Scientists Use the Light of Double Quasars to Measure the Structure of the Universe

Snapshot of a supercomuter simulation showing part of the cosmic web, 11.5 billion years ago. The researchers created this and other models of the universe and directly compared them with quasar pair data in order to measure the small-scale ripples in the cosmic web. The cube is 24 million light-years on a side.

Using the light of double quasars, a team led by researchers has made the first measurements of small-scale fluctuations in the cosmic web just 2 billion years after the Big Bang.
Astronomers believe that matter in intergalactic space is distributed in a vast network of interconnected filamentary structures known as the cosmic web. Nearly all the atoms in the Universe reside in this web, vestigial material left over from the Big Bang. A team led by researchers from the Max Planck Institute for Astronomy in Heidelberg have made the first measurements of small-scale fluctuations in the cosmic web just 2 billion years after the Big Bang. These measurements were enabled by a novel technique using pairs of quasars to probe the cosmic web along adjacent, closely separated lines of sight. They promise to help astronomers reconstruct an early chapter of cosmic history known as the epoch of reionization.
The most barren regions of the Universe are the far-flung corners of intergalactic space. In these vast expanses between the galaxies there are only a few atoms per cubic meter – a diffuse haze of hydrogen gas left over from the Big Bang. Viewed on the largest scales, this diffuse material nevertheless accounts for the majority of atoms in the Universe, and fills the cosmic web, its tangled strands spanning billions of light years.
Now, a team led by astronomers from the Max Planck Institute for Astronomy (MPIA) have made the first measurements of small-scale ripples in this primeval hydrogen gas. Although the regions of cosmic web they studied lie nearly 11 billion light years away, they were able to measure variations in its structure on scales a hundred thousand times smaller, comparable to the size of a single galaxy.
Intergalactic gas is so tenuous that it emits no light of its own. Instead astronomers study it indirectly by observing how it selectively absorbs the light coming from faraway sources known as quasars. Quasars constitute a brief hyperluminous phase of the galactic life-cycle, powered by the infall of matter onto a galaxy’s central supermassive black hole.
Quasars act like cosmic lighthouses – bright, distant beacons that allow astronomers to study intergalactic atoms residing between the quasars location and Earth. But because these hyperluminous episodes last only a tiny fraction of a galaxy’s lifetime, quasars are correspondingly rare on the sky, and are typically separated by hundreds of millions of light years from each other.
In order to probe the cosmic web on much smaller length scales, the astronomers exploited a fortuitous cosmic coincidence: They identified exceedingly rare pairs of quasars right next to each other on the sky, and measured subtle differences in the absorption of intergalactic atoms measured along the two sightlines.

 

Schematic representation of the technique used to probe the small-scale structure of the cosmic web using light from a rare quasar pair. The spectra (bottom right) contain information about the hydrogen gas the light has encountered on its journey to Earth, as well as the distance of that gas.

Alberto Rorai, a post-doctoral researcher at Cambridge university and the lead author of the study says: “One of the biggest challenges was developing the mathematical and statistical tools to quantify the tiny differences we measure in this new kind of data.”
Rorai developed these tools as part of the research for his doctoral degree at the MPIA, and applied his tools to spectra of quasars obtained with the largest telescopes in the world, including the 10 meter diameter Keck telescopes at the summit of Mauna Kea in Hawaii, as well as ESO’s 8 meter diameter Very Large Telescope on Cerro Paranal, and the 6.5 meter diameter Magellan telescope at Las Campanas Observatory, both located in the Chilean Atacama Desert.
The astronomers compared their measurements to supercomputer models that simulate the formation of cosmic structures from the Big Bang to the present. “The input to our simulations are the laws of Physics and the output is an artificial Universe which can be directly compared to astronomical data. I was delighted to see that these new measurements agree with the well-established paradigm for how cosmic structures form,” says Jose Oñorbe, a post-doctoral researcher at the MPIA, who led the supercomputer simulation effort.
On a single laptop, these complex calculations would have required almost a thousand years to complete, but modern supercomputers enabled the researchers to carry them out in just a few weeks.
Joseph Hennawi, who leads the research group at MPIA responsible for the measurement, explains: “One reason why these small-scale fluctuations are so interesting is that they encode information about the temperature of gas in the cosmic web just a few billion years after the Big Bang.” According to the current level of knowledge, the universe had quite a mercurial youth: initially, about 400,000 years after the Big Bang, the universe had cooled down to such an extent that neutral hydrogen could arise. At that point, there were practically no heavenly bodies yet and therefore no light. It was not until few hundred million years later that this ‘dark age’ ended and a new era began, in which stars and quasars lit up and emitted energetic ultraviolet rays. The latter were so intense that they robbed atoms in the intergalactic space of their electrons – the gas was ionized again.
How and when reionization occurred is one of the biggest open questions in the field of cosmology, and these new measurements provide important clues that will help narrate this chapter of cosmic history.

