what it's made of, how it's going to change in the future, then we will have a much better idea for how the universe will end," says Mack.
Astronomers propose a new location for the mysterious force that accelerates the universe.
- Astronomers predict that dark energy is located in the voids between galaxies.
- Dark energy is thought responsible for the acceleration of our universe.
- The intergalactic voids are known as GEODEs.
Dark energy has been estimated to take up to 68 percent of the known Universe, accelerating its expansion. One problem? No one has definitively found dark energy. Now, a new study from astronomers at the University of Hawaii at Manoa predicts that the location of the mysterious force is in the compact objects found in voids between galaxies called Generic Objects of Dark Energy (GEODEs).
The possible existence of GEODEs was first suggested in the mid-1960s. They would be formed upon the collapse of stellar objects, which would not create black holes but these unusual structures, proposed scientists. While looking almost like black holes to an outside observer, GEODEs would be different in conforming to Einstein's equations on singularities. They would consist of a spinning layer around a core of dark energy.
The new research looked at how such GEODEs would move through space. The researchers concluded that the movement is affected by the spinning layer around a GEODE. If the layer spins slowly, the GEODE would group faster than black holes, explains the University's press release. This is due to the unusual fact that GEODEs increase in mass from the universe's growth. If the GEODE's outer layer spins close to the speed of light, another effect comes into play and GEODEs would repel each other.
The science team included Kevin Croker, Jack Runburg, and Duncan Farrah from the University of Hawaii.
"The dependence on spin was really quite unexpected," said Farrah. "If confirmed by observation, it would be an entirely new class of phenomenon."
What is Dark Energy made of?
Many of the ancient stars, from the time when the universe was less than 2 percent of its age today, would have formed GEODEs upon their demise. When these GEODEs consumed other stars and interstellar gas, they started to spin rapidly, creating mutual repulsion that pushed them apart from each other into what gradually became empty voids between galaxies.
The scientists think their study can explain where the elusive dark energy resides while staying consistent with what we were able to observe about our universe. The dark energy conundrum would be solved as the number of ancient stars corresponds to the number of ancient GEODEs necessary to make the math work.
Still, research is ongoing and the astronomers look to improve upon their results. Croker stated that "now that we have a clearer understanding of how Einstein's equations link big and small, we've been able to make contact with data from many communities, and a coherent picture is beginning to form."
Check out their new study published in The Astrophysical Journal.
An Oxford scientist claims a Nobel-Prize-winning conclusion is wrong.
- Paper by Oxford University physicist Subir Sarkar and his colleagues challenges how conclusions about cosmic acceleration and dark energy were reached.
- Physicists who proved cosmic acceleration shared a Nobel Prize.
- Sarkar used statistical analysis to question key data, but his methodology also has detractors.
Is our Universe's expansion speeding up? The 2011 Nobel Prize went to three scientists for proving just that. But what if the evidence they used to come up with this conclusion was wrongly interpreted and the supposed cosmic acceleration is simply an artifact of our movement through a local part of the Universe? In the big picture, there's no speeding up. What's also not there is the mysterious dark energy, thought to be creating that acceleration, says a new paper from a group of physicists who take issue with the supernovae-related evidence that was used to come up with the original Nobel-worthy conclusion.
The Nobel Prize for the cosmic acceleration idea, if you're wondering, was won by Saul Perlmutter, Brian Schmidt, and Adam Riess for "for the discovery of the accelerating expansion of the Universe through observations of distant supernovae". They used evidence from exploded stars called "la supernovae" or "standard candles" to show that the Universe's expansion was getting faster. These kinds of supernovas are so bright that we actually know their absolute brightness. This fact allows scientists to calculate the distance of these explosions from Earth, while studying the red shift in the light they emit points to the Universe's rate of expansion. In 1998, groups led by Perlmutter and Schmidt found light from 50 supernova to be dimmer than it was supposed to be, leading them to conclude that cosmic expansion was actually accelerating (thanks to dark energy – a yet-to-be-directly-observed enigmatic force that supposedly takes up 68% of all mass-energy in the Universe while causing it to expand).
But while the expansion has become accepted as science fact, there have been some who see things differently. Following up on his 2015 paper on this subject, Oxford University physicist Subir Sarkar and his colleagues at the Niels Bohr Institute and the Paris Institute of Astrophysics now published a second study taking issue with the idea of a Universe growing with acceleration.
As explained in Physics World, by statistically analyzing a sample of 740 la supernovae in their 2015 paper, Sarkar's team found "only marginal" support for cosmic acceleration with low statistical significance. The difference in their approach was in how they looked at the procedures used to calculate the absolute brightness of supernovae and how their light is absorbed by dust that gets in the way.
