Tag: dark matter

New data supports theory of dark matter, but suggests inexplicably that it acts differently depending on the galaxy’s mass

9:13 am

The uncertainty of science: Astronomers analyzing twelve small and faint galaxies have determined that the existence of some form of mysterious undetected dark matter is necessary to explain the motions of their stars, and that another theory dubbed MOND that would make dark matter unnecessary fails to explain the data.

The authors found that the galaxies’ internal gravitational fields cannot be explained by visible matter alone, and that MOND predictions fail to reproduce the observed behaviour. They then compared their results with theoretical models that assume instead that these galaxies are surrounded by a massive halo of dark matter. Run on the UK’s DiRAC National Supercomputer facility, these dark matter models gave a much better match to the data.

Sounds good, eh? Not so fast. The research also found that large and small galaxies inexplicably interact with gravity and dark matter differently.

The research, published in Astronomy & Astrophysics, also challenges a long-standing assumption about how galaxies behave. Astronomers have long believed there is a simple link between the amount of visible matter in a galaxy and the strength of the gravitational pull it produces – known as the “radial acceleration relation.” While this relationship still holds for larger systems, the new study shows that it starts to break down in the smallest galaxies.

In other words, we don’t know enough yet to really explain the formation and behavior of galaxies. This really isn’t surprising, considering the time scales involved (billions of years) and the distances (millions to billions of light years).

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Astronomers claim radio data detects much of the universe’s “missing mass”

10:55 am

The uncertainty of science: Using radio data from 60 fast radio bursts scattered across the sky, astronomers think they have detected the signature of much of the universe’s “missing mass” that has until now been ascribed to some unknown material dubbed dark matter but in fact is mostly ordinary matter that was previously unobserved.

The results show that about 76% of baryonic matter is in the intergalactic medium, 15% is in the halos around galaxies and the rest is inside stars or cold galactic gas.

From the paper’s abstract:

Approximately half of the Universe’s dark matter resides in collapsed halos; significantly less than half of the baryonic matter (protons and neutrons) remains confined to halos. A small fraction of baryons are in stars and the interstellar medium within galaxies. The majority are diffuse (<10−3 cm−3) and ionized (neutral fraction <10−4), located in the intergalactic medium (IGM) and in the halos of galaxy clusters, groups and galaxies.

In other words, the dark matter is simply ordinary matter made up of ionized “diffuse ionized gas” that ” is notoriously difficult to measure.”

One major uncertainty of this result is its dependence on fast radio bursts. The scientists claim the sixty bursts they used came from distances ranging from 12 million to 9 billion light years, but it is unclear how they determined those distances. We do not currently know the source of fast radio bursts, which means we also do not really know exactly where they occur or how distant they are from us. This research however relies on that uncertain knowledge, because it measures the changes to each burst’s radio emissions as it travels through intergalactic space.

Nonetheless, if confirmed this result shouldn’t surprise us. The universe is gigantic and mostly hard to observe. For there to be a gigantic amount of undetected ordinary matter scattered between the galaxies is perfectly reasonable. Inventing something extraordinary — dark matter — is actually a far more unreasonable scientific strategy.

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Astronomers: a 9,000-light-year-long stream of gas and dust ripples like a wave due to the Milky Way’s gravity

11:24 am

According to an analysis of data from the space telescope Gaia, astronomers now believe that a 9,000-light- year-long stream of gas and dust that is only 500 light years away from the Sun at its nearest point ripples up and down like a wave, due to the Milky Way’s gravity.

Dubbed the Radcliffe Wave after the institute in which the astronomers were based who first discovered it, the scientists determined its wavelike behavior by mapping the motions of the star clusters along its length. Apparently, over time they are moving up and down, not unlike fans at a stadium doing the wave.

The data also includes these intriguing results:

“It turns out that no significant dark matter is needed to explain the motion we observe,” Konietzka said. “The gravity of ordinary matter alone is enough to drive the waving of the Wave.”

In addition, the discovery of the oscillation raises new questions about the preponderance of these waves both across the Milky Way and other galaxies. Since the Radcliffe Wave appears to form the backbone of the nearest spiral arm in the Milky Way, the waving of the Wave could imply that spiral arms of galaxies oscillate in general, making galaxies even more dynamic than previously thought. “The question is, what caused the displacement giving rise to the waving we see?,” Goodman said. “And does it happen all over the galaxy? In all galaxies? Does it happen occasionally? Does it happen all the time?”

That no dark matter is involved causes a lot of problems for the hypothesis that such material exists, causing the motions of stars in the outer regions all galaxies to orbit the galaxy faster than they should. Why would dark matter cause that increased rotation, but have no impact on this wave? It is a paradox that is not easily resolved.

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The dark matter in the Milky Way is not behaving as its supposed to

8:56 am

The uncertainty of science: Scientists using precise data of the motions of the outer stars of the Milky Way from the Gaia orbiting telescope have found they do not rotate the galaxy’s center as fast as expected, based on the theory of the existence of dark matter.

Dark matter was proposed to explain why in other galaxies the speed of rotation of outer stars does not appear to decline with distance (as seen for example with the planets in our solar system) but remains the same, no matter how far out you go. That extra speed suggests there must be unseen matter pulling on the stars.

