Mysterious Infrared Light From Space Resolved Perfectly

A research team using the Atacama Large Millimeter/submillimeter Array (ALMA) has detected the faintest millimeter-wave source ever observed. By accumulating millimeter-waves from faint objects like this throughout the Universe, the team finally determined that such objects are 100% responsible for the enigmatic infrared background light filling the Universe. By comparing these to optical and infrared images, the team found that 60% of them are faint galaxies, whereas the rest have no corresponding objects in optical/infrared wavelengths and their nature is still unknown.

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The Universe looks dark in the parts between stars and galaxies. However, astronomers have found that there is faint but uniform light, called the “cosmic background emission,” coming from all directions. This background emission consists of three main components; Cosmic Optical Background (COB), Cosmic Microwave Background (CMB), and Cosmic Infrared Background (CIB).

The origins of the first two have already been revealed. The COB comes from a huge number of stars, and the CMB comes from hot gas just after the Big Bang. However, the origin of the CIB was still to be solved. Various research projects, including past ALMA observations, have been conducted, but they could only explain half of the CIB.

A research team led by a graduate student, Seiji Fujimoto, and an associate professor, Masami Ouchi, at the University of Tokyo, tackled this mysterious infrared background by examining the ALMA data archive. ALMA is the perfect tool to investigate the source of the CIB thanks to its unprecedented sensitivity and resolution.

They went through the vast amount of ALMA data taken during about 900 days in total looking for faint objects. They also searched the datasets extensively for lensed sources, where huge gravity has magnified the source making even fainter objects visible.

“The origin of the CIB is a long-standing missing piece in the energy coming from the Universe,” said Seiji Fujimoto, now studying at the Institute of Cosmic Ray Research, the University of Tokyo. “We devoted ourselves to analyzing the gigantic ALMA data in order to find the missing piece.”

Finally, the team discovered 133 faint objects, including an object five times fainter than any other ever detected. The researchers found that the entire CIB can be explained by summing up the emissions from such objects (note).

What is the nature of those sources? By comparing the ALMA data with the data taken by the Hubble Space Telescope and the Subaru Telescope, the team found that 60% of them are galaxies which can also be seen in the optical/infrared images. Dust in galaxies absorbs optical and infrared light and re-emits the energy in longer millimeter waves which can be detected with ALMA.

“However, we have no idea what the rest of them are. I speculate that they are galaxies obscured by dust. Considering their darkness, they would be very low-mass galaxies.” Masami Ouchi explained passionately. “This means that such small galaxies contain great amounts of dust. That conflicts with our current understanding: small galaxies should contain small amounts of dust. Our results might indicate the existence of many unexpected objects in the distant Universe. We are eager to unmask these new enigmatic sources with future ALMA observations.”

Note: ALMA detected a part of the CIB with 1 mm wavelengths. The CIB in millimeter and submillimeter waves does not become weak even if the source is located far away. Therefore this wavelength is suitable for looking through the Universe to the most distant parts.

Dark Matter Satellites Trigger Massive Birth Of Stars

One of the main predictions of the current model of the creation of structures in the universe, known at the Lambda Cold Dark Mattermodel, is that galaxies are embedded in very extended and massive halos of dark matter that are surrounded by many thousands of smaller sub-halos also made from dark matter.

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Around large galaxies, such as the Milky Way, these dark matter sub-halos are large enough to host enough gas and dust to form small galaxies on their own, and some of these galactic companions, known as satellite galaxies, can be observed. These satellite galaxies can orbit for billions of years around their host before a potential merger. Mergers cause the central galaxy to add large amount of gas and stars, triggering violent episodes of new star formation ?known as starbursts? due to the excess gas brought in by the companion. The host’s shape or morphology can also be disturbed due to the gravitational interaction.

Smaller halos form dwarf galaxies, which at the same time will be orbited by even smaller satellite sub-halos of dark matter which are now far too tiny to have gas or stars in them. These dark satellites therefore are invisible to telescopes, but readily appear in theoretical models run in computer simulations. A direct observation of their interaction with their host galaxies is required to prove their existence.

