BREAKING NEWS: New Study Finds Mantle Plumes, Not Global Warming, Cause of Ice Melt

To understand Greenland’s ice of today – researchers have to go far back into Earth’s history. The island’s lithosphere has hot depths which originate in its distant geological past and cause Greenland’s ice to rapidly flow and melt from below.

greenland-iceland-mantle-plume3

An anomaly zone crosses Greenland from west to east where present-day accelerated ‘mantle plumes’ are shown to be the cause of ice sheets melting in Greenland and Iceland along the Mid-Atlantic-Ridge. With this anomaly, an international team of geoscientists led by Irina Rogozhina and Alexey Petrunin from the GFZ German Research Center for Geosciences could explain observations from radar and ice core drilling data that indicate a widespread melting beneath the ice sheet and increased sliding at the base of the ice that drives the rapid ice flow over a distance of 750 kilometers from the summit area of the Greenland ice sheet to the North Atlantic Ocean.

Iceland - Greenland Mid-Atlantic Ridge3

The North Atlantic Ocean is an area of active plate tectonics. Between 80 and 35 million years ago tectonic processes moved Greenland over an area of abnormally hot mantle material that still today is responsible for the volcanic activity of Iceland. The mantle material heated and thinned Greenland at depth producing a strong geothermal anomaly that spans a quarter of the land area of Greenland.

greenland-iceland-mid-atlantic-ridge

This ancient and long-lived source of heat has created a region where subglacial meltwater is abundant, lubricating the base of the ice and making it flow rapidly. The study indicates that about a half of the ice in north-central Greenland is resting on a thawed bed and that the meltwater is routed to the ocean through a dense hydrological network beneath the ice.

iceland mantle plume

The team of geoscientists has now, for the first time, been able to prove strong coupling between processes deep in the Earth’s interior with the flow dynamics and subglacial hydrology of large ice sheets: “The geothermal anomaly which resulted from the Icelandic mantle-plume tens of millions of years ago is an important motor for today’s hydrology under the ice sheet and for the high flow-rate of the ice” explains Irina Rogozhina. “This, in turn, broadly influences the dynamic behavior of ice masses and must be included in studies of the future response to climate change.”

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New Study Shows How Black Holes and Galaxies Formed

Until recently, many researchers thought supermassive black holes were seeded by the collapse of some of the first stars. But modeling work by several groups has suggested that this process would only lead to small black holes.

how galaxies and black holes formed.jpg

Kentaro Nagamine at Osaka University’s Department of Earth and Space Science, Isaac Shlosman at the University of Kentucky and co-workers simulated a different situation, in which supermassive black holes are seeded by clouds of gas falling into potential wells created by dark matter – the invisible matter that astronomers believe makes up 85% of the mass of the Universe.

Simulating the dynamics of huge gas clouds is extremely complex, so the team had to use some numerical tricks called ‘sink particles’ to simplify the problem.

“Although we have access to extremely powerful supercomputers at Osaka University’s Cybermedia Center and the National Astronomical Observatory of Japan, we can’t simulate every single gas particle,” explains Nagamine. “Instead, we model small spatial scales using sink particles, which grow as the surrounding gas evolves. This allows us to simulate much longer timescales than was previously possible.”

The researchers found that most seed particles in their simulations did not grow very much, except for one central seed, which grew rapidly to more than 2 million Sun-masses in just 2 million years, representing a feasible path toward a supermassive black hole. Moreover, as the gas spun and collapsed around the central seed it formed two misaligned accretion discs, which have never been observed before.

In other recent work, Nagamine and co-workers described the growth of massive galaxies that formed around the same time as supermassive black holes. “We like to push the frontier of how far back in time we can see,” says Nagamine. The researchers hope their simulations will be validated by real data when NASA’s James Webb Space Telescope, due to be launched in 2018, observes distant sources where direct gas collapse is happening.

Chemistry of Star and Planet Formation

In the last two decades, humanity has discovered thousands of extrasolar planetary systems. Recent studies of star- and planet-formation have shown that chemistry plays a pivotal role in both shaping these systems and delivering water and organic species to the surfaces of nascent terrestrial planets. Professor Geoffrey A. Blake in Chemical Engineering at the California Institute of Technology talked to Duke faculty and students over late-afternoon pizza in the Physics building on the role of chemistry in star and planet formation and finding other Earth-like planets.

chemistry of stars

In the late 18th century, French scholar Pierre-Simon Laplace analyzed what our solar system could tell us about the formation & evolution of planetary systems. Since then, scientists have used the combination our knowledge for small bodies – asteroids – and large bodies – planets – to figure out how solar systems and planets are formed.

