Astronomy

Is there evidence for galactic “seasons”?

Is there evidence for galactic “seasons”?


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The Solar Year has huge effects on our climate, and the signs of passing seasons are physically evident on Earth. I recently learned about the Galactic Year. To my understanding, our sun orbits the Milky Way galactic center about every 200-225 million years. Do we know if there are any "seasonal" changes due to our position in the galaxy? One season of the orbital period (50+ million years) feels like a long enough time to leave a mark, if any effect exists:

  • in the formation of solar system objects?
  • the bombardment of planets and moons with meteors?
  • the number, type, distribution, or trajectory of comets?
  • the shape or density of the Oort Cloud?
  • in Earth's geologic record?
  • (at a stretch) mass extinction events?

Obviously you can just say "gravity affects everything, of course the solar system is influenced to some degree by other objects." But I mean specifically, is there evidence for any cyclical pattern which might be related to our position in the galaxy?


Mass extinctions have been linked with the Solar System's oscillations up and down through the galactic plane (the Galactic Cycle). You could also take a look at this question.


3.3-Billion-Light-Year-Long Arc of Galaxies Discovered

An international team of astronomers from the United States and the United Kingdom has made the discovery of a giant, almost symmetrical arc of galaxies by looking at absorption lines in the spectra towards quasars from the Sloan Digital Sky Survey (SDSS).

The Giant Arc: the gray contours represent the Mg II absorbers, which indicate the distribution of galaxies and galaxy clusters the blue dots represent the background quasars the Giant Arc is centered on this figure spanning -600 to +400 Mpc on the x-axis. Image credit: Lopez et al.

The newly-discovered arc of galaxies is located more than 9.2 billion light-years away in the constellation of Boötes.

Named as the Giant Arc, it spans approximately 3.3 billion light-years in length and 330 million light-years in width.

The structure is twice the size of the striking Sloan Great Wall of galaxies and clusters that is seen in the nearby Universe.

Its discovery adds to an accumulating set of cautious challenges to the Cosmological Principle.

“The growing number of large-scale structures over the size limit of what is considered theoretically viable is becoming harder to ignore,” said Alexia Lopez, a Ph.D. student in the Jeremiah Horrocks Institute at the University of Central Lancashire.

“According to cosmologists, the current theoretical limit is calculated to be 1.2 billion light-years, which makes the Giant Arc almost three times larger.”

“Can the Standard Model of cosmology account for these huge structures in the Universe as just rare flukes, or is there more to it than that?”

Lopez and colleagues made the discovery by observing the intervening magnesium (Mg) II absorption systems backlit by quasars, which are remote super-luminous galaxies that emit extraordinary amounts of energy and light.

“A quasar acts like a giant lamp shining a spotlight through other galaxies, with the light eventually reaching us here on Earth,” Lopez said.

“We can use telescopes to measure the spectra of these quasars, which essentially tells us the journey that the quasar light has been through, and in particular where the light has been absorbed.”

“We can locate where the quasar light has passed through galaxies by a signature Mg II doublet feature, which is a distinctive pair of absorption lines in the spectra.”

“From this easily identified absorption ‘fingerprint,’ we can map low luminosity matter that would usually go unseen due to its faint light emitted in comparison to the quasars.”

“When viewed on such a large scale, we expect to see a statistically smooth distribution of matter across the Universe, based on the Cosmological Principle introduced by Einstein to make the maths easier, that the Universe is isotropic and homogeneous.”

“It means that the night sky, when viewed on a sufficiently large scale, should look the same, regardless of the observers’ locations or the directions in which they are looking.”

“The Giant Arc we are seeing certainly raises more questions than answers as it may expand the notion of ‘sufficiently large.’ The key question is, what do we consider to be ‘sufficiently large’?”

“We are seeing the Giant Arc now, but in reality, the data we’re looking at show the Universe as it was half its lifetime ago because the light has been en route, traveling towards, us for billions of years. It was so long ago that the Universe at the time was about 1.8 times smaller than it is now.”


