SAO: Weekly Science Updates 2017

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The Remarkable Jet of the Quasar 4C+19.44

Postby bystander » Fri Oct 13, 2017 5:58 pm

The Remarkable Jet of the Quasar 4C+19.44
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Oct 13

Quasars are galaxies with massive black holes at their cores. So much energy is being radiated from near the nucleus of a quasar that it is much brighter than the rest of the entire galaxy. Much of that radiation is at radio wavelengths, produced by electrons ejected from the core at speeds very close to that of light, often in narrow, bipolar jets that are hundreds of thousands of light-years long. The fast-moving charged particles can also scatter photons of light, kicking them up in energy into the X-ray range. Even after more than two decades of study, however, there is still no clear conclusion as to the physical mechanism actually responsible for the X-ray emission. In more powerful quasars, it does appear that this scattering process dominates. In lower power jets, however, the emission characteristics suggest that the X-ray emission is dominated by magnetic field effects, not scattering.

The lead author of a new paper on the remarkable jet in the quasar 4C+19.44 is CfA astronomer Dan Harris, who very sadly passed away in December, 2015, after a long and productive career. His CfA teammates on this project, Dan Schwartz with Nicholas Lee and Aneta Siemiginowska, worked to finish the research together with an international team of colleagues. The scientists undertook a detailed, high spatial resolution study of the straight, three hundred thousand light-year long jet in this quasar using multiwavelength data from the Chandra (X-ray), Spitzer (infrared), and Hubble (optical) space observatories as well as from the Very Large Array (radio).

The combination of multiwavelength observations with high spatial resolution enabled the team to measure the characteristics of the emission systematically in ten distinct knots along the jets. They find that both the magnetic field strength and the particle velocities are (remarkably) quite constant all along the length of this jet, at least when presuming the scattering process dominates. But the scientists are not able to exclude magnetic effects as producing some of the X-ray emission. They do conclude, however, that for the magnetic process to be active, any electrons contributing to it must belong to a separate population that is distinct from the electrons that dominate the scattering.

A Multi-Band Study of the Remarkable Jet in Quasar 4C+19.44 - Daniel Harris et al
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The Atmospheres of Water Worlds

Postby bystander » Fri Oct 20, 2017 2:29 pm

The Atmospheres of Water Worlds
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Oct 20

There are currently about fifty known exoplanets with diameters that range from Mars-sized to several times the Earth's and that also reside within their stars' habitable zone – the orbital range within which their surface temperatures permit water to remain liquid. A "water world" is an extreme case, an exoplanet defined as being covered by a deep ocean, perhaps as deep as hundreds of kilometers, and among these fifty are several that might be candidates for this category. Astronomers note that at least two of the terrestrial planets in our solar system, Earth and Venus, may possibly also have been water worlds early in their evolution.

One of the critical factors in determining if a planet could really be habitable is the presence of an enduring atmosphere. The deep oceans on a water world offer a reservoir for water vapor for its atmosphere, and so scientists have been trying to calculate how stable an exoplanet’s ocean and atmosphere are, especially to effects like evaporation by winds from the star. Since most of the fifty known examples orbit close to their small, host M stars, they are heavily exposed to stellar winds and related stellar space weather events even though their temperatures may be moderate.

CfA astronomer Manasvi Lingam was a member of a team of astronomers who modeled the effects of the stellar wind on a water world under a variety of possible scenarios. They include effects of stellar magnetic fields, coronal mass ejections, and atmospheric ionization and ejection. Their computer simulations are in good agreement with the current Earth-Sun system, but in some of the more extreme possibilities, as for example might exist on the set of exoplanets around M-stars, the situation is very different and the escape rates may be as much as or more than one thousand times greater. The result means that even a water world, if it orbits an M-dwarf star, could lose its atmosphere after about one billion years, a relatively brief time for possible development of life. ...

The Dehydration of Water Worlds via Atmospheric Losses - Chuanfei Dong et al
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Measuring the Distance to the Far Side of the Galaxy

Postby bystander » Fri Oct 27, 2017 4:34 pm

Measuring the Distance to the Far Side of the Galaxy
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Oct 27

The size and shape of our home galaxy, the Milky Way, reflect not only its current structure but also its evolutionary history, providing details that form the basis for our understanding of all galaxies. The information is also important because it helps enable astronomers determine distances to objects in the Milky Way relative to other object's distances. Distance is often the main uncertainty when calculating a star’s inherent (not apparent) luminosity, its mass, or other physical attributes. Conversely, knowing the precise distances to objects in the Milky Way enables astronomers to construct a coherent picture of the galaxy's size and shape. Currently, for many objects in the galaxy, and especially for molecular clouds and others not bright in the optical, astronomers distances by measuring their velocities and fitting them to a rotating model of the galaxy thus roughly associating velocities with the corresponding "kinematic" distances.