In 2015, Professor Blake and other researchers investigated more into ingredients in planets necessary for the development of life.
Using the Earth and our solar system as the basis for their data, they explored the relative disposition of carbon and nitrogen in each stage of star and planet formation to learn more about core formation and atmospheric escape. Analyzing the carbon-silicon atomic ratio in planets and comets, Professor Blake discovered that rocky bodies in the solar system are generally carbon-poor. Since carbon is essential for our survival, however, Blake needed to determine the range of carbon content that terrestrial planets can have and still have active biosystem.

With the Kepler mission, scientists have detected a variety of planetary objects in the universe. How many of these star-planet systems – based on measured distributions – have ‘solar system’ like outcomes? A “solar system” like planetary system has at least one Earth-like planet at approximately 1 astronomical unit (AU) from the star – where more ideal conditions for life can develop – and at least one ice giant like Jupiter at 3-5 AU in order to keep away comets from the Earth-like planet. In our galaxy alone, there are around 10 billion stars and at least 10 million planets. For those stars similar to our sun, there exist over 4 million planetary systems similar to our solar system, with the closest Earth-like planet at 20 light years away. With the rapid improvement of scientific knowledge and technology, Professor Blake estimates that we would be able to collect evidence within next 5-6 years of planets within 40-50 light years to determine if they have a habitable atmosphere.

How does an Earth and a Jupiter form at their ideal distances from a star? Let’s take a closer look at how stars and planets are created – via the astrochemical cycle. Essentially, dense clouds of gas and dust become so opaque and cold that they collapse into a disk. The disk, rotating around a to-be star, begins to transport mass in toward the center and angular momentum outward. Then, approximately 1% of the star mass is left over from the process, which is enough to form planets. This is also why planets around stars are ubiquitous.

How are the planets formed? The dust grains unused by the star collide and grow, forming larger particles at specific distances from the star – called snowlines – where water vapor turns into ice and solidifies. These “dust bunnies” grow into planetesimals (~10-50 km diameter), such as asteroids and comets. If the force of gravity is large enough, the planetesimals increase further in size to form oligarchs (~0.1-10 times the mass of the Earth), that then become the large planets of the solar system.

In our solar system, a process called dynamic reorganization occurred that restructured the order of our planets, putting Uranus before Neptune. This means that if other solar systems did not undergo such dynamic reorganization at an early point in formation of solar system, then other Earths may have lower organic and water content than our Earth. In that case, what constraints do we need to apply to determine if a water/organic delivery mechanism exists for exo-Earths? Although we do not currently have the scientific knowledge to answer this, with ALMA and the next generation of optical/IR telescopes, we will be able image the birth of solar systems directly and better understand how our universe came to be.

To the chemistry students at Duke, Professor Blake relayed an important message: learn chemistry fundamentals very carefully while in college. Over the next 40-50 years, your interests will change gears many times. Strong fundamentals, however, will serve you well, since you are now equipped to learn in many different areas and careers.

BREAKING NEWS: New Study Suggests Moon Has Great Influence on Earth’s Magnetic Field

The Earth’s magnetic field permanently protects us from the charged particles and radiation produced by our Sun. This shield is created by the geodynamo process, the rapid motion of huge quantities of liquid iron alloy in the Earth’s outer core. To maintain this magnetic field until the present day, the classical model required the Earth’s core to have cooled by around 3,000° C over the past 4.3 billion years.

moon's geodynamo

Now, a team of researchers from French National Center for Scientific Research (CNRS) and Université Blaise Pascal1 suggests that, on the contrary, its temperature has fallen by only 300° C. The action of the moon, overlooked until now, is thought to have compensated for this difference and kept the geodynamo active. Their work is published in the March 30 2016 journal Earth and Planetary Science Letters.

moon's magnetic field2

The classical model of the formation of Earth’s magnetic field has raised a major paradox. For the geodynamo to work, the Earth would have had to be totally molten four billion years ago, and its core would have had to slowly cool from around 6800° C at that time to 3800° C today. However, recent modeling of the early evolution of the internal temperature of the planet, together with geochemical studies of the composition of the oldest carbonatites and basalts, do not support such cooling. With such high temperatures being ruled out, the researchers propose another source of energy in their study.

The gravitational effects associated with the presence of the Moon and Sun on Earth induces cyclic deformation of the mantle and oscillations of the axis of rotation. This mechanical forcing applied to the entire planet induces strong currents in the outer core made of an iron alloy of very low viscosity. These currents are sufficient to generate the Earth’s magnetic field.

