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Correlations detected in a quantum vacuum

posted by Shifu RC

A vacuum as described by quantum mechanics is perhaps the most fundamental but mysterious state in physics. The discovery of correlations between electric-field fluctuations in such a vacuum represents a major advance.

A surprising result in quantum mechanics is that a vacuum is not empty. Particles can appear out of nothing for very short periods of time. This phenomenon can be understood as a consequence of the energy–time uncertainty principle, whereby restriction of a measurement to an extremely short time interval leads to large fluctuations in energy in the interval. Although indirect effects of these ‘virtual’ particles are well studied, it is only by probing a vacuum on very short timescales that the particles become ‘real’ and can be directly observed1. But do these particles appear completely randomly, or are they correlated in space and time? Writing in Nature, Benea-Chelmus et al.2 provide an answer to this question by finding evidence for correlations between fluctuations in the electric field of a vacuum.

Read the paper: Electric field correlation measurements on the electromagnetic vacuum state

One way to measure correlations in fields is through interference, such as in the double-slit experiment of British physicist Thomas Young3. In this experiment, light waves pass through two slits and interfere with each other to produce an interference pattern on a screen. This simple, but profound, experiment was originally developed to probe wave effects and was later used to illuminate the duality between particles and waves in quantum physics. In the past, variations of the double-slit experiment have been realized for photons, electrons, atoms and large molecules4. Current attempts are even looking for multipath interferences for biological objects, such as viruses5.

A comparably counter-intuitive enterprise is to search for interferences between separated parts of a vacuum. Benea-Chelmus and colleagues devoted their experimental study to exactly this task. For a simple, conceptual physical explanation of their work, consider a version of the double-slit experiment that is based on an instrument called a Mach–Zehnder interferometer6 (Fig. 1a). Moreover, let us limit the discussion to temporal correlations and consider the case in which thermal radiation is incident on the interferometer.


posted by Shifu RC

ABSTRACT We describe a new approach to studying the intergalactic and circumgalactic medium in the local Universe: direct detection through narrow-band imaging of ultra-low surface brightness visible-wavelength line emission. We use the hydrodynamical cosmological simulation EAGLE to investigate the expected brightness of this emission at low redshift (z . 0.2). Hα emission in extended halos (analogous to the extended Lyα halos/blobs detected around galaxies at high redshifts) has a surface brightness of & 700 photons cm−2 sr−1 s −1 out to ∼100 kpc. Mock observations show that the Dragonfly Telephoto Array, equipped with state-of-the-art narrow-band filters, could directly image these structures in exposure times of ∼10 hours. Hα fluorescence emission from this gas can be used to place strong constraints on the local ultra-violet background, and on gas flows around galaxies. Detecting Hα emission from the diffuse intergalactic medium (the “cosmic web”) is beyond current capabilities, but would be possible with a hypothetical 1000-lens Dragonfly array. Keywords: galaxies: halos – galaxies: evolution – intergalactic medium – large-scale structure of universe


posted by Shifu RC

ABSTRACT Recent advances in laboratory spectroscopy lead to the claim of ionized Buckminsterfullerene (C+ 60) as the carrier of two diffuse interstellar bands (DIBs) in the near-infrared. However, irrefutable identification of interstellar C+ 60 requires a match between the wavelengths and the expected strengths of all absorption features detectable in the laboratory and in space. Here we present Hubble Space Telescope (HST) spectra of the region covering the C+ 60 9348, 9365, 9428 and 9577 Å absorption bands toward seven heavily-reddened stars. We focus in particular on searching for the weaker laboratory C+ 60 bands, the very presence of which has been a matter for recent debate. Using the novel STIS-scanning technique to obtain ultra-high signal-to-noise spectra without contamination from telluric absorption that afflicted previous ground-based observations, we obtained reliable detections of the (weak) 9365, 9428 Å and (strong) 9577 Å C+ 60 bands. The band wavelengths and strength ratios are sufficiently similar to those determined in the latest laboratory experiments that we consider this the first robust identification of the 9428 Å band, and a conclusive confirmation of interstellar C+ 60. Subject headings: ISM: molecules — instrumentation: spectrographs — Techniques: spectroscopic — line: identification

Dark Matter Strikes Back at the Galactic Center

posted by Shifu RC

Statistical evidence has previously suggested that the Galactic Center GeV Excess (GCE) originates largely from point sources, and not from annihilating dark matter. We examine the impact of unmodeled source populations on identifying the true origin of the GCE using non-Poissonian template fitting (NPTF) methods. In a proof-of-principle example with simulated data, we discover that unmodeled sources in the Fermi Bubbles can lead to a dark matter signal being misattributed to point sources by the NPTF. We discover striking behavior consistent with a mismodeling effect in the real Fermi data, finding that large artificial injected dark matter signals are completely misattributed to point sources. Consequently, we conclude that dark matter may provide a dominant contribution to the GCE after all.