[N]ew results that combine Gaia measurements with those from APOGEE (Apache Point Observatory Galactic Evolution Experiment), performed on a ground-based telescope in New Mexico, USA, and which measures the physical properties of stars to better judge their distance, have indeed measured the Milky Way’s rotation curve for stars out farther than ever before, to about 100,000 light years. “What we were really surprised to see was that this curve remained flat, flat, flat out to a certain distance, and then it started tanking,” says Lina Necib, who is an assistant professor of physics at MIT, said in a statement. “This means the outer stars are rotating a little slower than expected, which is a very surprising result.”

…The decline in orbital velocity at these distances implies that there is less dark matter in the center of our galaxy than expected. The research team describe the galaxy’s halo of dark matter as having been “cored,” somewhat like an apple. The crew also says there’s not enough gravity from what dark matter there seems to exist there, to reach all the way out to 100,000 light years and keep stars moving at the same velocity.

The rotation data of other galaxies, while somewhat robust, also includes a number of assumptions might be fooling us into thinking that the speeds are higher than expected. The more precise data gathered nearby, in the Milky Way, is now suggesting those assumptions and that distant data must be questioned.

Or to put it more bluntly, dark matter remains an ad hoc solution to a mystery that astronomers really don’t understand, or have sufficient data to explain. It might very well be a wild goose chase that has made them miss the real answer, whatever that might be.

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The uncertainty of science as proven by the Webb Space Telescope

9:38 am

A long detailed article was released today at Space.com, describing the many contradictions in the data coming back from the Webb Space Telescope that seriously challenge all the theories of cosmologists about the nature of the universe as well as its beginning in a single Big Bang.

The article is definitely worth reading, but be warned that it treats science as a certainty that should never have such contradictions, as illustrated first by its very headline: “After 2 years in space, the James Webb Space Telescope has broken cosmology. Can it be fixed?”

“Science” isn’t broken in the slightest. All Webb has done is provide new data that does not fit the theories. As physicist Richard Feynman once stated bluntly in teaching students the scientific method,

“It doesn’t make a difference how beautiful your guess is, it doesn’t make a difference how smart you are, who made the guess, or what his name is. If it disagrees with experiment, it’s wrong.”

Cosmologists for decades have been guessing in proposing their theories about the Big Bang, the expansion of the universe, and dark matter, based on only a tiny amount of data that had been obtained with enormous assumptions and uncertainties. It is therefore not surprising (nor was it ever surprising) that Webb has blown holes in their theories.

For example, the article spends a lot of time discussing the Hubble constant, describing how observations using different instruments (including Webb) have come up with two conflicting numbers for it — either 67 or 74 kilometers per second per megaparsec. No one can resolve this contradiction. No theory explains it.

To me the irony is that back in the 1990s, when Hubble made its first good measurements of the Hubble constant, these same scientists were certain then that the number Hubble came up with, around 90 kilometers per second per megaparsec, was now correct.

They didn’t really understand reality then, and they don’t yet understand it now.

What cosmologists must do is back away from their theories and recognize the vast areas of ignorance that exist. Once that is done, they might have a chance to resolve the conflict between the data obtained and the theories proposed, and come up with new theories that might work (with great emphasis on the word “might”). Complaining about the paradoxes will accomplish nothing.

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Despite good first images from Euclid, the orbiting telescope has a problem

10:05 am

Even though the first light images from Euclid have been sharp and exactly what astronomers want, the orbiting telescope designed to make a 3D map of billions of galaxies has an issue that will likely put some limits to that map.

When the telescope started booting up, ESA observers were concerned by the appearance of light markings on the first images relayed to Earth. This, it confirmed, was due to sunlight filtering into the telescope, “probably through a tiny gap”.

A correction to Euclid’s position was able to offset this issue. It means that while the ESA is confident Euclid will be fine to proceed with its mapping mission, particular orientations for the telescope may not be possible.

A limitation like this means that the telescope will not being able to look in some directions and get mapping images. Thus, the overall map will have gaps, though it appears at this moment that the scientists think those gaps will not seriously impact the telescope’s overall work. We shall see.

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Euclid’s first images look good

9:19 am

Scientists have determined that the first test images from the two cameras on the recently launched orbiting Euclid space telescope are sharp and as expected.

Both VIS and NISP provided these unprocessed raw images. Compared to commercial products, the cameras are immensely more complex. VIS comprises 36 individual CCDs with a total of 609 megapixels and produces high-resolution images of billions of galaxies in visible light. This is how astronomers determine their shape. The first images already give an impression of the abundance that the data will provide.

NISP’s detector consists of 16 chips with a total of 64 megapixels. It operates in the near-infrared at wavelengths between 1 and 2 microns. In addition, NISP serves as a spectrograph, which splits the light of the captured objects similar to a rainbow and allows for a finer analysis. These data will allow the mapping of the three-dimensional distribution of galaxies.

Knowing that 3D distribution will allow scientists to better determine the nature of both dark energy (related to the acceleration of the universe’s expansion) and dark matter (related to an undiscovered mass that affects the formation and shape of galaxies).

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Astronomers discover galaxy with no dark matter

3:46 pm

The uncertainty of science: Astronomers have detected a galaxy about 250 million light years away that shows no evidence of any dark matter, a phenomenon that defies the accepted theories about dark matter.

