The Role Of Magnetic Fields In Star Formation

The star forming molecular clump W43-MM1 is very massive and dense, containing about 2100 solar masses of material in a region only one-third of a light year across (for comparison, the nearest star to the Sun is a bit over four light years away).

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Previous observations of this clump found evidence for infalling motions (signaling that material is still accumulating onto a new star) and weak magnetic fields. These fields are detected by looking for polarized light, which is produced when radiation scatters off of elongated dust grains aligned by magnetic fields. The Submillimeter Array recently probed this source with high spatial resolutions and found evidence for even stronger magnetic fields in places. One of the outstanding issues in star formation is the extent to which magnetic fields inhibit the collapse of material onto stars, and this source seems to offer a particularly useful example.

CfA astronomers Josep Girart and TK Sridharan and their colleagues have used the ALMA submillimeter facility to obtain images with spatial scales as small as 0.03 light years. Their detailed polarization maps show that the magnetic field is well ordered all across the clump, which itself is actually fifteen smaller fragments, one of which (at 312 solar masses) appears to be the most massive fragment known.

The scientists analyze the magnetic field strengths and show that, even in the least massive fragment the field is not strong enough to inhibit gravitational collapse. In fact, they find indications that gravity, as it pulls material inward, drags the magnetic field lines along. They are, however, unable to rule out possible further fragmentation. The research is the most precise study of magnetic fields in star forming massive clumps yet undertaken, and provides a new reference point for theoretical models.

Scientists Observe A Superluminous Supernova That Appears To Have Exploded Twice

Supernovae are among the most violent phenomena in the universe. They are huge explosions that end the lives of certain types of stars. These explosions release immense amounts of energy, so much that some can be observed from Earth with the naked eye, appearing as points of light that are briefly brighter than all the millions of stars in the galaxies where they are found. Following an intense burst of light lasting a few weeks, supernovae start to fade gradually until they have effectively burned out.

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There are several types of supernovae. The astronomers classify them by their observable characteristics, which give clues about their origin. Among the most well known are those of type Ia .When a white dwarf, the final state of a star slightly more massive than the sun, absorbs mass from another nearby star or merges with another white dwarf, its mass grows until it becomes unstable and a thermonuclear explosion occurs. As these events produce a characteristic luminosity, they can be used by astronomers as “standard candles” to measure large distances in the universe, like sailors to inferring the distance of a known lighthouse at night by estimating its brightness.

The other types of supernovae are produced when very massive stars exhaust their fuel, so that nuclear fusion in their interiors comes to an end. This fusion not only causes stars to emit light and heat, but keeps them in equilibrium so that they don’t collapse under their own gravity. When the fusion stops, the centre of the star collapses and the outer layers are flung outwards with violence, causing a supernova, while the centre implodes, leaving a neutron star—or for very massive stars, a black hole.

In recent years, a new type of supernova has been discovered, about which very little is yet known, and which are brighter and longer-lasting. Astronomers call them superluminous supernovae (SLSN). Although only about a dozen of them are known, an international group of researchers has used the Gran Telescopio CANARIAS (GTC) to observe a superluminous supernova almost from the moment it occurred. The research has revealed surprising behaviour, because this supernova showed an initial increase in brightness that later declined for a few days, and then increased again much more strongly. The scientists have combined from the GTC with other observations in order to try to explain the origin of the phenomenon.

“Superluminous supernovas are up to a hundred times more energetic than type 1a supernovae because they can remain bright for up to six months before fading, rather than just a few weeks,” explains Mathew Smith, a postdoctoral researcher at the University of Southampton (UK) and the person directing this study, whose results have been published in the specialized journal The Astrophysical Journal Letters. “What we have managed to observe, which is completely new, is that before the major explosion, there is a shorter, less luminous outburst, which we can pick out because it is followed by a dip in the light curve, and which lasts just a few days.”

It is the first time that something like this has been observed in a supernova. “From our data, we have tried to determine if this is a characteristic unique to this object, or whether it is a common feature of all superluminous supernovae, but has not been observed before, which is perfectly possible given their unpredictable nature,” says the scientist.

This new, intriguing object, given the cryptic name of DES14X3taz by the astronomers, was discovered on December 21, 2014 by the Dark Energy Survey, an international project that surveys the night sky, making precision measurements of over 300 million galaxies that are situated thousands of millions of light years from Earth, and incidentally detecting thousands of supernovae and other transient phenomena. The objective of this survey is to explain the expansion of the universe, and to find clues to the nature of dark energy. To do this, astronomers are using an extremely sensitive 570 megapixel digital camera on the four metre Victor M. Blanco telescope at the Inter-American Observatory at Cerro Tololo (Chile).

