We are familiar with the solar lithium problem. Lithium is of low abundance in the universe, and like the abundance of any element, this is a result of stellar nucleosynthesis. It is of even lower abundance in our sun, and this problem remains unsolved.  We are beginning to discover other places where anomalous concentrations of Lithium exist, and these stellar, interstellar, and exoplanetary lithium problems may fundamentally change the way we see star formation.

We know that Lithium ‘burns’ in the atmosphere of the sun at a certain depth, and it is thought that during different times in a star’s development, the convective cells extend to different depths.  The surface abundance of Li on the Sun is 140 times less than the protostellar concentrations would have been, and in general it is less than other stars that we have spectroscopically observed.  In some stars, this is complicated by rotation, which changes the hydrostatic equilibrium and pressure at different latitudes.  As it turns out, other stars with planets, like our own, are also lithium poor.  In metal-poor stars, such as generation II, the lithium abundance is above that predicted by the composition set by the big bang.

As we find out more about the lithium problem, our models for stellar physics will likely change.

The solar, exoplanet and cosmological lithium problems. J. Melendez, I. Ramirez, L. Casagrande, M. Asplund, B. Gustafsson, D. Yong, J. D. do Nascimento Jr., M. Castro, M. Bazot   http://arxiv.org/abs/0910.5845

Anders, E. and Grevesse, N. (January 1989). “Abundances of the elements – Meteoritic and solar”. Geochimica et Cosmochimica Acta 53 (1): 197–214. Bibcode:1989GeCoA..53..197A. doi:10.1016/0016-7037(89)90286-X

Yes, you heard correctly.  Archeoastronomy is an interdisciplinary combination of archaeology and astronomy, and it is a real science(sortof).  The first civilizations had some time on their hands, and no electricity, so dark skies were of course the norm.  Many thousands of years ago, the night sky appeared very differently from it’s current configuration. Using the current proper motions of stars and backtracking, we can study the astronomy of ancient cultures as they might have seen it.  For example, Polaris, our north star, was not near the earth’s axis at all during the height of ancient Egypt, 4500 years ago.  Rather, another star, Thuban, served as the north celestial pole star.
The Great Pyramid was built with extreme precision.  Each side is aligned with astonishing accuracy to the cardinal directions, with no misalignment greater than 5.5 arcmin. No two sides differ in length by more than 20cm, it is nearly a perfect square.  But the strangest alignment featured in the great pyramid is astronomical.  By backtracking, astronomers have determined that the air shafts that connect to the king’s tomb are aligned with the past positions of stars.  The Pharoh’s soul needed to travel to join Osiris, which we now know is the modern constellation Orion. The other air shaft points toward Thuban.  While the ancient understanding of the stars was far different than ours today, it was one filled with similar reverence and wonder.

From Intro to Modern Astro, Ch 1.3.

Space is empty… almost.  When we say vacuum, we mean space that is devoid of matter, but interestingly, creating a real vacuum on earth in a laboratory has been impossible.  Just how empty are different degrees of vacuum? How empty are the depths of space?  Between planets? Between stars? Between galaxies? We can go through a quick scale of emptiness.  As it turns out, space beats out our best efforts by a longshot.

Table borrowed from http://en.wikipedia.org/wiki/Vacuum

There are some surprising conclusions.  The commercial vacuum is ironically not much of a vacuum at all; it only reduces pressure by about 20%.

Mars’ atmosphere is 1/100th the density of Earth’s.

The moon does have an atmosphere, and it gives about the same surface pressure as our BEST vacuums on earth.

Interplanetary space is densely populated in comparison to the cold, dark space between stars and galaxies.

The quantum description of the vacuum is quite different, but we can save that for later.

Öpik, E. J. (1962). “The lunar atmosphere”. Planetary and Space Science 9 (5): 211. Bibcode:1962P&SS….9..211O. doi:10.1016/0032-0633(62)90149-6.

Chambers, Austin (2004). Modern Vacuum Physics. Boca Raton: CRC Press. ISBN 0-8493-2438-6. OCLC 55000526.^{[page needed]}

University of New Hampshire Experimental Space Plasma Group. “What is the Interstellar Medium”. The Interstellar Medium, an online tutorial. Retrieved 2006-03-15.

Tonight we will all watch a lunar eclipse, which will last a while.  As we learn some of the basics of general relativity, maybe it is relevant to think about how it’s acceptance gradually came to be, since it’s conclusions are often counter-intuitive.

