A Violent Wind Blown From The Heart Of A Galaxy Tells The Tale Of A Merger

An international team led by a researcher from Hiroshima University has succeeded in revealing the detailed structure of a massive ionized gas outflow streaming from the starburst galaxy NGC 6240. The team used the Suprime-Cam mounted on the 8.2-meter Subaru Telescope on Maunakea in Hawaii.

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The ionized gas the astronomers observed extends across 300,000 light-years and is carried out of the galaxy by a powerful superwind. That wind is driven by intense star-forming activity at the galactic center. The light-collecting power and high spatial resolution of Subaru Telescope made it possible to study, for the first time, the complex structure of one of the largest known superwinds being driven by starbirth — and star death.

The term “starburst” indicates large-scale intensive star-forming activity, making a “starburst galaxy” one where starbirth is occurring on a grand scale. The star formation rate (SFR) of our Milky Way Galaxy is approximately one solar mass per year. By contrast, the SFRs of starburst galaxies reach ten, or even a hundred to a thousand solar masses per year.

Starburst activity is a very important part of galaxy evolution. When a starburst occurs, the intense episode star formation rapidly consumes the galaxy’s interstellar gas. In addition, ultraviolet light from newborn massive stars as well as gas heating and ram pressure from supernova explosions blows much of a galaxy’s gas away into intergalactic space. This galactic-scale energetic wind is called a “galactic wind” or “superwind.” Its action forces interstellar gas out of the galaxy very efficiently, which accelerates the galaxy’s gas-loss rate. It also chokes off star formation.

The metal-rich gas expelled from the galaxy’s disk pollutes its halo as well as intergalactic space. Consequently, starburst and starburst-driven superwind significantly affect the evolution of the galaxy and the gas outside of that galaxy.

One of the mechanisms that seems to induce large-scale starburst activity is galaxy collision and merger. When two gas-rich giant spiral galaxies merge, the gravitational perturbation induced by the merging process disturbs the orbits of stars. At the same time, the gas in the galaxy disks loses its angular momentum via viscous process associated with gas mixture, and falls into the gravitational center of the merger. This creates a vast concentration of gas, which begins to coalesce, creating a starburst knot. The starburst also creates a huge amount of dust which emits strong infrared radiation as it absorbs ultraviolet light from the newly born massive stars.

NGC 6240 is a starburst galaxy fairly close to the Milky Way, at a distance of about 350 million light-years. Its SFR is estimated to be 25-80 times that of our galaxy. It has a peculiar, disturbed morphology which indicates that two spiral galaxies are merging. Due to the giant starburst at its heart as a result of the merger, NGC 6240 is very bright in infrared light being emitted from heated dust. The total infrared luminosity reaches almost a trillion times of that the Sun’s.

NGC 6240 is an important object to investigate in order to understand the physical and evolutional relationship among the processes of galaxy merger, the action of a starburst, and the phenomenon of an active galactic nucleus. Hence, it is one of the most-studied starburst galaxies in the nearby universe within 500 million light-years of the Sun.

The research team wanted a wide-field of NGC 6240. The Suprime-Cam optical camera was used on Subaru Telescope to zero in on the detailed structure of the starburst-driven superwind. In addition, the team searched for important clues to understanding the starburst history of NGC 6240. They observed the galaxy using a special band-pass filter that selectively transmits the light around an emission line produced by ionized hydrogen (called the H-alpha emission line). It allowed them to study the structure of the ionized gas associated with the superwind.

Their unprecedented deep observation (long-exposure images) revealed a complex giant ionized gas nebula (called an “H-alpha nebula”) surrounding NGC 6240. This nebula extends out about 300,000 light-years and contains complicated structures of filaments, loops, and blobs. Astronomers knew that such a large ionized gas nebula surrounds NGC 6240, but the depth of the observation significantly surpassed any previous studies and first allowed the Hiroshima team to study the some of the faintest, most detailed structure of the nebula. Large “broken bubbles” were detected in the northwestern and southeastern parts of the galaxy. These features are the evidence of a past energetic bipolar-shaped superwind that blew along the minor axis of the main galaxy disk (orthogonal to the main galactic disk).