Once DES14X3taz had been identified as a possible superluminous supernova, an immediate observation was requested on the GTC, which turned its powerful eye toward it over two nights of observation, January 26 and February 6, 2015. GTC devotes some of its observing time to “targets of opportunity,” so that other programmed observations can postponed to prioritize such transient phenomena, which may offer unrepeatable opportunities.

“The GTC, with its huge 10.4m mirror, and its OSIRIS instrument, is the ideal tool to observer this SNSL, which is at a vast distance and because we are looking for information in the visible and the near infrared,” says Smith, who is a participant in the Dark Energy Survey. Thanks to the observations made with the GTC and other telescopes, Smith and his collaborators could reconstruct the evolution of the brightness of DES14X3taz from almost the moment of its detection. They have also determined its absolute brightness with great precision, as well as its distance, some 6,400 million light years.

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After comparing their observations with several physical models, the astronomers concluded in their article that the most plausible explanation is that the mechanism causing this supernova is the birth of a “magnetar,” a neutron star that rotates very rapidly on its axis. In the data, the initial peak of the brightness graph is followed by rapid cooling of the object, after which there is a quicker rise in brightness. This is consistent with the emission of a huge bubble of material into the surrounding space, which cools rapidly as it grows in size.

“We think that a very massive star, some 200 times the mass of the Sun, collapses to form a magnetar. In the process, the first explosion occurs, which expels into space a quantity of matter equivalent to the mass of our sun, and this gives rise to the first peak of the graph. The second peak occurs when the star collapses to form the magnetar, which is a very dense object rotating rapidly on its axis, and which heats up the matter expelled from the first explosion. This heating is what generates the second peak in the luminosity,” explains Smith.

This understanding may allow us to “standardize” superluminous supernovae as has occurred for the type Ia supernovae for use as a reference source for distance measurement on large scales in the universe. Its high luminosity may make these objects useful for calculating distances on larger scales, and with greater accuracy than current techniques. However, before we get to that point, we need a much deeper understanding of their origin and their nature.

Another mystery about this new type of supernova is that, until recently, all the examples detected have been in small galaxies with low metallicity (low content in heavy elements), which is not well understood. “It is a part of the mystery of these objects,” says Smith, and adds that among future priorities, we need to detect more superluminous supernovae and observe them from the moment they explode in real time with a telescope the size of the GTC.

Experimentation Suggests Vikings Could Have Used Sunstone To Navigate

A team of researchers from several institutions in Hungary has conducted experiments meant to test the possibility that the Vikings actually did use sunstones to navigate. In their paper published in Proceedings of the Royal Society A, the team describes the experiments they carried out, their results and why they now believe it is possible to use a sunstone as a navigational aid during times when the skies are covered with clouds.

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The exploits of the Vikings have been well documented—they conducted raids across Europe from the late 790s till 1066, when the Normans famously conquered England. But as more recent research has established, they were also long-distance seafaring travelers, venturing as far as the Middle East and North America. But how they found their way across vast stretches of ocean has been a bit of a mystery, particularly during times when there were no stars or sun in the sky to guide them. Some historical evidence such as Icelandic legends have mentioned travel under snowy skies using sunstones and a study of a Viking wreck conducted in 2002 revealed that a crystal (Icelandic spar) had been onboard that was found near other implements used for navigation.

Modern sunstone is a type of crystal that, when viewed from different angles, offers a spangled optical effect. In this new effort, the researchers have conducted a study designed to test the possibility that such crystals could really have helped Vikings find their way across the ocean.

They believe it was a three step process: (1) determine the direction of light from the sky using the sunstone held up to the sky, (2) use that information to determine the direction of sunlight and then (3) use a shadow stick to determine which direction was north. The team previously conducted tests to measure the accuracy of the first two steps and, apparently satisfied with the results, have now conducted experiments with the third.

To test the third step, the researchers asked 10 volunteers to try to work out the position of the sun in a digital planetarium using dots to stand in for results of using a sunstone. After conducting a total of 2,400 trials, the researchers report that 48 percent resulted in producing an accurate reading to within just one degree. They noted also that the volunteers did best when the virtual sun was near the horizon, showing that the method worked best at dawn and dusk. The team suggests their results indicate that it was possible that the Vikings used sunstones to navigate under cloudy skies.