One of the most important tests of general relativity came in 1919, during a total solar eclipse.  Arthur Eddington traveled to the African Island of Principe to observe the eclipse.  Eddington was an astronomer, mathematician, internationalist, and pacifist.  Immediately after the great war, he was still willing to consider the new theories of a young German physicist, and he put them to the test during the 6 minutes and 51 seconds of total eclipse.  General relativity predicts a bending of light due to the curvature of space-time near a large mass.  The sun, while massive, is not very dense, and measuring the effect of the curvature of space-time near it’s surface requires extreme precision. Observations were made simultaneously in Brazil and West-Africa. Only during an eclipse is starlight visible next to the surface of the sun. They were monitoring a specific star, looking for a deviation from it’s expected position.  Dyson, Eddington and Davidson published their results the following year, and Einstein’s general relativity became the prevailing theory of gravity over the Newtonian, with headlines in newspapers around the world.

Famously, when asked by his assistant what his reaction would have been if general relativity had not been confirmed by Eddington and Dyson in 1919, Einstein replied: “Then I would feel sorry for the dear Lord. The theory is correct anyway.”

Rosenthal-Schneider, Ilse: Reality and Scientific Truth. Detroit: Wayne State University Press, 1980. p 74. See also Calaprice, Alice: The New Quotable Einstein. Princeton: Princeton University Press, 2005. p 227.)

Dyson, F.W.; Eddington, A.S.; Davidson, C.R. (1920). “A Determination of the Deflection of Light by the Sun’s Gravitational Field, from Observations Made at the Solar eclipse of May 29, 1919”. Phil. Trans. Roy. Soc. A 220 (571-581): 291–333. Bibcode:1920RSPTA.220..291D. doi:10.1098/rsta.1920.0009.

We are protected from the constant stream of charged particles coming from our sun by the magnetic field, which deflects them around the earth and directs some of the wind to the poles.  Our sun has a strong magnetic field generated by a strong dynamo of moving charges within it’s powerful convection cells.

Similarly, the liquid portion of Earth’s mantle churns and generates the field that protects our oceans, atmosphere, and life from the solar wind.  In the last post I discussed the atmosphere and water that Mars may have had in it’s past, and how the progressive freezing of it’s core contributed to the weakening of it’s magnetic field, and the subsequent stripping of it’s atmosphere.

The sun reverses polarity on an 11 year cycle.  Earth does the same, but with less regularity.  As you can see from the plot, we are overdue for one. As we look back at the basaltic rock record expanding from the mid ocean ridges, we can see from samples of magnetite that Earth’s polarity has reversed many times in our geologic history.  What would happen on earth during one of these reversals, when the field is weak and chaotic?  In class, freshman year, I naively asked if there would be aurora everywhere.  While this would be amazing, it is unlikely.  Rather, the scattered and multiplied poles would channel less of the total solar wind, and while they may exhibit their own aurora, it would be less intense than that which we observe now.  During the last brief reversal, the field is estimated to have had 5% of it’s current strength. It would be likely that one of these periods ranging from 200 to 10,000 years would be hard on life, but reversals do not correlate with extinctions in the fossil record, so it is likely that we would live through it.

This photo is from a computer simulation of earth’s convective liquid mantle. The polarity reversed at irregular intervals, and the behavior of earth’s field was actually well matched.

Vacquier, Victor (1972). Geomagnetism in marine geology (2nd ed.). Amsterdam: Elsevier Science. p. 38. ISBN 9780080870427.

Glatzmaier, Gary. “The Geodynamo”.

“Earth’s Inconstant Magnetic Field”. Retrieved 01-07-11.

Merrill, Ronald T.; McElhinny, Michael W.; McFadden, Phillip L. (1998). The magnetic field of the earth: paleomagnetism, the core, and the deep mantle. Academic Press. ISBN 978-0-12-491246-5.

Mars is brilliantly visible right now as it rises in the eastern sky during each evening.  It is near closest approach to earth, and with a small telescope can be resolved to show the distinctive disk of a nearby planet, along with a red color that gives it a peculiarity in the night sky.

Our nearest neighbor has been well studied, enough so that some speculation has taken place on it’s past climate.  Some would perhaps like to imagine an earthlike ancient past with a thick atmosphere and liquid water oceans.  After a violent history of volcanism, the internal dynamo in the convective mantel of the planet slowed down progressively. Mars no longer has the necessary magnetic field strength to protect itself from solar wind in the way that Earth does, so it is known that its atmosphere may have been stripped of much of it’s density, and as a result Mars has lost it’s insulating properties.

