Friday, May 31, 2013

Type Ia supernova - Wikipedia, the free encyclopedia

Type Ia supernova - Wikipedia, the free encyclopedia:

 "Type Ia supernovae occur in binary systems (two stars orbiting one another) in which one of the stars is a white dwarf while the other can vary from a giant star to even a smaller white dwarf.[2]"

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Wednesday, May 29, 2013

Why Does Nature Form Exoplanets Easily?

Kevin Heng
University of Bern
Center for Space and Habitability
Sidlerstrasse 5, CH-3012, Bern, Switzerland
Abstract

The ubiquity of worlds beyond our Solar System confounds us.

An area of research that has attracted a lot of attention in the field of astronomy and astrophysics is planet formation: the study of how planets (in our Solar System) and exoplanets (orbiting other stars) form. Astronomers harness the power of telescopes with meter-sized or larger mirrors to search the night sky for exoplanets—and they find loads of them. In the past two years, NASA’s Kepler Space Telescope has located nearly 3,000 exoplanet candidates ranging from sub-Earth-sized minions to gas giants that dwarf our own Jupiter. Their densities range from that of styrofoam to iron. Astronomers find them close to their parent or host stars with scorching temperatures of a few thousand degrees; they also find them distant from their stars, more than 10 times farther away than Jupiter is from our Sun. Perhaps most significant, the Kepler results demonstrate that rocky exoplanets are common in our local cosmic neighborhood—and by extension, our universe at large. Nature seems to have a penchant for forming exoplanets.

As astrophysicists, our goal is to construct hypotheses to explain what we see in nature. We create model universes and exoplanetary systems on paper and in our computers. When our hypotheses stand the tests of data and time, they eventually become accepted as theories. Hypotheses of planet formation are usually forged within two accepted paradigms: core accretion and gravitational instability. Core accretion is the “bottomup” approach: Large objects form from smaller ones, eventually building up to exoplanets. Gravitational instability is the “topdown” method: Exoplanets form directly from larger structures in the primordial disks of gas and dust orbiting young stars. But when astrophysicists zoom in on the physical details, we find ourselves (and our hypotheses) flummoxed and, quite simply, outclassed by nature. Dust grains do not seem to readily stick. Even if rocks form, they then drift into the star much too quickly, fast enough to preclude their coalescence into larger objects. These larger, kilometer-sized objects, known as planetesimals, are in principle the building blocks of planets. For our Solar System, theorists struggle in modeling to form the rocky cores of the gas giants, Jupiter and Saturn, before the primordial gas of the natal disk dissipates. Even forming Neptune within the paradigm of core accretion takes too long due to its relative remoteness from the Sun. The devil is in the details and, unfortunately, they do matter when trying to construct synthetic exoplanets.

Rocks are Hard to See

The hardest thing to observe with a telescope is a rock. Astronomers can see disks of gas and dust swirling around nascent stars, as well as fully formed exoplanets orbiting mature stars. But it is terribly difficult—if not impossible—to detect the presence of planetesimals, at least outside of our Solar System. An entire cottage industry of astronomers is engaged in the study of protostellar or protoplanetary disks, the purported birthplaces of exoplanets. They find a rich cacophony of features in these disks: asymmetries, gaps, warps, dust made from exotic substances. Sometimes, they even find exoplanets embedded in the disks (which often cause the features themselves). A decisive test of planet formation hypotheses is to study the properties of planetesimals within these disks, but these objects are practically invisible. Planetesimals are neither numerous (compared to dust grains) nor large enough (compared to exoplanets) to re-emit significant radiation that can be detected by telescopes. Any link to them is indirect and uncertain at best, made through assumptions of their relationship to the observed dust grains. Even estimating the masses of these disks remains a crude exercise at best and requires Solar Systemcentric assumptions on the opacity of the dust grains and the relative amounts of dust and gas present in the disk. We find ourselves bombarded with information, but knowledge eludes us.