The galaxy in question, AGC 114905, is about 250 million light-years away. It is classified as an ultra-diffuse dwarf galaxy, with the name ‘dwarf galaxy’ referring to its luminosity and not to its size. The galaxy is about the size of our own Milky Way but contains a thousand times fewer stars. The prevailing idea is that all galaxies, and certainly ultra-diffuse dwarf galaxies, can only exist if they are held together by dark matter.
Galaxy AGC 114905

The researchers collected data on the rotation of gas in AGC 114905 for 40 hours between July and October 2020 using the VLA telescope. Subsequently, they made a graph showing the distance of the gas from the center of the galaxy on the x-axis and the rotation speed of the gas on the y-axis. This is a standard way to reveal the presence of dark matter. The graph shows that the motions of the gas in AGC 114905 can be completely explained by just normal matter.

“This is, of course, what we thought and hoped for because it confirms our previous measurements,” says Pavel Mancera Piña. “But now the problem remains that the theory predicts that there must be dark matter in AGC 114905, but our observations say there isn’t. In fact, the difference between theory and observation is only getting bigger.”

The evidence for dark matter in almost all galaxies is the motion of gas and stars in the outer perimeter. Routinely they move faster than expected based merely on visible ordinary matter. To account for the faster speed, astronomers beginning in the late 1950s invented dark matter, an invisible material with a mass sufficient to increase the speeds of objects and gas in the outer regions of galaxies.

That increasingly astronomers are finding galaxies with no evidence of dark matter, based on rotation speeds, only makes this mystery all the more baffling.

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New data confirms lack of dark matter in one galaxy

12:00 pm

The uncertainty of science: Astronomers have strengthened their evidence that one particular nearby galaxy is completely devoid of dark matter, a situation that challenges the existing theories about dark matter which suggest it comprises the bulk of all matter in the universe.

The astronomers had made their first claim that this galaxy, NGC 1052-DF2, lacked dark matter back in 2018, a claim that was strongly disputed by others.

The claim however would only hold up if the galaxy’s distance from Earth was as far away as they then estimated, 65 million light years (not the 42 million light years estimated by others). If it were closer, as other scientists insisted, then NCC 1052-DF2 likely did have dark matter, and the theorists could sleep at night knowing that their theory about dark matter was right.

To test their claim, the astronomers used the Hubble Space Telescope to get a better, more tightly constrained estimate of the distance, and discovered the galaxy was even farther away then previously believed.

Team member Zili Shen, from Yale University, says that the new Hubble observations help them confirm that DF2 is not only farther from Earth than some astronomers suggest, but also slightly more distant than the team’s original estimates.

The new distance estimate is that DF2 is 72 million light-years as opposed to 42 million light-years, as reported by other independent teams. This places the galaxy farther than the original Hubble 2018 estimate of 65 light-years distance.

So, does this discovery invalidate the theories about dark matter? Yes and no. The theories now have to account for the existence of galaxies with no dark matter. Previously it was assumed that dark matter was to be found as blobs at the locations of all galaxies. Apparently it is not.

However, the lack of dark matter at this one galaxy does not prove that dark matter is not real. As noted by the lead astronomer in this research,

“In our 2018 paper, we suggested that if you have a galaxy without dark matter, and other similar galaxies seem to have it, that means that dark matter is actually real and it exists,” van Dokkum said. “It’s not a mirage.

Ah, the uncertainty of science. Isn’t it wonderful?

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Astronomers find 19 more galaxies showing lack of dark matter

9:11 am

The uncertainty of science: Astronomers have discovered 19 more dwarf galaxies, now totaling 23, that appear to have significant deficits of dark matter.

Of 324 dwarf galaxies analyzed, 19 appear to be missing similarly large stores of dark matter. Those 19 are all within about 500 million light-years of Earth, and five are in or near other groups of galaxies. In those cases, the researchers note, perhaps their galactic neighbors have somehow siphoned off their dark matter. But the remaining 14 are far from other galaxies. Either these oddballs were born different, or some internal machinations such as exploding stars have upset their balance of dark matter and everyday matter, or baryons.

It may not be a case of missing dark matter, says James Bullock, an astrophysicist at the University of California, Irvine. Instead, maybe these dwarf galaxies have clung to their normal matter — or even stolen some — and so “have too many baryons.” Either way, he says, “this is telling us something about the diversity of galaxy formation…. Exactly what that’s telling us, that’s the trick.”

Since we do not know what dark matter is to begin with, finding galaxies lacking it only makes more difficult to create a theory to explain it. Something causes most galaxies to rotate faster than they should, based on their visible mass. What that is remains an unknown.

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New analysis suggests photon could make dark matter unnecessary

1:28 pm

The uncertainty of science: A new analysis by physicists that assumes a very very low mass for the photon, the particle that transmits light, could very well explain the motions of stars in galaxies and make dark matter unnecessary.

Professor Dmitri Ryutov, who recently retired from the Lawrence Livermore National Laboratory in California, USA, is an expert in plasma physics. He was awarded the American Physical Society’s (APS) 2017 Maxwell Prize for Plasma Physics for his achievements in the field. Physicists generally credit Ryutov with establishing the upper limit for the mass of the photon. As this mass, even if it is nonzero, is extremely small, it is usually ignored when analyzing atomic and nuclear processes. But even a vanishingly tiny mass of the photon could, according to the scientists’ collaborative proposal, have an effect on large-scale astrophysical phenomena.

While visiting Johannes Gutenberg University Mainz (JGU), Ryutov, his host Professor Dmitry Budker of the Helmholtz Institute Mainz (HIM), and Professor Victor Flambaum, Fellow of the Gutenberg Research College of Mainz University, decided to take a closer look at the idea. They were interested in how the infinitesimally small mass of the photon could have an effect on massive galaxies. The mechanism at the core of the physicists’ assumption is a consequence of what is known as Maxwell-Proca equations. These would allow additional centripetal forces to be generated as a result of the electromagnetic stresses in a galaxy.

