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Universe consisting of fuzzy dark matter galaxies visualized by researchers

Universe consisting of fuzzy dark matter galaxies visualized by researchers

Dark matter is considered to be the initial ingredient for the first galaxies in the universe. After the Big Bang, dark matter particles would have combined in gravitational “halos”, pulling gas into cores which on condensation resulted in the first galaxies. Scientists, however, know very little about these particles since they have not been detected directly. 

Researchers at Princeton, MIT and Cambridge discovered that the appearance of the very first galaxies would differ a lot depending on the type of dark matter. The team has successfully simulated the appearance of early galaxies if the dark matter were “fuzzy” instead of cold or warm. The findings appear in the Physical Review Letters journal. 

Dark matter is cold in most scenarios composed of slow-moving particles and does not interact with normal matter besides gravitational forces. The warm version is lighter and faster than cold dark matter. On the other hand, fuzzy dark matter consists of ultralight particles, each with the mass of 1 octillionth of an electron mass, cold dark matter particle is 105 times heavier than an electron. 

It was found in simulations that when dark matter is cold, the first galaxies would have been formed in spherical halos. But with the dark matter being warm or fuzzy, the early galaxies would have formed in tail-like filaments. Researchers can look back into the earlier universes with telescopes coming online and deduce from the galaxy formation patterns if the dark matter is fuzzy instead of being warm or cold. 

Mark Vogelsberger, a physics professor at Kavli Institute for Astrophysics and Space Research, MIT said the type of dark matter present today may be known from the earlier universes. If the filament pattern is visible, then it is a fuzzy dark matter. 

Till now the hypothesis of dark matter being cold has been successful in the description of the grand scale of the observable universe. Hence, galaxy formation is modeled on the assumption that dark matter is cold. However, Vogelsberger pointed out some of the discrepancies between predictions and observations of cold dark matter. This is highlighted in the case of smaller galaxies where the theoretical models do not agree with the actual distribution of dark matter. This is where alternate theories of warm and fuzzy dark matter have been proposed.

Anastasia Fialkov of Cambridge University, co-author of the paper said that the motivation of fuzzy dark matter is from fundamental physics such as string theory. The final validation lies in the cosmic structures. 

Fuzzy dark matter consists of particles so light that they exhibit quantum, wave behavior instead of individual particles. Philip Mocz of Princeton University, the lead author of the paper said that the first galaxies would differ from the galaxies in the late universe providing hints about the nature of the dark matter. 

A cubic portion of the early universe measuring 3 million light-years was simulated by the researchers to observe a fuzzy and cold early universe. It was tested through different periods of time to understand the formation of galaxies if the dark matter were either cold or warm or fuzzy. 

Simulations of how galaxies form in cold, warm and fuzzy (left to right) dark matter scenarios. Credit: Universities of Princeton, Sussex, Cambridge

Simulations of how galaxies form in cold, warm and fuzzy (left to right) dark matter scenarios. (Credit: Universities of Princeton, Sussex, Cambridge

The simulation was started based on the dark matter distribution known to researchers based on cosmic microwave radiation, “relic radiation” detected 400,000 years after Big Bang took place.  Vogelsberger said that there is no constant density for dark matter. For warm and cold scenarios, existing algorithms were used for simulation. However, for fuzzy dark matter, a new method was used. 

The simulation of cold dark matter was modified for solving two extra equations in order to simulate the formation of galaxies under the fuzzy dark matter. Schrodinger’s equation describes the behavior of quantum particle as a wave and Poisson’s equation tells how the wave creates a density field, dark matter distribution leading to gravity which is the pulling force for the formation of galaxies. This was added to the model about gas behavior in the universe and how it condenses to galaxies responding to gravity. 

In each of the scenarios, the formation of galaxies took place where the concentration of dark matter collapsed from gravitation was high. The pattern differed on it being cold or warm or fuzzy. 

