Magnetism and the Lunar Eclipse

Being away from home and in a very difficult environment, I have had the opportunity to be mesmerised by the many loving and genuine young people that I have met, so peaceful and kind with some of the most heartbreaking stories I have ever heard. It is wonderful to see the awe in their eyes when I explained to them some of the upcoming events that our galaxy is offering. On Friday the 27th of July at 8.15pm, we will have the chance to witness the Lunar Eclipse begin, reaching full eclipse by 10.30pm and often known as ‘blood moon’ (it will go a deep burnt red due to refraction of light from our atmosphere much like a sunset) that will be the longest lunar eclipse of the century. In addition, the planet Mars will be at opposition when it will be at its most brightest and nearing its closest to earth in 15 years, accompanied with the International Space Station passing on what will be a clear summer’s evening that I will be spending on the rooftop of this dilapidated building in the heart of the Middle East. While light pollution is a significant issue, everyone will get a chance to witness naked eye these phenomenal galactic events that gives them a glimpse into a series of astronomical narratives that will no doubt provoke questions about our planet, orbits and space. These events arrive at the same time I hear the amazing news that my program working with refugees and asylum seekers back home in Australia will be funded, where I will take disadvantaged girls and young women out on hikes, camping and viewings over my telescope where I will teach them about stargazing. It has given me inspiration on my only afternoon off for the week to write this blog post!

I was asked today, “how does all this happen?” and I attempted – albeit due to language barriers rather awfully! – a brief explanation of the moon crossing the ecliptic where the Earth, Sun and Moon are aligned when the moon orbits through the shadow of Earth. Planets orbit around the sun, the gravity pulling and keeping them in orbit and gravity acts as a powerful force between two objects with a mass. You can read more on the eclipse in a previous blog post that I wrote. Magnetism is an entirely separate force despite similarities and it depends more on particular properties rather than simply mass, such as electrons and can both push and pull. Magnetism is present throughout the universe and we can experience it in many ways; when I am out hiking, my compass explains the pressure of magnetism and direction with the movement of the needle as it is attracted by the force.

There are a number of properties and varieties of magnetic forces that explain invisible fields that applies a force that influence objects or material from the magnetism. There are rules that confirm magnetic fields are dipolar and just like earth has both a north and south magnetic pole and the ‘magnetic flux’ explains how the force and attraction between the poles – usually represented by lines as visible in the image below – that can be averaged by the magnetic field and the perpendicular area the field infiltrates. Measurements of the force is determined by the mathematical formula F= qvB (Lorentz Force Law), which is the magnetic force, the charge, the velocity and the magnetic field and the unit of these field are measured in terms of Standard International (SI) units known as tesla.

Earth’s magnetic field is known as a geomagnetic field and magnetosphere the predominate reason for the magnetic field is the liquid iron core surrounding the solid inner core is the source of this phenomenon, the very ‘magnet’ where the electric currents produced by the flow of iron and other metals including nickel cause convection currents from the inertial force of the Coriolis Effect that ultimately splits the field into a surrounding force that envelops Earth and aligns back into the same direction. The changes in temperature and composition of the liquid core creating the currents that rise or sink matter all play a part in Earths magnetic field, that can be captured visually when solar winds collide with it (usually where the magnetic force is much stronger near the north and south poles) and the charged particles trapped by the magnetic field produce the aurora borealis or the aurora australis.

ple-nord-magntique-carte-populationdatanet-15011841258n4kg

The picture explains the rotational poles but that their alignment geographically differs from our north and south poles on earth, whereby the magnetic south poles resides further north of Antarctic’ South Pole and quite close to the south of Australia while the north magnetic pole is closer to northern Canada and thus south of the North Pole. The magnetic lines explain the streamlined flow of the magnetic field that makes it easier to ascertain the process mathematically. Jupiter has a number of powerful toroidal magnetic fields where the intensity is said to have formed from the dynamic movements of the metallic hydrogen within; the field on the surface of the clouds is almost ten times stronger than earth’s. The Milky Way also has magnetic fields as do galaxies and the universe contains some colossal magnetic fields, where observations of galaxy clusters have found magnetic fields extending millions of light years!

The magnetic force is the attraction or the repulsion (as you experience when attempting to connect two magnets with equal poles) occurs from the magnetic field. The properties of electrical fields (pole) with a positive and negative charge differ with that of magnetic fields (dipole) despite a close correlation, because electromagnetism involves a magnetic dipole producing an electric field as it moves and conversely an electric field can produce a magnetic field meaning the difference is an elementary change in the field. A magnet does not have an electric charge as two separate poles, while a dipole interacts as a charge as visualised in the following image. What this means is that the electrical force itself behaves on a charged particle in the direction of the field and does not need motion while a magnetic force requires this motion and acts perpendicular to the magnetic field.

Gravitational fields also acts as force fields for mass and the gravitational force itself depends on the mass and the mass experiences the gravitational force. The gravitational field has a place in every direction and point in space and known by the formula g = F/m where F is the force of gravity. While this may be a brief example of the difference between magnetism and gravitational fields, it will be a wonderful experience with the full lunar eclipse and Mars showcasing the marvels of the universe over a hot, clear night here in Jerusalem!