A new kind of cyclic universe

posted by Shifu RC

Abstract Combining intervals of ekpyrotic (ultra-slow) contraction with a (non-singular) classical bounce naturally leads to a novel cyclic theory of the universe in which the Hubble parameter, energy density and temperature oscillate periodically, but the scale factor grows by an exponential factor from one cycle to the next. The resulting cosmology not only resolves the homogeneity, isotropy, flatness and monopole problems and generates a nearly scale invariant spectrum of density perturbations, but it also addresses a number of age-old cosmological issues that big bang inflationary cosmology does not. There may also be potential wider-ranging implications for fundamental physics, black holes and quantum measurement. Keywords: cyclic universe, cosmological bounce, ekpyrotic contraction 

Meteoroid Strikes Eject Precious Water From Moon

posted by Shifu RC

Researchers from NASA and the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, report that streams of meteoroids striking the Moon infuse the thin lunar atmosphere with a short-lived water vapor.

The findings will help scientists understand the history of lunar water — a potential resource for sustaining long term operations on the Moon and human exploration of deep space. Models had predicted that meteoroid impacts could release water from the Moon as a vapor, but scientists hadn’t yet observed the phenomenon. 

Now, the team has found dozens of these events in data collected by NASA’s Lunar Atmosphere and Dust Environment Explorer. LADEE was a robotic mission that orbited the Moon to gather detailed information about the structure and composition of the thin lunar atmosphere, and determine whether dust is lofted into the lunar sky.

Scientists have discovered that water is being released from the moon during meteor showers. When a speck of comet debris strikes the moon it vaporizes on impact, creating a shock wave in the lunar soil. For a sufficiently large impactor, this shock wave can breach the soil's dry upper layer and release water molecules from the hydrated layer below. The LADEE spacecraft detects these water molecules as they enter the tenuous lunar atmosphere. This discovery provides a potential resource for future exploration, and it improves our understanding the moon's geologic past and its continued evolution.
Credits: NASA/Goddard/Dan Gallagher

Evidence for a prolonged Permian–Triassic extinction interval from global marine mercury records

posted by Shifu RC


The latest Permian mass extinction, the most devastating biocrisis of the Phanerozoic, has been widely attributed to eruptions of the Siberian Traps Large Igneous Province, although evidence of a direct link has been scant to date. Here, we measure mercury (Hg), assumed to reflect shifts in volcanic activity, across the Permian-Triassic boundary in ten marine sections across the Northern Hemisphere. Hg concentration peaks close to the Permian-Triassic boundary suggest coupling of biotic extinction and increased volcanic activity. Additionally, Hg isotopic data for a subset of these sections provide evidence for largely atmospheric rather than terrestrial Hg sources, further linking Hg enrichment to increased volcanic activity. Hg peaks in shallow-water sections were nearly synchronous with the end-Permian extinction horizon, while those in deep-water sections occurred tens of thousands of years before the main extinction, possibly supporting a globally diachronous biotic turnover and protracted mass extinction event.


The mass extinction at the end of the Permian, ~252 million years ago, was the largest biocrisis of the Phanerozoic Eon and featured ~90% of marine invertebrate taxa going extinct in a geologically short time interval (~61 ± 48 kyr1,2,3). The main cause of the latest Permian mass extinction (LPME) is generally thought to be linked to severe environmental perturbations caused by eruptions of the Siberian Traps Large Igneous Province (LIP)4,5. Although the near-synchronous occurrence of increased volcanic activity and the LPME is well established1,3,6, geochemical evidence of a direct relationship between the LPME and the Siberian Traps LIP has been generated from only for a few marine sites in Arctic Canada and southern China (e.g., refs. 7,8,9,10,11).

Why lightning often strikes twice

posted by Shifu RC

New study reveals needle-like structures in positively charged lightning leaders
17 April 2019

In contrast to popular belief, lightning often does strike twice, but the reason why a lightning channel is ‘reused’ has remained a mystery. Now, an international research team led by the University of Groningen has used the LOFAR radio telescope to study the development of lightning flashes in unprecedented detail. Their work reveals that the negative charges inside a thundercloud are not discharged all in a single flash, but are in part stored alongside the leader channel at interruptions. This occurs inside structures which the researchers have called needles. Through these needles, a negative charge may cause a repeated discharge to the ground. The results were published on 18 April in the science journal Nature.

Olaf Scholten LOFAR onweerLightning above the central part of LOFAR "Superterp", by: Danielle Futselaar

“This finding is in sharp contrast to the present picture, in which the charge flows along plasma channels directly from one part of the cloud to another, or to the ground”, explains Olaf Scholten, Professor of Physics at the KVI-CART institute of the University of Groningen. The reason why the needles have never been seen before lies in the ‘supreme capabilities’ of LOFAR, adds his colleague Dr Brian Hare, first author of the paper: “These needles can have a length of 100 metres and a diameter of less than five metres, and are too small and too short-lived for other lightning detections systems.”