Are the effects as strong as those exerted by dark matter?

“The hypothetical effect we are investigating is not the result of increased gravity,” explained Dmitry Budker. This effect may occur concurrently with the assumed influence of dark matter. It may even – under certain circumstances – completely eliminate the need to evoke dark matter as a factor when it comes to explaining rotation curves. Rotation curves express the relationship between the orbital speeds of stars in a galaxy and their radial distance from the galaxy’s center. “By assuming a certain photon mass, much smaller than the current upper limit, we can show that this mass would be sufficient to generate additional forces in a galaxy and that these forces would be roughly large enough to explain the rotation curves,” said Budker. “This conclusion is extremely exciting.” [emphasis mine]

They readily admit that this first analysis is very preliminary, and causes some additional theoretical problems that conflict with known data. Nonetheless, this simple idea could eliminate the need for the additional dark matter particle that physicists have had trouble explaining or even finding.

In fact, I am somewhat baffled why physicists had not proposed this decades ago. It provides a much more straightforward explanation for the higher rotational curves in the outer parts of galaxies, and does not require any new physics.

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Most popular theorized particle for explaining dark matter now eliminated

11:54 am

The uncertainty of science: The WIMP particle (Weakly Interacting Massive Particle), the most popular theorized particle to explain dark matter, has now been eliminated by experiments.

These experiments have now been ongoing for decades, and have seen no dark matter [WIMPs].

…Theorists can always tweak their models, and have done so many times, pushing the anticipated cross-section down and down as null result after null result rolls in. That’s the worst kind of science you can do, however: simply shifting the goalposts for no physical reason other than your experimental constraints have become more severe. There is no longer any motivation, other than preferring a conclusion that the data rules out, in doing.

Other theorized but less favored particles could still be proved to be dark matter, but the problem is getting harder and harder to solve, as presently assumed.

Dark matter has always been an invention created to explain the too-fast orbital velocities of stars in the other regions of galaxies. It could very well be however that the problem comes not from new physics and a newly contrived particle we can’t see, but from a deficiency in our overall observations of galaxies and what is there, within the constraints of the physics we know now.

Hat tip Mike Buford.

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Astronomers dispute existence of galaxy without dark matter

10:40 am

The uncertainty of science: A new analysis by astronomers disputes the conclusion of different astronomers earlier this year that they had found a galaxy that lacked any dark matter.

The original paper from March based its stunning claim of a dark-matter-free galaxy on the way clusters of stars moved through the thin, diffuse galaxy called NGC1052–DF2: They appeared to move at exactly the speed Einstein’s equations of general relativity would predict based on the visible matter (so, slower than they would if the galaxy held dark matter).

This new paper on arXiv suggested otherwise: First, the authors pointed out that NGC1052–DF2 was already discovered way back in 1976 and has previously been referred to by three different names: KKSG04, PGC3097693 and [KKS2000]04.

Then, using those names and then finding all the available data on the galaxy, the researchers argued that the researchers from the March paper simply mismeasured the distance between that galaxy and Earth. This means the galaxy is probably much closer to us than the original researchers thought.

Astronomers calculate the mass of galaxies based on the objects’ brightness and distance. If the galaxy examined in the paper is closer to Earth than previously thought, then its dimness means it’s also much less massive than researchers thought. And at the newly calculated, lighter mass, all the other features of the galaxy make a lot more sense, the researchers in the new paper said. Its globular clusters aren’t moving slowly because they’re in some strange dark matter-desert; instead, they’re moving at the regular speed for a very lightweight galaxy, the arXiv authors said.

To put it bluntly, the astronomers don’t have enough solid data to decide this issue one way or the other. Moreover, the dispute indicates once again that the whole dark matter theory itself is based on very limited data with large margins of error. It might be the best theory we’ve got to explain the data we have, but no good scientist takes it too seriously. We just don’t know enough yet.

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Hubble finds galaxy with no evidence of dark matter

12:29 pm

The uncertainty of science: Using the Hubble Space Telescope astronomers have discovered a nearby galaxy that apparently has little or no evidence of dark matter.

The unique galaxy, called NGC 1052-DF2, contains at most 1/400th the amount of dark matter that astronomers had expected. The galaxy is as large as our Milky Way, but it had escaped attention because it contains only 1/200th the number of stars. Given the object’s large size and faint appearance, astronomers classify NGC 1052-DF2 as an ultra-diffuse galaxy. A 2015 survey of the Coma galaxy cluster showed these large, faint objects to be surprisingly common.

But none of the ultra-diffuse galaxies discovered so far have been found to be lacking in dark matter. So even among this unusual class of galaxy, NGC 1052-DF2 is an oddball.

Van Dokkum and his team spotted the galaxy with the Dragonfly Telephoto Array, a custom-built telescope in New Mexico they designed to find these ghostly galaxies. They then used the W.M. Keck Observatory in Hawaii to measure the motions of 10 giant groupings of stars called globular clusters in the galaxy. Keck revealed that the globular clusters were moving at relatively low speeds, less than 23,000 miles per hour. Stars and clusters in the outskirts of galaxies containing dark matter move at least three times faster. From those measurements, the team calculated the galaxy’s mass. “If there is any dark matter at all, it’s very little,” van Dokkum explained. “The stars in the galaxy can account for all the mass, and there doesn’t seem to be any room for dark matter.”