Figure 1: NASA’s Kepler Space Telescope mission has found thousands of candidate exoplanets that are passing in front of their stars in its field of view. Of these, 361 systems of more than one planet are depicted here, along with their catalog numbers (a separate color is used for each planet in a system). Many of these systems have multiple exoplanets tightly packed together. The orbital distances are on one scale, and the planet radii are on a separate scale. The terrestrial planets of the Solar System (at lower left and labeled “ours”) are also shown for comparison. This conglomeration is called the Kepler Orrery, named after the mechanical device that shows the positions and motions of the planets and moons in the Solar System. (Image courtesy of Dan Fabrycky of the University of Chicago.)

The prevalence of rocky exoplanets in nature lends credence to the paradigm of core accretion. Astrophysicists hoping to model formation by this mechanism appear to have their work cut out for them: They must start with micrometer-sized dust grains and congregate them to produce larger particles, either on paper, in computer simulations or in the laboratory. The task is daunting, because there is conceivably a factor of a billion in size between dust grains and planetesimals. The protoplanetary disk conspires to exacerbate matters—gas orbiting a star tends to move at slower speeds than for the dust grains, because of the self-exerted pressure support. The dust grains experience a “head wind,” which acts like friction, causing them to spiral into the star. The time scale on which this “gas drag” phenomenon occurs is, uncomfortably, shorter than any conceivable time scale for grain growth. This conundrum is commonly called the “meter-size problem,” because it afflicts meter-sized objects the most when they are located at the same distance from the Sun as the Earth.

Proposed solutions to the meter-size problem are plentiful. Some astrophysicists devote their careers to re-creating in their computers the conditions for encounters between dust grains. These simulations capture the intricate details of collisions, both constructive and destructive: coagulating, chipping, bouncing, deflecting, shattering. Dust grains of all sizes and shapes are studied. Again, we are awash in information, but knowledge is slower to come. Nature is hinting to us that planet formation is a robust phenomenon—surely, the mechanism involved cannot be privy to all of the micro-details of the dust grains and must be related somehow to the global properties of the protoplanetary disk. Although it cannot serve as a proof, we are guided by principles such as Occam’s razor—when faced with many explanations, we pick the simplest one.

Working on Theories

Theorists studying core accretion use two approaches. The first is to isolate a piece of the puzzle—such as the meter-size problem—and study the microphysics involved. Such approaches shed light on important pieces of the puzzle of planet formation but lose the big picture. A complementary approach is to use population synthesis, which is an attempt to incorporate all of the physics and chemistry involved in core accretion, starting from dust grains and ending up with exoplanets. Gaps in our knowledge of the details currently prevent the population synthesis framework from being a complete theory, but its redeeming quality is that it provides some falsifiable predictions.

Another solution is to bypass the intermediate steps of growth between dust grains and planetesimals. Protoplanetary disks are usually massive enough that gravity may triumph over pressure support. The fragments that result from gravitational instability may be the size of planetesimals or even exoplanets. The issue then is not that one cannot form structures, but rather that the gravitational instability paradigm lacks predictive power. Again, the devil is in the details. A successful theory of gravitational instability should start from the initial properties of the protoplanetary disk and the conditions imposed upon it by the star—the strength of irradiation, the metallicity of the natal gas (the abundance of elements that are heavier than hydrogen and helium), the mass of the disk—and predict the number of exoplanets that ensue, including their masses and interior structures. In other words, theorists need to build a population synthesis framework for gravitational instability. A theory with such completeness currently eludes us.