Atheist gets her PhD in astronomy and astrophysics and finds evidence for God

Christian apologist Terrell Clemmons tweeted this testimony by Sarah Salviander, a research scientist in astronomy and astrophysics at the prestigious University of Texas at Austin.

I was born in the U.S., but grew up in Canada. My parents were socialists and political activists who thought British Columbia would be a better place for us to live, since it had the only socialist government in North America at the time. My parents were also atheists, though they eschewed that label in favor of “agnostic.” They were kind, loving, and moral, but religion played no part in my life. Instead, my childhood revolved around education, particularly science. I remember how important it was to my parents that my brother and I did well in school.

I just want to point out that I hope that all you Christian parents are taking seriously the obligation to make your kids do well in school, because even if they start out as atheists when they are young, they can still find their way back to God through study, as Sarah did.

She had a bad start, that’s for sure:

I grew up in the 1970s and 1980s, a time when science fiction was enjoying a renaissance, thanks largely to the popularity of Star Wars. I remember how fascinated I was by the original Star Wars trilogy. It had almost nothing to do with science—it’s more properly characterized as space opera—but it got me thinking about space in a big way. I also loved the original Star Trek, which was more science fiction. The stoic and logical character of Mr. Spock was particularly appealing to me. Popular science was also experiencing a renaissance at that time, which had a lot to do with Carl Sagan’s television show, Cosmos, which I adored. The combination of these influences led to such an intense wonder about outer space and the universe, that by the time I was nine years old I knew I would be a space scientist someday.

Canada was already post-Christian by the 1970s, so I grew up with no religion. In retrospect, it’s amazing that for the first 25 years of my life, I met only three people who identified as Christian. My view of Christianity was negative from an early age, and by the time I was in my twenties, I was actively hostile toward Christianity. Looking back, I realized a lot of this was the unconscious absorption of the general hostility toward Christianity that is common in places like Canada and Europe my hostility certainly wasn’t based on actually knowing anything about Christianity. I had come to believe that Christianity made people weak and foolish I thought it was philosophically trivial. I was ignorant not only of the Bible, but also of the deep philosophy of Christianity and the scientific discoveries that shed new light on the origins of the universe and life on Earth.

She documents a phase of following Ayn Rand and embracing “Objectivism”, but eventually she rejects it for failing to answer the big questions of life.

I began to focus all of my energy on my studies, and became very dedicated to my physics and math courses. I joined campus clubs, started to make friends, and, for the first time in my life, I was meeting Christians. They weren’t like Objectivists—they were joyous and content. And, they were smart, too. I was astonished to find that my physics professors, whom I admired, were Christian. Their personal example began to have an influence on me, and I found myself growing less hostile to Christianity.

This is why I think it is so important for Christian parents to raise their children to get advanced degrees… either to become professors themselves, or to finance others (e.g. – our own children) to do advanced degrees. It is so important for university students to see Christian professors on campus. And failing that, it’s important that we bring Christian speakers in to debate non-Christian speakers on the important issues. This will not happen unless we recognize how important it is, and then make a plan to achieve it.

I had joined a group in the Center for Astrophysics and Space Sciences (CASS) that was researching evidence for the big bang. The cosmic background radiation—the leftover radiation from the big bang—provides the strongest evidence for the theory, but cosmologists need other, independent lines of evidence to confirm it. My group was studying deuterium abundances in the early universe. Deuterium is an isotope of hydrogen, and its abundance in the early universe is sensitive to the amount of ordinary mass contained in the entire universe. Believe it or not, this one measurement tells us whether the big bang model is correct.