It is likely that the liquid metallic cores of many early asteroids generated dynamo magnetic fields.
It is likely that the liquid metallic cores of many early asteroids generated dynamo magnetic fields.

The Earth has a slightly flattened shape and rotates about an inclined axis that wobbles around the poles. Its mantle deforms elastically due to tidal effects caused by the moon. The researchers show that this effect could continuously stimulate the motion of the liquid iron alloy making up the outer core, and in return generate Earth’s magnetic field. The Earth continuously receives 3700 billion watts of power through the transfer of the gravitational and rotational energy of the Earth-moon-Sun system, and over 1,000 billion watts is thought to be available to bring about this type of motion in the outer core. This energy is enough to generate the Earth’s magnetic field, which together with the moon, resolves the major paradox in the classical theory. The effect of gravitational forces on a planet’s magnetic field has already been well documented for two of Jupiter’s moons, Io and Europa, and for a number of exoplanets.

moon's core

As neither the rotation of the Earth around its axis, or orientation of the axis, or the orbit of the moon are perfectly regular – their combined influence on Earth’s inner and outer core, becomes unstable causing fluctuations in the geodynamo. This phenomenon helps explain what would be the catalyst for the ebb and flow of mantle plumes.

Historically, this could lead to melting peaks in the deep mantle and possible major volcanic events on the surface of the Earth. This new model underlines that the influence of the moon on the Earth therefore goes well beyond the simple case of the tides.

 

INTEGRAL Sets Limits on Gamma Rays from Merging Black Holes

The terrestrial Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves – fluctuations in the fabric of space-time – produced by a pair of black holes as they spiraled towards each other before merging. The signal lasted less than half a second.

gravitational waves

The discovery was the first direct observation of gravitational waves, predicted by Albert Einstein a century ago.

Two days after the detection, the LIGO team alerted a number of ground- and space-based astronomical facilities to look for a possible counterpart to the source of gravitational waves. The nature of the source was unclear at the time, and it was hoped that follow-up observations across the electromagnetic spectrum might provide valuable information about the culprit.

Gravitational waves are released when massive bodies are accelerated, and strong emission should occur when dense stellar remnants such as neutron stars or black holes spiral towards each other before coalescing.

Models predict that the merging of two stellar-mass black holes would not produce light at any wavelength, but if one or two neutron stars were involved in the process, then a characteristic signature should be observable across the electromagnetic spectrum.

Another possible source of gravitational waves would be an asymmetric supernova explosion, also known to emit light over a range of wavelengths.
It was not possible to pinpoint the LIGO source – its position could only be narrowed down to a very long strip across the sky.

Observatories searched their archives in case data had been serendipitously collected anywhere along this strip around the time of the gravitational wave detection. They were also asked to point their telescopes to the same region in search for any possible ‘afterglow’ emission.

INTEGRAL is sensitive to transient sources of high-energy emission over the whole sky, and thus a team of scientists searched through its data, seeking signs of a sudden burst of hard X-rays or gamma rays that might have been recorded at the same time as the gravitational waves were detected.

“We searched through all the available INTEGRAL data, but did not find any indication of high-energy emission associated with the LIGO detection,” says Volodymyr Savchenko of the François Arago Centre in Paris, France. Volodymyr is the lead author of a paper reporting the results, published today in Astrophysical Journal Letters.

The team analysed data from the Anti-Coincidence Shield on INTEGRAL’s SPI instrument. The shield helps to screen out radiation and particles coming from directions other than that where the instrument is pointing, as well as to detect transient high-energy sources across the whole sky.

The team also looked at data from INTEGRAL’s IBIS instrument, although at the time it was not pointing at the strip where the source of gravitational waves was thought to be located.

“The source detected by LIGO released a huge amount of energy in gravitational waves, and the limits set by the INTEGRAL data on a possible simultaneous emission of gamma rays are one million times lower than that,” says co-author Carlo Ferrigno from the INTEGRAL Science Data Center at the University of Geneva, Switzerland.

Subsequent analysis of the LIGO data has shown that the gravitational waves were produced by a pair of coalescing black holes, each with a mass roughly 30 times that of our Sun, located about 1.3 billion light years away. Scientists do not expect to see any significant emission of light at any wavelength from such events, and thus INTEGRAL’s null detection is consistent with this scenario.

Similarly, nothing was seen by the great majority of the other astronomical facilities making observations from radio and infrared to optical and X-ray wavelengths.