The galaxy is unusual in many other ways.

The Hubble images also revealed the galaxy’s unusual appearance. “I spent an hour just staring at the Hubble image,” van Dokkum recalled. “It’s so rare, particularly these days after so many years of Hubble, that you get an image of something and you say, ‘I’ve never seen that before.’ This thing is astonishing: a gigantic blob that you can look through. It’s so sparse that you see all of the galaxies behind it. It is literally a see-through galaxy.”

The ghostly galaxy doesn’t have a noticeable central region, or even spiral arms and a disk, typical features of a spiral galaxy. But it doesn’t look like an elliptical galaxy, either. The galaxy also shows no evidence that it houses a central black hole. Based on the colors of its globular clusters, the galaxy is about 10 billion years old. Even the globular clusters are oddballs: they are twice as large as typical stellar groupings seen in other galaxies.

The bottom line here is that we have only circumstantial evidence that dark matter exists, based solely on the fact that in all other measured galaxies, the outer stars rotate much faster than they should. That rotation speed however does not guarantee the existence of dark matter, only that something is causing the fast rotation. And the lack thereof in this galaxy puts a big crimp in the theory that dark matter exists, since the theories that posit its existence almost require it to be present in every galaxy.

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Physicists look for new alternatives to explain dark matter

6:55 pm

The uncertainty of science: Having failed to detect WIMPs, their primary dark matter suspect, physicists are now looking at new and different candidates that might explain dark matter, and the new leading candidate is something called SIMPs.

The intensive, worldwide search for dark matter, the missing mass in the universe, has so far failed to find an abundance of dark, massive stars or scads of strange new weakly interacting particles (WIMPs), but a new candidate is slowly gaining followers and observational support.

Called SIMPs – strongly interacting massive particles – they were proposed three years ago by UC Berkeley theoretical physicist Hitoshi Murayama, a professor of physics and director of the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) in Japan, and former UC Berkeley postdoc Yonit Hochberg, now at Hebrew University in Israel.

Murayama says that recent observations of a nearby galactic pile-up could be evidence for the existence of SIMPs, and he anticipates that future particle physics experiments will discover one of them.

We shall see. The mystery remains, that we do not understand why most galaxies do not fly apart because their outer stars simply move too fast. Since all searches for ordinary matter have come up well short, dark matter remains the simplest explanation, though it still reminds me the theories of ether that once dominated physics, and never existed.

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Chinese space probe detects possible dark matter signal

8:56 am

The uncertainty of science: A Chinese space probe designed to measure cosmic rays has detected a pattern that could be evidence of the existence of dark matter.

Researchers launched the spacecraft from the Jiuquan Satellite Launch Center in the Gobi Desert, about 1600 kilometers west of Beijing, in December 2015. Its primary instrument—a stack of thin, crisscrossed detector strips—is tuned to observe the incoming direction, energy, and electric charge of the particles that make up cosmic rays, particularly electrons and positrons, the antimatter counterparts of electrons. Cosmic rays emanate from conventional astrophysical objects, like exploding supernovae in the galaxy. But if dark matter consists of WIMPs, these would occasionally annihilate each other and create electron-positron pairs, which might be detected as an excess over the expected abundance of particles from conventional objects.

In its first 530 days of scientific observations, DAMPE detected 1.5 million cosmic ray electrons and positrons above a certain energy threshold. When researchers plot of the number of particles against their energy, they’d expect to see a smooth curve. But previous experiments have hinted at an anomalous break in the curve. Now, DAMPE has confirmed that deviation. “It may be evidence of dark matter,” but the break in the curve “may be from some other cosmic ray source,” says astrophysicist Chang Jin, who leads the collaboration at the Chinese Academy of Science’s (CAS’s) Purple Mountain Observatory (PMO) in Nanjing. [emphasis mine]

I must emphasize the large uncertainty here. They have not detected dark matter. Not even close. What they have detected is a pattern in how the spacecraft is detecting cosmic rays that was predicted by the existence of dark matter. That pattern however could have other causes, and the consistent failure of other efforts to directly find dark matter strengthens the possibility that this break is caused by those other causes.

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Physicists once again fail to detect dark matter

9:25 am

The uncertainty of science: The most sensitive detector yet created by physicists has once again failed to detect dark matter, casting strong doubt on all present theories for its existence.

The latest results from an experiment called XENON1T at the Gran Sasso National Laboratory in Italy, published on 30 October, continue a dry spell stretching back 30 years in the quest to nab dark-matter particles. An attempt by a Chinese team to detect the elusive stuff, the results of which were published on the same day, also came up empty-handed. Ongoing attempts by space-based telescopes, as well as at CERN, the European particle-physics laboratory near Geneva, Switzerland, have also not spotted any hints of dark-matter particles.

The findings have left researchers struggling for answers. “We do not understand how the Universe works at a deeper and more profound level than most of us care to admit,” says Stacy McGaugh, an astrophysicist at Case Western Reserve University in Cleveland, Ohio.

The process here has been a good demonstration of the scientific method. Observers detect a phenomenon that does not make sense, which in this case was that the outer regions of galaxies rotate so fast that they should fly apart. Theorists then come up with a hypothesis to explain the phenomenon, which here was dark matter, subatomic particles that have weight but do not generally interact with the rest of the universe except by their mass, which acts to hold the galaxies together. Observers than try to prove the hypothesis by finding these theorized particles.