Laura Sales, an assistant professor at the University of California, Riverside’s Department of Physics and Astronomy, collaborated with Tjitske Starkenburg and Amina Helmi, both of the Kapteyn Astronomical Institute in The Netherlands, to present a novel analysis of computer simulations, based on theoretical models, that study the interaction of a dwarf galaxy with a dark satellite.

The findings were outlined in a just-published paper, “Dark influences II: gas and star formation in minor mergers of dwarf galaxies with dark satellites,” in the journal Astronomy & Astrophysics.

The researchers found that during a dark satellite’s closest approach to a dwarf galaxy, through gravity it compresses the gas in the dwarf, triggering significant episodes of starbursts. These star forming episodes may last for several billions of years, depending on the mass, orbit and concentration of the dark satellite.

This scenario predicts that many of the dwarf galaxies that we readily observe today should be forming stars at a higher rate than expected –or should be experiencing a starburst– which is exactly what telescope observations have found.

Furthermore, similarly to mergers between more massive galaxies, the interaction between the dwarf galaxy and the dark satellite triggers morphological disturbances in the dwarf, which can completely change its structure from mainly disk-shaped to a spherical/elliptical system. This mechanism also offers an explanation to the origin of isolated spheroidal dwarf galaxies, a puzzle that has remained unsolved for several decades.

Deciphering Compact Galaxies In The Young Universe

A group of researchers using the Suprime-Cam instrument on the Subaru Telescope has discovered about 80 young galaxies that existed in the early universe about 1.2 billion years after the Big Bang. The team made detailed analyses of imaging data of these galaxies taken by the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. At least 54 of the galaxies are spatially resolved in the ACS images. Among them, eight galaxies show double-component structures (Figure 1) and the remaining 46 seem to have elongated structures (Figure 2). Further investigations using a computer simulation revealed that the observed elongated structures can be reproduced if two or more galaxies reside in close proximity to each other.

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These results strongly suggest that 1.2 billion years after the Big Bang, galactic clumps in the young universe grow to become large galaxies through mergers, which then cause active star formation. This research was conducted as part of the treasury program of Hubble Space Telescope Cosmic Evolution Survey (COSMOS). The powerful survey capability of the Subaru Telescope provided the essential database of the candidate objects in the early universe for this research project.

The Importance of Studying Early Galaxies

In the present universe, 13.8 billion years after the Big Bang, there are many giant galaxies like our Milky Way, which contains about 200 billion stars in a disk a hundred thousand light years across. However, there were definitely no galaxies like it in the epoch just after the Big Bang.

Pre-galactic clumps appear to have formed in the universe about 200 million years after the Big Bang. These were cold gas clouds much smaller than the present giant galaxies by a factor of 100, with masses smaller by a factor of a million. The first galaxies were formed when the first stars were born in these gas clumps. These small galactic clumps then experienced continuous mergers with surrounding clumps and eventually grew into large galaxies.

Deciphering compact galaxies in the young universe.

Much effort has been made through deep surveys to detect active star-forming galaxies in the young universe. As a result, the distances of the earliest galaxies are now known to be at more than 13 billion light years. We see them at a time when the age of the universe was only 800 million years (or about 6 percent of the present age). However, since most of the galaxies in the young universe were quite small, their detailed structures have not yet been observed.

Exploring the Young Universe Using Subaru Telescope and Hubble Space Telescope.

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While the wide field of view of the Subaru Telescope has played an important role in finding such young galaxies, the high spatial resolution of the Hubble Space Telescope (HST) is required to investigate the details of their shapes and internal structures. The research team looked back to a point 12.6 billion years ago using a two-pronged approach. The first step was to use the Subaru Telescope in a deep survey to search out the early galaxies, and then follow that up to investigate their shapes using the Advanced Camera for Surveys (ACS) on board the HST. The ACS revealed eight out of 54 galaxies to have double-component structures in which two galaxies seem to be merging with each other, as shown in Figure 1.

Then a question arose as to whether the remaining 46 galaxies are really single galaxies. Here, the research team questioned why many of these galaxies show elongated shapes in the HST/ACS images (Figure 2). This is because such elongated shapes, together with the positive correlation between ellipticity and size (Figure 3), strongly suggest a possibility that two small galaxies reside so close to each other that they cannot be resolved into two distinct galaxies, even using ACS.