Further Reading:

Maurizio Gasperini, Theory of Gravitational Interactions, Springer (2016) 115
Stephen Blundell, Magnetism: A Very Short Introduction, Oxford (2012) 106
Anupam Garg, Classical Electromagnetism in a Nutshell, Princeton University Press (2012) 83

The Cassini-Huygens Mission to Saturn and Titan

Following the painstaking experience watching Titan on Netflix last night (I highly recommend you don’t watch it) which was about the possibility of life on Saturn’ moon following an existential crises plaguing earth, out of sheer agitation I decided to look into this theme and find out more. The Cassini-Huygens mission was a seven year journey of the NASA Cassini Orbiter along with the European Space Agency’ Huygens Probe intended to travel to the Saturn system. Titan IVB-Centaur rocket was launched from Cape Canaveral carrying the orbiter and probe in 1997 and passing Venus, Earth and our moon, an Asteroid Belt and Jupiter, the Huygens Probe successfully landed on Saturn’s moon Titan in 2005. The Cassini spacecraft also managed to capture new and detailed information and images including a number of new moons such as Methone and Pallene, as well as the first spacecraft to orbit Saturn that showcased surprising activity on Enceladus, new rings around Saturn, and a plethora of additional information not previously known by scientists. The 2 hour 27 minute descent to the surface was matched with 72 minutes on the frozen ground until contact with Cassini was lost, and the probe managed to obtain images of Titan’s geology and meteorology to reveal astonishing similarities to Earth. But is Titan really similar to Earth?

The primary scientific goal of the mission was to explore Saturn’s interior and atmosphere, the ring system and the magnetosphere and plasma environment, as well as the magnetic field and origins of Saturn. In addition, a strong focus Saturn’ second largest moon, Titan when the Huygens probe was launched into the moon through the thick atmosphere during its descent to the surface. The probe was intended to study both the atmosphere and the surface composition and contain six instruments that enabled this, such as the Huygens Atmospheric Structure Instrument (HASI) designed to measure the electrical and physical properties of Titan.[1] It was additionally equipped with the following experiments:

Surface Science Package (SSP) aimed at determining the properties of the surface where the probe landed in order to ascertain further details of its composition and measure other aspects of the landing site.

Descent Imager Spectral Radiometer (DISR) that used sensors to uncover spectral measurements of the surface and as it descended toward the surface took images of the spectra.

Gas Chromatograph and Mass Spectrometer (GCMS) that attempted to identify gaseous atmospheric properties and captured material that it analysed as it descended to the surface.

Aerosol Collector and Pyrolyser (ACP) is a device that collected chemical and aerosol samples of the atmosphere and analysed the material taken from the atmosphere.

Doppler Wind Experiment (DWE) detected Doppler shifts that the probe experienced and caused by the atmosphere and winds was measured along with other properties through radio signals.[2]

The atmosphere of Titan contains the chemical composition mostly of nitrogen, but also a mixture of methane, ethane and other hydrocarbons, which makes the composition itself similar to that of Earth that contains 80% nitrogen,[3] particularly as it is the only other planetary body in our solar system that has evidence of liquid on the surface. Images from Cassini show how the surface of the moon contains rivers of ethane and methane and explains why it is the only moon that has clouds and a thick atmosphere. The orbital period of Titan around Saturn nears 16 days and is tidally-locked to Saturn, while the distance to the sun is almost ten times further than earth at 9.54 AU making the solar energy captured by the moon at a much lower rate, however the atmosphere enables Titan to capture solar energy. “It’s partial transparency to significant amounts of sunlight, and its high opacity to longer wavelengths… [s]ome of the energy from the Sun reaches the surface of Titan because solar radiation consists mostly of photons at near-visible wavelengths and the atmosphere is partially transparent at those wavelengths,”[4] that allows only about 10% of the energy to reach the surface. This energy is then absorbed by the surface that releases infrared heat out and back into the atmosphere that re-radiates by out and back down and the phenomenon of this greenhouse effect contributes to the temperature, which is at 92k (-180 degrees Celsius). The atmospheric pressure of Titan is 60% greater than Earth and the radius is almost half, but as the mass of Titan is 1.3452 x 10^23 kg compared to this size, the gravity cannot hold the gas and thus the atmosphere is much greater than that of Earth.

Seasonal variations to do exist on Titan and the Cassini mission aided researchers to ameliorate their understanding of the patterns of atmospheric changes, arriving on the northern hemisphere of Titan during winter.[5] Seasonal changes, however, are incredibly slow as it is driven by the eccentricity of Saturn’ 29.5 yearlong orbit around the sun, and the atmosphere responds to the effects of these changes in rising and falling temperatures as well as day to night variations. The orbital configuration has resulted in an imbalance of methane lakes and rivers in the northern and southern hemispheres of Titan that transports chemicals through evaporation and precipitation differently. The atmospheric pressure on the surface is at 1500mbar and researchers have confirmed the moon experiences cryovolcanism captured by observations from Cassini where the eruption style and composition is similar to volcanoes erupting liquid instead of lava.[6] Among the other important findings include the origins of Titan’ methane and the chemistry of the atmosphere as the gas increased during the descent of the probe, until it reached the surface when a spike was detected at almost 40% increase in methane suggest the possibility during the formation and accretion period, methane became trapped in the ice and reached the surface through cryovolcanism. In addition, radiogenic argon-40 (40Ar) was also detected that further confirms details of Titan’ interior since 40Ar can only form through the decay of potassium-40 (40K) that is found in rocks.[7]

HASI findings also enabled scientists to measure the density of the upper atmosphere and showed the thermosphere to be warmer and with a greater density. Atmospheric circulation and the transportation of heat was captured by the DISR by the “imbalance seen in the radiative flux measurements”[8] and it indicates winds verified by the probe as it encountered the flow from west to east and therefore the same direction as the rotation of Titan. Models have since showed that the captured data confirmed a reversal of direction and different points during the descent of the probe caused by temperature variations between the northern and southern hemispheres and within the Hadley cell that circulates from the north and south poles.[9] The super rotating winds measured the Doppler shift during the descent of the probe and measured large variations in wind speeds as it decreased the closer it reached the surface and the findings also suggest that Titan does not have a mesosphere as was predicted.

