Like all planets, Earth is the product of gravity. Bit by bit, the growing mass of dust and rock drew in sufficient material to become a swollen sphere of mineral we now call home.
Still today gravity continues to mould our planet from within, in far more delicate ways than we might imagine. A new study highlights the subtle gravitational effects deep-lying structures can have on the rise and fall of the crust above.
The researchers behind the study compare it to the mass of ice attached to an iceberg under the water, which isn’t immediately visible but which still has an important role to play in the structure and the shifts that transpire higher up.
These deep gravitational pulls and pushes are able to create some dramatic movements along faults in Earth’s crust, collapsing mountain belts and exposing rocks that had previously been as far as 24 kilometers or 15 miles below the surface, producing structures known as metamorphic core complexes.
While numerous studies have previously tried to explain the precise mechanisms behind the formation of metamorphic core complexes, the conditions of their evolution remain something of a mystery. Weighing into the decades-long debate about the origins and mechanics of these complexes, the researchers identified key geological processes behind their formation.
The team studied metamorphic core complexes around Phoenix and Las Vegas in the US, confirming they appear to be remnants of previously collapsed mountain belts.
Using computer modeling to chart how the landscape had most likely shifted over time, the researchers found the main driver of metamorphic core complex formation seems to be a thickening and then a weakening of their crustal roots.
Crustal roots form where lighter crust thickens beneath a mountain range, intruding into and replacing the heavier mantle. Weakened through processes including heat, fluid movement, and rock melt, the researchers explain, these thickened mountain footings can collapse, distorting contrasting layers of crust below.
This exposes the surface of metamorphic core complexes in a “domed upwarp” and traces of their turbulent formation can be seen in deformed rocks known as mylonites.
According to the researcher’s models, this extensional collapse is driven entirely by gravity tugging on different densities of material in the overlaying crust and its boundary with the mantle.
Computer modeling was used to identify the gravitational forces at work. (Bahadori et al., Nature Communications, 2022)
The research builds on two previous and related studies from the same team of researchers: in a 2022 study, they modeled the same region of the US Southwest, showing how it might have looked before, during, and after the metamorphic core complexes, linking tectonic movement with climate shifts.
Before that, a 2021 study from the same group showed how deep Earth forces combine with climate to influence the landscape, and impact mammal diversification and species dispersal found within the fossil record.
The new research could change the way that we understand the history of Earth and predict how its geology might continue to evolve in the future as gravity plucks and prods at its crust.
What’s more, the researchers think that their modeling approach might help geologists understand other mountainous areas around in the world, where crustal roots have thickened and partly collapsed.
According to the researchers, the study findings “likely explain many exposures of ancient gneissic domes around the world, where the brittle cover has likely been removed through erosion, exposing the core of the uplifted metamorphic dome”.
The research has been published in Nature Communications.
The dwarf galaxy NGC1427A flies through the Fornax galaxy cluster and undergoes disturbances that would not be possible if this galaxy were surrounded by a heavy and extended dark matter halo, as required by standard cosmology. Credit: ESO
Disturbances in the dwarf galaxies of one of Earth’s closest galaxy clusters point to a different gravity theory.
Dwarf galaxies are small, faint galaxies that are often found in or close to bigger galaxies or galaxy clusters. As a result, they could be impacted by their larger companions’ gravitational effects.
“We introduce an innovative way of testing the standard model based on how much dwarf galaxies are disturbed by gravitational tides’ from nearby larger galaxies,” said Elena Asencio, a Ph.D. student at the University of Bonn and the lead author of the story.
Tides occur when gravity from one body pulls on various areas of another body differently. These are comparable to tides on Earth, which form when the moon exerts a stronger pull on the side of the Earth that faces the moon.
The Fornax Cluster is home to a rich population of dwarf galaxies. Recent observations suggest that several of these dwarfs seem distorted as if the cluster environment had perturbed them. “Such perturbations in the Fornax dwarfs are not expected according to the Standard Model,” said Pavel Kroupa, Professor at the University of Bonn and Charles University in Prague. “This is because, according to the standard model, the dark matter halos of these dwarfs should partly shield them from tides raised by the cluster.”
The scientists examined the expected amount of disturbance of the dwarfs, which is determined by their internal properties and distance from the gravitationally powerful cluster center. Large galaxies with low stellar masses, as well as galaxies near the cluster center, are more easily perturbed or destroyed. They matched the findings to the amount of disturbance shown in photos taken by the European Southern Observatory’s VLT Survey Telescope.
“The comparison showed that, if one wants to explain the observations in the standard model” – said Elena Asencio – “the Fornax dwarfs should already be destroyed by gravity from the cluster center even when the tides it raises on a dwarf are sixty-four times weaker than the dwarf’s own self-gravity.” Not only is this counter-intuitive, she said, it also contradicts previous studies, which found that the external force needed to disturb a dwarf galaxy is about the same as the dwarf’s self-gravity.
Contradiction to the standard model
From this, the authors concluded that, in the standard model, it is not possible to explain the observed morphologies of the Fornax dwarfs in a self-consistent way. They repeated the analysis using Milgromian dynamics (MOND). Instead of assuming dark matter halos surrounding galaxies, the MOND theory proposes a correction to Newtonian dynamics by which gravity experiences a boost in the regime of low accelerations.