In cold dark matter, the formation of galaxies took place in spherical halos and subhalos. Warm dark matter created galaxies in filaments resembling tails with the absence of subhalos. The fuzzy dark matter led to formation along filaments succeeded by effects of quantum wave as a result of which galaxies took shape of striated filaments. This is due to interference, overlapping of waves which resulted in an alternating pattern of dark matter concentrations, over-dense and under dense. 

Vogelsberger said that there would be high gravity in over-dense regions resulting in the formation of galaxies in such areas. This is replicated throughout the early universe. Researchers are developing detailed predictions of the appearances of early galaxies in a universe of fuzzy dark matter. The main target is to give a map to telescopes such as James Webb Space Telescope that can run back in time to find the earliest galaxies. If filamentary galaxies are observed, then it is the indication that dark matter is fuzzy. 

Journal Reference: Physical Review Letters

Researchers discover galaxies undergoing dramatic transitions

Researchers discover galaxies undergoing dramatic transitions

We tend to think of the galactic system occurrences as those that occur uncommonly slowly compared to our short human life. It’s not always the case, though.

Six galaxies have just experienced an enormous transformation in just a matter of months in a moving way. They have moved from relatively peaceful galaxies to active quasars-the brightest of all galaxies, blasting vast quantities of radiation into the Universe.

This is not only incredibly amazing, but these occurrences could assist resolve a long-standing discussion about what generates the light in a specific galaxy type. In reality, they may show a sort of galactic nucleus activity that was earlier unknown.

The six galaxies began as galaxies of the low-ionization nuclear emission-line region (LINER); in terms of brightness, it’s kind of like being a galactic particle.

A third of all known galaxies are brighter than those with dormant supermassive black holes in the center, but not as bright as active galaxies (known as Seyfert galaxies), whose supermassive black holes are cosmic.

Now, the most brilliant of such active galaxies are quasar galaxies; indeed, they are among the most colorful objects in the Universe. The light and radio emissions we see are triggered by black hole material, called an accretion disk.

That disk includes dust and gas swirling at tremendous speeds like water running down a drain, creating enormous friction as it is pulled by the black hole’s substantial gravitational force in the center. This friction generates intense heat and light; large spray tanks emit radio waves from the polar regions of the black hole.

But when a team of astronomers led by the University of Maryland astronomer Sara Frederick walked through the first nine months of automated sky survey information from the Zwicky Transient Facility, they discovered six LINER galaxies doing something strange.

changes in galaxies

Image credit: Pixabay

“We first believed we observed a tidal disruption event for one of the six objects, which occurs when a star goes too close to a supermassive black hole and gets shredded,” Frederick said.

Frederick and her colleagues want to understand how a previously quiet galaxy with a calm nucleus can suddenly transition to a bright beacon of galactic radiation. To learn more, they performed follow-up observations on the objects with the Discovery Channel Telescope, which is operated by the Lowell Observatory in partnership with UMD, Boston University, the University of Toledo and Northern Arizona University. These observations helped to clarify aspects of the transitions, including how the rapidly transforming galactic nuclei interacted with their host galaxies.


UGC 2369

Hubble Space Telescope captures merging galaxies in a dazzling dance

The Hubble Space Telescope has managed to capture two galaxies making contact for the first time. The pair known as UGC 2369 will merge to become a single galaxy in the future. For now, the two galaxies are in close proximity thanks to gravitational forces.

The galaxies have been observed to be swirling around each other due to gravity. As per the European Space Agency, they are currently connected by a bridge of dust, gas and stars akin to a situation of holding hands. Right now UGC 2369 is 424 million light-years away from us.

Galaxies primarily belong to galactic groups or clusters making them “extroverts”. As a result of which it is quite common for two galaxies to have an interaction between them. Even though there is no collision between galaxies, the shape of the galaxy can be distorted by the strong gravitational pull. This makes galactic observations fascinating to view. In phenomena where no contact is made such as galaxy fly-bys, there can be a creation of permanent warps, tidal tails extending from the center of the galaxy resulting in strange shapes. It also induces bursts of star formation.