The atmosphere of Titan was found to be stratified comparatively to Earth’ troposphere where variations in temperature produce layers and while the amount of sunlight is minimal, the icy moon still contains wind and clouds, where clear by images by Cassini indicate massive dunes on the surface.[10] This provides greater details of the structure of the atmosphere including its temperature, as the DISR captured images of the surface and terrain and showed a plateau of dried river beds and lakes with narrow channels and dendritic networks that parallel the fluvial configuration you’ll find on Earth particularly erosion which DISR detected and indicative of such activity. Buried below the icy surface together with the discovery of what is known as Schumann resonance, very low radio signals in the atmosphere (around 36 Hertz) and for such signals to be reflected, “an ocean of water and ammonia which is buried at a depth of 55-80km below a non-conducting, icy crust”[11] could explain this.

There were a number of reasons for destroying the Cassini orbiter by incinerating it through the powerful atmosphere of Saturn. Not only will it provide additional information to scientists both gaining closer access to the rings of Saturn and the upper atmosphere that provide a glimpse of the interior structure and the opportunity to accurately ascertain the age and composition through closer inspection of the mass of the rings surrounding the planet, but also because of regulations vis-à-vis interplanetary contamination. The preservation of the integrity of the solar system in order to prevent and potentially damage both other planets and our own has led to all spacecraft to undergo sterilisation processes to avoid microbe contamination, particularly of planets or moons that may be capable of organic habitat. The Cassini spacecraft detected a number of new finds on Enceladus that verifies the possible conditions for contamination of microbes from Earth. Cassini itself captured vapour being released from Enceladus that confirmed an oceanic subsurface Knowing that the craft itself has a maximum output of fuel, to prevent any risk of it contaminating the integrity of the moon, scientists decided to plan the death of the device.[12]

While Titan does have similarities to Earth, particularly for having a thick atmosphere and a high percentage of nitrogen, but a number of other missing or differing constituents make these similarities marginal at best. The benefits of the Cassini-Huygens mission to Saturn and Titan enabled scientists to gain further insight to clarify these terrestrial and atmospheric differences.

[1]Fulchignoni, M., Ferri, F., Angrilli, F. et al. Space Science Reviews (2002) 104: 395. https://doi.org/10.1023/A:1023688607077:
[2] Patrick Irwin, Giant Planets of Our Solar System: Atmospheres, Composition, and Structure, Springer Science & Business Media (2003) 330
[3] http://www.lmd.jussieu.fr/~sllmd/pub/REF/2012Icar..218..707L.pdf
[4] Athena Coustenis, Fred Taylor, F. W. Taylor, Titan: The Earth-like Moon World Scientific (1999) 62
[5] Ingo Müller-Wodarg, Caitlin A. Griffith, Emmanuel Lellouch, Thomas E. Cravens, Titan: Interior, Surface, Atmosphere, and Space Environment, Cambridge University Press (2014) 215
[6] R. M. C. Lopes, Cryovolcanism on Titan: New results from Cassini RADAR and VIMS: https://doi.org/10.1002/jgre.20062
[7] Robert Brown, Jean Pierre Lebreton, Hunter Waite, Titan from Cassini-Huygens, Springer Science & Business Media (2009) 182
[8]Ibid., Titan from Cassini-Huygens, 345
[9] https://www.nasa.gov/mission_pages/cassini/whycassini/cassinif-20070601-05.html
[10] http://pirlwww.lpl.arizona.edu/~jani/radebaugh-titandunes-aeolian13.pdf
[11] http://sci.esa.int/cassini-huygens/55230-science-highlights-from-huygens-9-schumann-like-resonances-hints-of-a-subsurface-ocean/
[12] http://www.spacesafetymagazine.com/space-exploration/extraterrestrial-life/cassini-huygens-preventing-biological-contamination/

The ‘Seeds’ of Super Massive Black Holes

Stellar black holes are scattered throughout the universe, formed under the right conditions when stars reach the end of their life cycle as it collapses into itself when it no longer contains the fuel to counteract the pressure of gravity and resist compression. In order to produce a black hole, the exploding star would need to have a mass greater than our sun (at least twenty times greater) so that there is enough material – which is dispersed following the supernova – to form a black hole and will continue to grow as it consumes material such as gas and stars that draws them into the dense space. Super Massive Black Holes (SMBH) are comparatively galactic monsters that live in the centre of most galaxies and while their origins are indeed more difficult to ascertain, a number of theoretical possibilities continue to elude astronomers. Do they having the humble beginning by starting as stellar black holes that grow over billions of years through accretion and even mergers with other black holes? The confirmation that Sagittarius A* located 26,000 light years away is a SMBH located in our very own galaxy and a number of techniques have been used to ascertain its position, particularly through comparative observations found in the properties of other host galaxies and quasars. The recent quasar, J1342+0928, has given astronomers a glimpse into the possible causes of such huge SMBH.

Albert Einstein predicted the existence of black holes through his general theory of relativity, however it was not until Sir Martin Rees proposed the idea that extremely massive black holes could exist within the Active Galactic Nuclei (AGN)[1] of our own and most galaxies. His theory pieced together a detection of an unknown radio source by Bruce Balick and Robert Brown at the centre of the Milky Way and a possible demonstration that the object with such powerful gravitational force could be caused by an SMBH. AGNs are the centre of an active galaxy and depending on the properties and activity that occur within name, AGNs can be called Quasars, Seyfert Nuclei, Blazers, Liners, Radio Galaxies and BL-LAC objects and a number of other names that verifies the diversity of activity the centre of galaxies can have.[2] Host galaxies themselves also present unique characteristics and types including the elliptical, spiral and irregular galaxies and each have different components. Classification of galaxies was initially developed by Edwin Hubble that divided and then subdivided commonly found features that exhibit unique properties the he coded into a general system; a spiral galaxy, for instance, contains a bulge at the centre, surrounded by a halo and a disk structured as arms like spirals around the galaxy. Further classifications developed as the study of galaxies improved including de Vaucouleurs’s classification of galaxies that helped classify unusual properties or peculiarities, such as Quasars.[3]