“We were not sure that the dwarf galaxies would be able to survive the extreme environment of a galaxy cluster in MOND, due to the absence of protective dark matter halos in this model – admitted Dr. Indranil Banik from the University of St. Andrews – “but our results show a remarkable agreement between observations and the MOND expectations for the level of disturbance of the Fornax dwarfs.”
“It is exciting to see that the data we obtained with the VLT survey telescope allowed such a thorough test of cosmological models,” said Aku Venhola from the University of Oulu (Finland) and Steffen Mieske from the European Southern Observatory, co-authors of the study.
This is not the first time that a study testing the effect of dark matter on the dynamics and evolution of galaxies concluded that observations are better explained when they are not surrounded by dark matter. “The number of publications showing incompatibilities between observations and the dark matter paradigm just keeps increasing every year. It is time to start investing more resources into more promising theories,” said Pavel Kroupa, a member of the Transdisciplinary Research Areas “Modelling” and “Matter” at the University of Bonn.
Dr. Hongsheng Zhao from the University of St. Andrews added: “Our results have major implications for fundamental physics. We expect to find more disturbed dwarfs in other clusters, a prediction which other teams should verify.”
Reference: “The distribution and morphologies of Fornax Cluster dwarf galaxies suggest they lack dark matter” by Elena Asencio, Indranil Banik, Steffen Mieske, Aku Venhola, Pavel Kroupa and Hongsheng Zhao, 25 June 2022, Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stac1765
Jordan Poole holds a sizable piece of the Warriors’ future in his hands, though he didn’t ask for this. It was transferred to him when Draymond Green took offense at something Poole did or said, charged at Poole during Wednesday’s practice and punched him.
Poole didn’t volunteer for this. By all accounts, the fourth-year Warriors guard was engaging in normal training-camp practice byplay with Draymond, pushed Draymond when he was charged and then was levelled by the punch. It’s all there in the video, acquired by TMZ and released Friday morning.
But Poole wasn’t backing down in that incident. And knowing him, he probably isn’t backing down from this inescapable moment in the expanded days of the Warriors’ dynasty, either. Poole has credibility after playing such a key role in last season’s championship run. He’s also taken a lot of verbal heat from the veterans and flourished. He occasionally has talked back, but he’s used his rhetorical backbone constructively. Every time he walks into the media room, he jokes that he’ll only talk for 90 seconds and pretends he hates it up at the podium; but he always stays longer, is increasingly thoughtful with his answers and sometimes even seems to like it.
A young woman who is “allergic to gravity” is speaking out about her debilitating condition, claiming she spends 23 hours a day in bed and is unable to stand upright for more than three minutes without passing out.
Lyndsi Johnson, 28, suffers from postural orthostatic tachycardia syndrome — a condition that creates reduced blood volume and an abnormal increase in heart rate when a person stands or sits up.
“I’m allergic to gravity,” Johnson told South West News Service in an interview about her unusual illness. “It sounds crazy but it’s true.”
“I can’t stand up for longer than three minutes without feeling faint, being sick or passing out,” the Bangor, Maine, resident further explained. “I feel much better if I’m lying down. I’m in bed all day.”
Johnson was working as an aviation diesel mechanic for the Navy in 2015 when she began experiencing symptoms of POTS.
Lyndsi Johnson, 28, suffers from postural orthostatic tachycardia syndrome — a condition that creates reduced blood volume and an abnormal increase in heart rate when a person stands or sits up. Courtesy Lyndsi Johnson / SWNSJohnson (left) worked as an aviation diesel mechanic for the Navy before she was medically discharged in 2018. Courtesy Lyndsi Johnson / SWNS
The young recruit suffered severe back and abdominal pain, and soon began fainting on a regular basis.
“It was really scary,” Johnson recalled, saying doctors initially believed she was experiencing “anxiety.”
“I was passing out everywhere,” she stated. “I would be shopping at the supermarket and I had to sit down because I felt faint. I’ve even passed out after my dog has barked.”
The super-fit Maine resident was used to being on her feet all day before she began experiencing symptoms of POTS. Courtesy Lyndsi Johnson / SWNSJohnson underwent a “tilt” test to determine if she had POTS.Courtesy Lyndsi Johnson / SWNS
In May 2018, Johnson was medically discharged from the military due to her mystery illness, but her symptoms only worsened.
By early 2022, she was unable to keep food down and was projectile vomiting on a regular basis.
“I’d throw up so much my heart would start having prolonged QT intervals and I’d be in the hospital on cardiac monitoring,” the mechanic revealed.
A cardiologist subsequently theorized that Johnson might have POTS and suggested she undergo a “tilt” test — during which the patient is secured to a table while lying down and the table is slowly tilted upright, with doctors monitoring heart rate, blood pressure and blood oxygen and exhaled carbon dioxide levels.
In February, she was officially diagnosed with the syndrome.