However, the galactic mergers are quite destructive in nature. It amplifies when the size of the two galaxies are almost the same. The frequency of these huge events is lower than the normal mergers. It is considered that the Milky Way might face a merger in the future. Currently, two dwarf galaxies in the vicinity of the Milky Way, Canis Major and Sagittarius are being destroyed and absorbed in the Milky Way.

Astronomers are pretty sure that Andromeda and the Milky Way will collide at some point in the future, even though it might be after several billion years and result in one galaxy. The details of how it is supposed to occur are still up for debates. This new galaxy is termed as “Milkomeda” by ESA.

Hubble Space Telescope has captured several galaxies in its 30 years of operations. It has also captured galaxies dating as far as the time just after the Big Bang occurred. It released the Ultra Deep Field in 2016. The merger of UGC 2369 is at an advanced stage. By training the Telescope on this merger, we can understand the fate of our own galaxy in the future.

Chris Martin KCWI Cold flow

Spiraling Filaments Feed Young Galaxies

Galaxies grow by accumulating gas from their surroundings and converting it to stars, but the details of this process have remained murky. New observations, made using the Keck Cosmic Web Imager (KCWI) at the W. M. Keck Observatory in Hawaii, now provide the clearest, most direct evidence yet that filaments of cool gas spiral into young galaxies, supplying the fuel for stars.

“For the first time, we are seeing filaments of gas directly spiral into a galaxy. It’s like a pipeline going straight in,” says Christopher Martin, a professor of physics at Caltech and lead author of a new paper appearing in the July 1 issue of the journal Nature Astronomy. “This pipeline of gas sustains star formation, explaining how galaxies can make stars on very fast timescales.”

For years, astronomers have debated exactly how gas makes its way to the center of galaxies. Does it heat up dramatically as it collides with the surrounding hot gas? Or does it stream in along thin dense filaments, remaining relatively cold? “Modern theory suggests that the answer is probably a mix of both, but proving the existence of these cold streams of gas had remained a major challenge until now,” says co-author Donal O’Sullivan (MS ’15), a PhD student in Martin’s group who built part of KCWI.

KCWI, designed and built at Caltech, is a state-of-the-art spectral imaging camera. Called an integral-field unit spectrograph, it allows astronomers to take images such that every pixel in the image contains a dispersed spectrum of light. Installed at Keck in early 2017, KCWI is the successor to the Cosmic Web Imager (CWI), an instrument that has operated at Palomar Observatory near San Diego since 2010. KCWI has eight times the spatial resolution and 10 times the sensitivity of CWI.

“The main driver for building KCWI was understanding and characterizing the cosmic web, but the instrument is very flexible, and scientists have used it, among other things, to study the nature of dark matter, to investigate black holes, and to refine our understanding of star formation,” says co-author Mateusz (Matt) Matuszewski (MS ’02, PhD ’12), a senior instrument scientist at Caltech.

The question of how galaxies and stars form out of a network of wispy filaments in space—what is known as the cosmic web—has fascinated Martin since he was a graduate student. To find answers, he led the teams that built both CWI and KCWI. In 2017, Martin and his team used KCWI to acquire data on two active galaxies known as quasars, named UM 287 and CSO 38, but it was not the quasars themselves they wanted to study. Nearby each of these two quasars is a growing galaxy within its own giant nebula, larger than the Milky Way and visible thanks to the strong illumination of the quasars. By looking at light emitted by hydrogen in the nebulas—specifically an atomic emission line called hydrogen Lyman-alpha—they were able to map the velocity of the gas. From previous observations at Palomar, the team already knew there were signs of rotation in the nebulas, but the Keck data revealed much more.

“When we used Palomar’s CWI previously, we were able to see what looked like a rotating disk of gas, but we couldn’t make out any filaments,” says O’Sullivan. “Now, with the increase in sensitivity and resolution with KCWI, we have more sophisticated models and can see that these objects are being fed by gas flowing in from attached filaments, which is strong evidence that the cosmic web is connected to and fueling this disk.”

Martin and colleagues developed a mathematical model to explain the velocities they were seeing in the gas and tested it on the galaxies near UM 287 and CSO 38 as well as on a simulated galaxy.