R0CjB

Following Balick and Brown’ discovery, there were clear limitations to radio observations to verify whether the source was specifically a SMBH and continued efforts led to NASA’s Chandra X-Ray Observatory to spot never before seen x-ray emissions by penetrating the galactic dust and clouds that blurred the possibility of a closer investigation to this blackness at the heart of our galaxy using radio sources, giving us more insight about the activity and behaviour of SMBH.  The Very Large Array as part of the National Radio Astronomy Observatory (NRAO) includes 27 radio antennas configured to provide images that would give the resolution of one dish at almost 130 metres in diameter.[4] The image below is one such image taken from the observatory in New Mexio and shows a central source – now known to be Sag A* – has forced ionized gas into a mini-spiral rotating around centre and revealing the possible features of a concentration of dark matter, but whether this concentration was a SMBH was not confirmed as well as raising the question and nature of SMBH as apparently motionless. “The implied minimum dark matter density of ~3×10.9 M  pc^-3, however, still allowed a cluster of dark objects, such as neutron stars or stellar mass black holes, as one of the alternatives to a single supermassive black hole because the measurements did not force the cluster’s lifetime to be shorter than the age of the Galaxy.”[5]

Picture 1

As observations have also included evidence of the emission of radiation including Infrared, X-ray and Gamma-Ray sources, other telescopes including the Very Large Telescope (VLA) managed by the European Southern Observatory in the Atacama Desert of northern Chile and the 10m W. M. Keck I telescope on the summit of Mauna Kea in Hawaii has mapped the orbits of stars and objects that are within one parsec (about 3.26 light-years) of the central dark object, enabling astronomers to measure the mass of Sgr A* utilising Kepler’s Laws that calculate the length of time it takes for the orbiting object to encircle the galactic centre together with the semi-major axis, leading astronomers to believe the centre of our galaxy is contained by a SMBH equivalent to 4 million solar masses.[6] “Orbits are derived simultaneously so that they jointly constrain the central dark objects properties: its mass, its position, and, for the first time using orbits, its motion on the plane of the sky.”[7] This is because the dark central object has a powerful mass within such a small radius nearing 100 AU (1 AU is the distance between Earth and the Sun or about 150 million kilometres) that suggested dark matter to be confined in a space of 0.015pc ruling out the possibility of a cluster of stellar black holes as the source, leading to the conclusion that it is a SMBH. The Fermion Ball Hypothesis offers an alternative possibility for the blackness problem as it attempts to explain the supermassive dark object at the centre to be a ball of self-gravitating, non-interacting, degenerate fermions.[8] Fermion balls may have been formed in the early universe and studies show the analysis of the orbits of stars S0-1 and S0-2 around Sgr A* was initially consistent to the FB scenario as the pressure from the degeneracy maintains a balance with the gravitational attraction to the fermions.[9] Continued observations of the S0-2 orbit revealed that a mass of 3.6‡ 0.6 x 10^6 MΘ  is located within a sphere radius of 0.6mps Sgr A*[10] that excludes the possibility of the FB Hypothesis as such a mass density would impact on the fermion ball particles.

These advances in telescopic technology including the use of Very-Long Baseline Interferometry (VLBI) techniques that captures high resolution radio sources from different locations before being combined into following the meticulous measurement of time differences all fed into one central location on a supercomputer with enormous data capacity to enable this to occur efficiently have recently made it possible to capture the shadow of the event horizon, the boundary surrounding the SMBH. As the diameter of the telescope increases the resolution, sensitivity and baseline, and the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA) combines multiple telescopes around earth to simulate the power that an earth-sized telescope would capture. The boundary surrounding a black hole is an event horizon because while gravity is very strong, objects can still escape from the gravitational pull and thus energy can be detected near the horizon while anything that travels beyond that an observer cannot see.[11]

The Event Horizon Telescope and Global mm-VLBI Array on the Eart

Quasars are the most luminous AGN and they have a very strong correlation to SMBH as the latter is required to give Quasars the immense power that they project. “Quasars rank amongst the most luminous sources of radiation in the universe and are believed to be powered by SMBH.”[12] M–σ or the M-Sigma relation indicates a correlation between the mass of a SMBH and the stellar velocity dispersion in their host galaxies[13] and confirm SMBH to be a fundamental element of host galaxies with Quasars. Quasars are said to exist in predominantly larger galaxies during the active phase of gas accretion and therefore the early life of a galaxy, where particles or matter are heated and accelerated away like a jet or stream of light from the ionization around the boundary of an SMBH at velocities almost at the speed of light and emitting powerful energy and therefore luminosity that exceeds all the sources of light within the entire galaxy.[14] In December 2017, the most distant quasar J1342+0928 at a redshift of z=7.54 was found and provided a glimpse into the cosmological timeline by using Planck parameters that confirmed the age of galaxy to be barely 690 Myr after the big bang[15] with an SMBH that contains a mass of 8e8 Msun (800 million solar masses!).[16] The existence of a SMBH during such an early epoch of the universe’ existence confirms a number of models about how black holes can grow to such a supermassive size as it captures nearby material and ultimately engines the power of a quasar. The standard view is that following supernova explosions, the gravitational interactions form stellar black holes and continue to grow through mergers and accretion, however the accretion theory does not explain the SMBH in quasars so old and powerful as J1342+0928 known as the quasar seed problem, indicating that the conditions to have formed them must have been achieved by direct collapse.[17] A large ‘seed’ to form a black hole as colossal as 100,000+ solar masses and therefore thousands of times bigger than black holes shaped by a supernova is possible in the right conditions during the early universe as it required an equally colossal star collapse that would supress star formation because the temperature of the ultraviolet photos ensure that the surrounding gas remains hot enough. Stars usually form when the cloud cools as the gas is dispersed, but the conditions in the early universe confirm that such a supermassive ‘seed’ could be possible before it begins to attract matter and gas to grow over billions of years into its colossal size.[18]