If anyone is interested in how this works, I’ll describe it, but for now I’ll spare you the gruesome details. Suffice it to say that an amazing convergence of physical properties is necessary in order to study deuterium abundances in the early universe, and yet this convergence is exactly what we get. I remember being astounded by this, blown away, completely and utterly awed. It seemed incredible to me that there was a way to find the answer to this question we had about the universe. In fact, it seems that every question we have about the universe is answerable. There’s no reason it has to be this way, and it made me think of Einstein’s observation that the most incomprehensible thing about the world is that it’s comprehensible. I started to sense an underlying order to the universe. Without knowing it, I was awakening to what Psalm 19 tells us so clearly, “The heavens declare the glory of God the skies proclaim the work of his hands.”

That summer, I’d picked up a copy of The Count of Monte Cristo by Alexandre Dumas and was reading it in my off hours. Previous to this, I’d only known it as an exciting story of revenge, since that’s what the countless movie and TV adaptations always focused on. But it’s more than just a revenge story, it’s a philosophically deep examination of forgiveness and God’s role in giving justice. I was surprised by this, and was starting to realize that the concept of God and religion was not as philosophically trivial as I had thought.

All of this culminated one day, as I was walking across that beautiful La Jolla campus. I stopped in my tracks when it hit me—I believed in God! I was so happy it was like a weight had been lifted from my heart. I realized that most of the pain I’d experienced in my life was of my own making, but that God had used it to make me wiser and more compassionate. It was a great relief to discover that there was a reason for suffering, and that it was because God was loving and just. God could not be perfectly just unless I—just like everyone else—was made to suffer for the bad things I’d done.

The Count of Monte Cristo is one of my favorite, favorite books as well, and had the same impact on me as it did on her.

OK, that’s enough for this post. Go read the rest, and please share it.

I spoke to her recently and she told me that she is working on several projects that are designed to get people more familiar with science and Bible issues. This woman is an expert Christian apologist and her life will have an influence. Are you going to be like her? Will you mentor others to be like her? Will you marry someone like her? Will you raise children who are like her? I think we should all have a plan to study the areas that are important and have an influence for God with what we learn.


Decades of hunting detects footprint of cosmic ray superaccelerators in our galaxy

Ultrahigh-energy diffuse gamma rays (yellow points) are distributed along the Milky Way galaxy. The background color contour shows the atomic hydrogen distribution in the galactic coordinates. The gray shaded area indicates what is outside of the field of view. Credit: HEASARC / LAMBDA / NASA / GFSC

An enormous telescope complex in Tibet has captured the first evidence of ultrahigh-energy gamma rays spread across the Milky Way. The findings offer proof that undetected starry accelerators churn out cosmic rays, which have floated around our galaxy for millions of years. The research is to be published in the journal Physical Review Letters on Monday, April 5.

"We found 23 ultrahigh-energy cosmic gamma rays along the Milky Way," said Kazumasa Kawata, a coauthor from the University of Tokyo. "The highest energy among them amounts to a world record: nearly one petaelectron volt."

That's three orders of magnitude greater than any known cosmic-ray-induced gamma ray—or any particle humans have accelerated in state-of-the-art laboratories on Earth.

Since 1990, dozens of researchers from China and Japan have hunted for the elusive high-energy cosmic gamma rays. The Tibet ASγ Collaboration made its discovery using nearly 70,000 square meters of ground arrays and underground muon detectors on the Tibetan Plateau, sitting more than 14,000 feet above sea level.

"Scientists believe high energy gamma rays can be produced by the nuclear interaction between high energy cosmic rays escaping from the most powerful galactic sources and interstellar gas in the Milky Way galaxy," said Huang Jing, a coauthor from Institute of High Energy Physics, Chinese Academy of Sciences.

Chen Ding of the National Astronomical Observatories, Chinese Academy of Sciences, another coauthor, added, "The detection of diffuse gamma rays above 100 teraelectron volts is a key to understanding the origin of very-high-energy cosmic rays, which has been a mystery since their discovery in 1912."