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Sloan Digital Sky Survey Provides New Insight Into Dark Matter Halos

An image of a simulated galaxy cluster showing evidence for a boundary, or “edge” from a 2015 paper in the Astrophysical Journal by Surhud More, Benedikt Diemer and Andre Kravtsov.

Using the Sloan Digital Sky Survey to look at the distribution of dark matter around galaxies, astronomers at the University of Pennsylvania shed new light on one of the most mysterious substances in the universe.
In the 1970s, researchers noticed something strange about the motion of galaxies. All the matter at the edge of spiral galaxies was rotating just as fast as material in the inner part of the galaxy. But according to the laws of gravity, objects on the outskirts should be moving slower.
The explanation: A form of matter called dark matter that does not directly interact with light. Many researchers now believe that more than 80 percent of the matter of the universe is locked away in mysterious, as yet undetected, particles of dark matter, which affect everything from how objects move within a galaxy to how galaxies and galaxy clusters clump together in the first place. This dark matter extends far beyond the reach of the furthest stars in the galaxy, forming what researchers call a dark matter halo. While stars within the galaxy all rotate in a neat, organized disk, these dark matter particles are like a swarm of bees, moving chaotically in random directions, which keeps them puffed up to balance the inward pull of gravity.

Bhuvnesh Jain, a physics professor in Penn’s School of Arts & Sciences, and postdoc Eric Baxter are conducting research that could give new insights into the structure of these halos. They investigated whether these dark matter halos have an edge or boundary.
“People have generally imagined a pretty smooth transition from the matter bound to the galaxy to the matter between galaxies, which is also gravitationally attracted to the galaxies and clusters,” Jain said. “But theoretically, using computer simulations a few years ago, researchers at the University of Chicago showed that for galaxy clusters a sharp boundary is expected, providing a distinct transition that we should be able to see through a careful analysis of the data.”
​​​​​​​​​​​​​​Scientists believe that this region, or “edge” is due to the “splashback effect.” “You have this big dark matter halo sitting there,” Baxter said, “and it’s been accreting matter gravitationally over its entire history. As that matter gets pulled in, it gets faster and faster. When it finally falls into the halo, it turns around and starts to orbit. That turnaround is what people have started calling splashback, because stuff is splashing back in some sense.”
As the matter “splashes back,” it slows down. Because this effect is happening in many different directions, it leads to a buildup of matter right at the edge of the halo and a steep fall-off in the amount of matter right outside of that position. This is what the Penn researchers explored in the data.
Using the Sloan Digital Sky Survey, or SDSS, Baxter and Jain looked at the distribution of galaxies around clusters. They formed teams of experts at institutions around the world to examine thousands of galaxy clusters. Using statistical tools to do a joint analysis of several million galaxies around them, they found a drop at the edge of the cluster. Baxter and collaborator Chihway Chang at the University of Chicago led a paper reporting the findings, accepted for publication in the Astrophysical Journal.
In addition to seeing this edge when they looked at galaxy distribution, the team also saw evidence of it in the form of galaxy colors. When a galaxy is full of gas and forming many big, hot stars, the heat causes it to appear blue when scientists takes images of it. “But those big stars live very short lives,” Baxter said. “They blow up. What you’re left with are these smaller, older stars that live for long periods of time, and those are red.”