Jupiter’s Great Red Spot Heats Planet’s Upper Atmosphere

Researchers from Boston University’s (BU) Center for Space Physics report today in Nature that Jupiter’s Great Red Spot may provide the mysterious source of energy required to heat the planet’s upper atmosphere to the unusually high values observed.

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Sunlight reaching Earth efficiently heats the terrestrial atmosphere at altitudes well above the sur-face—even at 250 miles high, for example, where the International Space Station orbits. Jupiter is over five times more distant from the Sun, and yet its upper atmosphere has temperatures, on av-erage, comparable to those found at Earth. The sources of the non-solar energy responsible for this extra heating have remained elusive to scientists studying processes in the outer solar system.

“With solar heating from above ruled out, we designed observations to map the heat distribution over the entire planet in search for any temperature anomalies that might yield clues as to where the energy is coming from,” explained Dr. James O’Donoghue, research scientist at BU, and lead author of the study.

Astronomers measure the temperature of a planet by observing the non-visible, infra-red (IR) light it emits. The visible cloud tops we see at Jupiter are about 30 miles above its rim; the IR emissions used by the BU team came from heights about 500 miles higher. When the BU observ-ers looked at their results, they found high altitude temperatures much larger than anticipated whenever their telescope looked at certain latitudes and longitudes in the planet’s southern hemi-sphere.

“We could see almost immediately that our maximum temperatures at high altitudes were above the Great Red Spot far below—a weird coincidence or a major clue?” O’Donoghue added.

Jupiter’s Great Red Spot (GRS) is one of the marvels of our solar system. Discovered within years of Galileo’s introduction of telescopic astronomy in the 17th Century, its swirling pattern of colorful gases is often called a “perpetual hurricane.” The GRS has varied is size and color over the centuries, spans a distance equal to three earth-diameters, and has winds that take six days to complete one spin. Jupiter itself spins very quickly, completing one revolution in only ten hours.

“The Great Red Spot is a terrific source of energy to heat the upper atmosphere at Jupiter, but we had no prior evidence of its actual effects upon observed temperatures at high altitudes,” ex-plained Dr. Luke Moore, a study co-author and research scientist in the Center for Space Physics at BU.

Solving an “energy crisis” on a distant planet has implications within our solar system, as well as for planets orbiting other stars. As the BU scientists point out, the unusually high temperatures far above Jupiter’s visible disk is not a unique aspect of our solar system. The dilemma also oc-curs at Saturn, Uranus and Neptune, and probably for all giant exoplanets outside our solar sys-tem.

“Energy transfer to the upper atmosphere from below has been simulated for planetary atmos-pheres, but not yet backed up by observations,” O’Donoghue said. “The extremely high tempera-tures observed above the storm appear to be the ‘smoking gun’ of this energy transfer, indicating that planet-wide heating is a plausible explanation for the ‘energy crisis.’ “

The Case Of The Missing Craters

When NASA’s Dawn spacecraft arrived to orbit the dwarf planet Ceres in March 2015, mission scientists expected to find a heavily cratered body generally resembling the protoplanet Vesta, Dawn’s previous port of call.

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Instead, as the spacecraft drew near to Ceres, a somewhat different picture began to emerge: Something has happened to Ceres to remove its biggest impact basins.

Now, writing in the online journal Nature Communications, a team of Dawn scientists led by Simone Marchi of the Southwest Research Institute in Boulder, Colorado, reports on their computer simulations of Ceres’ history. These suggest that Ceres has experienced significant geological evolution, possibly erasing the large basins.

The Dawn team includes Arizona State University’s David Williams, who is the director of the Ronald Greeley Center for Planetary Studies in ASU’s School of Earth and Space Exploration. Wiliams oversees a team of researchers using Dawn data to map the geology of Ceres.

He says, “When we first starting looking at Ceres images, we noticed that there weren’t any really large impact basins on the surface.” None are larger than 177 miles (285 kilometers) across. This presents a mystery, he says, because Ceres must have been struck by large asteroids many times over its 4.5-billion-year history.

“Even Vesta, only about half of Ceres’ size, has two big basins at its south pole. But at Ceres, all we saw was the Kerwan Basin, just 177 miles in diameter,” Williams says. “That was a big red flag that something had happened to Ceres.”

The Kerwan Basin’s name was proposed by Williams, and it commemorates the Hopi Indian spirit of the sprouting corn.

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Dawn lead investigator Marchi notes, “We concluded that a significant population of large craters on Ceres has been obliterated beyond recognition over geological time scales, which is likely the result of Ceres’ peculiar composition and internal evolution.”