Balloon experiments first identified cosmic rays, revealing they were a key source of radiation on Earth. Cosmic rays are highly energetic particles, mostly protons, that travel across space. Millions of these particles pass through your body every day. (They are believed harmless.)

But where do cosmic rays come from?

"We live together with cosmic-ray muons, though we are usually not sensitive to them," said Kawata. "Isn't it a fantasy to think of where and how these cosmic rays are produced and accelerated, traveling all the way to Earth?"

A popular theory argues that accelerators known as "PeVatrons" spew cosmic rays at energies up to one petaelectron volt (PeV). Possible PeVatrons include supernova explosions, star-forming regions, and the supermassive black hole at the center of our galaxy.

So far, no one has detected any such accelerators. If PeVatrons exist, their cosmic rays should leave trails of glowing gamma rays strewn across the galaxy. The new study reports the first evidence of this highly-energetic haze.

"These gamma rays did not point back to the most powerful known high-energy gamma-ray sources, but spread out along the Milky Way," said Masato Takita, a coauthor and colleague of Kawata. "Our discovery confirms evidence of the existence of PeVatrons."

The Tibet air shower array located 4300 m above sea level in Tibet, China. Credit: Institute of High Energy Physics

The researchers now want to determine if the probable PeVatrons are active or dead.

"From dead PeVatrons, which are extinct like dinosaurs, we can only see the footprint—the cosmic rays they produced over a few million years, spread over the galactic disk," said Takita.

"But if we can locate real, active PeVatrons, we can study many more questions," he said. "What type of star emits our sub-PeV gamma rays and related cosmic rays? How can a star accelerate cosmic rays up to PeV energies? How do the rays propagate inside our galactic disk?"

Other future directions include looking for PeVatron footprints in the southern hemisphere and confirming the gamma-ray results using neutrino detectors in Antarctica and beyond.

The research could also aid in the quest for dark matter. Underground detectors allowed the researchers to cut away cosmic-ray background noise, revealing the kind of pure, diffuse gamma rays predicted to emanate from dark matter.

"We can reduce the cosmic ray background by a factor of one million. Then we see a high-purity gamma ray sky," said Takita.

The experimental achievement moves physicists significantly closer to discovering where cosmic rays are born.

"This pioneering work opens a new window for the exploration of the extreme universe," said Huang. "The observational evidence marks an important milestone toward revealing cosmic ray origins, which have puzzled mankind for more than one century."


Recycling galaxies caught in the act

When astronomers add up all the gas and dust contained in ordinary galaxies (like our own Milky Way), they find a discrepancy: there is not nearly enough matter for stars to form at the observed rates for long. As a (partial) solution, a matter cycle on gigantic scales has been proposed. In our local galactic neighbourhood, traces of this mechanism had already been found. Now, a study led by Kate Rubin of the Max Planck Institute for Astronomy has found the first direct evidence of such gas flowing back into distant galaxies that are actively forming new stars, validating a key part of "galactic recycling".

Star formation regions, such as the Orion nebula, create some of the most beautiful astronomical sights. It is estimated that in our home galaxy, the Milky Way, on average one solar mass's worth of matter per year is turned into stars. Yet a survey of the available raw material, clouds of gas and dust, shows that, using only its own resources, our galaxy could not keep up this rate of star formation for longer than a couple of billion years. Is our home galaxy currently undergoing a rather special, short-lived era of star formation? Both stellar age determinations and comparison with other spiral galaxies show that not to be the case. One solar mass per year is a typical star formation rate, and the problem of insufficient raw matter appears to be universal as well.

Evidently, additional matter finds its way into galaxies. One possibility is an inflow from huge low-density gas reservoirs filling the intergalactic voids there is, however, very little evidence that this is happening. Another possibility, closer to home, involves a gigantic cosmic matter cycle. Gas is observed to flow away from many galaxies, and may be pushed by several different mechanisms, including violent supernova explosions (which are how massive stars end their lives), and the sheer pressure exerted by light emitted by bright stars on gas in their cosmic neighbourhood.