The true answer may lie in between the two paradigms. Giant structures may form in the disk, which then collect dust grains within them to form larger particles. An intriguing possibility is the existence of vortices, essentially giant cyclones or hurricanes forming out of the gas in the disk. Vortices have the ability to trap particles within them, much like dust devils on Earth—an old concept with its roots spanning back to the German philosopher Immanuel Kant. An attractive feature of this idea is that vortices would arise naturally from the turbulent gas if it behaves like a two-dimensional fluid. A parcel of fluid “lives” in a two-dimensional world if it is sufficiently buoyant in the third dimension—as it is displaced from its plane of existence, it returns to its original position quickly. The gas swirling around a protoplanetary disk may be regarded as a fluid; the disk also has a finite thickness. Dust tends to collect mostly at the midplane of the disk. It turns out that the midplanes of protoplanetary disks behave like three-dimensional fluids, whereas locations farther away from the midplane, where the solid material needed to grow structure is found in less abundance, behave like two-dimensional fluids. A successful theory of planet formation involving vortices has to identify a mechanism for producing them, predict their lifetimes and elucidate the means by which they will be destroyed.

Perhaps an easier way to provide constraints on hypotheses of planet formation is simply to stare at the planets themselves. Gas giants appear to be more common around stars with higher metallicities, consistent with the notion that one needs more solid material to construct larger cores and trigger runaway accretion of the natal gas. No trend in stellar metallicity is found for the occurrence of rocky exoplanets. When they are found, they tend to be social creatures, located in systems with other rocky brethren. These exoplanetary systems also tend to be “flat,” just like our Solar System—the orbits of the rocky exoplanets lie roughly within the same plane. We now know that “hot Jupiters”—gas giants found implausibly close to their host stars, such that their temperatures are a few thousand degrees—are oddballs (comprising less than one percent of the entire exoplanet population) and loners (without nearby exoplanets as companions), despite being the most common type of exoplanets initially found due to their brightness and large sizes. Furthermore, hot Jupiters are often found in orbital planes that are misaligned with the spin axes of their host stars—in stark contrast to the systems hosting multiple, rocky exoplanets—perhaps providing a clue that they were delivered to their present locations via some kind of scattering mechanism.

Taking a Look

Some of the Kepler telescope discoveries present invaluable puzzles and challenges to our current ideas of planet formation. The Kepler-11 system plays host to six exoplanets with radii ranging from twice to five times that of Earth. Three of these exoplanets have densities less than that of water. All six appear to lie roughly in the same orbital plane. The Kepler-16 system consists of a pair of stars orbited by a Saturnlike exoplanet, a harsh environment for any exoplanet to survive in because of the enhanced gravitational tugs of the stars. A diminutive red dwarf sits at the center of the Kepler-32 system, yet it is orbited by five exoplanets within a distance a third the size of Mercury’s orbit. Perhaps the most puzzling case study comes from the Kepler-36 system. Two planets are found at roughly the same distance from the star: one with a density less than that of water, whereas the other is as dense as iron. Theorists are just coming to grips with these discoveries. The venerable theory of migration—the notion that exoplanets and their progenitors drift through the gaseous disk during assembly—is coming under scrutiny. It may turn out that migration, although an attractive idea for constructing our Solar System, is not really needed to form exoplanetary systems populated by close-in super Earths—Earthlike exoplanets somewhat larger than our Earth, which seem to be an omnipresent breed. Our Solar System appears not to be the dominant outcome of planet formation and it may be exerting a provincial influence on our theoretical ideas. In seeking to map out the universe, we find ourselves to be the exception rather than the norm.

An intriguing idea, suggested during a recent conference on Kepler exoplanets by Renu Malhotra of the University of Arizona, is to search for the transits of planetesimals around the corpses of stars known as white dwarfs. During a transit, a body passes in front of its host star, causing a dip in electromagnetic emissions from the star. By coincidence, the relative size of a planetesimal orbiting a white dwarf is equivalent to that of an Earth orbiting a Sunlike star. Because the Kepler Space Telescope is detecting Earthlike exoplanets around Sunlike stars, the reasoning is that it will be able to do the same for planetesimals transiting white dwarfs. If this idea meets with success, it will be the first time information on planetesimals outside of the Solar System will be obtained. Another fascinating idea concerns the hunt for moons around exoplanets—“exomoons.” The idea is that these exomoons are formed during the final stages of assembly, during a phase of planet formation known as “clean-up,” and may provide some clues on the properties of planetesimals.