When the particles are not found, the theorists begin to rethink their theories. Maybe dark matter does not exist. Maybe (as is mentioned near the end of the article) a rethinking of the nature of gravity itself might be necessary. Or possibly the unseen matter is not subatomic, but ordinary matter not yet detected.

If only the climate field would apply this basic scientific method to its work. There, scientists found that carbon dioxide is increasing in the atmosphere. Some theorists posited an hypothesis that said that this increase might cause the climate to warm, and created numerous (almost a hundred) models to predict this warming. After more than thirty years, however, none of those models has successfully worked. The climate has not warmed as predicted, which suggests the hypothesis is flawed, and needs rethinking. Sadly, the leaders in the climate field refuse to do this rethinking. Instead, they appear willing to adjust and change their data to make it fit, sometimes in ways that are downright fraudulent.

This is not how science is done, and it is doing a terrible disservice to both science and society in general.

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Less evidence of dark matter in early universe

10:49 pm

The uncertainty of science: Astronomers have discovered less evidence of dark matter surrounding galaxies in early universe.

Stars in the outer regions of some far-off galaxies move more slowly than stars closer to the center, indicating a lack of dark matter, astronomer Reinhard Genzel and colleagues report online March 15 in Nature. If confirmed, the result could lead astronomers to reconsider the role dark matter played in early galaxy evolution and might also offer clues to how nearby elliptical galaxies evolved.

In contrast with these distant galaxies, stars orbiting on the outskirts of the Milky Way and other nearby galaxies move too fast for their velocities to result only from the gravity of gas and stars closer to the galactic center. If visible galactic matter is embedded in a cloud of invisible dark matter, though, gravity from the invisible matter can explain the high stellar velocities. Using stars’ orbital velocities in nearby galaxies as a reference, astronomers expected that stars in galaxies farther away would behave similarly. “Turns out that is not the case,” says study coauthor Stijn Wuyts of the University of Bath in England.

In other words, scientists at this moment really have no idea what causes the faster rotation in the outskirts of modern nearby galaxies.

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Vera Rubin R.I.P.

9:17 pm

Vera Rubin, whose work helped confirm the existence of dark matter, passed away December 25 at the age of 88.

In the 1960s, Rubin’s interest in how stars orbit their galactic centers led her and colleague Kent Ford to study the Andromeda galaxy, M31, a nearby spiral. The two scientists wanted to determine the distribution of mass in M31 by looking at the orbital speeds of stars and gas at varying distances from the galactic center. They expected the speeds to conform to Newtonian gravitational theory, whereby an object farther from its central mass orbits slower than those closer in. To their surprise, the scientists found that stars far from the center traveled as fast as those near the center.

After observing dozens more galaxies by the 1970s, Rubin and colleagues found that something other than the visible mass was responsible for the stars’ motions. Each spiral galaxy is embedded in a “halo” of dark matter—material that does not emit light and extends beyond the optical galaxy. They found it contains 5 to 10 times as much mass as the luminous galaxy. As a result of Rubin’s groundbreaking work, it has become apparent that more than 90% of the universe is composed of this invisible material. The first inkling that dark matter existed came in 1933 when Swiss astrophysicist Fritz Zwicky of Caltech proposed it. But it was not until Rubin’s work that dark matter was confirmed.

Rubin was a top notch astronomer, which is why she was part of this important discovery. She was also an exception, as at the time relatively few women were interested in becoming astronomers. Be prepared, however, for a slew of articles in the next few days focused not about her work and her contributions to science, but focused instead almost entirely on the sexist oppression she had to overcome in the evil sexist male chauvinist society of mid-twentieth-century America.

All those articles will be wrong. While there were certainly obstacles in Rubin’s way because of her sex, they were hardly as bad as it will be made out to be. Worse, this focus on gender and oppression will distract from honoring the passing of a great astronomer. It will also distract from the significance of her discovery, which continues to baffle astronomers a half century later.

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Dark matter unnecessary?

9:06 pm

The uncertainty of science: A new analysis of the infrared data from 153 galaxies using the Spitzer Space Telescope suggests that dark matter might not be necessary to explain the rotation of galaxies.

First, this concise and nicely written explanation from the link of why dark matter has been proposed:

Newton’s laws of motion predict that planets that revolve closer to a star move faster than those that are farther away. In principle this should also hold true for stars circling the cores of galaxies, but for nearly a century, astronomers have seen that stars near the outskirts of galaxies orbit at nearly the same velocities as ones near galactic centers.

To explain why these outlying stars travel as quickly as they do without flying out into the void beyond, researchers came up with the idea of dark matter, a substance whose gravitational pull is thought to keep whirling stars in check. Scientists have largely ruled out all known particles as possible explanations for dark matter, and the consensus is that dark matter must be a kind of invisible, intangible material that is only detectable via its gravitational influence.

However, despite decades of trying, researchers have failed to capture a single mote of dark matter, even though it is supposed to make up roughly five-sixths of all matter in the universe. This raises the possibility that dark matter might not be real.

The new research, which I must admit I do not really understand, supposedly suggests that dark matter is unnecessary to explain the motions of stars.

Previous analyses of the orbital velocities of the stars in galaxies often depended on visible wavelengths of light. However, the stars that produce the most visible light are relatively short-lived and prone to fluctuations, and so may not provide the best picture of how matter is scattered overall throughout a galaxy. Instead, McGaugh and his colleagues analyzed near-infrared images collected by NASA’s Spitzer Space Telescope over the past five years. “The stars that generate the most near-infrared light are red giants, that are pretty stable in their output, and so are much better representative of a galaxy’s total mass of stars,” McGaugh said.