Then a question arose as to whether the remaining 46 galaxies are really single galaxies. Here, the research team questioned why many of these galaxies show elongated shapes in the HST/ACS images (Figure 2). This is because such elongated shapes, together with the positive correlation between ellipticity and size (Figure 3), strongly suggest a possibility that two small galaxies reside so close to each other that they cannot be resolved into two distinct galaxies, even using ACS.

If this idea is valid for the galaxies that appear to be single, then it’s possible to assume that the galaxies with the highest rate of activities have the smallest sizes. This is expected because the smallest sizes imply the smallest separation between two merging galaxies. If this is the case, such galaxies would experience intense star formation activity triggered by their mergers.

On the other hand, some galaxies with the smallest sizes are moderately separated pairs, but are observed along the line of sight, or are just single, isolated star-forming galaxies. These are basically the same as large-size galaxies.

The research team has confirmed that the observed relation between star formation activity and size is consistently explained by the team’s idea.
To date, the shapes and structures of small young galaxies have been investigated by using ACS on HST. If a source was detected as a single ACS source, it was treated as a single galaxy and its morphological parameters were evaluated. This research suggests that such a small galaxy can consist of two or perhaps, more interacting/merging galaxies located so close together that they cannot be resolved by even the high angular resolution of the ACS.

Looking into the Future of Studying the Past

Current galaxy formation theories predict that small galaxies in the young universe evolve into large galaxies via successive mergers. What is the next step in observational studies for galaxy formation in the young universe? This is one of the frontier fields that requires future “super telescopes,” e.g. the Thirty Meter Telescope (TMT) and the James Webb Space Telescope (JWST). They will enable the next breakthroughs in the study of early galaxy formation and evolution.

Faults Control The Amount Of Water Flowing Into The Earth During Continental Breakup

New light has been shed on the processes by which ocean water enters the solid Earth during continental breakup.

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Research led by geoscientists at the University of Southampton, and published in Nature Geoscience this week, is the first to show a direct link on geological timescales between fault activity and the amount of water entering the Earth’s mantle along faults.

When water and carbon is transferred from the ocean to the mantle it reacts with a dry rock called peridotite, which makes up most of the mantle beneath the crust, to form serpentinite.

Dr Gaye Bayrakci, Research Fellow in Geophysics, and Professor Tim Minshull, from Ocean and Earth Science, with colleagues at the University of Southampton and six other institutions, measured the amount of water that had entered the Earth by using sound waves to map the distribution of serpentinite.

The sound waves travel through the crust and mantle and can be detected by sensitive instruments placed on the ocean floor. The time taken for the signals to travel from an acoustic seismic source to the seafloor instruments reveals how fast sound travels in the rocks, and the amount of serpentinite present can be determined from this speed.

The four-month experiment, which involved two research ships (the R/V Marcus Langseth and the F/S Poseidon), mapped an 80 by 20 km area of seafloor west of Spain called the Deep Galicia Margin where the fault structures were formed when North America broke away from Europe about 120 million years ago.

The results showed that the amount of serpentinite formed at the bottom of each fault was directly proportional to the displacement on that fault, which in turn is closely related to the duration of fault activity.

Dr Bayracki said: “One of the aims of our survey was to explore the relationship between the faults, which we knew already were there, and the presence of serpentinite, which we also knew was there but knew little about its distribution. The link between fault activity and formation of serpentinite was something we might have hoped for but did not really expect to see so clearly.

“This implies that seawater reaches the mantle only when the faults are active and that brittle processes in the crust may ultimately control the global amount of seawater entering the solid Earth.”

In other tectonic settings where serpentinite is present such as mid ocean ridges and subduction zones, the focused flow of seawater along faults provides a setting for diverse hydrothermal ecosystems where life-forms live off the chemicals stripped out of the rocks by the water as it flows into and then out of the Earth’s mantle.