As this gas drifts away, it is pulled back by the galaxy's gravity, and could re-enter the same galaxy in time scales of one to several billion years. This process might solve the mystery: the gas we find inside galaxies may only be about half of the raw material that ends up as fuel for star formation. Large amounts of gas are caught in transit, but will re-enter the galaxy in due time. Add up the galaxy's gas and the gas currently undergoing cosmic recycling, and there is a sufficient amount of raw matter to account for the observed rates of star formation.

There was, however, uncertainty about the viability of this proposal for cosmic recycling. Would such gas indeed fall back, or would it more likely reach the galaxy's escape velocity, flying ever further out into space, never to return? For local galaxies out to a few hundred million light-years in distance, there had indeed been studies showing evidence for inflows of previously-expelled gas. But what about more distant galaxies, where outflows are known to be much more powerful &ndash would gravity still be sufficient to pull the gas back? If no, astronomers might have been forced to radically rethink their models for how star formation is fueled on galactic scales.

Now, a team of astronomers led by Kate Rubin (MPIA) has used the Keck I telescope on Mauna Kea, Hawai'i, to examine gas associated with a hundred galaxies at distances between 5 and 8 billion light-years (z

0.5 &ndash 1), finding, in six of those galaxies, the first direct evidence that gas adrift in intergalactic space does indeed flow back into star-forming galaxies. As the observed rate of inflow might well depend on a galaxy's orientation relative to the observer, and as Rubin and her team can only measure average gas motion, the real proportion of galaxies with this kind of inflow is likely to be higher than the 6% directly suggested by their data, and could be as high as 40%. This is a key piece of the puzzle and important evidence that cosmic recycling ("galactic fountains") could indeed solve the mystery of the missing raw matter.


Virgin Galactic announces another human-tended science flight

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Virgin Galactic announced a new contract Thursday for human-tended research aboard its suborbital spacecraft, VSS Unity. The company said that Kellie Gerardi, a researcher and science communicator, would conduct two experiments during an upcoming flight that could happen as early as 2022.

The announcement is notable because it suggests there may be a viable business for Virgin in this kind of microgravity research and because the news provides further evidence that "regular" people may one day be able to go into space as more companies start flying there.

Further Reading

Gerardi has been involved in the commercial space industry, including working for the Commercial Space Federation, for about a decade. She obtained this flight by partnering with the International Institute for Astronautical Sciences to secure research contracts with the National Research Council of Canada and the Canadian Space Agency.

During her flight, she will wear an "Astroskin" that will monitor her vital signs. With about three to four minutes of weightlessness to work with, Gerardi will also conduct a free-floating fluid configuration experiment.

Virgin Galactic did not say how much this seat—likely one of four on a future dedicated research mission—cost. However, Gerardi said in an interview that the flight was within the realm of affordability. "There are so many people on Twitter who say they are future astronauts, and I think this proves that that can be true," she said. "Now, that aspiration actually has this avenue to become true."

Gerardi said she had full confidence in Virgin Galactic getting its VSS Unity spacecraft ready for commercial service and in the safety of the company's launch system, which uses a carrier aircraft and sleek spacecraft to rocket above 80 km.

Virgin Galactic recently launched its first successful test flight from New Mexico, and it intends to complete its test campaign this calendar year, said Sirisha Bandla, vice president of government affairs for the company.

Next up for Virgin Galactic is a test flight with employees in the passenger cabin. This test will be followed by a flight carrying the company's founder, Sir Richard Branson. Finally, the company will launch a flight for researchers and astronauts-in-training in the Italian Air Force. "We're going to finish our test flight program this year, and we'll make scheduling decisions after this program has been completed," Bandla said.

