New Herschel Maps Reveal Stellar Nurseries

ESA’s Herschel mission releases today a series of unprecedented maps of star-forming hubs in the plane of our Milky Way galaxy. This is accompanied by a set of catalogs of hundreds of thousands of compact sources that span all phases leading to the birth of stars in our Galaxy.

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These maps and catalogs will be very valuable resources for astronomers, to exploit scientifically and for planning follow-up studies of particularly interesting regions in the Galactic Plane.

During its four years of operations (2009-2013), the Herschel space observatory scanned the sky at far-infrared and sub-millimeter wavelengths. Observations in this portion of the electromagnetic spectrum are sensitive to some of the coldest objects in the Universe, including cosmic dust, a minor but crucial component of the interstellar material from which stars are born.

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The Herschel infrared Galactic Plane Survey (Hi-GAL) is the largest of all observing programs carried out with Herschel, in terms of both observing time – over 900 hours of total observations, equivalent to almost 40 days – and sky coverage – about 800 square degrees, or two percent of the entire sky. Its aim was to map the entire disc of the Milky Way, where most of its stars form and reside, in five of Herschel’s wavelength channels: 70, 160, 250, 350 and 500 μm.

Over the past two years, the Hi-GAL team has processed the data to obtain a series of calibrated maps of extraordinary quality and resolution. With a dynamical range of at least two orders of magnitude, these maps reveal the emission by diffuse material as well as huge filament structures and individual, point-like sources scattered across the images.

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The images provide an unprecedented view of the Galactic Plane, ranging from diffuse interstellar material to denser filament structures of gas and dust that fragment into clumps where star formation sets in. They include pre-stellar clumps, proto-stars in various evolutionary stages and compact cores on the verge of turning into stars, as well as fully-fledged stars and the bubbles carved by their highly energetic radiation.

Today, the team releases the first part of this data set, consisting of 70 maps, each measuring two times two degrees, and provided in the five surveyed wavelengths.

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“These maps are not only stunning from an aesthetic point of view, but they represent a rich data set for astronomers to investigate the different phases of star formation in our Galaxy,” explains Sergio Molinari from IAPS/INAF, Italy, Principal Investigator for the Hi-GAL Project.

Astronomers have been able to avail of data from Hi-GAL from the very beginning of the observing program since the team agreed to waive their right to a proprietary period. The observations have been made available through the ESA Herschel Science Archive, including raw data as well as data products generated by systematic pipeline processing. The data has regularly been reprocessed to gradually higher quality and fidelity products.

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The present release represents an extra step in the data processing. The newly released maps are accompanied by source catalogs in each of the five bands, which can be directly used by the community to study a variety of subjects, including the distribution of diffuse dust and of star-forming regions across the Galactic Plane.

The maps cover the inner part of the Milky Way, towards the Galactic Center as seen from the Sun, with Galactic longitudes between +68° and -70°. A second release, with the remaining part of the survey, is foreseen for the end of 2016.

“It is not straightforward to extract compact sources from far-infrared images, where pre-stellar clumps and other proto-stellar objects are embedded in the diffuse interstellar medium that also shines brightly at the same wavelengths,” explains Molinari.

“For this reason, we developed a special technique to extract individual sources from the maps, maximising the contrast in order to amplify the compact objects with respect to the background.”

The result is a set of five catalogs, one for each of the surveyed wavelengths, listing the source position, flux, size, signal-to-noise ratio and other parameters related to their emission. The largest catalogue is the one compiled from the 160-μm maps, with over 300 000 sources.

“The Hi-GAL maps and catalogs provide a complete census of stellar nurseries in the inner Galaxy,” says Göran Pilbratt, Herschel Project Scientist at ESA.

“These will be an extremely useful resource for studies of star formation across the Milky Way, helping astronomers to delve into the Galactic Plane and also to identify targets for follow-up observations with other facilities.”