Johnson was officially diagnosed with POTS in February of this year. She spends 23 hours a day lying down in bed. Courtesy Lyndsi Johnson / SWNS“It’s really debilitating,” Johnson said. “I can’t do chores and [my husband] James has to cook, clean and help me shower and wash myself.”Courtesy Lyndsi Johnson / SWNS
While there is no cure, she now takes beta blockers, which reduce her fainting to three times a day and help with her nausea.
However, she is still unable to live a normal life and relies on her husband, James, to be her caregiver.
“It’s really debilitating,” she said. “I can’t do chores and James has to cook, clean and help me shower and wash myself. I’ve gone weeks without brushing my teeth because it just makes me feel awful.”
Johnson is now pursuing a music business degree from the confines of her bed. Courtesy Lyndsi Johnson / SWNS
The ex-mechanic — who used to pride herself on being super active — says the diagnosis feels like “the rug has been ripped from under my feet.”
A determined Johnson is now pursuing a music business degree from the confines of her bed, and hopes to be able to get back to work — in a job where she can work remotely and lie down.
“I’ve really had to adapt to this new life,” she declared. “I can’t do a lot of what I used to be able to, but I’ve come to terms with that now. I’m grateful for what I have.”
For over a century, astronomers have known that the Universe has been expanding since the Big Bang. For the first eight billion years, the expansion rate was relatively consistent since it was held back by the force of gravitation. However, thanks to missions like the Hubble Space Telescope, astronomers have since learned that roughly five billion years ago, the rate of expansion has been accelerating. This led to the widely-accepted theory that a mysterious force is behind the expansion (known as Dark Energy), while some insist that the force of gravity may have changed over time.
This is a contentious hypothesis since it means that Einstein’s General Theory of Relativity (which has been validated nine ways from Sunday) is wrong. But according to a new study by the international Dark Energy Survey (DES) Collaboration, the nature of gravity has remained the same throughout the entire history of the Universe. These findings come shortly before two next-generation space telescopes (Nancy Grace Roman and Euclid) are sent to space to conduct even more precise measurements of gravity and its role in cosmic evolution.
The DES Collaboration comprises researchers from universities and institutes in the U.S., U.K., Canada, Chile, Spain, Brazil, Germany, Japan, Italy, Australia, Norway, and Switzerland. Their third-year findings were presented at the International Conference on Particle Physics and Cosmology (COSMO’22), which took place in Rio de Janeiro from August 22nd to 26th. They were also shared in a paper titled “Dark Energy Survey Year 3 Results: Constraints on extensions to Lambda CDM with weak lensing and galaxy clustering” that appeared in the American Physical Society journal Physical Review D.
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Einstein’s General Theory of Relativity, which he finalized in 1915, describes how the curvature of spacetime is altered in the presence of gravity. For over a century, this theory has accurately predicted almost everything in our Universe, from Mercury’s orbit and gravitational lensing to the existence of black holes. But between the 1960s and 1990s, two discrepancies were discovered that led astronomers to wonder if Einstein’s theory was correct. First, astronomers noted that the gravitational effects of massive structures (like galaxies and galaxy clusters) did not accord with their observed mass.
This gave rise to the theory that space is filled with an invisible mass that interacts with “normal” (aka. “luminous” or visible) matter via gravity. Meanwhile, the observed expansion of the cosmos (and how it is subject to acceleration) gave rise to the theory of Dark Energy and the Lambda Cold Dark Matter (Lambda CDM) cosmological model. Cold Dark Matter is an interpretation where this mass is composed of large, slow-moving particles while Lambda represents Dark Energy. In theory, these two forces constitute 95% of the total mass-energy content of the Universe, yet all attempts to find direct evidence of them have failed.
The only possible alternative is that Relativity needs to be modified to account for these discrepancies. To find out if that’s the case, members of the DES used the Victor M. Blanco 4-meter Telescope at the Cerro Telolo Inter-American Observatory in Chile to observe galaxies up to 5 billion light-years away. They hoped to determine if gravity has varied over the past 5 billion years (since the acceleration began) or over cosmic distances. They also consulted data from other telescopes, including the ESA’s Planck satellite, which has been mapping the Cosmic Microwave Background (CMB) since 2009.
They paid close attention to how the images they saw contained subtle distortions due to dark matter (gravitational lenses). As the first image released from the James Webb Space Telescope (JWST) illustrated, scientists can infer the strength of gravity by analyzing the extent to which a gravitational lens distorts spacetime. So far, the DES Collaboration has measured the shapes of over 100 million galaxies, and the observations all match what General Relativity predicts. The good news is that Einstein’s theory still holds, but this also means that the mystery of Dark Energy persists for the time being.
Artist’s impression of the Nancy Grace Roman Space Telescope, named after NASA’s first Chief of Astronomy. Credits: NASA
Luckily, astronomers will not have to wait long before new and more detailed data is available. First, there’s the ESA’s Euclid mission, slated for launch by 2023 at the latest. This mission will map the geometry of the Universe, looking 8 billion years into the past to measure the effects of Dark Matter and Dark Energy. By May 2027, it will be joined by NASA’s Nancy Grace Roman Space Telescope, which will look back over 11 billion years. These will be the most detailed cosmological surveys ever conducted and are expected to provide the most compelling evidence for (or against) the Lambda-CDM model.