The researchers found an extraordinarily close association between the location of normal matter and the way it accelerates around the centers of galaxies. “We were surprised at how tight that relationship was,” McGaugh said. “It looks tantamount to a law of nature.”

Neither the article nor the scientists who did this research however explain clearly how this tight association negates the need for dark matter.

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WIMP detector finds nothing

8:36 am

The uncertainty of science: A detector buried a mile underground so that it could only detect the predicted Weak Interacting Massive Particles (WIMP) thought to comprise dark matter has found nothing

Dark matter is thought to account for more than four-fifths of the mass in the universe. Scientists are confident of its existence because the effects of its gravity can be seen in the rotation of galaxies and in the way light bends as it travels through the universe, but experiments have yet to make direct contact with a dark matter particle. The LUX experiment was designed to look for weakly interacting massive particles, or WIMPs, the leading theoretical candidate for a dark matter particle. If the WIMP idea is correct, billions of these particles pass through your hand every second, and also through the Earth and everything on it. But because WIMPs interact so weakly with ordinary matter, this ghostly traverse goes entirely unnoticed.

…“We worked hard and stayed vigilant over more than a year and a half to keep the detector running in optimal conditions and maximize useful data time,” said Simon Fiorucci, a physicist at Berkeley Lab and Science Coordination Manager for the experiment. “The result is unambiguous data we can be proud of and a timely result in this very competitive field—even if it is not the positive detection we were all hoping for.”

This null result, which has its own uncertainties that require confirmation by another experimental test, places significant constraints on the possible nature of the dark matter particle, assuming it exists. And if confirmed, this result makes the hunt to explain the gravitational data of galaxy rotation, something that has been confirmed repeatedly, far more difficult.

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Universe’s expansion rate contradicts dark energy data

8:42 am

The uncertainty of science: New measurements of the universe’s expansion rate, dubbed the Hubble constant, contradict theoretical predictions based on previous data.

For their latest paper, Riess’s team studied two types of standard candles in 18 galaxies using hundreds of hours of observing time on the Hubble Space Telescope. “We’ve been going gangbusters with this,” says Riess.

Their paper, which has been submitted to a journal and posted on the arXiv online repository on 6 April, reports that they measured the constant with an uncertainty of 2.4%, down from a previous best result2 of 3.3%. They find the speed of expansion to be about 8% faster than that predicted based on Planck data, says Riess. [emphasis mine]

I highlight the number of galaxies used to get this data because I think these scientists, are being a bit over-confident about the uncertainty of their data. The universe has untold trillions of galaxies. To say they have narrowed their uncertainty down to only 2.4% based on 18 is the height of silliness.

But then, the lead scientist, Adam Riess, recognizes this, as he is also quoted in the article saying “I think that there is something in the standard cosmological model that we don’t understand.”

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Astronomers successfully predict appearance of supernova

11:35 pm

For the first time ever astronomers have been able to predict and photograph the appearance of a supernova, its light focused by the gravitational lensing caused by a galaxy and the dark matter that surrounds it.

The NASA/ESA Hubble Space Telescope has captured the image of the first-ever predicted supernova explosion. The reappearance of the Refsdal supernova was calculated from different models of the galaxy cluster whose immense gravity is warping the supernova’s light.

What makes this significant is that the prediction models were based on the theory of gravitational lensing and required the presence of dark matter to work. That they worked and were successful in predicting the appearance of this gravitationally bent light (bent by the dark matter it passed through) is a very strong confirmation of both concepts. Up until now I have been somewhat skeptical of gravitational lensing. This confirmation removes some of that skepticism.

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Technical problems for cosmic ray detector on ISS

9:53 am

The failure of a second of four cooling pumps on the Alpha Magnetic Spectrometer on ISS threatens the science instrument’s ability to continue its observations.

The AMS continues to gather science data using the three remaining pumps. They are part of a liquid carbon dioxide cooling system that is meant to dissipate heat as the AMS, which is on the outside of the space station, cycles in and out of sunlight during each 90-minute orbit of Earth Only one pump is needed at any given time. One failed in February 2014 and at least one of the other three is showing possible signs of trouble.

Since the 8.5-tonne AMS began operating in 2011, it has tracked more than 69 billion cosmic rays flying through its detectors. Its goal is to search for antimatter and dark matter. In 2013, AMS scientists reported measuring numbers and energies of positrons that hinted at, but did not confirm, the existence of dark matter.

The news article suggests that the instrument is now working with only one reliable pump. It also is possible that repairs might be done by astronauts on ISS during a spacewalk.

Some background: AMS cost $2 billion and about 20 years to build. It only got launched because Congress ordered NASA to launch one more shuttle mission to ISS to get it there.

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Is it dark matter, or a previously unrecognized failure of Newton?

9:42 am

Dark matter?

The uncertainty of science: Using new data gathered by the 10-meter Keck telescope in Hawaii, astronomers have found that the outer stars of elliptical galaxies exhibit the same behavior as the outer stars of spirals, suggesting once again the existence of dark matter.