The question becomes, how different was it during this time, say, on the order of 1GYA.

Some surface features can only be accounted for if we consider short periods of massive flooding, but new findings published in nature suggest that this ancient ocean world was the exception and not the rule.  Instead, most of Mars’s history was spent with conditions much colder than that of earth.  It never possessed the atmosphere to encourage runaway warming and greenhouse effect. Don’t let this dampen your imagination though, because there is much more to learn about the past of our cold and not-so-distant neighbor.

http://www.nature.com/news/ancient-mars-probably-too-cold-for-liquid-water-1.15042

A couple of weeks ago, the ESO announced that they had discovered rings around an asteroid.  They observed an occultation of starlight during Chariklo 10199’s passing, and the resulting light curve was symmetrical and indicative of a double ring system.  Chariklo is small and not perfectly spherical.  It was discovered in 1997, but this has been the first oppurtunity to image it.  It is small enough that it’s escape velocity could be attained by a fast car(350km/s).  The mechanism by which is gained rings is as yet unknown.  It is possible that a collision with another object released debris into orbit.  Prior to the discovery of the rings, a spectral signature for water ice was detected, and it is now thought that ice and dust in the rings are responsible.  In the future a search may continue for shepherd moons or other small satellites that may be associated with the rings.

At 248 km in diameter, it is the largest Centaur yet discovered. Centaurs are a special class of small object in our solar system that cross orbit with the giant planets.  They are not expected to keep these orbits.  They remain stable for estimated times on the order of millions of years before a gravitational interaction with one of the giant planets, or less probably, a collision disturbs their orbit.  Chariklo is very near to 4:3 resonance with Uranus, and so it’s orbit is relatively stable as compared to other centaurs.

http://www.eso.org/public/news/eso1410/

Jewitt; Brown (2001-04-17). “Infrared Observations of Centaur 10119 Chariklo with possible surface variation”. Retrieved 2006-11-09.

“JPL Small-Body Database Browser: 10199 Chariklo (1997 CU26)”. 2008-07-03. Retrieved 2008-10-21.

Braga-Ribas, F.; Sicardy, B.; Ortiz, J. L.; Snodgrass, C.; Roques, F.; Vieira-Martins, R.; Camargo, J. I. B.; Assafin, M.; Duffard, R.; Jehin, E.; Pollock, J.; Leiva, R.; Emilio, M.; Machado, D. I.; Colazo, C.; Lellouch, E.; Skottfelt, J.; Gillon, M.; Ligier, N.; Maquet, L.; Benedetti-Rossi, G.; Gomes, A. R.; Kervella, P.; Monteiro, H.; Sfair, R.; Moutamid, M. E.; Tancredi, G.; Spagnotto, J.; Maury, A. et al. (2014). “A ring system detected around the Centaur (10199) Chariklo”. Nature 508 (7494): 72. doi:10.1038/nature13155. edit

On the other side of the range of stars lie the supermassive, superluminous, and very unstable stars.  It is believed that all of them are supernova progenitors. While extremely rare, gravitational collapse of star forming clouds can result in the formation of stars with 20-200 solar masses.  They live violent and short lives of only a few million years.  They burn through their available hydrogen very quickly, with surface temperatures on the order of 30,000 to 200,000K, or about 6 to 35 times that of the sun.  Especially towards the end of their short lives, they experience a ‘wind’, which ejects over a billion times the mass of our sun’s wind.  This extreme mass loss results in emission lines, and this is how we can detect WR stars.
The most luminous stars discovered reside within the Tarantula nebula in the LMC.  While still very bright in the visual spectrum, they produce most of their luminosity in the UV and soft X-rays due to their high surface temperature.  Their stellar winds sculpt the surrounding gas and dust, and will likely clear out the star forming material within the nebula in the near future.
The Wolf-Rayet characteristics are thought to exist for all supermassive stars during the later stages of their lives. As a star this massive dies, it will eject all of it’s outer envelope of hydrogen, leaving a massive, superluminous blue core rich in metals.  This core is destined to undergo a core collapse supernova.  There is nothing that can support a core of this mass against complete collapse, and it will become a singularity of infinite density, or a black hole.