Low Frequency Array (LOFAR) is a Dutch radio telescope consisting of thousands of rather simple antennas spread out over Northern Europe. These antennas are connected with a central computer through fibre-optic cables, which means that they can operate as a single entity. LOFAR is developed primarily for radio astronomy observations, but the frequency range of the antennas also makes it suitable for lightning research, as discharges produce bursts in the VHF (very high frequency) radio band.

Inside the cloud

For the present lightning observations, the scientists have used only the Dutch LOFAR stations, which cover an area of 3,200 square kilometres. This new study analysed the raw time-traces (which are accurate to one nanosecond) as measured in the 30-80 MHz band. Brian Hare: “These data allow us to detect lightning propagation at a scale where, for the first time, we can distinguish the primary processes. Furthermore, the use of radio waves allows us to look inside the thundercloud, where most of the lightning resides.”

A Closer Look at Mercury’s Spin and Gravity Reveals the Planet’s Inner Solid Core

posted by Shifu RC

How do you explore the interior of a planet without ever touching down on it? Start by watching the way the planet spins, then measure how your spacecraft orbits it — very, very carefully. This is exactly what NASA planetary scientists did, using data from the agency’s former mission to Mercury. 

It has long been known that Mercury and the Earth have metallic cores. Like Earth, Mercury’s outer core is composed of liquid metal, but there have only been hints that Mercury’s innermost core is solid. Now, in a new study, scientists from NASA’s Goddard Space Flight Center in Greenbelt, Maryland have found evidence that Mercury’s inner core is indeed solid and that it is very nearly the same size as Earth’s inner core. 

Some scientists compare Mercury to a cannonball because its metal core fills nearly 85 percent of the volume of the planet. This large core — huge compared to the other rocky planets in our solar system — has long been one of the most intriguing mysteries about Mercury.  Scientists had also wondered whether Mercury might have a solid inner core.

image of mercury with cutaway showing orange core
A graphical representation of Mercury’s internal structure.
Credits: NASA's Goddard Space Flight Center

The findings of Mercury’s solid inner core, described in Geophysical Research Letters, certainly adds to a better understanding of Mercury, but there are larger ramifications. Just how similar, and how different, the cores of the planets are may give us clues about how the solar system formed and how rocky planets change over time. 

“Mercury’s interior is still active, due to the molten core that powers the planet’s weak magnetic field, relative to Earth’s,” said Antonio Genova, an assistant professor at the Sapienza University of Rome who led the research while at NASA Goddard. “Mercury’s interior has cooled more rapidly than our planet’s. Mercury may help us predict how Earth’s magnetic field will change as the core cools."  

To figure out what the core of Mercury is made of, Genova and his colleagues had to get, figuratively, closer. The team used several observations from the MESSENGER (Mercury Surface, Space Environment, GEochemistry and Ranging) mission to probe the interior of Mercury. The researchers looked, most importantly, at the planet’s spin and gravity.

The MESSENGER spacecraft entered orbit around Mercury in March 2011, and spent four years observing this nearest planet to our Sun until it was deliberately brought down to the planet’s surface in April 2015.

Radio observations from MESSENGER were used to determine the gravitational anomalies (areas of local increases or decreases in mass) and the location of its rotational pole, which allowed scientists to understand the orientation of the planet.

Each planet spins on an axis, also known as the pole. Mercury spins much more slowly than Earth, with its day lasting about 58 Earth days. Scientists often use tiny variations in the way an object spins to reveal clues about its internal structure. In 2007, radar observations made from Earth revealed small shifts in the spin of Mercury, called librations, that proved some of Mercury’s core must be liquid-molten metal. But observations of the spin rate alone were not sufficient to give a clear measurement of what the inner core was like. Could there be a solid core lurking underneath, scientists wondered? 

A “Jellyfish” Galaxy Swims Into View of NASA’s Upcoming Webb Telescope

posted by Shifu RC

If you look at the galaxy ESO 137-001 in visible light, you can see why it’s considered an example of a “jellyfish” galaxy. Blue ribbons of young stars dangle from the galaxy’s disk like cosmic tentacles. If you look at the galaxy in X-ray light, however, you will find a giant tail of hot gas streaming behind the galaxy. After launch, NASA’s James Webb Space Telescope will study ESO 137-001 to learn how the gas is being removed from the galaxy, and why stars are forming within that gaseous tail.

Spiral galaxy ESO 137-001
The spiral galaxy ESO 137-001 is an example of a “jellyfish” galaxy, because blue tendrils of star formation stream away from it like jellyfish tentacles. NASA’s Webb Space Telescope will study those sites of star formation to learn more about conditions there.
Credits: NASA, ESA

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