Month: February 2017

Moon Periodically Showered with Oxygen Ions from Earth

A team of researchers affiliated with several institutions in Japan, examining data from that country’s moon-orbiting Kaguya spacecraft, has found evidence of oxygen from Earth’s atmosphere making its way to the surface of the moon for a few days every month. In their paper published in the journal Nature Astronomy, the researchers describe what data from the spacecraft revealed.

Scientists have known for some time that the moon is constantly bombarded with particles from the solar wind and have also known that once a month, as the Earth is positioned between the Sun and moon, the moon is protected from the solar wind. In this new effort, the researchers describe evidence of oxygen ion transport from Earth’s outer atmosphere to the lunar surface during this short periodic time- period.

Prior research has shown that oxygen atoms become ionized in Earth’s upper atmosphere when they are struck by ultraviolet light. Sometimes, this causes them to speed up to the point that they break away from the atmosphere and move into what is known as the magnetosphere, a cocoon that surrounds our planet that is stretched like a flag away from the direction of the Sun due to the solar wind—so far, in fact, that it covers the moon for five days each lunar cycle, causing the moon to be bombarded with a variety of ions. Data from Kaguya now suggests that some of those ions are oxygen. The researchers found that approximately 26,000 oxygen ions per second hit every square centimeter of the moon’s surface during the deluge.

Because the moon is protected from the solar wind by the Earth when the increase in oxygen ions was recorded, the researchers are confident they come from the Earth. Adding even more credence is that the ions were found to be moving slower than those that normally arrive via the solar wind. Also, they note, prior research has found lunar soil samples containing some degree of oxygen-17 and oxygen-18 isotopes, which are not typically found in space, but are found in the ozone layer covering Earth.

Both Push and Pull Drive Our Galaxy’s Race Through Space

Although we can’t feel it, we’re in constant motion: the earth spins on its axis at about 1,600 km/h; it orbits around the Sun at about 100,000 km/h; the Sun orbits our Milky Way galaxy at about 850,000 km/h; and the Milky Way galaxy and its companion galaxy Andromeda are moving with respect to the expanding universe at roughly 2 million km/h (630 km per second). But what is propelling the Milky Way’s race through space?

Until now, scientists assumed that a dense region of the universe is pulling us toward it, in the same way that gravity made Newton’s apple fall to earth. The initial “prime suspect” was called the Great Attractor, a region of a half dozen rich clusters of galaxies 150 million lightyears from the Milky Way. Soon after, attention was drawn to an area of more than two dozen rich clusters, called the Shapley Concentration, which sits 600 million lightyears beyond the Great Attractor.

Now researchers led by Prof. Yehuda Hoffman at the Hebrew University of Jerusalem report that our galaxy is not only being pulled, but also pushed. In a new study in the forthcoming issue of Nature Astronomy, they describe a previously unknown, very large region in our extragalactic neighborhood. Largely devoid of galaxies, this void exerts a repelling force on our Local Group of galaxies.

“By 3-d mapping the flow of galaxies through space, we found that our Milky Way galaxy is speeding away from a large, previously unidentified region of low density. Because it repels rather than attracts, we call this region the Dipole Repeller,” said Prof. Yehuda Hoffman. “In addition to being pulled towards the known Shapley Concentration, we are also being pushed away from the newly discovered Dipole Repeller. Thus it has become apparent that push and pull are of comparable importance at our location.”

The presence of such a low density region has been suggested previously, but confirming the absence of galaxies by observation has proved challenging. But in this new study, Hoffman, at the Hebrew university’s Racah Institutes of Physics, working with colleagues in the USA and France, tried a different approach.

Using powerful telescopes, among them the Hubble Space Telescope, they constructed a 3-dimensional map of the galaxy flow field. Flows are direct responses to the distribution of matter, away from regions that are relatively empty and toward regions of mass concentration; the large scale structure of the universe is encoded in the ?ow ?eld of galaxies.

They studied the peculiar velocities – those in excess of the Universe’s rate of expansion – of galaxies around the Milky Way, combining different datasets of peculiar velocities with a rigorous statistical analysis of their properties. They thereby inferred the underlying mass distribution that consists of dark matter and luminous galaxies—over-dense regions that attract and under-dense ones that repel.