The research team performed detailed data analysis and found that NGC 6240 has experienced violent starbursts at least three times in the past and each starburst drove an energetic superwind. Those superwinds form complex structure in the H-alpha nebula. The oldest starburst started about 80 million years ago. Astronomers think that the galaxy merger process of NGC 6240 began about a billion years ago, so this work suggests that the later stages of the merger are what excited the gigantic starbursts and subsequent superwinds. These results contribute new information to the studies of galaxy evolution and its relation to galaxy-galaxy mergers.

Rare Sub-Antarctic Volcano Eruption Captured

Scientists have caught a rare glimpse of ice and fire, witnessing an eruption of the Big Ben volcano, situated on the remote Australian territory of Heard Island in the sub-Antarctic.

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While Big Ben is known to have erupted at least three other times since 2000, catching the volcano massif in the act is extremely unlikely, given how truly removed Heard Island is. Lying some 4,099 kilometres (2,547 miles) southwest of Perth in Western Australia, and almost as far to the southeast of Madagascar, the island ranks among the most remote places on Earth – and researchers haven’t set foot on it in almost 30 years.

Which makes it all the more serendipitous that scientists on board Australia’s CSIRO research vessel, Investigator, on a voyage to the Kerguelen Plateau happened to observe the eruption, in addition to seeing volcanic activity at the neighbouring McDonald Islands – Australia’s only other active volcano.

“Seeing vapour emanating from both of Australia’s active volcanoes and witnessing an eruption at Mawson Peak have been an amazing coda to this week’s submarine research,” said the voyage’s chief scientist, Mike Coffin of the Institute of Marine and Antarctic Studies. “We have 10 excited geoscientists aboard Investigator, and our enthusiasm has spread to our 50 shipmates.”

Seeing Big Ben’s summit – the 2,745-metre (9,000 foot) tall Mawson Peak – in the act of erupting was particularly surprising to those on board, as inclement weather in the area (signs of which you can see in these photos) meant it was highly probable that the elevated peak wouldn’t be visible at all.

“I’m doing my PhD on Heard Island volcanism, and to see lava emanating from Mawson Peak and flowing down the flank of Big Ben over a glacier has been incredible,” said Jodi Fox, a student researcher at the University of Tasmania. “Given persistent cloud cover and generally foul weather, I didn’t think we’d even see Mawson Peak on this voyage.”

Using shipboard sonar systems, the researchers are imaging the seafloor and water column in the area looking for underwater plumes that could represent hydrothermal systems associated with active underwater volcanoes. Although less than halfway through their 58-day trip, the scientists have identified over 50 such potential plumes already.

But, despite the progress made so far, it’s pretty clear what the most memorable highlight of the voyage is likely to be.

“Seeing land after being at sea for a couple of weeks is exciting, but to see dynamic Earth processes such as volcanoes erupting is an added bonus,” said Coffin.

NASA’s Juno Spacecraft Burns for Jupiter

NASA’s solar-powered Juno spacecraft successfully executed a maneuver to adjust its flight path today, Feb. 3. The maneuver refined the spacecraft’s trajectory, helping set the stage for Juno’s arrival at the solar system’s largest planetary inhabitant five months and a day from now.

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“This is the first of two trajectory adjustments that fine tune Juno’s orbit around the sun, perfecting our rendezvous with Jupiter on July 4th at 8:18 p.m. PDT [11:18 p.m. EDT],” said Scott Bolton, Juno principal investigator at the Southwest Research Institute in San Antonio.

The maneuver began at 10:38 a.m. PST (1:38 p.m. EST). ). The Juno spacecraft’s thrusters consumed about 1.3 pounds (0.6 kilograms) of fuel during the burn, and changed the spacecraft’s speed by 1 foot (0.31 meters), per second. At the time of the maneuver, Juno was about 51 million miles (82 million kilometers) from Jupiter and approximately 425 million miles (684 million kilometers) from Earth. The next trajectory correction maneuver is scheduled for May 31.