Cosmic Beacons Reveal The Milky Way’s Ancient Core

An international team of astronomers led by Dr. Andrea Kunder of the Leibniz Institute for Astrophysics Potsdam (AIP) in Germany has discovered that the central 2000 light years within the Milky Way Galaxy hosts an ancient population of stars. These stars are more than 10 billion years old and their orbits in space preserve the early history of the formation of the Milky Way.

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For the first time the team kinematically disentangled this ancient component from the stellar population that currently dominates the mass of the central Galaxy. The astronomers used the AAOmega spectrograph on the Anglo Australian Telescope near Siding Spring, Australia, and focussed on a well-known and ancient class of stars, called RR Lyrae variables. These stars pulsate in brightness roughly once a day, which make them more challenging to study than their static counterparts, but they have the advantage of being “standard candles.” RR Lyrae stars allow exact distance estimations and are found only in stellar populations more than 10 billion years old, for example, in ancient halo globular clusters. The velocities of hundreds of stars were simultaneously recorded toward the constellation of Sagittarius over an area of the sky larger than the full moon. The team therefore was able to use the age stamp on the stars to explore the conditions in the central part of our Milky Way when it was formed.

Just as London and Paris are built on more ancient Roman or even older remains, our Milky Way galaxy also has multiple generations of stars that span the time from its formation to the present. Since heavy elements, referred to by astronomers as “metals,” are brewed in stars, subsequent stellar generations become more and more metal-rich. Therefore, the most ancient components of our Milky Way are expected to be metal-poor stars. Most of our Galaxy’s central regions are dominated by metal-rich stars, meaning that they have approximately the same metal content as our Sun, and are arrayed in a football-shaped structure called the “bar.” These stars in the bar were found to orbit in roughly the same direction around the Galactic Centre. Hydrogen gas in the Milky Way also follows this rotation. Hence it was widely believed that all stars in the centre would rotate in this way.

But to the astronomers’ astonishment, the RR Lyrae stars do not follow football-shaped orbits, but have large random motions more consistent with their having formed at a great distance from the centre of the Milky Way. “We expected to find that these stars rotate just like the rest of the bar” states lead investigator Kunder. Coauthor Juntai Shen of the Shanghai Astronomical Observatory adds, “They account for only one percent of the total mass of the bar, but this even more ancient population of stars appears to have a completely different origin than other stars there, consistent with having been one of the first parts of the Milky Way to form.”

The RR Lyrae stars are moving targets — their pulsations result in changes in their apparent velocity over the course of a day. The team accounted for this, and was able to show that the velocity dispersion or random motion of the RR Lyrae star population was very high relative to the other stars in the Milky Way’s center. The next steps will be to measure the exact metal content of the RR Lyrae population, which gives additional clues to the history of the stars, and enhance by three or four times the number of stars studied, that presently stands at almost 1000.

Meteor Activity Outlook for April 23-29, 2016

During this period the moon wanes from its full phase to nearly one-half illuminated. This is the worst time of the month to try and view meteor activity as the bright moonlight will obscure all but the brightest meteors.

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The estimated total hourly meteor rates for evening observers this week is near 2 for observers located in the northern hemisphere and 3 for observers located south of the equator. For morning observers the estimated total hourly rates should be near 7 as seen from mid-northern latitudes (45N) and 9 as seen from tropical southern locations (25S).

Rates are reduced during this period due to moonlight. The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity. Note that the hourly rates listed below are estimates as viewed from dark sky sites away from urban light sources. Observers viewing from urban areas will see less activity as only the brightes t meteors will be visible from such locations.

The radiant (the area of the sky where meteors appear to shoot from) positions and rates listed below are exact for Saturday night/Sunday morning April 23/24. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.

Most star atlases (available at science stores and planetariums) will provide maps with grid lines of the celestial coordinates so that you may find out exactly where these positions are located in the sky. A planisphere or computer planetarium program is also useful in showing the sky at any time of night on any date of the year.