As study co-author Agnès Ferté, who conducted the research as a postdoctoral researcher at JPL, said in a recent NASA press release:
“There is still room to challenge Einstein’s theory of gravity, as measurements get more and more precise. But we still have so much to do before we’re ready for Euclid and Roman. So it’s essential we continue to collaborate with scientists around the world on this problem as we’ve done with the Dark Energy Survey.”
In addition, observations provided by Webb of the earliest stars and galaxies in the Universe will allow astronomers to chart the evolution of the cosmos from its earliest periods. These efforts have the potential to answer some of the most pressing mysteries in the Universe. These include how Relativity and the observed mass and expansion of the Universe coincide but could also provide insight into how gravity and the other fundamental forces of the Universe (as described by quantum mechanics) interact – a Theory of Everything (ToE).
If there’s one thing that characterizes the current era of astronomy, it is the way that long-term surveys and next-generation instruments are coming together to test what has been the stuff of theory until now. The potential breakthroughs that these could lead to are sure to both delight and confound us. But ultimately, they will revolutionize the way we look at the Universe.
Dark energy illustration. Credit: Visualization by Frank Summers, Space Telescope Science Institute. Simulation by Martin White, UC Berkeley and Lars Hernquist, Harvard University
Could one of the biggest puzzles in astrophysics be solved by reworking Albert Einstein’s theory of gravity? Not yet, according to a new study co-authored by
A new study marks the latest effort to determine whether this is all simply a misunderstanding: that expectations for how gravity works at the scale of the entire universe are flawed or incomplete. This potential misunderstanding might help researchers explain dark energy. However, the study – one of the most precise tests yet of Albert Einstein’s theory of gravity at cosmic scales – finds that the current understanding still appears to be correct. The study was from the international Dark Energy Survey, using the Victor M. Blanco 4-meter Telescope in Chile.
The results, authored by a group of scientists that includes some from NASA’s Jet Propulsion Laboratory (
This image – the first released from NASA’s James Webb Space Telescope – shows the galaxy cluster SMACS 0723. Some of the galaxies appear smeared or stretched due to a phenomenon called gravitational lensing. This effect can help scientists map the presence of dark matter in the universe. Credit: NASA, ESA, CSA, and STScI
More than a century ago, Albert Einstein developed his Theory of General Relativity to describe gravity. Thus far it has accurately predicted everything from the orbit of Mercury to the existence of black holes. But some scientists have argued that if this theory can’t explain dark energy, then maybe they need to modify some of its equations or add new components.
To find out if that’s the case, members of the Dark Energy Survey looked for evidence that gravity’s strength has varied throughout the universe’s history or over cosmic distances. A positive finding would indicate that Einstein’s theory is incomplete, which might help explain the universe’s accelerating expansion. They also examined data from other telescopes in addition to Blanco, including the ESA (European Space Agency) Planck satellite, and reached the same conclusion.
Einstein’s theory still works, according to the study. So no there’s no explanation for dark energy yet. However, this research will feed into two upcoming missions: ESA’s Euclid mission, slated for launch no earlier than 2023, which has contributions from NASA; and NASA’s Nancy Grace Roman Space Telescope, targeted for launch no later than May 2027. Both telescopes will search for changes in the strength of gravity over time or distance.
Blurred Vision
How do scientists know what happened in the universe’s past? By looking at distant objects. A light-year is a measure of the distance light can travel in a year (about 6 trillion miles, or about 9.5 trillion kilometers). That means an object one light-year away appears to us as it was one year ago, when the light first left the object. And galaxies billions of light-years away appear to us as they did billions of years ago. The new study looked at galaxies stretching back about 5 billion years in the past. Euclid will peer 8 billion years into the past, and Roman will look back 11 billion years.
The galaxies themselves don’t reveal the strength of gravity, but how they look when viewed from Earth does. Most matter in our universe is dark matter, which does not emit, reflect, or otherwise interact with light. While physicists don’t know what it’s made of, they know it’s there, because its gravity gives it away: Large reservoirs of dark matter in our universe warp space itself. As light travels through space, it encounters these portions of warped space, causing images of distant galaxies to appear curved or smeared. This was on display in one of first images released from NASA’s James Webb Space Telescope.
This video explains the phenomenon called gravitational lensing, which can cause images of galaxies to appear warped or smeared. This distortion is caused by gravity, and scientists can use the effect to detect dark matter, which does not emit or reflect light. Credit: NASA’s Goddard Space Flight Center
Dark Energy Survey scientists search galaxy images for more subtle distortions due to dark matter bending space, an effect called weak gravitational lensing. The strength of gravity determines the size and distribution of dark matter structures, and the size and distribution, in turn, determine how warped those galaxies appear to us. That’s how images can reveal the strength of gravity at different distances from Earth and distant times throughout the universe’s history. The group has now measured the shapes of over 100 million galaxies, and so far, the observations match what’s predicted by Einstein’s theory.