1. Shara, M. M.; Faherty, J. K.; Zurek, D.; Moffat, A. F. J.; Gerke, J.; Doyon, R.; Artigau, E.; Drissen, L. (2012). “A Near-Infrared Survey of the Inner Galactic Plane for Wolf-Rayet Stars. Ii. Going Fainter: 71 More New W-R Stars”. The Astronomical Journal 143 (6): 149. arXiv:1106.2196. Bibcode:2012AJ….143..149S. doi:10.1088/0004-6256/143/6/149. edit
2. Sander, A.; Hamann, W. -R.; Todt, H. (2012). “The Galactic WC stars”. Astronomy & Astrophysics 540: A144. arXiv:1201.6354. Bibcode:2012A&A…540A.144S. doi:10.1051/0004-6361/201117830. edit

In January 2014, the European Southern Observatory’s VLT recently gave us some fantastic images of a very small star of low luminosity, WISE J104915.57-531906.1B, now known as Luhman 16B.  It is a brown dwarf, a class of small stars with very cool surface temperatures. Luhman 16B and its binary partner are the closest brown dwarfs yet discovered at around 6 light years from earth. They blur the boundary between Jupiter-like substellar objects and stars, sustaining only minimal fusion in their cores and exhibiting surface weather that is similar to our gas giant planets.  Above about 13 Jupiter Masses, deuterium fusion can occur.  Above about 65 Jupiter Masses, fusion of lithium can occur as well.  To be technically considered a star, an object should be fusing hydrogen, and this occurs above 75-80 Jupiter masses.  In any case, these stars are very difficult to detect in the visual wavelengths, since they emit most of their energy in the infrared.

Like other dwarf stars of low luminosity, they can become incredibly dense.  Since there is very little pressure from fusion to sustain an expanded gas envelope, the object is supported by the thermal energy left over from initial gravitational collapse.  As the star ages, it consistently shrinks, supported at first by coulomb pressure and later by electron degeneracy pressure.  Of particular interest is their usual radii.  For a brown-dwarf star that has had time to settle, it can contain perhaps 20 times the mass of Jupiter in as little as 1.5 Jupiter Radii.

Many brown dwarfs exhibit extreme weather.  They tend to rotate rapidly and sustain convection throughout, which in turn creates strong and variable magnetic fields.  Brown Dwarfs have been identified as X-ray sources, likely the result of flares due to magnetic activity.

f

dfa

1. Tables VII, VIII, Empirical bolometric corrections for the main-sequence, G. M. H. J. Habets and J. R. W. Heinze, Astronomy and Astrophysics Supplement Series 46 (November 1981), pp. 193–237, Bibcode: 1981A&AS…46..193H. Luminosities are derived from M_bol figures, using M_bol(☉)=4.75.
2. T. J. Dupuy & A. L. Kraus; Kraus (2013). “Distances, Luminosities, and Temperatures of the Coldest Known Substellar Objects”. Science. published online 5 September 2013 (6153): 1492–1495. arXiv:1309.1422. Bibcode:2013arXiv1309.1422D. doi:10.1126/science.1241917.
3. First weather map of a brown Dwarf”           http://www.eso.org/public/news/eso1404/  “
4. “X-rays from a Brown Dwarf’s Corona”. April 14, 2003.

Read a report about a rare meteorological phenomenon that is beautiful and fascinating: Rime ice.  The report is the work of Dave Whiteman, Research Professor at the University of Utah and Rolando Garibotti, an expert on the mountains of Patagonia.

Specific conditions are necessary for the formation of rime.  Supercooled water droplets must be suspended in the atmosphere, (water that is liquid below 0C).  This occurs during rapid topographic uplifting of wet, maritime airmasses downwind of water.  They must not cool much below -10c because then the water tends to freeze independent of a surface to stick to.  The rock surface of a mountain must be below freezing, and rime collides with it during high winds, and is accreted in layers.  Above is a photo of Cerro Torre, a mountain in Argentine Patagonia.  Conditions are conducive to rime formation for much of the year, and the formations can grow to huge proportions. Here is Dave Whiteman’s formula for the mass growth of rime ice:

dM/dt=awUA [kg/s]       where w is the supercooled liquid water content of the passing cloud, U is the wind velocity in m/s, A is the area of the obstacle perpendicular to the wind, and a is the droplet-obstacle collision efficiency, between 0 and 1.

Throughout the course of a year wet weather deposits rime steadily on the faces of exposed, windswept ridges and summits.  In the photo above, these ‘mushrooms’ can grow to thicknesses of over 30m.