The catalyst that enables supermassive black holes to form remains unconfirmed, but as technology enables astronomers to locate and verify new hints about the galaxy, we are inching closer and closer to verification of theories

 

[1] Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research, Ferrarese & Ford 2005, Space Science Reviews, Volume 116, Issue 3-4, pp. 523-624
[2] Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research, Ferrarese & Ford 2005, Space Science Reviews, Volume 116, Issue 3-4, pp. 523-624
[3] Sidney Van den Bergh, Galaxy Morphology and Classification, Cambridge University Press (1998) 13
[4] http://www.vla.nrao.edu/
[5] Stellar Orbits around the Galactic Center Black Hole, Ghez et al. 2005, The Astrophysical Journal, v.620, p.74
[6] Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research, Ferrarese & Ford 2005, Space Science Reviews, Volume 116, Issue 3-4, pp. 523-624
[7] Stellar Orbits around the Galactic Center Black Hole, Ghez et al. 2005, The Astrophysical Journal, v.620, p.74
[8] Neven Bilic, Supermassive Fermion Balls and Constrains From Stellar Dynamics Near Sgr A∗: https://arxiv.org/pdf/astro-ph/0310172
[9] http://iopscience.iop.org/article/10.1086/323949/fulltext/
[10] Siegfried Röser, From Cosmological Structures to the Milky Way, John Wiley & Sons (2006) 196
[11] Jim Al-Khalili, Black Holes, Wormholes and Time Machines, Taylor & Francis (2016) 64
[12] Formation of z~6 Quasars from Hierarchical Galaxy Mergers, Li et al. 2007, The Astrophysical Journal, v.665, p.187
[13] Raphael Sadoun, M- sigma relation between SMBHs and the velocity dispersion of globular cluster systems: arXiv:1204.0144 [astro-ph.CO]
[14] Andrew C. Fabian, Active Galactic Nuclei: Proc Natl Acad Sci U S A. 1999 Apr 27; 96(9): 4749–4751.
[15] Fulvio Melia, J1342+0928 Confirms the Cosmological Timeline in R_h=ct: arXiv:1712.03306 [astro-ph.CO]
[16] E. Bañados,, An 800 million solar mass black hole in a significantly neutral universe at redshift 7.5: arXiv:1712.01860 [astro-ph.GA]
[17] Bhaskar Agarwal, Formation of massive seed black holes by direct collapse in the early Universe, Dissertation (2013) pp 24
[18] Silvia Bonoli, Massive black hole seeds born via direct gas collapse in galaxy mergers: their properties, statistics and environment, https://arxiv.org/pdf/1211.3752.pdf

A History of the Eclipse: The Birth of Science

A solar eclipse is a clear demonstration of celestial mechanics as the position of the moon and the sun temporarily shadows the sunlight on earth, and indeed for centuries has led to a number of mythologies that attempt to explain the geometry of the unknown universe and where civilisations and formidable historical figures came to greatly influence the study of science and astronomy as we know of it today. The ancient Babylonians, Egyptians and Chinese were so entrenched in these myths that they formed methodical processes aimed at calculating and predicting occurrences and did so with great accuracy that led to the development of the necessary instruments to aid in their observational techniques. For instance, the Babylonians believed that the solar eclipse could potentially be a bad omen that would predict the death of the King and this fear evoked constant study that soon thereafter established the 223 month Saros cycle of eclipses, something that we still use today. Have eclipses prompted astronomers and philosophers to theorise celestial geometry and planetary motion that ultimately enhanced scientific tools prior to the invention of the telescope by Hans Lippershey in 1608 and led to what is known as science?

Several shadows are formed between the earth and the moon that occurs during both lunar and solar eclipses, the latter a result when the moons’ shadow hits the earth, though the sun is four hundred times larger than the moon. During a total solar eclipse, this shadow is called an Umbra,[1] whereby the very center of the shadow’ core is blocked by the moon as it eclipses the sunlight and as this ends, the shadow becomes an Antumbra that forms the lighter section of this shadow. During an annular solar eclipse, when the light source contains a larger diameter due to the distance of the moon during an Apogee (when the moon is at its farthest distance on the elliptical from the earth), the moon appears smaller and thus silhouettes the heat of the outer edge of the sun, forming a visible ‘ring of fire’.[2] When the moon’ distance from the earth is at a Perigree and therefore at its closest range, it enables a total eclipse as the diameter roughly matches and covers the entire sun.[3] It is estimated that a total solar eclipse in a location only occurs once every several hundred years and being an exceedingly rare phenomenon and difficult to predict only added to the mysteries of the heavens.[4]

Prior to the use of the telescope, astronomers recorded their observations using a number of tools, once such being the Armillary Sphere or the Spherical Astrolabe that was used both as a teaching tool and to aid observations. Aristotle, notwithstanding his vast array of knowledge on a number of subjects, included in his curriculum vitae the title of amateur astronomer and authored On the Heavens that observed the material nature of the cosmos through concentric celestial spheres. For Aristotle, the world is both celestial and terrestrial, with the latter sphere composed of changing and chaotic elements of fire, water, earth and air that is surrounded within a perfect and unchanging celestial universe. His theories of motion and cosmology dominated the subject for centuries and remained similar to that of Eudoxus (c 337 BC) who stated that with the earth being the center of the universe, rotating spheres on individual axis moved at various speeds and angles around the earth.[5] As the earth is spherical in shape, it remains stationary as the sun, moon and planets rotated around the earth and the motions of these spheres carried all celestial activity including the fixed stars and ecliptic rotations. As Aristotle’ work survived and being highly influential unlike many of his predecessors, his cosmological views remained dominant until Ptolemy wrote Almagest, a voluminous encyclopedia of astronomy that summarised all knowledge of astronomy available at the time. He also had his own version of a planetary system that was based on the notion of spheres but instead adopted a preference for circular eccentricity or a circular shape of the ellipse (equant) that rotates at various speeds.[6] Accordingly, his system also abandoned Earth’ positon as the center of the system and thus changed the centuries-old influence of Aristotle.