“There is still room to challenge Einstein’s theory of gravity, as measurements get more and more precise,” said study co-author Agnès Ferté, who conducted the research as a postdoctoral researcher at JPL. “But we still have so much to do before we’re ready for Euclid and Roman. So it’s essential we continue to collaborate with scientists around the world on this problem as we’ve done with the Dark Energy Survey.”
Reference: “Dark Energy Survey Year 3 Results: Constraints on extensions to ΛCDM with weak lensing and galaxy clustering” by DES Collaboration: T. M. C. Abbott, M. Aguena, A. Alarcon, O. Alves, A. Amon, J. Annis, S. Avila, D. Bacon, E. Baxter, K. Bechtol, M. R. Becker, G. M. Bernstein, S. Birrer, J. Blazek, S. Bocquet, A. Brandao-Souza, S. L. Bridle, D. Brooks, D. L. Burke, H. Camacho, A. Campos, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, F. J. Castander, R. Cawthon, C. Chang, A. Chen, R. Chen, A. Choi, C. Conselice, J. Cordero, M. Costanzi, M. Crocce, L. N. da Costa, M. E. S. Pereira, C. Davis, T. M. Davis, J. DeRose, S. Desai, E. Di Valentino, H. T. Diehl, S. Dodelson, P. Doel, C. Doux, A. Drlica-Wagner, K. Eckert, T. F. Eifler, F. Elsner, J. Elvin-Poole, S. Everett, X. Fang, A. Farahi, I. Ferrero, A. Ferté, B. Flaugher, P. Fosalba, D. Friedel, O. Friedrich, J. Frieman, J. García-Bellido, M. Gatti, L. Giani, T. Giannantonio, G. Giannini, D. Gruen, R. A. Gruendl, J. Gschwend, G. Gutierrez, N. Hamaus, I. Harrison, W. G. Hartley, K. Herner, S. R. Hinton, D. L. Hollowood, K. Honscheid, H. Huang, E. M. Huff, D. Huterer, B. Jain, D. J. James, M. Jarvis, N. Jeffrey, T. Jeltema, A. Kovacs, E. Krause, K. Kuehn, N. Kuropatkin, O. Lahav, S. Lee, P.-F. Leget, P. Lemos, C. D. Leonard, A. R. Liddle, M. Lima, H. Lin, N. MacCrann, J. L. Marshall, J. McCullough , J. Mena-Fernández, F. Menanteau, R. Miquel, V. Miranda, J. J. Mohr, J. Muir, J. Myles, S. Nadathur, A. Navarro-Alsina, R. C. Nichol, R. L. C. Ogando, Y. Omori, A. Palmese, S. Pandey, Y. Park, M. Paterno, F. Paz-Chinchón, W. J. Percival, A. Pieres, A. A. Plazas Malagón, A. Porredon, J. Prat, M. Raveri, M. Rodriguez-Monroy, P. Rogozenski, R. P. Rollins, A. K. Romer, A. Roodman, R. Rosenfeld, A. J. Ross, E. S. Rykoff, S. Samuroff, C. Sánchez, E. Sanchez, J. Sanchez, D. Sanchez Cid, V. Scarpine, D. Scolnic, L. F. Secco, I. Sevilla-Noarbe, E. Sheldon, T. Shin, M. Smith, M. Soares-Santos, E. Suchyta, M. Tabbutt, G. Tarle, D. Thomas, C. To, A. Troja, M. A. Troxel, I. Tutusaus, T. N. Varga, M. Vincenzi, A. R. Walker, N. Weaverdyck, R. H. Wechsler, J. Weller, B. Yanny, B. Yin, Y. Zhang and J. Zuntz, 12 July 2022, Astrophysics > Cosmology and Nongalactic Astrophysics. arXiv:2207.05766
This image – the first released from NASA’s James Webb Space Telescope – shows the galaxy cluster SMACS 0723. Some of the galaxies appear smeared or stretched due to a phenomenon called gravitational lensing. This effect can help scientists map the presence of dark matter in the universe. Credit: NASA, ESA, CSA, STScI
Could one of the biggest puzzles in astrophysics be solved by reworking Albert Einstein’s theory of gravity? A new study co-authored by NASA scientists says not yet.
The universe is expanding at an accelerating rate, and scientists don’t know why. This phenomenon seems to contradict everything researchers understand about gravity’s effect on the cosmos: It’s as if you threw an apple in the air and it continued upward, faster and faster. The cause of the acceleration, dubbed dark energy, remains a mystery.
A new study from the international Dark Energy Survey, using the Victor M. Blanco 4-meter Telescope in Chile, marks the latest effort to determine whether this is all simply a misunderstanding: that expectations for how gravity works at the scale of the entire universe are flawed or incomplete. This potential misunderstanding might help scientists explain dark energy. But the study—one of the most precise tests yet of Albert Einstein’s theory of gravity at cosmic scales—finds that the current understanding still appears to be correct.
The results, authored by a group of scientists that includes some from NASA’s Jet Propulsion Laboratory, were presented Wednesday, Aug. 23, at the International Conference on Particle Physics and Cosmology (COSMO’22) in Rio de Janeiro. The work helps set the stage for two upcoming space telescopes that will probe our understanding of gravity with even higher precision than the new study and perhaps finally solve the mystery.