Activity from each radiant is best seen when it is positioned highest in the sky, either due north or south along the meridian, depending on your latitude. It must be remembered that meteor activity is rarely seen at the radiant position. Rather they shoot outwards from the radiant so it is best to center your field of view so that the radiant lies at the edge and not the center.

Viewing there will allow you to easily trace the path of each meteor back to the radiant (if it is a shower member) or in another direction if it is a sporadic. Meteor activity is not seen from radiants that are located far below the horizon. The positions below are listed in a west to east manner in order of right ascension (celestial longitude). The positions listed first are located further west therefore are accessible earlier in the night while those listed further down the list rise later in the night.
These sources of meteoric activity are expected to be active this week.

Earth-Like Planet May Exist in Nearby Star System

An Earth-like planet may be lurking in a star system located just 16 light years away, according to a new research. The star, named Gliese 832, was recently investigated by a team of astronomers searching for additional exoplanets that may be residing between the two currently known alien worlds in this system. A paper detailing the finding was published online on Apr. 15 in the arXiv journal.

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Gliese 832 is a red dwarf and has just under half the mass and radius of our Sun. The star is orbited by a giant Jupiter-like exoplanet designated Gliese 832b and by a super-Earth mass planet Gliese 832c. The gas giant, with a mass of 0.64 Jupiter masses, is orbiting the star at a distance of 3.53 AU, while the other planet is potentially a rocky world, around five times more massive than the Earth, residing very close its host star—about 0.16 AU.

Now, a team of astronomers, led by Suman Satyal of the University of Texas at Arlington, has reanalyzed the available data on this nearby planetary system hoping to find more extrasolar worlds that may be located in a vast space between the two known planets. The researchers have conducted numerical simulations to check the possibility of existence of other celestial bodies around the red dwarf.

Gliese 832b and Gliese 832c were discovered by the radial velocity technique, from which the scientists extracted the orbital parameters by using the best-fit solutions. These parameters were used as the initial conditions for starting their simulations.

“We also used the integrated data from the time evolution of orbital parameters to generate the synthetic radial velocity curves of the known and the Earth-like planets in the system. Moreover, based on the maximum amplitude of the radial velocity curve obtained from the observation of the inner planet, the approximate mass and distance from the star for the Earth-like planet were computed using the radial velocity signature of the Keplerian motion,” the researchers wrote in the paper.

The team’s computations revealed that an additional Earth-like planet with a dynamically stable configuration may be residing at a distance ranging from 0.25 to 2.0 AU from the star. According to the measurements, this hypothetical alien world would probably be more massive than our planet with a mass between one to 15 Earth’s masses.

“We obtained several radial velocity curves for varying masses and distances for the middle planet,” the astronomers noted.

For instance, if the planet is located around one AU from the star, it has an upper mass limit of ten Earth masses and a generated radial velocity signal of 1.4 m/s. A planet with about the mass of the Earth at the same location would have radial velocity signal of only 0.14 m/s, thus much smaller.

In general, the existence of this possible planet is supported by long-term orbital stability of the system, orbital dynamics and the synthetic radial velocity signal analysis.

The scientists emphasized that their main goal was to provide a general idea to the observers of where and what to look for in this system. They concluded that a significantly large number of radial velocity observations, transit method studies, as well as the direct imaging are still needed to confirm the presence of possible new planets in the Gliese 832 system.

NASA Missions Measure Solar Flare Electromagnetic Phenomenon

Solar flares are intense bursts of light from the Sun. They are created when complicated magnetic fields suddenly and explosively rearrange themselves, converting magnetic energy into light through a process called magnetic reconnection – at least, that’s the theory, because the signatures of this process are hard to detect. But during a December 2013 solar flare, three solar observatories captured the most comprehensive observations of an electromagnetic phenomenon called a current sheet, strengthening the evidence that this understanding of solar flares is correct.