However, prior to Aristotle’ astronomical accounts the Ionian philosophers perhaps beginning with Thales of Miletus (c624 BC) who is said to have predicted the solar eclipse of the 585 BC[7] became highly influential in the development of natural philosophy. According to Herodotus, this solar eclipse had such a powerful influence that the war between the Lydians and the Medes came to an end when they viewed the eclipse as a sign and a warning from the gods.[8] While the Egyptians and Babylonians had already formed extensive observations of the night sky, the latter in particular employing the Saros that determines periodicity of eclipses governed by a repetitive cycle spanning 18 years, 11 days and 8 hours and enabled them with the skill to predict eclipses,[9] they were restricted by the superstitions and myths formed in their pagan rituals that viewed these eclipses as bad omens, particularly for the ruling class. The Greek philosophers were empowered with more intellectual maneuverability that established a better scientific approach to astronomy that was instead viewed to be governed by natural laws; what made up the universe was material rather than supernatural and the Armillary Sphere exemplified this as a teaching tool. Thales studied geometry in Egypt and this mathematical knowledge was brought back to Greece as he soon thereafter became credited to developing a number of advancements in the subject that attempted to explain unknown astronomical concepts. The earth, for instance, was a large mass floating on water and earthquakes were evidence of oceanic turbulence. Thales stated that the material that formed the universe was water (our dark matter) and is the fundamental element that all the material world. Cosmological theories continued with his followers such as Anaximander and Anaximenes that questioned the origin of the universe. Anaximenes took it one step further, purporting that the element that forms water – air – is the building block of all material things and water is merely the compressed form of this element.

Anaximander was far more interesting as he purported that the universe was formed by a chaos of infinite opposites (such as hot and cold) and his cosmological model of the universe was intriguing to say the least, suggesting a cylindrical earth surrounded by wheels of fire from the sun that we are able to see through holes that rotate past us. This period is clearly marked a great many discussions on the physics of the universe that attempted to explain the appearances of celestial objects, when things are static or dynamic, constant or eternal. Hipparchus (c190 BC) discovered the precession of the equinoxes by using the solar eclipse by estimating the distance of the moon from the earth.[10] The Armillary Sphere were devices that enabled a demonstration of the rings that represented the celestial spheres and attached to them were fixed globes set to an elliptical axis and were “sometimes mounted on handles, but often were set like globes into cradles so that the sphere could be adjusted to represent the heavens as seen from any latitude.”[11] A number of spheres continued to be developed and adjusted from Ptolemy to Copernicus as an instrument to explain and observe equatorial coordinates and through Aristotle moved into the Islamic world.

The cosmological and astronomical theories during this period nevertheless contained the practice of supernatural and mystical influences that viewed the heavens as practical tools for predicting events throughout the passage of time. While methods of observations and the tools that strengthened how they recorded data steadily advanced, the observations continued to be shrouded by such celestial mysteries that evoked a sense of fear and awe. In China, for instance, the Emperor had control of the heavens and therefore predicting eclipses and other activities (lifa) along with the study of astronomical phenomena (tianwen) played a powerful role in his position as supreme leader.[12] Without an orderly understanding of astronomical event, it was viewed as a bad omen and a sign of problems ahead. China is attributed as having the first record of a solar eclipse (c. 2134 BC).[13] Like the ancient Hellenistic astronomers, China also used their own version of an ancillary sphere and took it even one step further by developing a mechanically powered globe using a sophisticated haudralic system during the Han Dynasty.[14] However, Shen Kuo (c1095) who is said to have developed the magnetic-needle compass did so following his observations of planetary motions and by using the models of solar eclipses was able to verify that celestial objects were in fact round.[15]

While such celestial activity was during the time of the Egyptians and Babylonians shrouded with pagan mysticism, astronomy soon thereafter through Saint Thomas Aquinas enabled the world to view Aristotelian cosmology through a Christian lens, one clearly visible when Copernicus’ model that the earth revolves around the sun was met with denunciation by the dominant Catholic influences of the time. Scholastic astronomy was introduced to medieval Europe from the Islamic Golden Age following the decline of the Roman Empire and the new Ottoman Empire steadily controlling the Middle East and North Africa attained access to the library of Alexandria and thus the work of the ancient Greeks, translating them into Arabic and improving a number of astronomical models that advanced an understanding of the elliptical movements of planets and the moon. Translations of the Arabic to Latin enabled Aristotelian and all scientific writing to move into Europe when the Christians conquered the Moors in Spain and Aquinas successfully incorporated Aristotelian philosophy into Christendom. Thinkers such as Casanus began to combine theological influences to cosmological theories, purporting that the universe is infinite and that there was no specific location of space, instead space was everywhere. The subject of eclipses developed intense interest during the Islamic Golden Age as Islam required a sophisticated approach to prayer that required the correct direction toward Mecca during important periods of sunrise and sunset together with the calendrical system of the moon that inevitably enhanced the study and the equipment thereof including sundials and quadrants.[16] However, it is the Equatorium that was developed by Ibn al-Samh and al-Zarqali and translated in Castille under the patronage of King Alfonso X[17] in the book Libros Del Saber De Astronomia (Books of the knowledge of astronomy)[18] that assisted with astronomical calculations.

It is clear that studies of the solar eclipse prior to the development of the telescope have led to a great many developments in the study of astronomy and science as a whole. As the ancient Hellenistic community of philosophers approached the subject with more freedom of religious constraint, natural philosophy contributed vastly to the subject that even included mathematical advancements, such as the Pythagorean Theorem where the square of the hypotenuse is equal to the sum of the square of the remaining sides of a triangle. Pythagoras himself believed that reality is formed through numbers or that the material world can be reduced to simple numbers and by bringing with him the knowledge from the Babylonians that the earth is spherical in shape, visible during a curved shadow on the moon during eclipses, changed the study of astronomy and ultimately influenced the development of the study of science as we know today.