More than a century ago, Albert Einstein developed his Theory of General Relativity to describe gravity, and so far it has accurately predicted everything from the orbit of Mercury to the existence of black holes. But if this theory can’t explain dark energy, some scientists have argued, then maybe they need to modify some of its equations or add new components.
To find out if that’s the case, members of the Dark Energy Survey looked for evidence that gravity’s strength has varied throughout the universe’s history or over cosmic distances. A positive finding would indicate that Einstein’s theory is incomplete, which might help explain the universe’s accelerating expansion. They also examined data from other telescopes in addition to Blanco, including the ESA (European Space Agency) Planck satellite, and reached the same conclusion.
This video explains the phenomenon called gravitational lensing, which can cause images of galaxies to appear warped or smeared. This distortion is caused by gravity, and scientists can use the effect to detect dark matter, which does not emit or reflect light. Credit: NASA’s Goddard Space Flight Center
The study finds Einstein’s theory still works. So no explanation for dark energy yet. But this research will feed into two upcoming missions: ESA’s Euclid mission, slated for launch no earlier than 2023, which has contributions from NASA; and NASA’s Nancy Grace Roman Space Telescope, targeted for launch no later than May 2027. Both telescopes will search for changes in the strength of gravity over time or distance.
Blurred Vision
How do scientists know what happened in the universe’s past? By looking at distant objects. A light-year is a measure of the distance light can travel in a year (about 6 trillion miles, or about 9.5 trillion kilometers). That means an object one light-year away appears to us as it was one year ago, when the light first left the object. And galaxies billions of light-years away appear to us as they did billions of years ago. The new study looked at galaxies stretching back about 5 billion years in the past. Euclid will peer 8 billion years into the past, and Roman will look back 11 billion years.
The galaxies themselves don’t reveal the strength of gravity, but how they look when viewed from Earth does. Most matter in our universe is dark matter, which does not emit, reflect, or otherwise interact with light. While scientists don’t know what it’s made of, they know it’s there, because its gravity gives it away: Large reservoirs of dark matter in our universe warp space itself. As light travels through space, it encounters these portions of warped space, causing images of distant galaxies to appear curved or smeared. This was on display in one of first images released from NASA’s James Webb Space Telescope.
Dark Energy Survey scientists search galaxy images for more subtle distortions due to dark matter bending space, an effect called weak gravitational lensing. The strength of gravity determines the size and distribution of dark matter structures, and the size and distribution in turn determine how warped those galaxies appear to us. That’s how images can reveal the strength of gravity at different distances from Earth and distant times throughout the universe’s history. The group has now measured the shapes of over 100 million galaxies, and so far, the observations match what’s predicted by Einstein’s theory.
“There is still room to challenge Einstein’s theory of gravity, as measurements gets more and more precise,” said study co-author Agnès Ferté, who conducted the research as a postdoctoral researcher at JPL. “But we still have so much to do before we’re ready for Euclid and Roman. So it’s essential we continue to collaborate with scientists around the world on this problem as we’ve done with the Dark Energy Survey.”
NASA’s Roman mission will test competing cosmic acceleration theories
More information:
Dark Energy Survey Year 3 Results: Constraints on extensions to ΛCDM with weak lensing and galaxy clustering, arXiv:2207.05766 [astro-ph.CO] arxiv.org/abs/2207.05766
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Scientists help probe dark energy by testing gravity (2022, August 24)
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The emission from M87 has now been resolved into a bright, thin ring (orange colormap), arising from the infinite sequence of additional images of the emission region, and the more diffuse primary image, produced by the photons that come directly toward Earth (in blue contours). When viewed at the imaging resolution of the Event Horizon Telescope, the two components blur together. However, by separately searching for the thin ring, it is possible to sharpen the view of M87, isolating the fingerprint of strong gravity. Credit: Broderick et al. 2022, ApJ, 935, 61
In a vivid confirmation of theoretical prediction, scientists have discerned a sharp ring of light created by photons whipping around the back of a supermassive
Simulations predicted that there should be a thin, bright ring of light, hidden behind the glare of the diffuse orange glow, created by photons flung around the back of the black hole by its intense gravity.
Astrophysicist Avery Broderick led a team of researchers who used sophisticated imaging algorithms to essentially “remaster” the original imagery of the supermassive black hole at the center of the M87 galaxy.
“We turned off the searchlight to see the fireflies,” said Broderick, an associate faculty member at Perimeter Institute and the
By essentially “peeling off” elements of the imagery, says co-author Hung-Yi Pu, an assistant professor at National Taiwan Normal University, “the environment around the black hole can then be clearly revealed.”
To accomplish this, the team of researchers used a new imaging algorithm within the Event Horizon Telescope (EHT) analysis framework THEMIS to isolate and extract the distinct ring feature from the original observations of the M87 black hole. They were also able to detect the telltale footprint of a powerful jet blasting outward from the black hole.
The scientists’ findings both confirm theoretical predictions and offer new ways to explore these mysterious objects, which are thought to reside at the heart of most galaxies.