2011 Nobel Laureates in Physics, Saul Perlmutter, Brian P. Schmidt and Adam G. Riess2011 Nobel Laureates in Physics, Perlmutter, Schmidt and Riess, describe how an assumed error turned into the surprise discovery that the universe is expandi...
Critics of that paper abounded, taking issues with their methodology and pointing to other data that showed acceleration. Now, in the second paper, to be published in Astronomy and Astrophysics, the scientists continue to assail the supernovae evidence and the idea of cosmic acceleration by pointing to anomalies in the red-shift data and how calculations with respect to the Cosmic Microwave Background (CMB) are carried out.
"If you look at supernovae in only a small part of the sky, it would look like you had cosmic acceleration," Sarkar says. "But we are saying that it is just a local effect, that we are non-Copernican observers. It has nothing to do with the overall dynamics of the universe and therefore nothing to do with dark energy."
Riess disagrees with Sarkar's conclusions and data, calling it outdated. His team used data from 1,300 supernovae in their latest study and came up with clear-cut support for the acceleration's existence. Furthermore, he stated, "The evidence for cosmic acceleration and dark energy are much broader than only the supernovae Ia sample."
Who would argue with a Nobel Prize-winner? Subir Sarkar, who believes that "The CMB does not directly measure dark energy," adding "That is a widely propagated myth."
You can check out his new paper for yourself at arXiv.
Lisa Randall: Dark Energy Will Take Over
Physicist Lisa Randall on why dark energy doesn't dilute as the universe expands.
A new method promises to capture an elusive dark world particle.
- Scientists working on the Large Hadron Collider (LHC) devised a method for trapping dark matter particles.
- Dark matter is estimated to take up 26.8% of all matter in the Universe.
- The researchers will be able to try their approach in 2021, when the LHC goes back online.
After finding one mysterious particle – the Higgs Boson – scientists working with the Large Hadron Collider are looking to discover another needle in a haystack - dark matter.
It is supposed to be quite well dispersed around us - in fact, dark matter is estimated to take up about 26.8% of all the content of the universe. The other 68.3% is gobbled up by dark energy, a no less-mysterious conjecture. Both are essentially keeping our Universe bound together. Normal matter, if you are wondering, takes up about 4.9% of everything. Not all that much for the part that includes us.
One big problem with dark matter - no one has seen it. We just know of it from its effects like seeing how gravity affects it. How to finally spot dark matter directly is what scientists from the University of Chicago were looking to figure out in their new paper. They came up with a novel method for trapping dark matter in the Large Hadron Collider by taking advantage of the dark particle's lower speed.
The study was conducted by Lian-Tao Wang, a University of Chicago professor of physics, UChicago postdoctoral fellow Jia Liu and Fermilab scientist Zhen Liu (now at the University of Maryland).
"We know for sure there's a dark world, and there's more energy in it than there is in ours," said Lian-Tao Wang.
The theorists propose that one kind of dark particle is heavier and slower and some times interacts with normal matter. It also has a somewhat longer lifetime of up to one tenth of a second. The scientists believe that there are occasions in each decade when such particles can be found within the proton collisions engineered at the LHC.
In a press release, Wang explained that these special dark particles could be "coupled to the Higgs boson in some fashion". This would make the Higgs boson, "a portal to the dark world," said Wang.
One possibility is that the Higgs actually turns into these longer-living dark particles as it decays.
What Is Dark Matter? Michio Kaku explains.
But how to trap the dark particle among the billions of collisions happening at the LHC every second? Liu, the first author of the study, thinks that such a dark particle would be heavier and thus travel slower than the speed of light. That would keep it separated from the others. The method devised by the scientists would zero in on such particles that decay at a lower rate.
The difference could be as small as a nanosecond or even smaller. But the sensors of the LHC, already an amazing machine, would be able to detect such anomalies.
Liu believes the LHC has the capability to try their idea out and find the particles. One problem, however – their team will have to wait.
Most famous for the discovery of the Higgs Boson particle, the Large Hadron Collider (LHC), the world's largest scientific instrument, is currently offline. It is undergoing improvements that will give it a power boost. When it goes back up online in 2021, the LHC's energy output will be a trillion electron volts higher, at 14 trillion volts.
The road to High Luminosity: what's next for the LHC?
Will the extra power, the Swiss-based 27-km collider operated by CERN, can help us find dark matter, argues Liu. "We think it has great potential for discovery," he said, adding, "If the particle is there, we just have to find a way to dig it out. Usually, the key is finding the question to ask."
You can read the new paper in Physical Review Letters.