One of the most important scientific discoveries of the 20th century was that the spectacular spiral galaxies, such as our own Milky Way, rotate much faster than expected, powered by [the] extra gravitational force of invisible “dark matter” as it is now called. Since this discovery 40 years ago, we have learned that this mysterious substance, which is probably an exotic elementary particle, makes up about 85 percent of the mass in the Universe, leaving only 15 percent to be the ordinary stuff encountered in our everyday lives. Dark matter is central to our understanding of how galaxies form and evolve – and is ultimately one of the reasons for the existence of life on Earth – yet we know almost nothing about it.

“The surprising finding of our study was that elliptical galaxies maintain a remarkably constant circular speed out to large distances from their centers, in the same way that spiral galaxies are already known to do,” said Cappellari. “This means that in these very different types of galaxies, stars and dark matter conspire to redistribute themselves to produce this effect, with stars dominating in the inner regions of the galaxies, and a gradual shift in the outer regions to dark matter dominance.”

What is most fascinating about this press release, however, is that it also noted that dark matter is only one explanation for the data, and that the failure of Newtonian physics at large distances, instead of dark matter, might also provide an explanation.

However, the [solution] does not come out naturally from models of dark matter, and some disturbing fine-tuning is required to explain the observations. For this reason, the [problem] even led some authors to suggest that, rather than being due to dark matter, it may be due to Newton’s law of gravity becoming progressively less accurate at large distances. Remarkably, decades after it was proposed, this alternative theory (without dark matter) still cannot be conclusively ruled out.

Physicists call this other theory MOND, for modified Newtonian dynamics. It is not a very popular theory, however, and is almost always ignored, even though it appears to work as well as dark matter to explain the motion of stars in galaxies. Instead, most scientists favor dark matter.

For this press release to mention it as suggests the new data favors it over dark matter, which would make this a significant discovery.

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Dark matter is even more of a mystery that expected

4:36 pm

The uncertainty of science: Using the Hubble and Chandra space telescopes astronomers have discovered that dark matter is not only invisible to direct observation, it is invisible to itself!

In this new research, Harvey and his team realized just how invisible this stuff is, even to itself. As two galactic clusters collide, the stars, gas and dark matter interact in different ways. The clouds of gas suffer drag, slow down and often stop, whereas the stars zip past one another, unless they collide — which is rare. On studying what happens to dark matter during these collisions, the researchers realized that, like stars, the colliding clouds of dark matter have little effect on one another.

Thought to be spread evenly throughout each cluster, it seems logical to assume that the clouds of dark matter would have a strong interaction — much like the colliding clouds of gas as the colliding dark matter particles should come into very close proximity. But rather than creating drag, the dark matter clouds slide through one another seamlessly.

I guarantee that this result is not definitive. The data here is on the very edge of reality, built on too many assumptions. We know that something undetected as yet is influencing the motions of galaxies, but what exactly it is remains completely unknown. These results only make the mystery more mysterious.

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Astronomers find an invisible dwarf galaxy

10:05 am

Using dark matter data that suggested the existence of a faint dwarf galaxy 300,000 light years away on the other side of the Milky Way, astronomers have pinpointed its location by finding a tiny cluster of bright Cepheid variable stars, also located at that distance.

“These young stars are likely the signature of this predicted galaxy,” said Chakrabarti, assistant professor in RIT’s School of Physics and Astronomy. “They can’t be part of our galaxy because the disk of the Milky Way terminates at 48,000 light years.” Invisible particles known as dark matter make up 23 percent of the mass of the universe. The mysterious matter represents a fundamental problem in astronomy because it is not understood, Chakrabarti said.

This result is intriguing because it not only found a previously unknown dwarf galaxy orbiting the Milky Way, it also provides further evidence that dark matter, whatever it is, does exist. The dark matter of this unseen dwarf galaxy showed its gravitational effects on Milky Way stars, and when the astronomers looked at the right spot suggested by those effects, they found distant stars that had to belong to the invisible dwarf galaxy, proving it was there. This is comparable to finding Neptune and Pluto by analyzing their gravitational effects and then predicting their location in the sky.

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New measurements cut dark matter in Milky Way by half

7:10 pm

The uncertainty of science: New more robust measurements by Australian astronomers has shown that the amount of dark matter in the Milky Way galaxy is about half of what previous measurements had estimated.

Without doubt something is causing the outer stars in galaxies to orbit their galaxies at much greater speeds than they should. The answer that astronomers have posited since the late 1950s is that there is additional unidentified mass, dubbed dark matter, lurking as a halo around each galaxy, pulling on those outer stars and making them move faster.

The problem remains that no one has as yet detected this unidentified dark matter. Moreover, there are enormous uncertainties in the measurements of the motions of stars. This result helps narrow those uncertainties.

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A new dark matter detector has failed to detect any dark matter after its first three months of operation.

1:09 pm

The uncertainty of science: A new dark matter detector has failed to detect any dark matter after its first three months of operation.

Buried about a mile underground in a repurposed South Dakota gold mine, the LUX experiment searches for signs of dark matter particles colliding with the atoms in a vat of liquid xenon. During its first three months of operation, the detector found no such signals whatsoever. “We looked hard for these dark matter particles and we didn’t see anything,” says physicist Rick Gaitskell of Brown University, co-spokesperson for the LUX experiment. The results, presented at a seminar today and submitted to Physical Review Letters for publication, rule out a number of possible masses and characteristics for the particles that make up dark matter. The null result also conflicts with earlier experiments that had reported possible signals of dark matter.

This experiment has not proven that dark matter does not exist. It merely has narrowed significantly the kinds of particles that dark matter could be made of. That the results also contradict evidence from other detectors, however, leaves this specific area of science particularly uncertain.

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