Black holes were long considered unseeable until scientists coaxed them out of hiding with the EHT, a globe-spanning network of telescopes. Using eight observatories on four continents, all pointed at the same spot in the sky and linked together with nanosecond timing; the EHT researchers observed two black holes in 2017.
The EHT collaboration first unveiled the supermassive black hole in M87 in 2019. Then in 2022, it revealed the comparatively small but tumultuous black hole at the heart of our own
Reference: “The Photon Ring in M87*” by Avery E. Broderick, Dominic W. Pesce, Roman Gold, Paul Tiede, Hung-Yi Pu, Richard Anantua, Silke Britzen, Chiara Ceccobello, Koushik Chatterjee, Yongjun Chen, Nicholas S. Conroy, Geoffrey B. Crew, Alejandro Cruz-Osorio, Yuzhu Cui, Sheperd S. Doeleman, Razieh Emami, Joseph Farah, Christian M. Fromm, Peter Galison, Boris Georgiev, Luis C. Ho, David J. James, Britton Jeter, Alejandra Jimenez-Rosales, Jun Yi Koay, Carsten Kramer, Thomas P. Krichbaum, Sang-Sung Lee, Michael Lindqvist, Iván Martí-Vidal, Karl M. Menten, Yosuke Mizuno, James M. Moran, Monika Moscibrodzka, Antonios Nathanail, Joey Neilsen, Chunchong Ni, Jongho Park, Vincent Piétu, Luciano Rezzolla, Angelo Ricarte, Bart Ripperda, Lijing Shao, Fumie Tazaki, Kenji Toma, Pablo Torne, Jonathan Weintroub, Maciek Wielgus, Feng Yuan, Shan-Shan Zhao and Shuo Zhang, 16 August 2022, The Astrophysical Journal. DOI: 10.3847/1538-4357/ac7c1d
Lunar Glass is the proposed project that will simulate gravity through centrifugal force. Gif: Kajima Corporation/Gizmodo
Interest in the Moon has been reignited recently, and Japan is looking to get in on the fun. Researchers and engineers from Kyoto University and the Kajima Corporation have released their joint proposal for a three-pronged approach to sustainable human life on the Moon and beyond.
The future of space exploration will likely include longer stays in low gravity environments, whether in orbit or on the surface of another planet. Problem is, long stays in space can wreak havoc on our physiology; recent research shows that astronauts can suffer a decade of bone loss during months in space, and that their bones never return to normal. Thankfully, researchers from Kyoto University and the Kajima Corporation are seeking to engineer a potential solution.
The proposal, announced in a press release last week, looks like something ripped straight from the pages of a sci-fi novel. The plan consists of three distinct elements, the first of which, called “The Glass,” aims to bring simulated gravity to the Moon and Mars through centrifugal force.
02 ルナグラスと交通機関
Gravity on the Moon and Mars is about 16.5% and 37.9% of that on Earth, respectively. Lunar Glass and Mars Glass could bridge that gap; they are massive, spinning cones that will use centrifugal force to simulate the effects of Earth’s gravity. These spinning cones will have an approximate radius of 328 feet (100 meters) and height of 1,312 feet (400 meters), and will complete one rotation every 20 seconds, creating a 1g experience for those inside (1g being the gravity on Earth). The researchers are targeting the back half of the 21st century for the construction of Lunar Glass, which seems unreasonably optimistic given the apparent technological expertise required to pull this off.
The second element of the plan is the “core biome complex” for “relocating a reduced ecosystem to space,” according to a Google-translated version of the press release. The core biome complex would exist within the Moon Glass/Mars Glass structure and it’s where the human explorers would live, according to the proposal. The final element of the proposal is the “Hexagon Space Track,” or Hexatrack, a high-speed transportation infrastructure that could connect Earth, Mars, and the Moon. Hexatrack will require at least three different stations, one on Mars’s moon Phobos, one in Earth orbit, and one around the Moon (likely the planned Lunar Gateway).
The journey back to the Moon is getting nearer while interest in settling Mars is growing. A major obstacle in the way of long-term stays on these bodies is gravity. The proposal from Kyoto University and the Kajima Corporation is exciting and promising, but it’s not something we should expect any time soon.
More:NASA’s CAPSTONE Probe Is Officially en Route to the Moon
ByIndranil Banik, Postdoctoral Research Fellow of Astrophysics, University of St Andrews July 10, 2022
Dark matter was proposed to explain why stars at a galaxy’s far edge were able to move much faster than predicted with Newton. An alternative theory of gravity might be a better explanation.
Using Newton’s laws of physics, we can model the motions of planets in the Solar System quite accurately. However, in the early 1970s, scientists discovered that this didn’t work for disc galaxies – stars at their outer edges, far from the gravitational force of all the matter at their center – were moving much faster than predicted by Newton’s theory.
As a result, physicists proposed that an invisible substance called “dark matter” was providing extra gravitational pull, causing the stars to speed up – a theory that’s become widely accepted. However, in a recent review my colleagues and I suggest that observations across a vast range of scales are much better explained in an alternative theory of gravity called Milgromian dynamics or Mond – requiring no invisible matter. It was first proposed by Israeli physicist Mordehai Milgrom in 1982.