When scientists look at galaxies within clusters, they appear red because they aren’t forming stars. “Previous studies have shown that there are interactions inside of the cluster that can cause galaxies to stop forming stars,” Baxter said. “You could imagine for instance that a galaxy falls into a cluster, and the gas from the galaxy gets stripped off by gas within the cluster. After losing its gas, the galaxy will be unable to form many stars.” Because of this, researchers expect that galaxies that have spent more time orbiting through a cluster will appear red, while galaxies that are just starting to fall in will appear blue.
The researchers noticed a sudden shift in the colors of galaxies right at the boundary, providing them with more evidence that dark matter halos have an edge. “It was really interesting and surprising to see this sharp change in colors,” Jain said, “because the change of galaxy colors is a very slow and complex process.”
The researchers are working on another paper using a deeper survey of over a hundred million galaxies called the Dark Energy Survey, or DES. Both the SDSS and the DES make massive maps of the sky using a huge camera that Jain said isn’t very fundamentally different from the cameras in smartphones but bigger and more precise and costing millions of dollars to build.
In the DES, when the camera opens, it takes an exposure of a couple minutes, and then moves to a different part of the sky. This process is repeated during the course of several years using different filters to allow scientists to get a survey in multiple colors. The DES allows the researchers to do expanded measurements, pushing to higher distances.
Instead of measuring the distribution of galaxies, the researchers are using an astrophysical phenomenon called gravitational lensing to probe the dark matter halos. In gravitational lensing, light coming to an observer bends as matter exerts gravitational force on it. The researchers can analyze images of the sky to see how clusters stretch images of the galaxies behind them. “Light is going to bend if there’s mass,” Baxter said. “By measuring these deflections we can measure the mass directly which is cool because most of the mass is dark matter which we can’t see so it’s a unique way to probe the dark matter.”
In terms of fundamental understanding of the universe, Baxter said, dark matter is one of the biggest mysteries there is right now. “You look in the sky, even with the biggest optical telescopes, and you see nothing beyond the light of the galaxies,” Jain said. “There’s just this dark matter.”
The researchers hope that their research will contribute to a better understanding of the mysterious substance that makes up about 80 percent of matter in the universe. If they can mark the edge of a dark matter halo, it would allow them to test things like Einstein’s theory of gravity and the nature of dark matter.
“It’s just a new way of looking at clusters,” Jain said. “Once you find the boundary you can study both the standard physics of how galaxies interact with the cluster and the possible unknown physics of what the nature of dark matter and gravity is.”

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Mysterious Gamma-Ray Glow at the Center of the Milky Way Most Likely Caused by Pulsars, Not Dark Matter

An excess of gamma-rays coming from the center of the Milky Way is likely due to a population of pulsars – rapidly spinning, very dense and highly magnetized neutron stars that emit “beams” of gamma rays like cosmic lighthouses. The pulsars’ location in the oldest region of the galaxy suggests that they leach energy from companion stars, which prolongs the pulsars’ lifetime. The background image shows the galactic center as seen by NASA’s Chandra X-ray Observatory.