By identifying the Dipole Repeller, the researchers were able to reconcile both the direction of the Milky Way’s motion and its magnitude. They expect that future ultra-sensitive surveys at optical, near-infrared and radio wavelengths will directly identify the few galaxies expected to lie in this void, and directly confirm the void associated with the Dipole Repeller.

Fermi Sees Gamma Rays from ‘Hidden’ Solar Flares

An international science team says NASA’s Fermi Gamma-ray Space Telescope has observed high-energy light from solar eruptions located on the far side of the Sun, which should block direct light from these events. This apparent paradox is providing solar scientists with a unique tool for exploring how charged particles are accelerated to nearly the speed of light and move across the Sun during solar flares.

“Fermi is seeing gamma rays from the side of the Sun we’re facing, but the emission is produced by streams of particles blasted out of solar flares on the far side of the Sun,” said Nicola Omodei, a researcher at Stanford University in California. “These particles must travel some 300,000 miles within about five minutes of the eruption to produce this light.”

Omodei presented the findings on Monday, Jan. 30, at the American Physical Society meeting in Washington, and a paper describing the results will be published online in The Astrophysical Journal on Jan. 31.

Fermi has doubled the number of these rare events, called behind-the-limb flares, since it began scanning the sky in 2008. Its Large Area Telescope (LAT) has captured gamma rays with energies reaching 3 billion electron volts, some 30 times greater than the most energetic light previously associated with these “hidden” flares.

Thanks to NASA’s Solar Terrestrial Relations Observatory (STEREO) spacecraft, which were monitoring the solar far side when the eruptions occurred, the Fermi events mark the first time scientists have direct imaging of beyond-the-limb solar flares associated with high-energy gamma rays.

“Observations by Fermi’s LAT continue to have a significant impact on the solar physics community in their own right, but the addition of STEREO observations provides extremely valuable information of how they mesh with the big picture of solar activity,” said Melissa Pesce-Rollins, a researcher at the National Institute of Nuclear Physics in Pisa, Italy, and a co-author of the paper.

The hidden flares occurred Oct. 11, 2013, and Jan. 6 and Sept. 1, 2014. All three events were associated with fast coronal mass ejections (CMEs), where billion-ton clouds of solar plasma were launched into space. The CME from the most recent event was moving at nearly 5 million miles an hour as it left the Sun. Researchers suspect particles accelerated at the leading edge of the CMEs were responsible for the gamma-ray emission.

Large magnetic field structures can connect the acceleration site with distant part of the solar surface. Because charged particles must remain attached to magnetic field lines, the research team thinks particles accelerated at the CME traveled to the Sun’s visible side along magnetic field lines connecting both locations. As the particles impacted the surface, they generated gamma-ray emission through a variety of processes. One prominent mechanism is thought to be proton collisions that result in a particle called a pion, which quickly decays into gamma rays.

In its first eight years, Fermi has detected high-energy emission from more than 40 solar flares. More than half of these are ranked as moderate, or M class, events. In 2012, Fermi caught the highest-energy emission ever detected from the Sun during a powerful X-class flare, from which the LAT detected high­energy gamma rays for more than 20 record-setting hours.

Fermi Gamma-ray Space Telescope Discovers Most Extreme Blazars Yet

NASA’s Fermi Gamma-ray Space Telescope has identified the farthest gamma-ray blazars, a type of galaxy whose intense emissions are powered by supersized black holes. Light from the most distant object began its journey to us when the universe was 1.4 billion years old, or nearly 10 percent of its present age.

“Despite their youth, these far-flung blazars host some of the most massive black holes known,” said Roopesh Ojha, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “That they developed so early in cosmic history challenges current ideas of how supermassive black holes form and grow, and we want to find more of these objects to help us better understand the process.”

Ojha presented the findings Monday, Jan. 30, at the American Physical Society meeting in Washington, and a paper describing the results has been submitted to The Astrophysical Journal Letters.

Blazars constitute roughly half of the gamma-ray sources detected by Fermi’s Large Area Telescope (LAT). Astronomers think their high-energy emissions are powered by matter heated and torn apart as it falls from a storage, or accretion, disk toward a supermassive black hole with a million or more times the sun’s mass. A small part of this infalling material becomes redirected into a pair of particle jets, which blast outward in opposite directions at nearly the speed of light. Blazars appear bright in all forms of light, including gamma rays, the highest-energy light, when one of the jets happens to point almost directly toward us.