The only exception was the Gamma-Ray Burst Monitor on NASA’s Fermi Gamma-Ray Space Telescope, which observed what appears to be a sudden burst of gamma rays about 0.4 seconds after the gravitational waves were detected. The burst lasted about one second and came from a region of the sky that overlaps with the strip identified by LIGO.

This detection sparked a bounty of theoretical investigations, proposing possible scenarios in which two merging black holes of stellar mass could indeed have released gamma rays along with the gravitational waves.

However, if this gamma-ray flare had had a cosmic origin, either linked to the LIGO gravitational wave source or to any other astrophysical phenomenon in the Universe, it should have been detected by INTEGRAL as well. The absence of any such detection by both instruments on INTEGRAL suggests that the measurement from Fermi could be unrelated to the gravitational wave detection.

“This result highlights the importance of synergies between scientists and observing facilities worldwide in the quest for as many cosmic messengers as possible, from the recently-detected gravitational waves to particles and light across the spectrum,” says Erik Kuulkers, INTEGRAL Project Scientist at ESA.

This will become even more important when it becomes possible to observe gravitational waves from space. This has been identified as the goal for the L3 mission in ESA’s Cosmic Vision program, and the technology for building it is currently being tested in space by ESA’s LISA Pathfinder mission.

Such an observatory will be capable of detecting gravitational waves from the merging of supermassive black holes in the centers of galaxies for months prior to the final coalescence, making it possible to locate the source much more accurately and thus provide astronomical observatories with a place and a time to look out for associated electromagnetic emission.

“We are looking forward to further collaborations and discoveries in the newly-inaugurated era of gravitational astronomy,” concludes Erik.

Journey to the Center of Our Galaxy

Peering deep into the heart of our home galaxy, the Milky Way, the NASA/ESA Hubble Space Telescope reveals a rich tapestry of more than half a million stars. Apart from a few, blue, foreground stars, almost all of the stars pictured in the image are members of the Milky Way nuclear star cluster, the densest and most massive star cluster in the galaxy. Hidden in the center of this cluster is the Milky Way’s resident supermassive black hole.

Milky Way nuclear star cluster

The center of the Milky Way, 27 000 light-years away in the constellation of Sagittarius, is a crowded place. This region is so tightly packed that it is equivalent to having one million stars crammed into the volume of space between us and Alpha Centauri, located 4.3 light-years away. At the very hub of our galaxy, this dense nuclear star cluster surrounds the Milky Way’s central supermassive black hole, known as Sagittarius A*, which alone is about four million times the mass of the Sun.

Sagittarius A* is not the only mystery lurking in this part of the galaxy. The crowded center contains numerous objects that are hidden at visible wavelengths by thick clouds of dust in the galaxy’s disc. In order to truly understand the central part of our galaxy astronomers used the infrared vision of Hubble to peer through this obscuring dust. To reveal the image in all its glory the scientists then assigned visible colors to the different wavelengths of infrared light, which is invisible to human eyes.

The blue stars in the image are foreground stars, which are closer to Earth than the nuclear star cluster, whilst the red stars are either behind much more intervening dust, or are embedded in dust themselves. Some extremely dense clouds of gas and dust are seen in silhouette, appearing dark against the bright background stars. These clouds are so thick that even Hubble’s infrared capability cannot penetrate them. In addition to the stars hidden by the dust astronomers estimate that there are about 10 million stars in the cluster which are too faint to see, even for Hubble.

Using Hubble’s vantage point above the atmosphere and its high resolution, astronomers were able not only to reveal the stars in this cluster but also to measure their movements over a period of four years.

Using this information, they inferred important properties of the nuclear star cluster, such as its mass and structure. The motion of the stars may also offer astronomers a glimpse into how the nuclear star cluster was formed—whether it was built up over time from globular star clusters that happened to fall into the center of the galaxy, or from gas spiraling in from the Milky Way’s disc to form stars at the core.

Wellspring of New Brown Dwarf Stellar Companions

A new paper published this month in The Astronomical Journal by astronomers from the Sloan Digital Sky Survey (SDSS) reports a wellspring of new brown dwarf stellar companions, throwing cold water on the entire idea of the “brown dwarf desert,” the previously mystifying lack of these sub-stellar objects around stars.

brown-dwarf-plasmaspher

Most stars in our Galaxy have a traveling companion. Often, these companions are stars of similar mass, as is the case for our nearest stellar neighbors, the triple star system Alpha Centauri.

brown_dwarf_size

Our Sun, of course, has companions of its own – the planets of our Solar System. Planetary companions are vastly different from stellar companions: they are much smaller, and they do not shine with their own light created through nuclear fusion. Even the largest planet in our Solar System, Jupiter, would need to be 80 times more massive to even begin to shine this way.