Juno was launched on Aug. 5, 2011. The spacecraft will orbit the Jovian world 33 times, skimming to within 3,100 miles (5,000 kilometers) above the planet’s cloud tops every 14 days. During the flybys, Juno will probe beneath the obscuring cloud cover of Jupiter and study its aurorae to learn more about the planet’s origins, structure, atmosphere and magnetosphere.

Juno’s name comes from Greek and Roman mythology. The god Jupiter drew a veil of clouds around himself to hide his mischief, and his wife — the goddess Juno — was able to peer through the clouds and reveal Jupiter’s true nature.

NASA’s Jet Propulsion Laboratory, Pasadena, California, manages the Juno mission for the principal investigator, Scott Bolton, of Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for NASA’s Science Mission Directorate. Lockheed Martin Space Systems, Denver, built the spacecraft. The California Institute of Technology in Pasadena manages JPL for NASA.

Activity On Seafloor Linked To Icy Ebb And Flow On Surface

The last million years of Earth’s history has been dominated by the cyclic advance and retreat of ice sheets over large swaths of North America, with ice ages occurring every 40,000 years or so.

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While conventional wisdom says that this icy ebb and flow is an interaction between the water and atmosphere, the cause of the rapid transition between alternating cold glacial and warmer interglacial periods has been a mystery.

Until now. An article appearing in the Jan. 28 issue of the journal Science sheds new light on the role that the Earth itself may play in this climatological ballet.

UConn marine scientist David Lund and his colleagues studied hydrothermal activity along the mid-ocean ridge system – the longest mountain range in the world, which extends some 37,000 miles along the ocean floor – and found a link between pressure and temperature changes.

Their research suggests that the release of hot molten rock, or magma, from beneath the Earth’s crust in response to changes in sea level plays a significant role in the Earth’s climate by causing oceans to alternately warm and cool. This change in temperature is attributed to the release of heat and carbon dioxide (CO2) into the deep ocean.

During cold glacial intervals, ice sheets reached as far south as Long Island and Indiana, while during warm periods, the ice rapidly retreated to Greenland.

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There is evidence that when ice sheets grow, sea level lowers and significant pressure is taken off the ocean ridges. But, as the pressure lessens, the mantle begins melting, which, in turn, warms the water and causes the ice to begin melting. Then, as the ice melts, sea levels rise, causing pressure on the mountain ranges to increase and activity within the mountain ranges to slow.

Think of the effect that applying pressure to a wound has in slowing the flow of bleeding.

The release of molten rock through volcanic vents or fissures is driven by seafloor spreading and decompression melting of the upper mantle, the partially molten layer just beneath the earth’s crust.

Well documented sedimentary records from the East Pacific Rise (EPR) – a mid-ocean ridge extending roughly from Antarctica to the Gulf of California – show evidence of increased hydrothermal activity at the ends of the last two glacial eras.

Researchers also examined core samples from the ocean floor mountain ridges and determined concentrations of major and trace elements.

The results establish the timing of hydrothermal anomalies. Says Lund, “Our results support the hypothesis that enhanced ridge magmatism [the release of molten rock through volcanic vents or fissures], hydrothermal output, and perhaps mantle CO2 flux act to reduce the size of ice sheets.”

Seismic Data Suggests Slow Slip Events May Presage Larger Earthquakes

A team of researchers, two from Tohoku University in Japan and two from the University of California in the U.S., has found evidence that suggests that a speedup in small underground deformations may occur prior to larger earthquakes, possibly providing a means for sounding a warning. In their paper published in the journal Science, the team describes how they pored over seismic data that spanned 28 years and which included approximately 6,000 seismic events, and what they found as a result—they also suggest that their findings might one day lead to a true earthquake early warning system.