Previously, the most distant blazars detected by Fermi emitted their light when the universe was about 2.1 billion years old. Earlier observations showed that the most distant blazars produce most of their light at energies right in between the range detected by the LAT and current X-ray satellites, which made finding them extremely difficult.

Then, in 2015, the Fermi team released a full reprocessing of all LAT data, called Pass 8, that ushered in so many improvements astronomers said it was like having a brand new instrument. The LAT’s boosted sensitivity at lower energies increased the chances of discovering more far-off blazars.

The research team was led by Vaidehi Paliya and Marco Ajello at Clemson University in South Carolina and included Dario Gasparrini at the Italian Space Agency’s Science Data Center in Rome as well as Ojha. They began by searching for the most distant sources in a catalog of 1.4 million quasars, a galaxy class closely related to blazars. Because only the brightest sources can be detected at great cosmic distances, they then eliminated all but the brightest objects at radio wavelengths from the list. With a final sample of about 1,100 objects, the scientists then examined LAT data for all of them, resulting in the detection of five new gamma-ray blazars.

Expressed in terms of redshift, astronomers’ preferred measure of the deep cosmos, the new blazars range from redshift 3.3 to 4.31, which means the light we now detect from them started on its way when the universe was between 1.9 and 1.4 billion years old, respectively.

“Once we found these sources, we collected all the available multiwavelength data on them and derived properties like the black hole mass, the accretion disk luminosity, and the jet power,” said Paliya.

Two of the blazars boast black holes of a billion solar masses or more. All of the objects possess extremely luminous accretion disks that emit more than two trillion times the energy output of our sun. This means matter is continuously falling inward, corralled into a disk and heated before making the final plunge to the black hole.

“The main question now is how these huge black holes could have formed in such a young universe,” said Gasparrini. “We don’t know what mechanisms triggered their rapid development.”

In the meantime, the team plans to continue a deep search for additional examples.

“We think Fermi has detected just the tip of the iceberg, the first examples of a galaxy population that previously has not been detected in gamma rays,” said Ajello.

New Ocean Observations Improve Understanding of Motion

Oceanographers commonly calculate large scale surface ocean circulation from satellite sea level information using a concept called “geostrophy“, which describes the relationship between oceanic surface flows and sea level gradient. Conversely, researchers rely on data from in-water current meters to measure smaller scale motion.

New research led by University of Hawai’i at Mānoa (UHM) oceanographer Bo Qiu has determined from observational data the length scale at which using sea level height no longer offers a reliable calculation of circulation.

Upper-ocean processes dissipate heat, transport nutrients and impact the uptake of carbon dioxide—making circulation a critical driver of biological activity in the ocean. The movement of water in the ocean is determined by many factors including tides; winds; surface waves; internal waves, those that propagate within the layers of the ocean; and differences in temperature, salinity or sea level height. Additionally, like high and low pressure systems seen on TV weather maps, the ocean is full of eddies, slowly swirling masses of water.

“As length scales become smaller from several hundred miles to a few tens of miles, we discovered the point at which geostrophic balance becomes no longer valid—meaning that sea level is no longer useful for calculating ocean circulation,” said Qiu, professor at the UHM School of Ocean and Earth Science and Technology (SOEST). “That is due to the presence of oceanic internal wave motions which essentially disrupts the motion that would be caused by geostrophy.”

Scientists use sea level as a means to calculate ocean circulation because satellites circle Earth daily, acquiring sea level data frequently and accurately. Prior to this study, published in Nature Communications, oceanographers knew that sea level can be used to provide a picture of circulation in a general way but not in very fine detail. However, the specific level of detail that can be provided using this approach was not known, until this study.

Further, in areas of the ocean with persistent or frequent eddies, Qiu and co-authors from the Japan Meteorological Agency, Caltech and NASA Jet Propulsion Laboratory determined that sea level can reliably be used to calculate circulation at a fairly high resolution, that is, at fairly small length scales (resolution of 10 miles). However, in areas where motion is dominated by internal waves, satellite sea level can only be used to infer motion on a very large scale (resolution of 125 miles).

“This aspect of the study was a bit of a surprise,” said Qiu. “I didn’t anticipate that the transition point would vary by an order of magnitude within the western North Pacific.”

In the future, Qiu and colleagues hope to develop a mathematical approach to creating more detailed pictures of circulation based on sea level in more locations throughout the Pacific.