If nothing else, one upshot from the numerous recent results is that planet formation is hardly a straightforward process, perhaps going some distance to explaining why nature forms planets and exoplanets more easily than theorists are capable of doing. But ultimately, we still seek a theory of planet formation because we wish to determine how common exoplanets, and life, are in the universe. The Kepler Space Telescope is showing us that about one in 10 stars may have an exoplanet that resembles Earth. For the aficionados, this frequency factor of 0.1 is termed “eta Earth”; it is one of the several factors in Drake’s equation, which seeks to quantify how common exoplanets are around stars, how many of these exoplanets are capable of harboring life, and how many of them actually do host life. From extrapolating the Kepler results, Earthlike exoplanets likely number in the billions for our galaxy alone; unless life is an exceedingly rare event, it must exist elsewhere in the universe. We may never answer all of these questions, but understanding planet formation is a step in the right direction.

Acknowledgment

The author acknowledges financial and logistical support from the University of Bern, the University of Z¨urich and the Swiss-based MERAC Foundation. He is grateful to Eric Agol, Dan Fabrycky and Jack Lissauer for enlightening conversations during the Kepler multi-planet conference, held at the Aspen Center for Physics in February 2013, Scott Tremaine and Lucio Mayer for constructive comments on an earlier version of the article, and George Lake for encouragement.

References

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Reviews of Astronomy and Astrophysics, 48, 47
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T., 2010, “Images of a fourth planet orbiting HR 8799”,Nature, 468, 1080
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Rossby vortices in protoplanetary disks”, Astronomy and Astrophysics,
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Be Beautiful: Great Equations of Modern Science, edited by Graham
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arXiv

[1304.6104] Why Does Nature Form Exoplanets Easily?

[1304.6104] Why Does Nature Form Exoplanets Easily?:

Kevin Heng received his M.S. and Ph.D. in astrophysics from the Joint Institute for Laboratory Astrophysics (JILA) and the University of Colorado at Boulder. He joined the Institute
for Advanced Study in Princeton from 2007 to 2010, first as a Member and later as the Frank & Peggy Taplin Member. From 2010 to 2012 he was a Zwicky Prize Fellow at ETH Z¨urich
(the Swiss Federal Institute of Technology). In 2013, he joined the Center for Space and Habitability (CSH) at the University of Bern, Switzerland, as a tenure-track assistant professor,
where he leads the Exoplanets and Exoclimes Group. He has worked on, and maintains, a broad range of interests in astrophysics: shocks, extrasolar asteroid belts, planet formation,
fluid dynamics, brown dwarfs and exoplanets. He coordinatesthe Exoclimes Simulation Platform (ESP), an open-source set of theoretical tools designed for studying the basic physics and
chemistry of exoplanetary atmospheres and climates (www.exoclime.org). He is involved in the CHEOPS (Characterizing Exoplanet Satellite) space telescope, a mission approved by the
European Space Agency (ESA) and led by Switzerland. He spends a fair amount of time humbly learning the lessons gleaned from studying the Earth and Solar System planets, as related
to him by atmospheric, climate and planetary scientists. He received a Sigma Xi Grant-in-Aid of Research in 2006.

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Willkommen! 

Willkommen! :

 "“You can know the name of a bird in all the languages of the world, but when you are finished, you will know absolutely nothing whatsoever about the bird.  So let us look at the bird and see what it is doing --- that is what counts.  I learned very early the difference between knowing the name of something and knowing something.”"

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CfA Press Room

CfA Press Room:

 "Cambridge, MA - Newborn stars are difficult to photograph. They tend to hide in the nebulous stellar nurseries where they formed, enshrouded by thick layers of dust. Now, Smithsonian astronomer T.K. Sridharan (Harvard-Smithsonian Center for Astrophysics) and his colleagues have photographed a pair of stellar twins in infrared light, which penetrates the dust. And these babies are whoppers, weighing several times the mass of the Sun."