When I first heard of the eclipse in the United States in 2017 as I was in Hawaii, I never really thought that this celestial phenomenon could have had such a profound historical influence on the study of science. While the subject evoked many mythologies, mythologies even present today with theories of biblical Armageddon that the eclipse has stirred, there is no doubt that the motion of the moon around the earth, the sun and planetary models that attempted to explain geometric orbits from spheres to water, mathematical to theological, changed the face of history and enabled the beginning of the study of western science. While the origin of the universe continues to remain impossible to answer – I myself am controversially of the opinion that the origin of the universe is in God – the material world that we experience nevertheless can be scientifically explained without it being shrouded by theological superstition and bad omens. I think we can use science to quite easily predict that if Armageddon were coming, it is likely because of the United States along with many other countries that are ruining the earth without needing the book of revelations to tell us that.

 

[1] Martin Mobberley, Total Solar Eclipses and How to Observe Them, Springer Science & Business Media (2007) 38
[2] Nicholas Nigro, Knack Night Sky: Decoding the Solar System, from Constellations to Black Holes, Rowman & Littlefield (2010) 206
[3] Op. Cit., Mobberley, 39
[4] Michael Borgia, Human Vision and The Night Sky: How to Improve Your Observing Skills, Springer Science & Business Media (2006) 112. It is good to note that total solar eclipses occur regularly (every 18 months) but in one given location will span over 300 years.
[5] Richard Jones, The Medieval Natural World, Routledge (2013) 30
[6] Michael Zeilik, Astronomy: The Evolving Universe, Cambridge University Press (2002) 34
[7] Lisa Rezende, Chronology of Science, Infobase Publishing (2006) 21
[8] William Hales, Chronology and Geography, C.J.G. & F. Rivington, (1830) 71
[9] https://eclipse.gsfc.nasa.gov/SEsaros/SEsaros.html
[10] Lloyd Motz and Jefferson Hane Weaver, The Story of Astronomy, Springer (2013) 45
[11] John Lankford, History of Astronomy: An Encyclopedia, Taylor & Francis (1997) 34
[12] Frances Wood, Great Books of China (2017) in Almanac or Tongshu (c 1000 – c 600 BCE)
[13] Aaron Millar, The 50 Greatest Wonders of the World, Icon Books (2016)
[14] Joseph Needham, Science and Civilisation in China: Volume 3, Mathematics and the Sciences of the Heavens and the Earth, Cambridge University Press (1959) 458
[15] Ancient China’s Technology and Science: Compiled by the Institute of the History of Natural Sciences, Chinese Academy of Sciences. Foreign Languages Press (1983) 153
[16] Ludwig W. Adamec, Historical Dictionary of Islam, Rowman & Littlefield (2016) 393
[17] Roshdi Rashed, Encyclopedia of the History of Arabic Science, Routledge (2002) 256
[18] Belén Bistué, Collaborative Translation and Multi-Version Texts in Early Modern Europe, Routledge (2016) 65

Ripples Through The Universe: A Stellar Find

Albert Einstein has become synonymous with term ‘genius’ and having set the foundations that strengthened the study of physics with his Theory of Special Relativity [SR] early in the twentieth century – that determined the speed of light is observed the same in any frame of reference and that the laws of physics is invariant for observers moving at a constant – it is easy to see why. This set to motion his General Theory of Relativity [GR], the most important step forward in scientific history that ameliorated our understanding of both gravity and of the curvature of space and time interwoven into a continuum. Unlike Newtonian physics where gravity is understood as a force and while space is influenced by this force, gravity instead was understood as a field within space-time and curved by the mass of objects like planets and stars. Thus gravitational fields are curved by matter and fastened to the geometry of space and time that responds by telling matter how it should move. Further studies by physicists continued toward the latter half of the twentieth century when Nobel laureates Russell Hulse and Joseph Taylor discovered a new type of pulsar, and the discovery enabled revolutionary studies into understanding gravitation. The survival of remnants from a supernova core is so massive that it collapses into a neutron star by condensing the protons and electrons into a neutron and into a very compact and dense space. The core of the neutron star can have the mass of one sun and only the diameter of around 15 km . Neutron stars spin very rapidly and emit radio waves that are detected as ‘pulses’ and their discovery of PSR 1913+16 binary pulsar – a radiating neutron star – helped ignite the prediction in GR of gravitational waves. The Hulse-Taylor Binary star system that has two neutron stars orbiting one another would lose energy through the radiation of gravitational waves and as the rate of the orbital timescale is decreasing, it confirmed gravitational radiation as predicted in GR must be the cause.

It is amazing that my studies in astronomy have allowed me to find out that there is evidence to prove gravitational waves! As a consequence, scientists attempted to build technology to study the possibility of gravitational waves and built the aLIGO – Advanced Laser Interferometer Gravitational-Wave Observatory – an upgrade to the initial iLIGO that is capable of observing great distances at almost 300 million parsecs. There are current discussions to prepare a LIGO detection device – eLISA – for space where detection could be far more accurate. These L-shaped devices known simply as interferometers are shaped like the letter L with each side of this L at the length of four kilometres, and contain laser lighting that measures the length of each side. This is done at a very meticulous rate at 1×10-15 meters as any gravitational-wave that enters LIGO would change the measurements and the light would stream out the interferometer. These interferometers are located in two observatories in Washington and Louisiana and when the gravitational-wave hit earth, both shifted synchronically by 0.0007 seconds. This was the first official confirmation that physicists detected gravitational waves and confirmed Einstein’ theory. The detection is said to have been formed by the collision between two black holes 1.3 billion years ago at a combined mass of 62 suns. However, individually, one binary black hole had the mass of 29 suns and the other 36, with the violence of the collision forcing three solar masses to be released as energy out as gravitational-waves across the fabric of the universe.