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These eruptions on the Sun eject radiation in all directions. The strongest solar flares can impact the ionized part of Earth’s atmosphere – the ionosphere – and interfere with our communications systems, like radio and GPS, and also disrupt onboard satellite electronics. Additionally, high-energy particles – including electrons, protons and heavier ions – are accelerated by solar flares.

Unlike other space weather events, solar flares travel at the speed of light, meaning we get no warning that they’re coming. So scientists want to pin down the processes that create solar flares – and even some day predict them before our communications can be interrupted.

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“The existence of a current sheet is crucial in all our models of solar flares,” said James McAteer, an astrophysicist at New Mexico State University in Las Cruces and an author of a study on the December 2013 event, published on April 19, 2016, in the Astrophysical Journal Letters. “So these observations make us much more comfortable that our models are good.”

And better models lead to better forecasting, said Michael Kirk, a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who was not involved in the study. “These complementary observations allowed unprecedented measurements of magnetic reconnection in three dimensions,” Kirk said. “This will help refine how we model and predict the evolution of solar flares.”

A current sheet is a very fast, very flat flow of electrically-charged material, defined in part by its extreme thinness compared to its length and width. Current sheets form when two oppositely-aligned magnetic fields come in close contact, creating very high magnetic pressure. Electric current flowing through this high-pressure area is squeezed, compressing it down to a very fast and thin sheet. It’s a bit like putting your thumb over the opening of a water hose – the water, or, in this case, the electrical current, is forced out of a tiny opening much, much faster. This configuration of magnetic fields is unstable, meaning that
the same conditions that create current sheets are also ripe for magnetic reconnection.

“Magnetic reconnection happens at the interface of oppositely-aligned magnetic fields,” said Chunming Zhu, a space scientist at New Mexico State University and lead author on the study. “The magnetic fields break and reconnect, leading to a transformation of the magnetic energy into heat and light, producing a solar flare.”

Because current sheets are so closely associated with magnetic reconnection, observing a current sheet in such detail backs up the idea that magnetic reconnection is the force behind solar flares.

“You have to be watching at the right time, at the right angle, with the right instruments to see a current sheet,” said McAteer. “It’s hard to get all those ducks in a row.”

This isn’t the first time scientists have observed a current sheet during a solar flare, but this study is unique in that several measurements of the current sheet – such as speed, temperature, density and size – were observed from more than one angle or derived from more than method.

This multi-faceted view of the December 2013 flare was made possible by the wealth of instruments aboard three solar-watching missions: NASA’s Solar Dynamics Observatory, or SDO, NASA’s Solar and Terrestrial Relations Observatory, or STEREO – which has a unique viewing angle on the far side of the Sun – and Hinode, which is a collaboration between the space agencies of Japan, the United States, the United Kingdom and Europe led by the Japan Aerospace Exploration Agency.

Even when scientists think they’ve spotted something that might be a current sheet in solar data, they can’t be certain without ticking off a long list of attributes. Since this current sheet was so well-observed, the team was able to confirm that its temperature, density, and size over the course of the event were consistent with a current sheet.

As scientists work up a better picture of how current sheets and magnetic reconnection lead to solar eruptions, they’ll be able to produce better models of the complex physics happening there – providing us with ever more insight on how our closest star affects space all around us.

This research was funded by a CAREER grant from the National Science Foundation awarded to James McAteer.

JUST IN: New High-Energy Sources of Gamma and Cosmic Rays Discovered

A new sky map using the High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory shows many new gamma ray sources within our own Milky Way galaxy. HAWC gives us a new way to see the high-energy sky. “This new data from HAWC shows the galaxy in unprecedented detail, revealing new high-energy sources and previously unseen details about existing sources.” said Jordan Goodman, professor of physics at the University of Maryland.