Among those future missions are the dedicated research flight Gerardi will be a part of, a NASA-funded science mission that will include planetary scientist Alan Stern, and flights for about 600 people who have already bought tickets to become private astronauts. One big question facing Virgin Galactic is how often it will fly VSS Unity and any additional spacecraft it is building. So far, Virgin's flight rate has been low, but it certainly seems like there is ample demand for the company's services.


Is there evidence for galactic &ldquoseasons&rdquo? - Astronomy

New evidence for a long thin Galactic bar (in contradistinction to the bulge), as well as for the existence of the ring and the truncation of the inner disc, are sought in the DENIS survey. First, we examine DENIS and Two Micron Galactic Survey star counts for the characteristic signatures of an in-plane bar and ring. The star counts in the plane for 30 o >l>-30 o are shown to be highly asymmetric with considerably more sources at positive than at negative longitudes. At |b|

1.5 o , however, the counts are nearly symmetric. Therefore, the asymmetry is not due to the disc, which is shown to have an inner truncation, or to the bulge, so there has to be another major component in the inner Galaxy that is causing the asymmetries. This component provides up to 50% of the detected sources in the plane between the bulge and l=27 o or l=-14 o . This component is shown to be consistent with an in-plane bar with a position angle of 40 o and half-length of 3.9 kpc. However, there is also a major peak in the counts at l=-22 o , which coincides with the tangential point of the so-called 3 kpc arm. This is shown to be most probably a ring or a pseudo-ring. The extinction in the plane is also shown to be asymmetric with more extinction at negative than at positive longitudes. For l<8 o the extinction is shown to be slightly tilted with respect to b=0 o in the same manner as the HI disc. We conclude that the Galaxy is a fairly typical ringed barred spiral galaxy.


Factoring in gravitomagnetism could do away with dark matter

Observations of galactic rotation curves give one of the strongest lines of evidence pointing towards the existence of dark matter, a non-baryonic form of matter that makes up an estimated 85% of the matter in the observable Universe. Current assessments of galactic rotation curves are based upon a framework of Newtonian accounts of gravity, a new paper published in EPJ C, by Gerson Otto Ludwig, National Institute for Space Research, Brazil, suggests that if this is substituted with a general relativity-based model, the need to recourse to dark matter is relieved, replaced by the effects of gravitomagnetism.

The main role of dark matter, Ludwig points out in the paper, has historically been to resolve the disparity between astrophysical observations and current theories of gravity. Put simply, if baryonic matter -- the form of matter we see around us every day which is made up of protons, neutrons and electrons -- is the only form of matter, then there shouldn't be enough gravitational force to prevent galaxies from flying apart.

By disregarding general relativistic corrections to Newtonian gravity arising from mass currents, and by neglecting these mass currents, Ludwig asserts these models also miss significant modifications to rotational curves -- the orbital speeds of visible stars and gas plotted against their radial distance from their galaxy's centre. This is because of an effect in general relativity not present in Newton's theory of gravity -- frame-dragging or the Lense Thirring effect. This effect arises when a massive rotating object like a star or black hole 'drags' the very fabric of spacetime along with it, in turn giving rise to a gravitomagnetic field.

In this paper, Ludwig presents a new model for the rotational curves of galaxies which is in agreement with previous efforts involving general relativity. The researcher demonstrates that even though the effects of gravitomagnetic fields are weak, factoring them into models alleviates the difference between theories of gravity and observed rotational curves -- eliminating the need for dark matter. The theory still needs some development before it is widely accepted, with the author particularly pointing out that the time evolution of galaxies modelled with this framework is a complex problem that will require much deeper analysis.

Ludwig concludes by suggesting that all calculations performed with thin galactic disk models performed up until this point may have to be recalculated, and the very concept of dark matter itself, questioned.