The distances to nearby stars are precisely and accurately determined using the technique of parallax. When a celestial body is seen from different, widely separated viewing points, its position with respect to more distant background stars or galaxies varies: this angular difference is its parallax. Parallax is used to triangulate the distances to stars by measuring their apparent angular shifts six months apart, when the earth is on opposite sides of its orbit around the Sun. This traditional technique has in the past worked mostly for nearby stars because their angular parallaxes are comparatively large and the stars are bright enough to be clearly seen, and hence easy to measure. The technique is so straightforward that astronomers have been trying for nearly a century (since the Milky Way was recognized to be a galaxy) to piece together a more complete picture using increasingly precise angular measurements. ...

Mapping spiral structure on the far side of the Milky Way - Alberto Sanna et al

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A New Kind of Quantum Computer

Postby bystander » Sun Nov 05, 2017 6:52 pm

A New Kind of Quantum Computer
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Nov 03

Quantum mechanics incorporates some very non-intuitive properties of matter. Quantum superposition, for example, allows an atom to be simultaneously in two different states with its spin axis pointed both up and down, or combinations in between. A computer that uses quantum mechanical manipulation of atoms or particles therefore has many more possible options than a conventional one that works with "zeros" and "ones" and has only two choices, called bits. A quantum computer's memory uses instead what are called quantum bits - qubits - and each qubit can be in a superposition of these two states. As a result, theoretical physicists estimate a quantum computer with only about one hundred of these qubits could in principle exceed the computing power of the powerful current classical computers. Building a quantum computer is therefore one of the main technological goals in modern physics and astrophysics.

CfA physicist Hannes Pichler, of the CfA's Institute for Theoretical Atomic, Molecular and Optical Physics (ITAMP), and three colleagues have proposed a new way to build a quantum computer using just a single atom. Light quanta (photons) can be used as information carriers and act as qubits, but to use them in a quantum computer they must interact with each other. Under normal conditions, however, light does not interact with itself and so the challenge is to create correlations between them. The key idea of their new paper is to allow light photons from an atom to interact with their own mirror image reflections Photons that the atom emits are reflected by the mirror and can interact again with the atom but with a very slight time delay. That delay, the scientists show, results in the combined waveform of the photons being so complex that in principle any quantum computation can be achieved by simply measuring the emitted photons.

The theoretical discovery is not only a conceptual breakthrough in quantum optics and information, it opens the door to new technology. In particular, the proposed single atom setup is appealing since it minimizes the resources needed and relies only on elements that have already been demonstrated in state-of the-art experiments. ...

Universal Photonic Quantum Computation via Time-Delayed Feedback - Hannes Pichler et al
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Jupiter's Surprising Southern Aurora

Postby bystander » Fri Nov 10, 2017 2:38 pm

Jupiter's Surprising Southern Aurora
Smithsonian Astrophysical Observatory
Weekly Science Update | 2017 Nov 10

Aurorae are seen in all of the planets in our solar system that have magnetic fields, including of course the Earth, and have even been detected around brown dwarf stars (known for having strong magnetic fields in their upper layers). Only Jupiter's north pole aurora, however, has been spatially resolved in X-rays, and the bright hot spot is seen to pulse as charged particles around Jupiter, funneled by the magnetic field lines, smash into atoms in the atmosphere and emit bursts of X-rays. Surprisingly, however, no similar aurora had been clearly identified from Jupiter's south pole, although they had been expected assuming Jupiter’s magnetic field lines connected north and south polar regions (like the Earth's are connected).

CfA astronomers William Dunn and Ralph Kraft and a team of colleagues now report clearly identifying Jupiter’s southern X-ray aurora. The scientists used data from the Chandra X-ray Observatory and XMM-Newton missions from 2007 and 2016, when the Jupiter’s south pole was suitably oriented toward Earth. Jupiter's aurorae are complex. The visible ones result primarily from the excitation of hydrogen atoms and make it appear pinkish-purple, but the moon Io injects a large amount of volcanic material into Jupiter's environment which leads to the production of X-ray emission. The several sources of activity make Jupiter's aurorae the brightest in the solar system.

In contrast, the X-ray emission from the polar regions is much more variable and confined, and less well understood. The new results find, for example, that the periodic brightening occurs at different rates in the north and south, in contrast to the current models which expect that the magnetic processes are coherent. In fact, the south appears to host a persistent X-ray hot spot. The implications are that the physical processes at work are different and more complex than the solar wind effects that produce the Earth’s aurorae.

The Independent Pulsations of Jupiter’s Northern and Southern X-ray Auroras - W. R. Dunn et al

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Know the quiet place within your heart and touch the rainbow of possibility; be
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