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Scientists the world over have for years been searching for a way to predict when an earthquake will strike, with enough certainty to warn people in the area. To date such efforts have come up empty, though much has been learned in the process. In this new effort, the researchers report that they believe they may have found a possible indicator of an impending quake, and it is based on what are known as slips, small underground movement similar to earthquakes, but which happen so slowly that they don’t cause damage or even register on seismic monitors—the only way to detect them is to use GPS equipment.

To come to these conclusions, the researchers analyzed seismic data for Japan’s two largest islands, going back to 1984. Doing so led to the identification of 1,500 instances where there appeared to be a pattern of repetition—that allowed them to estimate the speed at which the tectonic plates below were moving. They then used statistics to correlate slippages with non-repeating measurable quakes with a magnitude of 5 or higher. Doing so revealed that there appeared to be a speedup in slippage just prior to major earthquakes. The team also looked at GPS data, which can actually be used to measure tectonic shifting, and report that it matched the rates they had calculated earlier.

The team acknowledges that much more work needs to be done before it can be confirmed that GPS monitoring devices could one day offer an early warning system, but suggest their research shows that there is the potential for such an outcome.

NASA: Understanding The Magnetic Sun

The surface of the Sun writhes and dances. Far from the still, whitish-yellow disk it appears to be from the ground, the Sun sports twisting, towering loops and swirling cyclones that reach into the solar upper atmosphere, the million-degree corona – but these cannot be seen in visible light. Then, in the 1950s, we got our first glimpse of this balletic solar material, which emits light only in wavelengths invisible to our eyes.

Once this dynamic system was spotted, the next step was to understand what caused it. For this, scientists have turned to a combination of real time observations and computer simulations to best analyze how material courses through the corona. We know that the answers lie in the fact that the Sun is a giant magnetic star, made of material that moves in concert with the laws of electromagnetism.

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“We’re not sure exactly where in the Sun the magnetic field is created,” said Dean Pesnell, a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It could be close to the solar surface or deep inside the Sun – or over a wide range of depths.”

Getting a handle on what drives that magnetic system is crucial for understanding the nature of space throughout the solar system: The Sun’s magnetic field is responsible for everything from the solar explosions that cause space weather on Earth – such as auroras – to the interplanetary magnetic field and radiation through which our spacecraft journeying around the solar system must travel.

So how do we even see these invisible fields? First, we observe the material on the Sun. The Sun is made of plasma, a gas-like state of matter in which electrons and ions have separated, creating a super-hot mix of charged particles. When charged particles move, they naturally create magnetic fields, which in turn have an additional effect on how the particles move. The plasma in the Sun, therefore, sets up a complicated system of cause and effect in which plasma flows inside the Sun – churned up by the enormous heat produced by nuclear fusion at the center of the Sun – create the Sun’s magnetic fields. This system is known as the solar dynamo.

We can observe the shape of the magnetic fields above the Sun’s surface because they guide the motion of that plasma – the loops and towers of material in the corona glow brightly in EUV images. Additionally, the footpoints on the Sun’s surface, or photosphere, of these magnetic loops can be more precisely measured using an instrument called a magnetograph, which measures the strength and direction of magnetic fields.

Next, scientists turn to models. They combine their observations – measurements of the magnetic field strength and direction on the solar surface – with an understanding of how solar material moves and magnetism to fill in the gaps. Simulations such as the Potential Field Source Surface, or PFSS, model – shown in the accompanying video – can help illustrate exactly how magnetic fields undulate around the Sun. Models like PFSS can give us a good idea of what the solar magnetic field looks like in the Sun’s corona and even on the Sun’s far side.

A complete understanding of the Sun’s magnetic field – including knowing exactly how it’s generated and its structure deep inside the Sun – is not yet mapped out, but scientists do know quite a bit. For one thing, the solar magnetic system is known to drive the approximately-11-year activity cycle on the Sun. With every eruption, the Sun’s magnetic field smooths out slightly until it reaches its simplest state. At that point the Sun experiences what’s known as solar minimum, when solar explosions are least frequent. From that point, the Sun’s magnetic field grows more complicated over time until it peaks at solar maximum, some 11 years after the previous solar maximum.