Stuck in the middle are “brown dwarfs,” much bigger than Jupiter but still too small to be shining stars. These brown dwarfs give off merely a dim glow as they slowly cool. The Universe is full of stars, and now we know that it is full of planets too. Astronomers expected that the Universe would also be teeming with brown dwarfs.

But strangely, that’s not what they had been finding. Although astronomers have found plenty of brown dwarfs floating through space on their own, they found very few as stellar companions. Even in recent years, as new and sensitive detection techniques have allowed them to discover thousands of extrasolar planets, brown dwarfs have remained elusive – in spite of the fact that they should be easier to find than planets.

In fact, until recently, so few brown dwarfs have been found orbiting close to other stars that astronomers refer to the phenomenon as the “brown dwarf desert.” This in turn created a problem for theorists, who have been scrambling to explain why astronomers have found so few. Therefore when SDSS astronomers started sifting through their data looking for brown dwarf companions to stars, they were hoping not to come up completely dry.

“We were shocked to find that so many of the stars in our sample have close-orbiting brown dwarf companions,” says Nick Troup of the University of Virginia, lead author of the paper. “We never expected to triple the total number of known brown dwarf companions with only a few years’ worth of observations.”

The team’s success is due to an unlikely tool in the race to find low-mass stellar companions. The Apache Point Observatory Galactic Evolution Experiment (APOGEE) was designed as a substantial survey of stars in our Milky Way to make a large-scale map of their motions and chemical compositions. But the instrument built for the APOGEE project is so sensitive to small stellar motions that companions orbiting these stars can be detected with APOGEE data.

When an object orbits a star, it tugs at it, causing the star to move on a little orbit of its own. For example, Jupiter tugs on the Sun enough to make it wobble around in space by more than its own diameter. To a distant observer, this wobble can be detected—and the mass of the tugging object can be determined—through changes in the motion of the star. This motion is seen through the Doppler effect, the same phenomenon that is the basis of the patrol officer’s speed gun and the meteorologist’s Doppler radar rain map. While APOGEE was designed to measure the grand motions of stars speeding around the Galaxy, it was never intended to do so at the subtle precisions needed to detect the much tinier wobbles induced by small sub-stellar companions.

“This level of precision was a serendipitous bonus of the design of the APOGEE spectrograph”, says John Wilson, University of Virginia astronomer and leader of the APOGEE instrument team. “The entire instrument has to be contained in a giant steel vessel in a vacuum at –320 degrees F, otherwise the instrument’s own heat would swamp the infrared signals from the stars.” It turns out that this tightly controlled environment makes it possible to use the APOGEE instrument to measure Doppler shifts reliably over the course of months or years, a feat not achievable by many other spectrographs.

“Even with the first data obtained a few years ago, it was clear that we could use APOGEE to detect the motions of planet-sized objects around our target stars,” says David Nidever of the University of Arizona and the Large Synoptic Survey Telescope, who was responsible for writing much of the software that measures the Doppler motions in APOGEE spectra. “It definitely opened our eyes to the possibilities of doing a more systematic search for planets and brown dwarfs.”

To undertake such a search, the team started with the 150,000 stars that APOGEE had observed. The astronomers winnowed that collection of stars down to a “prime sample” of about four hundred representing the best examples of stars with companions in the APOGEE data. Among these, they identified about 60 stars with evidence for planetary-mass candidates, which was already exciting.
But the real surprise came with the researchers’ extraordinary haul of 112 brown dwarf candidates – twice as many than had been found in the previous 15 years.

Why has the APOGEE team been so lucky in finding this oasis of brown dwarfs? Troup thinks it may have to do with the types of host stars that they are looking at. “Most people doing planet searches have been interested in finding the next Earth, so they’ve focused their efforts on stars similar to the Sun,” Troup says. “But we had to work with the stars that APOGEE surveyed, which are mostly giant stars.”

The reasons why brown dwarf companions are more common around giant stars is just one of many new questions raised by this new study that the Sloan team is investigating. And the team will continue to test their results with the ever-growing flow of APOGEE data.

“It’s completely unprecedented that this many brown dwarf companions have been found at once, so we are anxious to see if the trend persists as the APOGEE sample grows to several times larger,” Troup said.
Read more at: http://phys.org/news/2016-03-oasis-brown-dwarf-desertastronomers-relieved.html#jCp