Is there evidence for galactic &ldquoseasons&rdquo? - Astronomy

Context. Although there have been numerous studies of chemical abundances in the Galactic bulge, the central two degrees have been relatively unexplored due to the heavy and variable interstellar extinction, extreme stellar crowding, and the presence of complex foreground disk stellar populations.
Aims: In this paper we discuss the metallicity distribution function, vertical and radial gradients, and chemical abundances of α-elements in the inner two degrees of the Milky Way, as obtained by recent IR spectroscopic surveys.
Methods: We used a compilation of recent measurements of metallicities and α-element abundances derived from medium-high resolution spectroscopy. We compare these metallicities with low-resolution studies.
Results: Defining "metal-rich" as stars with [Fe/H] > 0, and "metal-poor" as stars with [Fe/H] < 0, we find compelling evidence for a higher fraction (˜80%) of metal-rich stars in the Galactic Center (GC) compared to the values (50-60%) measured in the low latitude fields within the innermost 600 pc. The high fraction of metal-rich stars in the GC region implies a very high mean metallicity of +0.2 dex, while in the inner 600 pc of the bulge the mean metallicity is rather homogenous around the solar value. A vertical metallicity gradient of -0.27 dex kpc -1 in the inner 600 pc is only measured if the GC is included, otherwise the distribution is about flat and consistent with no vertical gradient.
Conclusions: In addition to its high stellar density, the Galactic center/nuclear star cluster is also extreme in hosting high stellar abundances, compared to the surrounding inner bulge stellar populations this has implications for formation scenarios and strengthens the case for the nuclear star cluster being a distinct stellar system.


The Largest Rotating Objects in the Universe: Galactic Filaments Hundreds of Millions of Light-Years Long

We’ve known for a while about the large-scale structure of the Universe. Galaxies reside in filaments hundreds of millions of light-years long, on a backbone of dark matter. And, where those filaments meet, there are galaxy clusters. Between them are massive voids, where galaxies are sparse. Now a team of astronomers in Germany and their colleagues in China and Estonia have made an intriguing discovery.

These massive filaments are rotating, and this kind of rotation on such a massive scale has never been seen before.

Obviously, there’s no way to take an actual picture of the Universe’s large-scale structure. But there are some almost-famous images that come from the Millennium Simulation Program. The Millennium Simulation was a super-computer simulation of a cubic portion of the Universe over 2 billion light-years on each side. The image contains about 20 million individual galaxies organized in filaments and clumps, and it was our first real glimpse of the Universe’s LSS.

It’s remarkable to look at that image now and imagine those filaments rotating.

Image of the large-scale structure of the Universe, showing filaments and voids within the cosmic structure. Credit: Millennium Simulation Project

The team of astronomers behind this discovery worked with data from the Sloan Digital Sky Survey (SDSS.) The SDSS created a very detailed 3D map of the Universe, so SDSS data was critical to the team’s discovery.

“By mapping the motion of galaxies in these huge cosmic superhighways using the Sloan Digital Sky survey – a survey of hundreds of thousands of galaxies – we found a remarkable property of these filaments: they spin.” says Peng Wang, first author of the now published study and astronomer at the AIP (Institute for Astrophysics Potsdam).

Each of the galaxies in the filaments amounts to no more than a speck of dust on the grand scale, and they’re not only rotating but moving along the tendrils as if they’re pipelines.

“They move on helixes or corkscrew like orbits, circling around the middle of the filament while travelling along it.”

Noam Libeskind, Study Co-Author, AIP.

“Despite being thin cylinders – similar in dimension to pencils – hundreds of millions of light years long, but just a few million light years in diameter, these fantastic tendrils of matter rotate,” added Noam Libeskind, initiator of the project at the AIP. “On these scales the galaxies within them are themselves just specs of dust. They move on helixes or corkscrew like orbits, circling around the middle of the filament while travelling along it. Such a spin has never been seen before on such enormous scales, and the implication is that there must be an as yet unknown physical mechanism responsible for torquing these objects.”

The fact that these filaments spin is difficult to visualize, and fascinating once you succeed. But the discovery is about more than our own fascination. These are the largest objects we’ve ever seen spinning, and that means that angular momentum can take place on a massive scale. One of the mysteries in cosmology is how that angular momentum is generated on such a massive scale since there was no primordial rotation in the early Universe.