The researchers were able to estimate the average rate at which seawater entered the mantle through the faults at the Deep Galicia Margin and discovered that rate was comparable to those estimated for water circulation in hot rock at mid-ocean ridges, where such life-forms are more common. These results suggest that in continental rifting environment there may have been hydrothermal systems, which are known to support diverse ecosystems.

Co-Author and Professor of Geology at the University of Birmingham Tim Reston commented: “Understanding the transport of water during deformation has broad implications, ranging from hydrothermal systems to earthquake mechanics. The new results suggest a more direct link between faulting and water movements than we previously suspected.”

How Rivers Of Hot Ash And Gas Move When A Supervolcano Erupts

Supervolcanoes capable of unleashing hundreds of times the amount of magma that was expelled during the Mount St. Helens eruption of 1980 are found in populated areas around the world, including the western United States.

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A new study is providing insight into what may happen when one of these colossal entities explodes.

The research focuses on the Silver Creek caldera, which sits at the intersection of California, Nevada and Arizona. When this supervolcano erupted 18.8 million years ago, it flooded parts of all three states with river-like currents of hot ash and gas called pyroclastic flows. These tides of volcanic material traveled for huge distances — more than 100 miles.

The new study suggests that pyroclastic flows from the ancient eruption took the form of slow, dense currents — and not fast-moving jets as some experts previously thought.

The research combines recent laboratory experiments with field data from the 1980s — some of it captured in colorful Kodachrome slides — to show that the rivers of ash and gas emanating from the Silver Creek caldera likely traveled at modest speeds of about 10 to 45 miles per hour.

“Intuitively, most of us would think that for the pyroclastic flow to go such an extreme distance, it would have to start off with a very high speed,” says study co-author Olivier Roche. “But this isn’t consistent with what we found.”

The research was conducted by Roche at Blaise Pascal University in France, David C. Buesch at the United States Geological Survey and Greg A. Valentine at the University at Buffalo. It will be published on Monday, March 7 in Nature Communications.

Research on pyroclastic flows is important because it can help inform disaster preparedness efforts, says Valentine, a UB professor of geology and director of the Center for GeoHazards Studies in the UB College of Arts and Sciences.

“We want to understand these pyroclastic flows so we can do a good job of forecasting the behavior of these flows when a volcano erupts,” he says. “The character and speed of the flows will affect how much time you might have to get out of the way, although the only truly safe thing to do is to evacuate before a flow starts.”

New and vintage data come together to tell the story of a supervolcano

The new study favors one of two competing theories about how pyroclastic flows are able to cover long distances. One school of thought says the flows should resemble turbulent, hot, fast-moving sandstorms, made up mostly of gas, with few particles. The other theory states that the flows should be dense and fluid-like, with pressurized gas between ash particles. The new research supports this latter model, which requires sustained emissions from volcanoes, for many pyroclastic flows.

The findings were based on two sets of data: results from recent experiments that Roche ran to simulate the behavior of pyroclastic flows, and information that Buesch and Valentine gathered at the Silver Creek Caldera eruption site in the 1980s when they were PhD students at the University of California, Santa Barbara, supplemented by some more recent fieldwork.

“I always tell students that they should take good notes while they’re working in the field, because you never know when it could be useful,” says Valentine, who has a fat binder full of Kodachrome slides showing images he snapped around the Silver Creek caldera.

The data that he and Buesch collected included photographs and notes documenting the size, type and location of rocks that were lifted off the ground and moved short distances by pyroclastic flows during the ancient eruption.

Many of the rocks the pair observed were relatively large — too large to have been shifted by sandstorm-like pyroclastic flows, which do not pick up heavy objects easily. Denser flows, which can move sizable rocks more readily, likely accounted for the rock patterns Buesch and Valentine observed.

To figure out how fast these dense flows may have been moving when the Silver Creek caldera erupted 18.8 million years ago, the team relied on a model developed by Roche through experiments.

In his tests, Roche studied what happened when a gas and particle mixture resembling a dense pyroclastic flow traveled across a substrate of beads. He found that faster flows were able to lift and move heavier beads, and that there was a relationship between the velocity of a flow and the weight of the bead it was capable of lifting.