A newly published study reveals that the mysterious gamma-ray glow at the center of the Milky Way is most likely caused by pulsars, not dark matter.
A new analysis by an international team of astrophysicists concludes that the mysterious gamma-ray glow at the center of the Milky Way is most likely caused by pulsars – the incredibly dense, rapidly spinning cores of collapsed ancient stars that were up to 30 times more massive than the sun. The findings cast doubt on previous interpretations of the signal as a potential sign of dark matter – a form of matter that accounts for 85 percent of all matter in the universe but that so far has evaded detection.
“Our study shows that we don’t need dark matter to understand the gamma-ray emissions of our galaxy,” said Mattia Di Mauro from the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), a joint institute of Stanford University and SLAC. “Instead, we have identified a population of pulsars in the region around the galactic center, which sheds new light on the formation history of the Milky Way.”
Di Mauro led the analysis for the Fermi LAT Collaboration, an international team of researchers that looked at the glow with the Large Area Telescope (LAT) on NASA’s Fermi Gamma-ray Space Telescope, which has been orbiting Earth since 2008. The LAT – a sensitive “eye” for gamma rays, the most energetic form of light – was conceived of and assembled at SLAC, which also hosts its operations center.
A Mysterious Glow
Dark matter is one of the biggest mysteries of modern physics. Researchers know that dark matter exists because it bends light from distant galaxies and affects how galaxies rotate. But they don’t know what the substance is made of. Most scientists believe it’s composed of yet-to-be-discovered particles that almost never interact with regular matter other than through gravity, making it very hard to detect them.
One way scientific instruments might catch a glimpse of dark matter particles is when the particles either decay or collide and destroy each other. “Widely studied theories predict that these processes would produce gamma rays,” said Seth Digel, head of KIPAC’s Fermi group. “We search for this radiation with the LAT in regions of the universe that are rich in dark matter, such as the center of our galaxy.”
Previous studies have indeed shown that there are more gamma rays coming from the galactic center than expected, fueling some scientific papers and media reports that suggest the signal might hint at long-sought dark matter particles. However, gamma rays are produced in a number of other cosmic processes, which must be ruled out before any conclusion about dark matter can be drawn. This is particularly challenging because the galactic center is extremely complex, and astrophysicists don’t know all the details of what’s going on in that region.
Most of the Milky Way’s gamma rays originate in gas between the stars that is lit up by cosmic rays – charged particles produced in powerful star explosions, called supernovae. This creates a diffuse gamma-ray glow that extends throughout the galaxy. Gamma rays are also produced by supernova remnants, pulsars – collapsed stars that emit “beams” of gamma rays like cosmic lighthouses – and more exotic objects that appear as points of light.
“Two recent studies by teams in the U.S. and the Netherlands have shown that the gamma-ray excess at the galactic center is speckled, not smooth as we would expect for a dark matter signal,” said KIPAC’s Eric Charles, who contributed to the new analysis. “Those results suggest the speckles may be due to point sources that we can’t see as individual sources with the LAT because the density of gamma-ray sources is very high and the diffuse glow is brightest at the galactic center.”

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SOFIA Confirms Nearby Epsilon Eridani System Is Remarkably Similar To Our Solar System

Artist’s illustration of the Epsilon Eridani system showing Epsilon Eridani b. In the right foreground, a Jupiter-mass planet is shown orbiting its parent star at the outside edge of an asteroid belt. In the background can be seen another narrow asteroid or comet belt plus an outermost belt similar in size to our solar system’s Kuiper Belt. The similarity of the structure of the Epsilon Eridani system to our solar system is remarkable, although Epsilon Eridani is much younger than our sun. SOFIA observations confirmed the existence of the asteroid belt adjacent to the orbit of the Jovian planet.

Using data from NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA), astronomers confirm that the nearby Epsilon Eridani system has an architecture remarkably similar to that of our solar system.
The star Epsilon Eridani, eps Eri for short, is located 10.5 light-years away in the southern hemisphere of the constellation Eridanus. It is the closest planetary system around a star similar to the early sun. It is a prime location to research how planets form around stars like our sun, and is also the storied location of the Babylon 5 space station in the science fictional television series of the same name.
Previous studies indicate that eps Eri has a debris disk, which is the name astronomers give to leftover material still orbiting a star after planetary construction has completed. The debris can take the form of gas and dust, as well as small rocky and icy bodies. Debris disks can be broad, continuous disks or concentrated into belts of debris, similar to our solar system’s asteroid belt and the Kuiper Belt – the region beyond Neptune where hundreds of thousands of icy-rocky objects reside. Furthermore, careful measurements of the motion of eps Eri indicates that a planet with nearly the same mass as Jupiter circles the star at a distance comparable to Jupiter’s distance from the Sun.
Using new SOFIA images, Kate Su of the University of Arizona and her research team were able to distinguish between two theoretical models of the location of warm debris, such as dust and gas, in the eps Eri system. These models were based on prior data obtained with NASA’s Spitzer space telescope.
One model indicates that warm material is in two narrow rings of debris, which would correspond respectively to the positions of the asteroid belt and the orbit of Uranus in our solar system. Using this model, theorists indicate that the largest planet in a planetary system might normally be associated with an adjacent debris belt.
The other model attributes the warm material to dust originating in the outer Kuiper-Belt-like zone and filling in a disk of debris toward the central star. In this model, the warm material is in a broad disk, and is not concentrated into asteroid belt-like rings nor is it associated with any planets in the inner region.

