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Monthly Archives: March 2014

p. 563, Appendix 3C Our Solar System: Orbital Properties of Planets

The units of the ‘Semimajor Axis’ second column are out by a factor of 10; they should be 10^6 km, i.e. millions of kilometers. (The equivalent column is shown correctly in Appendix 3D.)

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Adapted from Carnegie Institution of Science press release, March 26, 2014:

A new distant dwarf planet, called 2012 VP113, has been discovered beyond the known edge of the Solar System. It is likely one of thousands of distant objects that are thought to form the so-called inner Oort cloud (see Section 8.2, p. 202). The findings were published March 27 in the journal Nature.

Credit: Scott Sheppard (Carnegie Institution of Science)

The known Solar System can be divided into three parts: the rocky planets like Earth, which are close to the Sun; the gas giant planets, which are further out; and the frozen objects of the Kuiper belt, which lie just beyond Neptune’s orbit. Beyond this, there appears to be an edge to the Solar System where only one object, Sedna, was previously known to exist for its entire orbit. But the newly found 2012 VP113 has an orbit that beyond Sedna’s, making it the furthest known in the solar system. The discovery of 2012 VP113 shows us that Sedna is not unique and is likely the second known member of the hypothesized inner Oort cloud, the likely origin of some comets.

2012 VP113’s closest orbit point to the Sun brings it to about 80 times the distance of the Earth from the Sun (80 AU). The Kuiper belt (composed of thousands of icy objects, including Pluto) ranges from 30 to 50 AU. The Solar System has a distinct edge at 50 AU – prior to this discovery, Sedna was the only object known to stay significantly beyond this outer boundary at 76 AU for its entire orbit.

Links: Carnegie Institution press release; NY Time coverage.

A total lunar eclipse will be visible throughout the continental United States on the night of Monday April 14-Tuesday April 15, 2014.  Eclipses of the Sun and of the Moon are discussed in Section 4.2, starting on p. 70.

Lunar eclipse

Credit: Michael Zeiler, eclipse-maps.com

An animation showing the visibility of the eclipse and all relevant times may be seen here: http://vimeo.com/89766307
It was made by Michael Zeiler (eclipse-maps.com); Mr. Zeiler accompanied author Jay M. Pasachoff on the expedition to observe the total solar eclipse of November 2013 from Gabon in Africa.

The opening partial phase of the eclipse begins about 2 a.m. Eastern Daylight Time, with the total eclipse lasting from about 3:07 am to 4:25 am EDT.  The closing partial phase of the eclipse ends at 5:33 am EDT, and will be visible from most of the U.S. and Canada but not from the East Coast.  In Pacific Daylight Time, the eclipse is 11 pm partial/12:07-1:25 am totality/-2:33 end.

Adapted from AIP Advances press release, March 18, 2014:

A powerful, new computer model provides fresh insight into the turbulent death throes of supernovae (see Section 13.2, p. 337).

Credit. W. D. Arnett, C. Meakin and M. Viallet/AIP Advances

The new model, developed by W. David Arnett (U. of Arizona) and colleagues, is the first to represent the start of a supernova collapse in three dimensions. It shows how the turbulent mixing of elements inside stars causes them to expand, contract, and spit out matter before they finally detonate. Arnett’s new model better matches what we observe in supernova remnants, with ejections of star material mixing with the material expelled during its final explosion.

The article, ‘Chaos and turbulent nucleosynthesis prior to a supernova explosion’ by David Arnett, Casey Meakin and Maxime Viallet is published in the journal AIP Advances.

Links: full AIP press release; the research article.

The Astronomy Picture of the Day (APOD) on March 17, 2014, shows warped star trails over Arches National Park, in Utah, USA.

Credit and copyright: Vincent Brady

The warping effect occurs because the picture is actually a full 360 degree panorama, horizontally compressed to fit your screen. As the Earth rotates, stars appear to circle both the North Celestial Pole, on the left, and the South Celestial Pole, just below the horizon on the right. While the eye-catching texture of ancient layered sandstone covers the image foreground, twenty-meter tall Delicate Arch is visible on the far right, and the distant arch of our Milky Way Galaxy and its dark dust lanes may be seen near the image center.

Credit: Vincent Brady

From a Harvard-Smithsonian Center for Astrophysics press release:

Almost 14 billion years ago, the Universe burst into existence in an extraordinary event that initiated the big bang. In the first fleeting fraction of a second, the Universe expanded exponentially, stretching far beyond the view of our best telescopes (see Section 19.5, p. 526).

Researchers announced on March 17, 2014, the first direct evidence for this cosmic inflation. Their data also represent the first images of gravitational waves – ripples in space-time. These waves have been described as the ‘first tremors of the big bang.’ Finally, the data confirm a deep connection between quantum mechanics and general relativity.

Credit: Steffen Richter (Harvard University)

These groundbreaking results came from observations by the BICEP2 telescope (pictured above) of the cosmic microwave background – the faint glow left over from the big bang. Tiny fluctuations in this afterglow provide clues to conditions in the early universe. For example, small differences in temperature across the sky show where parts of the Universe were denser, eventually condensing into galaxies and galactic clusters.

Since the cosmic microwave background is a form of light, it exhibits all the properties of light, including polarization. On Earth, sunlight is scattered by the atmosphere and becomes polarized, which is why polarized sunglasses help reduce glare. In space, the cosmic microwave background was scattered by atoms and electrons and became polarized too.

The researchers hunted for a special type of polarization called ‘B-modes,’ which represents a twisting or ‘curl’ pattern in the polarized orientations of the ancient light. Gravitational waves squeeze space as they travel, and this squeezing produces a distinct pattern in the cosmic microwave background. Gravitational waves have a ‘handedness,’ much like light waves, and can have left- and right-handed polarizations. The swirly B-mode pattern is a unique signature of gravitational waves because of their handedness.