Based on Roche’s model, the scientists determined that the ancient pyroclastic flows from the supervolcano would have had to travel at speeds of about 5 to 20 meters per second (10 to 45 miles per hour) to pick up rocks as heavy as the ones that Buesch and Valentine saw. It’s unlikely that the flows were going much faster than that because larger rocks on the landscape remained undisturbed, Valentine says.

The findings could have widespread applicability when it comes to supereruptions, says Valentine, who notes that patterns of rock deposits around some other supervolcanoes heavily resemble those around the Silver Creek caldera.

Mercury’s Mysterious ‘Darkness’ Explained

Scientists have long been puzzled about what makes Mercury’s surface so dark. The innermost planet reflects much less sunlight than the Moon, a body on which surface darkness is controlled by the abundance of iron-rich minerals. These are known to be rare at Mercury’s surface, so what is the “darkening agent” there?

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About a year ago, scientists proposed that Mercury’s darkness was due to carbon that gradually accumulated from the impact of comets that traveled into the inner Solar System. Now scientists, led by Patrick Peplowski of the Johns Hopkins University Applied Physics Laboratory, have used data from the MESSENGER mission* to confirm that a high abundance of carbon is present at Mercury’s surface. However, they also have also found that, rather than being delivered by comets, the carbon most likely originated deep below the surface, in the form of a now-disrupted and buried ancient graphite-rich crust, some of which was later brought to the surface by impact processes after most of Mercury’s current crust had formed. The results are published in the March 7, 2016, Advanced Online Publication of Nature Geoscience.

Co-author and Deputy Principal Investigator of the MESSENGER mission, Carnegie’s Larry Nittler, explained: “The previous proposal of comets delivering carbon to Mercury was based on modelling and simulation. Although we had prior suggestions that carbon may be the darkening agent, we had no direct evidence. We used MESSENGER’s Neutron Spectrometer to spatially resolve the distribution of carbon and found that it is correlated with the darkest material on Mercury, and this material most likely originated deep in the crust. Moreover, we used both neutrons and X-rays to confirm that the dark material is not enriched in iron, in contrast to the Moon where iron-rich minerals darken the surface.”

MESSENGER obtained its statistically robust data via many orbits on which the spacecraft passed lower than 60 miles (100 km) above the surface of the planet during its last year of operation. The data used to identify carbon included measurements taken just days before MESSENGER impacted Mercury in April 2015. Repeated Neutron Spectrometer measurements showed higher amounts of low-energy neutrons, a signature consistent with the presence of elevated carbon, coming from the surface when the spacecraft passed over concentrations of the darkest material. Estimating the amount of carbon present required combining the neutron measurements with other MESSENGER datasets, including X-ray measurements and reflectance spectra. Together, the data indicate that Mercury’s surface rocks are made up of as much as a few weight percent graphitic carbon, much higher than on other planets. Graphite has the best fit to the reflectance spectra, at visible wavelengths, and the likely conditions that produced the material.

When Mercury was very young, much of the planet was likely so hot that there was a global “ocean” of molten magma. From laboratory experiments and modeling, scientists have suggested that as this magma ocean cooled, most minerals that solidified would sink. A notable exception is graphite, which would have been buoyant and floated to form the original crust of Mercury.

“The finding of abundant carbon on the surface suggests that we may be seeing remnants of Mercury’s original ancient crust mixed into the volcanic rocks and impact ejecta that form the surface we see today. This result is a testament to the phenomenal success of the MESSENGER mission and adds to a long list of ways the innermost planet differs from its planetary neighbors and provides additional clues to the origin and early evolution of the inner Solar System,” concluded Nittler.

Ecuador Volcano Spews Towering Ash, Gas Plume

Ecuador’s Tungurahua volcano has been putting on a dramatic show, spewing lava from a cauldron-like crater and launching towering clouds of ash and gas.

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The country’s Geophysical Institute said Sunday the column of ash reached a maximum height of about 2 miles (3 km) in recent hours, while it hurled blocks of glowing rock about a mile (1.5 km) down its slopes.

The 16,480-foot (5,023 meter) peak is about 85 miles (140 km) south of Quito, the capital, and close to the tourist center of Banos. It’s been periodically erupting since 1999.