Illustration based on Spitzer observations of the inner and outer parts of the Epsilon Eridani system compared with the corresponding components of our solar system.

Using SOFIA, Su and her team ascertained that the warm material around eps Eri is in fact arranged like the first model suggests; it is in at least one narrow belt rather than in a broad continuous disk.
These observations were possible because SOFIA has a larger telescope diameter than Spitzer, 100 inches (2.5 meters) in diameter compared to Spitzer’s 33.5 inches (0.85 meters), which allowed the team onboard SOFIA to discern details that are three times smaller than what could be seen with Spitzer. Additionally, SOFIA’s powerful mid-infrared camera called FORCAST, the Faint Object infraRed CAmera for the SOFIA Telescope, allowed the team to study the strongest infrared emission from the warm material around eps Eri, at wavelengths between 25-40 microns, which are undetectable by ground-based observatories.
“The high spatial resolution of SOFIA combined with the unique wavelength coverage and impressive dynamic range of the FORCAST camera allowed us to resolve the warm emission around eps Eri, confirming the model that located the warm material near the Jovian planet’s orbit,” said Su. “Furthermore, a planetary mass object is needed to stop the sheet of dust from the outer zone, similar to Neptune’s role in our solar system. It really is impressive how eps Eri, a much younger version of our solar system, is put together like ours.”

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VISTA Captures Record-Breaking Image of the Small Magellanic Cloud

The infrared capabilities of the Visible and Infrared Survey Telescope (VISTA) reveal the myriad of stars in the Small Magellanic Cloud much more clearly than ever before. The result is this record-breaking image — the biggest infrared image ever taken of the Small Magellanic Cloud — with the whole frame filled with millions of stars. The Small Magellanic Cloud (SMC) is a dwarf galaxy, the more petite twin of the Large Magellanic Cloud (LMC). They are two of our closest galaxy neighbors in space — the SMC lies about 200,000 light-years away, just a twelfth of the distance to the more famous Andromeda Galaxy. Both are also rather peculiarly shaped, as a result of interactions with one another and with the Milky Way itself. Their relative proximity to Earth makes the Magellanic Clouds ideal candidates for studying how stars form and evolve. However, while the distribution and history of star formation in these dwarf galaxies were known to be complex, one of the biggest obstacles to obtaining clear observations of star formation in galaxies is interstellar dust. Enormous clouds of these tiny grains scatter and absorb some of the radiation emitted from the stars — especially visible light — limiting what can be seen by telescopes here on Earth. This is known as dust extinction. The SMC is full of dust, and the visible light emitted by its stars suffers significant extinction. Fortunately, not all electromagnetic radiation is equally affected by dust. Infrared radiation passes through interstellar dust much more easily than visible light, so by looking at the infrared light from a galaxy we can learn about the new stars forming within the clouds of dust and gas. 

 

This video takes a quick look at a remarkable new image from ESO’s VISTA survey telescope at the Paranal Observatory in Chile. The huge picture shows one of our neighboring galaxies, the Small Magellanic Cloud, in remarkable detail and in infrared light.

VISTA, the Visible and Infrared Survey Telescope, was designed to image infrared radiation. The VISTA Survey of the Magellanic Clouds (VMC) is focused on mapping the star formation history of the SMC and LMC, as well as mapping their three-dimensional structures. Millions of SMC stars have been imaged in the infrared thanks to the VMC, providing an unparalleled view almost unaffected by dust extinction.
The whole frame of this massive image is filled with stars belonging to the Small Magellanic Cloud. It also includes thousands of background galaxies and several bright star clusters, including 47 Tucanae at the right of the picture, which lies much closer to the Earth than the SMC.
The wealth of new information in this 1.6 gigapixel zoomable image (43,223 x 38,236 pixels) has been analyzed by an international team led by Stefano Rubele of the University of Padova. They have used cutting-edge stellar models to yield some surprising results.
The VMC has revealed that most of the stars within the SMC formed far more recently than those in larger neighboring galaxies. This early result from the survey is just a taster of the new discoveries still to come, as the survey continues to fill in blind spots in our maps of the Magellanic Clouds

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