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Spain: Higgs, Englert, Cern win Prince of Asturias award - Spain - ANSAMed.it

Spain: Higgs, Englert, Cern win Prince of Asturias award - Spain - ANSAMed.it:

"The jury, which gathered in Oviedo the capital of the principality in northern Spain, is understood to have recognised the ''pioneering works'' of the two scientists and the late Belgian physicist Robert Brout who established the theoretical basis for the existence of the Higgs boson."

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Spain: Higgs, Englert, Cern win Prince of Asturias award - Spain - ANSAMed.it

Spain: Higgs, Englert, Cern win Prince of Asturias award - Spain - ANSAMed.it:

"(ANSAmed) - MADRID, MAY 29 - British theoretical physicist Peter Higgs and his Belgian counterpart Francois Englert who identified the existence of a new subatomic particle known as the Higgs bosun were today awarded the 2013 Prince of Asturias award for scientific research."

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Herbig–Haro object - Wikipedia, the free encyclopedia

Herbig–Haro object - Wikipedia, the free encyclopedia:

 "Herbig–Haro objects (HH) are small patches of nebulosity associated with newly born stars, and are formed when narrow jets of gas ejected by young stars collide with clouds of gas and dust nearby at speeds of several hundred kilometres per second. Herbig–Haro objects are ubiquitous in star-forming regions, and several are often seen around a single star, aligned with its rotational axis."

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How to Get a Job - NYTimes.com

How to Get a Job - NYTimes.com:

Underneath the huge drop in demand that drove unemployment up to 9 percent during the recession, there’s been an important shift in the education-to-work model in America. Anyone who’s been looking for a job knows what I mean. It is best summed up by the mantra from the Harvard education expert Tony Wagner that the world doesn’t care anymore what you know; all it cares “is what you can do with what you know.” And since jobs are evolving so quickly, with so many new tools, a bachelor’s degree is no longer considered an adequate proxy by employers for your ability to do a particular job — and, therefore, be hired. So, more employers are designing their own tests to measure applicants’ skills. And they increasingly don’t care how those skills were acquired: home schooling, an online university, a massive open online course, or Yale. They just want to know one thing: Can you add value?

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Star formation - Wikipedia, the free encyclopedia

Star formation - Wikipedia, the free encyclopedia:

"Star formation is the process by which dense regions within molecular clouds in interstellar space, commonly referred to as "stellar nurseries", collapse into spheres of plasma to form stars. As a branch of astronomy, star formation includes the study of the interstellar medium and giant molecular clouds (GMC) as precursors to the star formation process, and the study of young stellar objects and planet formation as its immediate products. Star formation theory, as well as accounting for the formation of a single star, must also account for the statistics of binary stars and the initial mass function."

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[1305.6310] On the simultaneous evolution of massive protostars and their host cores

[1305.6310] On the simultaneous evolution of massive protostars and their host cores:

Studies of the evolution of massive protostars and the evolution of their host molecular cloud cores are commonly treated as separate problems. However, interdependencies between the two can be significant. Here, we study the simultaneous evolution of massive protostars and their host molecular cores using a multi-dimensional radiation hydrodynamics code that incorporates the effects of the thermal pressure and radiative acceleration feedback of the centrally forming protostar. The evolution of the massive protostar is computed simultaneously using the stellar evolution code STELLAR, modified to include the effects of variable accretion. The interdependencies are studied in three different collapse scenarios. For comparison, stellar evolutionary tracks at constant accretion rates and the evolution of the host cores using pre-computed stellar evolutionary tracks are computed. The resulting interdependencies of the protostellar evolution and the evolution of the environment are extremely diverse and depend on the order of events, in particular the time of circumstellar accretion disk formation with respect to the onset of the bloating phase of the star. Feedback mechanisms affect the instantaneous accretion rate and the protostar's radius, temperature and luminosity on timescales equal or smaller than 5 kyr, corresponding to the accretion timescale and Kelvin-Helmholtz contraction timescale, respectively. Nevertheless, it is possible to approximate the overall protostellar evolution in many cases by pre-computed stellar evolutionary tracks assuming appropriate constant average accretion rates.