The team’s simulations of collisions with Ceres predicted that it should have 10 to 15 craters larger than 250 miles (400 kilometers) in diameter, and at least 40 craters larger than 60 miles (100 kilometers) wide. In reality, however, Dawn found that Ceres has only 16 craters larger than 60 miles, and none larger than the 177-mile Kerwan Basin.

Further study of Dawn’s images revealed that Ceres does have three large-scale depressions called “planitiae” that are up to 500 miles (800 kilometers) wide. These have craters within them that formed in more recent times, but the depressions could be left over from bigger impacts.
One of the depressions, called Vendimia Planitia, is a sprawling area just north of the Kerwan Basin. Vendimia Planitia must have formed much earlier than Kerwan.

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So what removed Ceres’ large craters and basins?

“If Ceres were highly rocky, we’d expect impact craters of all sizes to be preserved. Remote sensing from Earth, however, told us even before Dawn arrived that the crust of Ceres holds a significant fraction of ice in some form,” Williams explains.

If Ceres’ crust contained a large proportion of ice—especially if mixed with salts—that would weaken the crust and let the topography of a large basin relax and become smoother, perhaps even disappear.

In addition, says Williams, Ceres must have generated some internal heat from the decay of radioactive elements after it formed. This too could also have helped soften or erase large-scale topographic features.

He adds, “Plus we do see evidence of cryovolcanism—icy volcanism—in the bright spots found scattered over Ceres, especially in Occator Crater.” Cryovolcanism behaves like the rocky kind, only at much lower temperatures, where “molten ice”—water or brine—substitutes for molten rock.

“It’s possible that there are layers or pockets of briny water in the crust of Ceres,” says Williams. “Under the right conditions, these could migrate to the surface and be sources for the bright spots.”

For example, in Occator Crater, he points out, “the central bright spot is a domed feature which looks as if it has erupted or been pushed up from below.”
NASA plans for Dawn to continue orbiting Ceres as the dwarf planet makes its closest approach to the Sun in April 2018. Scientists want to see if the increasing solar warmth triggers any activity or produces detectable changes in Ceres’ surface.

“Ceres is revealing only slowly the answers to her many mysteries,” Williams says. “Completing the geological maps over the next year, and further analysis of the compositional and gravity data, will help us understand better Ceres’ geologic evolution.”

Digging Deeper Into Mars

Water is the key to life on Earth. Scientists continue to unravel the mystery of life on Mars by investigating evidence of water in the planet’s soil. Previous observations of soil observed along crater slopes on Mars showed a significant amount of perchlorate salts, which tend to be associated with brines with a moderate pH level.

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However, researchers have stepped back to look at the bigger picture through data collected from the 2001: Mars Odyssey, named in reference to the science fiction novel by Arthur C. Clarke, “2001: A Space Odyssey,” and found a different chemical on Mars may be key. The researchers found that the bulk soil on Mars, across regional scales the size of the U.S. or larger, likely contains iron sulfates bearing chemically bound water, which typically result in acidic brines. This new observation suggests that iron sulfates may play a major role in hydrating martian soil.

This finding was made from data collected by the 2001: Mars Odyssey Gamma Ray Spectrometer, or GRS, which is sensitive enough to detect the composition of Mars soil up to one-half meter deep. This is generally deeper than other missions either on the ground or in orbit, and it informs the nature of bulk soil on Mars. This research was published recently in the Journal of Geophysical Research: Planets.

“This is exciting because it’s contributing to the story of water on Mars, which we’ve used as a path for our search for life on Mars,” said Nicole Button, LSU Department of Geology and Geophysics doctoral candidate and co-author in this study.

The authors expanded on previous work, which explored the chemical association of water with sulfur on Mars globally. They also characterized how, based on the association between hydrogen and sulfur, the soil hydration changes at finer regional scales. The study revealed that the older ancient southern hemisphere is more likely to contain chemically bound water while the sulfates and any chemically bound water are unlikely to be associated in the northerly regions of Mars.

The signature of strong association is strengthened in the southern hemisphere relative to previous work, even though sulfates become less hydrated heading southwards. In addition, the water concentration may affect the degree of sulfate hydration more than the sulfur concentration. Limited water availability in soil-atmosphere exchange and in any fluid movement from deeper soil layers could explain how salt hydration is water-limited on Mars. Differences in soil thickness, depth to any ground ice table, atmospheric circulation and sunshine may contribute to hemispheric differences in the progression of hydration along latitudes.