The first observation of gravitational waves known as GW150914 demonstrated binary black hole mergers that involve two black holes near one another. There are a number of ways that black holes can be formed and categorised depending on its mass and size, including the smallest primordial black holes, medium stellar black holes and the most common, as well as the largest supermassive black holes that contain the mass of one million suns that has been reported to exist at the centre of the galaxy. Stellar black holes begin its cycle during the end phase of the evolution of a star as it collapses in itself. To briefly ameliorate stellar evolution, when a protostar is small enough to heat and trigger nuclear fusion at its core, a star begins its life and the accumulation of particles continues to attract more as part of the accretion process until it generates a core temperature over 10,000K to enable it to sit on the Main Sequence, just like our sun. Otherwise, it will become a brown dwarf. When our sun – a yellow dwarf – becomes a red giant as hydrogen atoms are combined together to form helium atoms and along with the expansion of the surface area as the core continues to get hotter, the elements are transmogrified to heavy carbon and others until the helium stores are depleted. As the sun loses temperature, it really cannot do much with the carbon and thus gravity will enable it to expand and become unstable as outer layers disintegrate. The only remaining area of the star is the core – the white dwarf. At this point, the remnants of the red dwarf will cover the white dwarf with a planetary nebula and over time, it will cool down and into a black dwarf.

Hertzprung-Russel Diagrams [H-R diagram] contains details that explains the evolution vis-a-vis changes in the temperature and luminosity of a star and strengthens our understanding of where distinct group the brightest stars fall into [this includes supergiants, giants, subgiants and white dwarfs] and comparing it to our own sun that sits on the main sequence. Majority of our stars sit along the main sequence and all contain lumonsity scores that categorise them into spectral classes.

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Variable stars, however, are the least stable and often change luminosity and size rapidly both for intrinsic and extrinsic reasons. For instance, Rotating Ellipsoidal Variables is perhaps a simplified example of why the luminosity of stars change, whereby extrinsic variables implies that the fluctuations in luminosity are wholly external to the star’ dynamics. Brightness of stars is dependent on the surface area – hence why massive stars are more brighter – thus when a pair of stars appear side-by-side, their surface area increases [from where we see them] and thus a binary system where stars are close enough that their shapes become distorted. This shape appears somewhat egg-like rather than spherical. Changes to the stars shape and luminosity has enabled astronomers to measure the time it takes for the stars to rotate. Spica, the brightest star in the constellation Virgo, is considered a Ellipsoidal Variables but detection is difficult as fluctuations are minimal [0.92-1.04 magnitudes] though they have captured that the length of the rotation is four days. Spica A is 11 times greater than our sun whilst Spica B is 7, which is why it is one of the top brightest stars in the night sky.

AM Herculis is a part of a unique class of cataclysmic variable stars; a binary star containing a white dwarf where its magnetic field is so strong that it channels the flow or synchronisation of the rotational and orbital system with the red dwarf star. It is known as ‘AM Her Stars’ or ‘Polars’, magnetic cataclysmic variables that contain two stars – a dominate white dwarf together with a red dwarf star – where a circular polarization exists together with a strong magnetic field. Cataclysmic variables are distinguished between non-magnetic and magnetic and the case of AM Herculis, it is the latter (polars). Polars are also divided into two categories, intermediate DQ Her Stars [where the magnetosphere is not strong enough though an accretion disk is formed] along with AM Her stars, that contains a very strong magnetic field that it pulls the two stars together into a synchronous rotation where the magnetic field eventually dominates the entire system and does not form an accretion disk. That is the red dwarf loses material as it is channeled by the strength of the white dwarf’ magnetic field and prevents the formation of an accretion disk, instead forming a funnel or accretion stream toward the magnetic poles of the white dwarf that emits strong x-ray emissions. These emissions heat the area around the pole that the kinetic energy sources soft x-rays on the white dwarf’ surface. The flow of material is locked into this funnel preferentially to one magnetic pole of the white dwarf. Other variable star types can be found here.

The death of a star by supernova is a cataclysmic event or a cosmic explosion that releases remnants of gas and contain radio waves and X-ray emissions. However, sometimes as the star depletes nuclear fuel, it no longer contains the energy to resist gravity and therefore the elements or material in the core of the star is compressed by the force of the gravity until it collapses under the weight. An extremely large star – something around 3 solar masses or larger – may collapse into a black hole. While black holes are so dense that light cannot escape, astronomers have been capable of identifying the existence of them – such as Cygnus X-1  – through emitted X-rays from the hot accretion disks surrounding the black hole as it captures nearby gas from a star. A black hole, surprisingly, does not contain many properties, which are mass, spin and electrical charge  and it may be that the latter contains no ‘charge’ while theoretically the matter would continue to collapse until there was no longer a radius and thus infinite density. This compression is known as the singularity and discovered by Karl Schwarzschild following the release of Einstein’ GT as the curvature of spacetime becomes infinite.

The detection of gravitational waves confirms that Einstein was correct and will enable scientists to understand the early universe with more acumen. It will also set the stage for a new area of astronomy and I just had to write a little bit about it.

Hulse R A 1994 The discovery of the binary pulsar, Rev. Mod. Phys. 66 699 and Taylor J H 1994 Binary pulsars and relativistic gravity, Rev. Mod. Phys. 66 711
Otto Struve, Stellar Evolution: An Exploration from the Observatory, Princeton University Press (2015) 33
https://www.e-education.psu.edu/astro801/content/l5_p3.html
http://www.ligo.org/science/Publication-GW150914/
Beech, M, The Ellipsoidal Variable, Astrophysics and Space Science (ISSN 0004-640X), vol. 117, no. 1, Dec. 1985, p. 69-81.
Hessman, F.V., Gansicke, B.T., and Mattei, J.A., “The history and source of mass-transfer variations in AM Herculis”, Astron. Astrophys., 361, 952-958, 2000.