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Today, scientists operating HAWC released a new survey of the sky made from the highest energy gamma rays ever observed. The new sky map, which uses data collected since the observatory began running at full capacity last March, offers a deeper understanding of high-energy processes taking place in our galaxy and beyond.

In a region of the Milky Way where researchers previously identified a single gamma ray source named TeV J1930+188, HAWC identified several hot spots, indicating that the region is more complicated than previously thought.

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New Equation:
Increase Charged Particles  and Decreasing Magnetic Field → Increase Outer Core Convection → Increase of Mantle Plumes → Increase in Earthquake and Volcanoes → Cools Mantle and Outer Core → Return of Outer Core Convection (Mitch Battros – July 2012)

“Studying these objects at the highest energies can reveal the mechanism by which they produce gamma rays and possibly help us unravel the hundred-year-old mystery of the origin of high-energy cosmic rays that bombard Earth from space,” said Goodman.

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HAWC-located 13,500 feet above sea level on the slopes of Mexico’s Volcán Sierra Negra-contains 300 detector tanks, each holding 50,000 gallons of ultrapure water with four light sensors anchored to the floor. When gamma rays or cosmic rays reach Earth’s atmosphere they set off a cascade of charged particles, and when these particles reach the water in HAWC’s detectors, they produce a cone-shaped flash of light known as Cherenkov radiation. The effect is much like a sonic boom produced by a supersonic jet, because the particles are traveling slightly faster than the speed of light in water when they enter the detectors.

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Because HAWC observes 24 hours per day and year-round with a wide field-of-view and large area, the observatory boasts a higher energy reach for extended objects. In addition, HAWC can uniquely monitor for gamma ray flares by sources in our galaxy and other active galaxies, such as Markarian 421 and Markarian 501.

UPDATE: Supernova Iron Found on the Moon

Now scientists at the Technical University of Munich (TUM), together with colleagues from the US, have found increased concentrations of this supernova-iron in lunar samples as well. They believe both discoveries to originate from the same stellar explosion.

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A dying star ends its life in a cataclysmic explosion, shooting the majority of the star’s material, primarily new chemical elements created during the explosion, out into space.

One or more such supernovae appear to have occurred close to our solar system approximately two million years ago. Evidence of the fact has been found on the Earth in the form of increased concentrations of the iron isotope 60Fe detected in Pacific Ocean deep-sea crusts and in ocean-floor sediment samples.

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This evidence is highly compelling: The radioactive 60Fe isotope is created almost exclusively in supernova explosions. And with a half-life of 2.62 million years, relatively short compared to the age of our solar system, any radioactive 60Fe originating from the time of the solar system’s birth should have long ago decayed into stable elements and thus should no longer be found on the Earth.

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This supernova hypothesis was first put forth in 1999 by researchers at the Technical University of Munich (TUM) who had found initial evidence in a deep-sea crust. Now their claim has received further substantiation: Physicists at the TUM and their colleagues from the US have succeeded in demonstrating an unusually high concentration of 60Fe in lunar ground samples as well.

The samples were gathered between 1969 and 1972 during Apollo lunar missions 12, 15 and 16, which brought the lunar material back to Earth.

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It’s also conceivable that 60Fe can occur on the moon as the result of bombardment with cosmic particles, since these particles do not break up when colliding with air molecules, as is the case with the Earth’s atmosphere. Instead, they directly impact the lunar surface and can thus result in transmutation of elements. “But this can only account for a very small portion of the 60Fe found,” explains Dr. Gunther Korschinek, physicist at TUM and scientist of the Cluster of Excellence Structure and Origin of the Universe.

Since the moon generally provides a better cosmic record than the Earth, the scientists were also able to specify for the first time an upper limit for the flow of 60Fe that must have reached the moon. Among other athings, this also makes it possible for the researchers to infer the distance to the supernova event: “The measured 60Fe-flow corresponds to a supernova at a distance of about 300 light years,” says Korschinek. “This value is in good agreement with a recently theoretical estimation published in Nature.”