The discovery rests on observations of individual galaxies in the filaments and their Doppler shift. In this study, red-shift is a proxy for rotation, Red-shifted galaxies are receding, and blue-shifted galaxies are approaching.

This figure from the paper shows the filament rotation speed as a function of the distance between galaxies and the filament spine. The distance of galaxies from the filament spine in the receding region is displayed in red and ascribed positive values, while the distance of galaxies in the approaching region is marked in blue and ascribed negative values. Error bars represent the standard deviation about the mean. Image Credit: Wang et al 2021.

In the current working model of the Universe’s structural formation, overdensities grow via gravitational instability. Material from underdense regions flows into regions of overdensity. But that flow of material has no rotation or curl to it. That’s why cosmologists say that there was no rotation in the early Universe. And here’s where this discovery gets more interesting.

The rotation evident in these filaments of galaxies must be generated as the structures form. And these filaments and the rest of the cosmic web are connected to the formation and evolution of galaxies themselves. They also have a powerful effect on the spin of individual galaxies and can regulate how a galaxy and its dark matter halo rotate. There’s an unknown piece in all of this: scientists don’t yet know how our current understanding can predict that the filaments themselves spin.

“Such a spin has never been seen before on such enormous scales, and the implication is that there must be an as yet unknown physical mechanism responsible for torquing these objects.”

Noam Libeskind, Study Co-Author, AIP.

Before this study, other scientists have theorized that these filaments spin. For example, Dr. Mark Neyrinck, a Fellow at the Department of Theoretical Physics at the University of the Basque Country, Spain, is known for theorizing on this. He’s also known for developing the “origami” description of cosmic structure formation. In a 2016 article in The Paper he said, “…if galaxies rotate (and they do), so must filaments sticking out of them. Furthermore, galaxies joined by a filament should rotate mostly together, like objects attached to the ends of a rod. In fact, this is consistent with astronomical observations nearby galaxies tend to be spinning in the same direction.”

Dr. Neyrinck’s work was an important starting point for the team behind this paper.

“Motivated by the suggestion from the theorist Dr. Mark Neyrinck that filaments may spin, we examined the observed galaxy distribution, looking for filament rotation,” says co-author Noam Libeskind. “It’s fantastic to see this confirmation that intergalactic filaments rotate in the real Universe, as well as in computer simulation.”

The team used a sophisticated mapping method that divided the observed galaxy distribution into segments. Then each of the filaments was approximated by a cylinder. The galaxies in the filament were then divided into two regions on either side of the filament’s spine. Then they carefully measured the mean redshift difference between the two regions. “The mean redshift difference is a proxy for the velocity difference (the Doppler shift) between galaxies on the receding and approaching side of the filament tube,” the authors write. That’s how they measured the filaments’ rotation.

In their paper, the team writes that what they found cannot be random. “What is measured and presented here is the redshift difference between two regions on either side of a hypothesized spin axis that is coincident with the filament spine. The full distribution of this quantity is inconsistent with random regardless of the viewing angle formed with the line of sight…”

However, the researchers caution, their results don’t imply that every filament in the Universe is rotating. That would be an over-reach. “This work does not predict that every single filament in the Universe is rotating,” they write, “rather that there are subsamples—intimately connected to the viewing angle end point mass—that show a clear signal consistent with rotation. This is the main finding of this work.”

“Taken together,” the team writes in their conclusion, “the current study and Xia et al. (2021) demonstrate that angular momentum can be generated on unprecedented scales, opening the door to a new understanding of cosmic spin.”

Lead author of this work is Peng Wang, an astronomer at the Institute for Astrophysics Potsdam (AIP). The title of the paper is “Possible observational evidence for cosmic filament spin.” It’s published in Nature Astronomy.


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