The researchers considered several existing hypotheses in the context of their overall observations, which suggest a meaningful presence of iron-sulfate rich soils, which are wet compared to Mars’ typically desiccated soil. This type of wet soil was uncovered serendipitously by the Spirit Rover while dragging a broken wheel across the soil in the Paso Robles area of Columbia Hills at Gusev Crater. Key hypotheses of the origin of this soil include hydrothermal activity generating sulfate-rich, hydrated deposits on early Mars similar to what is found along the flanks of active Hawaiian volcanoes on Earth.
Alternatively, efflorescence, which creates the odd salt deposits on basement walls on Earth, may have contributed trace amounts of iron-sulfates over geologic time. A third key hypothesis involves acidic aerosols released at volcanic sites, such as acid fog, dispersed throughout the atmosphere, and interacting subsequently with the finer components of soil as a source of widespread hydrated iron-sulfate salts.

Among these hypotheses, the researchers identify acid fog and hydrothermal processes as more consistent with their observations than efflorescence, even though the sensitivity of GRS to elements, but not minerals, prevents a decisive inference. Hydrothermal sites, in particular, are increasingly recognized as important places where the exchange between the surface and deep parts of Earth’s biosphere are possible. This hypothesis is significant to the question of martian habitability.

“Our story narrows it to two hypotheses, but emphasizes the significance of all of them,” said LSU Department of Geology and Geophysics Assistant Professor Suniti Karunatillake, who is a fellow lead author. “The depth and breadth of these observation methods tell us about global significance, which can inform the big question of what happened to the hydrologic cycle on Mars.”

Seven New Embedded Clusters Detected In The Galactic Halo

A team of Brazilian astronomers, led by Denilso Camargo of the Federal University of Rio Grande do Sul in Porto Alegre, has discovered seven new embedded clusters located unusually far away from the Milky Way’s disc. The findings, presented in a paper published July 3 on arXiv.org, could provide new insights on star cluster formation.

Embedded clusters are stellar clusters encased in an interstellar dust or gas, consisting of extremely young stars. They are crucial for astronomers to better understand star formation and early stellar evolution. Studying these clusters could reveal the origin of stellar masses as well as the origin and evolution of protoplanetary disks, where planet formation processes take place.

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In the Milky Way galaxy, most of embedded clusters lie within the thin disc less than 1,000 light years from the galactic midplane, especially in the spiral arms. However, Camargo and his team detected two young stellar clusters earlier this year, and now, after spotting seven more, suggest that they could be more common on the outskirts of the galaxy than previously thought.

“Now, we discovered seven star clusters far away from the Milky Way disc. Thus, this work points to a new paradigm in the star and star cluster formation, in the sense that the formation of such objects occurs in the halo and it seems to be frequent,” Camargo told Phys.org.

The scientists found the new clusters by analyzing the data provided by NASA’s Wide-field Infrared Survey Explorer (WISE). This space telescope is monitoring the entire galaxy in infrared light, snapping pictures of mainly remote galaxies, stars and asteroids. WISE was chosen for this job as it captures embedded clusters that are invisible at optical wavelengths, due to the fact that they are engulfed in significant amounts of interstellar dust.

“WISE provided infrared images of the entire sky, allowing us to penetrate the gas and dust within giant molecular clouds, in which the star formation can take place. Recently, we discovered more than 1,000 embedded clusters using WISE,” Camargo said.

According to the research paper, three newly found objects, designated C 932, C 934, and C 939, are high-latitude embedded clusters, projected within the newly identified cloud complex. These clusters are located at a vertical distance of about 16,300 light years below the galactic disc. Other new clusters, named C 1074, C 1099, C 1100, and C 1101, are in the range from 5,500 to 10,400 light years above the disc. All these clusters are younger than five million years.

The team noted that the new findings indicate that a sterile galactic halo could host ongoing star formation. The newly detected embedded clusters provide evidence of widespread star cluster forming processes far away from the Milky Way’s disc.

“The discovery of stellar clusters far away from the disc suggests that the Galactic halo is more actively forming stars than previously thought. Moreover, since most young clusters do not survive for more than five million years, the halo may be raining stars into the disc. The halo harbors generations of stars formed in clusters like those hereby detected,” Camargo said.

Before the team’s paper was published, it was thought that star formation processes in the Milky Way occur in the disk, but not in the halo. Thus, as Camargo concluded, this new study represents a paradigm shift, in the sense that a sterile halo becomes now a host of ongoing star formation.