“It took us more than a year to come up with the mathematical model to explain the radial flow of the gas,” says Martin. “Once we did, we were shocked by how well the model works.”

The findings provide the best evidence to date for the cold-flow model of galaxy formation, which basically states that cool gas can flow directly into forming galaxies, where it is converted into stars. Before this model came into popularity, researchers had proposed that galaxies pull in gas and heat it up to extremely high temperatures. From there, the gas was thought to gradually cool, providing a steady but slow supply of fuel for stars. In 1996, research from Caltech’s Charles (Chuck) Steidel, the Lee A. DuBridge Professor of Astronomy and a co-author of the new study, threw this model into question. He and his colleagues showed that distant galaxies produce stars at a very high rate—too fast to be accounted for by the slow settling and cooling of hot gas that was a favored model for young galaxy fueling.

“Through the years, we’ve acquired more and more evidence for the cold-flow model,” says Martin. “We have nicknamed our new version of the model the ‘cold-flow inspiral,’ since we see the spiraling pattern in the gas.”

“These type of measurements are exactly the kind of science we want to do with KCWI,” says John O’Meara, the Keck Observatory chief scientist. “We combine the power of Keck’s telescope size, powerful instrumentation, and an amazing astronomical site to push the boundaries of what’s possible to observe. It’s very exciting to see this result in particular, since directly observing inflows has been something of a missing link in our ability to test models of galaxy formation and evolution. I can’t wait to see what’s coming next.”

The new study, titled, “Multi-Filament Inflows Fuel Young Star-Forming Galaxies,” was funded by the National Science Foundation (NSF), the W. M. Keck Observatory, Caltech, and the European Research Council. KCWI is funded by NSF, Keck Observatory, the Heising-Simons Foundation, and Caltech. The galaxy simulations were performed at NASA Advanced Supercomputing at NASA Ames Research Center. Other Caltech authors include former postdoc Erika Hamden, now at the University of Arizona; Patrick Morrissey, a visitor in space astrophysics who also works at JPL, which is managed by Caltech for NASA; and research scientist James D. (Don) Neill.

Materials provided by the California Institute of Technology

hubble image field of the universe

Scientists produce the widest image of the universe using 16 years data

Using NASA’s Hubble Space Telescope, astronomers have created the largest mosaic of the universe containing about 265,000 galaxies. This image is known as the Hubble Legacy Field, and it contains 265,000 galaxies which have been formed up to 500 million years after the Big Bang.

This is the widest view which has been taken of the universe using Hubble Space Telescope’s observations spanning 16 years. The faintest galaxies on the photograph are about one ten-billionth of the brightness which can be viewed by the human eye. This is a remarkable image as it enables us to view the entire history of the evolution of the universe and it also shows how changes occur in the galaxies over a period of time to come up as a giant galaxy.

The image has been possible due to the many deep field surveys which have been taken by Hubble which includes the eXtreme Deep Field(XDF) which is the deepest observation of the universe. The range of wavelength is from the ultraviolet light to the near-infrared light which enables to capture the main features of the changes in the galaxies as time passes.

Garth Illingworth, from the University of California, Santa Cruz, commented that as it has been possible to get a wider view in the universe than the previous surveys, many distant galaxies have been captured in the biggest ever dataset which has been produced by Hubble. A single image captures the entire history of the growth of galaxies.

Scientists feel that no image ever can compete with the image produced now, till space telescopes are launched in the future. Illingworth added that this image is meant to be a tool for studying by the astronomers and it will be an aid in the deeper understanding of the evolution of the universe.

Edwin Hubble once remarked that galaxies act as the markers of the space. They allow scientists to keep track of the expansion of the universe. This image is almost equal to the width of Full Moon. It is the culmination of the work of 31 Hubble programs which comprises several teams of astronomers.

Dan Magee, from the University of California, Santa Cruz, who is the data processing lead of the team explained that this legacy image has been made by judging the exposures spanning 16 years. It was not put in this manner previously and thus was not suitable for use by scientists. The Hubble Space Telescope is a project among several institutes such as NASA, ESA and Space Telescope Science Institute.

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