Credit: BICEP2 Collaboration

The figure above shows the actual B-mode pattern observed with the BICEP2 telescope, with the line segments showing the polarization from different spots on the sky. The red and blue shading shows the degree of clockwise and anti-clockwise twisting of this B-mode pattern.

Links: the Harvard-Smithsonian CfA press release including figures, Caltech press release, NY Times article by Dennis Overbye (including a cartoon explaining inflation), Union-Tribune San Diego article (including cartoon of polarization of light), APOD March 18, 2014 shows the observatory at the South Pole, all BICEP2 public pages.

A recent article in Nature describes how a supermassive black hole’s spin has been measured via the gravitational lens of a foreground galaxy, that fortuitously lies along the same line-of-sight. The new measurements have enabled astronomers to find that a supermassive black hole powering a distant quasar has grown through coherent, rather than random, episodes of mass accretion (see Section 17.3, p. 458-459). The following text is a digest of Guido Risalti’s summary in Nature‘s ‘News and views’ section, March 13, 2014.

Supermassive black holes are simple systems. They are characterized by just two quantities, their mass and their spin. Whereas the total amount of accretion and any mergers that a supermassive black hole undergoes are encoded in its mass, how this mass was assembled is encoded in its spin. A few ordered accretion events or mergers of large black holes produce high spins, and short, random accretion processes produce low spins. Measuring these spins is therefore a major goal of extragalactic astronomy: the spins of supermassive black holes hold a key to understanding the evolution of their host galaxies.

But how can we measure the spins? According to Einstein’s general theory of relativity, a black hole’s gravitational field twists space-time around it. Such twisting depends on the black hole’s spin, so measuring the twisting allows the spin to be estimated. The signature of space-time distortion is imprinted on the emission of radiation from regions close to the black hole’s event horizon – the surface beyond which no radiation can escape. The best way to perform such a measurement is to observe X-rays reflected by the disk.

In their study, R. C. Reis and colleagues break new ground by obtaining a spin measurement of a quasar at a distance of more than 6 billion light years from Earth, from a time when the Universe was about half its current age. This remarkable result was possible owing to the exceptional nature of the observed source – a quadruply imaged, gravitationally lensed quasar.

Credit: ACS & NICMOS/ESA/HST/STScI/AURA/NASA

The light from the distant quasar is both magnified and split into four different images by the gravitational field of a foreground elliptical galaxy (the lens) that, by chance, is on the line of sight of the quasar. For this reason, the authors could analyse four ‘copies’ of the X-ray spectrum of the quasar, each with an intensity significantly magnified by the lens. The resulting X-ray spectra have a quality that matches the best that has been obtained for nearby sources, and allowed a robust measurement of the black hole’s spin. As it turns out, the spin is large (close to the highest possible value that theory predicts), suggesting that the black hole acquired its mass through coherent phases of mass accretion.

Links: The Nature article (behind paywall); a widefield view of the lens via U. Michigan press release.

Robert Wilson and Arno Penzias accidentally discovered the afterglow of the big bang in 1964. Their now-famous horn antenna, built for Bell Labs in New Jersey, was supposed to be picking up the radio waves emitted by galaxy clusters and supernova remnants. But it recorded a temperature that was 3.5 kelvin hotter than it should have been, no matter where they pointed it (see Section 19.2a, p. 511).

Credit: © Roger Ressmeyer/CORBIS

We now know this was caused by the first photons to be released after the big bang, which still pervade the cosmos as radio waves. These days, Wilson keeps a sound recording of those waves on his cellphone (see audio link), as New Scientist magazine discovered when they interviewed him at a celebration marking half a century since the discovery.

Robert Wilson is now at the Harvard Smithsonian Center for Astrophysics. In 1978, he and Arno Penzias shared the Nobel prize in physics with Pyotr Kapitsa.

Links: the interview; the background hiss of the big bang audio (both via New Scientist).

Is Earth the only known world that can support life? In an effort to find life-habitable worlds outside our Solar System, stars similar to our Sun are being monitored for slight light decreases that indicate eclipsing, or transiting, planets (see section 9.2d, pp. 240-243). Many previously-unknown planets are being found, including over 700 worlds recently uncovered by NASA’s Kepler satellite.

Credit: Planetary Habitability Laboratory (UPR Arecibo)

Depicted above in artist’s illustrations are twelve extrasolar planets that orbit in the habitable zones of their parent stars. These exoplanets have the right temperature for water to be a liquid on their surfaces, and so water-based life on Earth might be able to survive on them. Although technology cannot yet detect resident life, finding habitable exoplanets is a step that helps humanity to better understand its place in the cosmos.

Links: APOD for full-size image; Kepler mission website.

Have you ever wondered what would it be like to see a sunset on Mars? To help find out, the robotic rover Spirit was deployed in 2005 to park and watch the Sun dip below the distant lip of Gusev crater.

Credit: Mars Exploration Rover Mission, Texas A&M, Cornell, JPL, NASA

Colors in the above image have been slightly exaggerated but would likely be apparent to a human explorer’s eye. Fine martian dust particles suspended in the thin atmosphere lend the sky a reddish color, but the dust also scatters blue light in the forward direction, creating a bluish sky glow near the setting Sun. Because Mars is farther away, the Sun is less bright and only about two thirds the diameter it appears to us from Earth. Images like this help atmospheric scientists understand not only the atmosphere of Mars, but atmospheres across the Solar System, including on our home planet, Earth.

Link: APOD March 2, 2014