“At solar maximum, the magnetic field has a very complicated shape with lots of small structures throughout – these are the active regions we see,” said Pesnell. “At solar minimum, the field is weaker and concentrated at the poles. It’s a very smooth structure that doesn’t form Sunspots.”

Take a look at the side-by-side comparison to see how the magnetic fields change, grew and subsided from January 2011 to July 2014. You can see that the magnetic field is much more concentrated near the poles in 2011, three years after solar minimum. By 2014, the magnetic field has become more tangled and disorderly, making conditions ripe for solar events like flares and coronal mass ejections.

Rapid Formation Of Bubbles In Magma May Trigger Sudden Volcanic Eruptions

It has long been observed that some volcanoes erupt with little prior warning. Now, scientists have come up with an explanation behind these sudden eruptions that could change the way observers monitor active or dormant volcanoes.

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Previously, it was thought eruptions were triggered by a build-up of pressure caused by the slow accumulation of bubbly, gas-saturated magma beneath volcanoes over tens to hundreds of years. But new research has shown that some eruptions may be triggered within days to months by the rapid formation of gas bubbles in magma chambers very late in their lifetime.

Using the Campi Flegrei volcano near Naples, southern Italy, as a case study, the team of scientists, from the universities of Oxford and Durham in the UK, and the Vesuvius Volcano Observatory in Italy, demonstrate this phenomenon for the first time and provide a mechanism to explain the increasing number of reported eruptions that occur with little or no warning.

The study is published in the journal Nature Geoscience.

Lead author Mike Stock, from the Department of Earth Sciences at the University of Oxford, said: ‘We have shown for the first time that processes that occur very late in magma chamber development can trigger explosive eruptions, perhaps in only a few days to months. This has significant implications for the way we monitor active and dormant volcanoes, suggesting that the signals we previously thought indicative of pre-eruptive activity – such as seismic activity or ground deformation – may in fact show the extension of a dormant period between eruptions.

‘Our findings suggest that, rather than seismic activity and ground deformation, a better sign of an impending eruption might be a change in the composition of gases emitted at the Earth’s surface. When the magma forms bubbles, the composition of gas at the surface should change, potentially providing an early warning sign.’
The researchers analysed tiny crystals of a mineral called apatite thrown out during an ancient explosive eruption of Campi Flegrei. This volcano last erupted in 1538 but has recently shown signs of unrest.

By looking at the composition of crystals trapped at different times during the evolution of the magma body – and with the apatite crystals in effect acting as ‘time capsules’ – the team was able to show that the magma that eventually erupted had spent most of its lifetime in a bubble-free state, becoming gas-saturated only very shortly before eruption. Under these conditions of slow magma chamber growth, earthquakes and ground deformation observed at the surface may not be signs of impending eruption, instead simply tracking the arrival of new batches of magma at depth.

Professor David Pyle from the Department of Earth Sciences at the University of Oxford, a co-author of the paper, said: ‘Now that we have demonstrated that this approach can work on a particular volcano, and given apatite is a mineral found in many volcanic systems, it is likely to stimulate interest in other volcanoes to see whether there is a similar pattern.

‘This research will also help us refine our ideas of what we want to measure in our volcanoes and how we interpret the long-term monitoring signals traditionally used by observers.’

The Campi Flegrei volcano system has had a colourful history. The Romans thought an area called Solfatara (where gas is emitted from the ground) was the home of Vulcan, the god of fire. Meanwhile, one of the craters in the system, Lake Avernus, was referred to as the entrance to Hades in ancient mythology.

Additionally, Campi Flegrei has long been a site of geological interest. In Charles Lyell’s 1830 Principles of Geology, he identified the burrows of marine fossils at the top of the Macellum of Pozzuoli (an ancient Roman market building), concluding that the ground around Naples rises and falls over geological time.