Mond’s primary postulate is that when gravity becomes very weak, as it does near the edge of galaxies, it starts behaving differently from Newtonian physics. In this way, it is possible to explain why stars, planets, and gas in the outskirts of over 150 galaxies rotate faster than expected based on just their visible mass. However, Mond doesn’t merely explain such rotation curves, in many cases, it predicts them.
Philosophers of science have argued that this power of prediction makes Mond superior to the standard cosmological model, which proposes there is more dark matter in the universe than visible matter. This is because, according to this model, galaxies have a highly uncertain amount of dark matter that depends on details of how the galaxy formed – which we don’t always know. This makes it impossible to predict how quickly galaxies should rotate. But such predictions are routinely made with Mond, and so far these have been confirmed.
Imagine that we know the distribution of visible mass in a galaxy but do not yet know its rotation speed. In the standard cosmological model, it would only be possible to say with some confidence that the rotation speed will come out between 100km/s and 300km/s on the outskirts. Mond makes a more definite prediction that the rotation speed must be in the range 180-190km/s.
If observations later reveal a rotation speed of 188km/s, then this is consistent with both theories – but clearly, Mond is preferred. This is a modern version of Occam’s razor – that the simplest solution is preferable to more complex ones, in this case that we should explain observations with as few “free parameters” as possible. Free parameters are constants – certain numbers that we must plug into equations to make them work. But they are not given by the theory itself – there’s no reason they should have any particular value – so we have to measure them observationally. An example is the gravitation constant, G, in Newton’s gravity theory or the amount of dark matter in galaxies within the standard cosmological model.
We introduced a concept known as “theoretical flexibility” to capture the underlying idea of Occam’s razor that a theory with more free parameters is consistent with a wider range of data – making it more complex. In our review, we used this concept when testing the standard cosmological model and Mond against various astronomical observations, such as the rotation of galaxies and the motions within galaxy clusters.
Each time, we gave a theoretical flexibility score between –2 and +2. A score of –2 indicates that a model makes a clear, precise prediction without peeking at the data. Conversely, +2 implies “anything goes” – theorists would have been able to fit almost any plausible observational result (because there are so many free parameters). We also rated how well each model matches the observations, with +2 indicating excellent agreement and –2 reserved for observations that clearly show the theory is wrong. We then subtract the theoretical flexibility score from that for the agreement with observations, since matching the data well is good – but being able to fit anything is bad.
A good theory would make clear predictions that are later confirmed, ideally getting a combined score of +4 in many different tests (+2 -(-2) = +4). A bad theory would get a score between 0 and -4 (-2 -(+2)= -4). Precise predictions would fail in this case – these are unlikely to work with the wrong physics.
We found an average score for the standard cosmological model of –0.25 across 32 tests, while Mond achieved an average of +1.69 across 29 tests. The scores for each theory in many different tests are shown in figures 1 and 2 below for the standard cosmological model and Mond, respectively.
Figure 1. Comparison of the standard cosmological model with observations based on how well the data matches the theory (improving bottom to top) and how much flexibility it had in the fit (rising left to right). The hollow circle is not counted in our assessment, as that data was used to set free parameters. Reproduced from table 3 of our review. Credit: Arxiv
Figure 2. Similar to Figure 1, but for Mond with hypothetical particles that only interact via gravity called sterile neutrinos. Notice the lack of clear falsifications. Reproduced from Table 4 of our review. Credit: Arxiv
It is immediately apparent that no major problems were identified for Mond, which at least plausibly agrees with all the data (notice that the bottom two rows denoting falsifications are blank in figure 2).
The problems with dark matter
One of the most striking failures of the standard cosmological model relates to “galaxy bars” – rod-shaped bright regions made of stars – that spiral galaxies often have in their central regions (see lead image). The bars rotate over time. If galaxies were embedded in massive halos of dark matter, their bars would slow down. However, most, if not all, observed galaxy bars are fast. This falsifies the standard cosmological model with very high confidence.
Another problem is that the original models that suggested galaxies have dark matter halos made a big mistake – they assumed that the dark matter particles provided gravity to the matter around it, but were not affected by the gravitational pull of the normal matter. This simplified the calculations, but it doesn’t reflect reality. When this was taken into account in subsequent simulations it was clear that dark matter halos around galaxies do not reliably explain their properties.
There are many other failures of the standard cosmological model that we investigated in our review, with Mond often able to naturally explain the observations. The reason the standard cosmological model is nevertheless so popular could be down to computational mistakes or limited knowledge about its failures, some of which were discovered quite recently. It could also be due to people’s reluctance to tweak a gravity theory that has been so successful in many other areas of physics.
The huge lead of Mond over the standard cosmological model in our study led us to conclude that Mond is strongly favored by the available observations. While we do not claim that Mond is perfect, we still think it gets the big picture correct – galaxies really do lack dark matter.
Written by Indranil Banik, Postdoctoral Research Fellow of Astrophysics, University of St Andrews.
This article was first published in The Conversation.
Reference: ” From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity by Indranil Banik and Hongsheng Zhao, 27 June 2022, Symmetry. DOI: 10.3390/sym14071331