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Rolf Kuiper: 3D Simulation

Tuesday, May 28, 2013

Syllabus Summer 2013



Syllabus
Webpage:http://relevantscience.blogspot.com/

MasteringAstronomy:

http://masteringastronomy.com/

Course ID:

CANTORALSUMMER2013


From June 10, to August 2, 2013


Midterm: 07/01/2013
Final: 07/31/2013


These exams are similar to weekly quizzes.
Term Paper Deadline: 07/31/2013


Rubric:



Class participation        20%
Term Paper & Quizzes 20%
Midterm                          20%
Final                                20%
Homework                      20%


Topic for Term Paper




Apart from  five pages for this report, I expect to see a write-up from each class, i.e., I want to see your class notes.


Course Topics:


1. The scale of the universe
2. The night sky and stellar observations
3. Cycles of the moon and sun
4. Archeoastronomy
5. Origins of modern astronomy; including the Copernican Revolution, Brahe, Kepler, Newton, and Einstein
6. Tools of astronomy; including light, radiation, and telescopes (ground, and space based)
7. Stellar evolution; including nebulae, and HR diagrams
8. Life and death of stars; including processes, and types, such as main sequence, variable stars, supernovae, white dwarfs, neutron stars, and black holes
9. Galaxies; including Hubble classification, AGN, and quasars
10. The solar system; its origin, inner planets, outer planets, asteroids, comets, KBOs
11. Cosmology; including Big Bang, Hubble equation, and current theories
12. Life in the universe


Calendar:
Chapter Date
1,2,3 6/12
4,5 6/19
6,7 6/26
8,9 7/3
10,11 7/10
12,13 7/17
14,15 7/24
16,17,18 7/31



Grading Criteria:


Final grade: Exams 40% ( 2 x 20% each), Homework assignments 20%, In-class work 20%, Term paper and quizzes 20%.


A: (90%) Outstanding performance in of the subject. Achievement of superior quality.
B: (80-89%) Consistent performance beyond the usual requirement of the course. Achievement of high quality.
C: (70-79%) Performance of a satisfactory nature; 'average' grade.
D: (60-69%) Minimally acceptable performance.
F: (≤60%) Achievement  at a level insufficient to demonstrate understanding of the basic elements of the course.
I: Incompletes will be granted only to students in good standing under extreme circumstances.
W: Instructor will only withdraw a student from this class due to disruptive conduct.


Cases of plagiarism will be given a score of 0, with possible referral to the Student Conduct Board.


Expectations:
Conduct yourself in all manners as an adult in a formal education environment; including assuming responsibility for your choices and actions (i.e., see make-up policy), adhering to proper classroom etiquette, and conforming to academic policies and deadlines. Disruptive behavior will not be tolerated.


You are prepared for each class discussion, including pre-class reading from the text. Students must obtain changes that are announced in class; it is your responsibility to seek for this new information.


Ask questions, even the 'dumb' ones!


Complete the assigned reading before class (remember 3 hours / credit per week!)


You should consult me promptly if you are struggling or consistently receive failing grades in the class.


Make Up Policy:


Make-up homework and exams will be granted only if you contact me BEFORE the   due date, and may only be for valid reasons such as emergencies or severe illness and if you can provide written verification. The validity of these reasons is at the discretion of the instructor. The following are NOT valid reasons for a make-up exam: vacations, oversleeping, forgetting, car troubles (mechanical or logistical). Missing exams or assignments can seriously affect affect your grade. If you are granted a make-up exam, your grade may be reduced.


Term Paper and Homework:


As I told you during the first lecture, I want a write-up of what you understood in the lecture. I prefer you post it online, I recommend the Google service I am using right now. It is called Blogger, register in http://www.blogger.com . Each write-up should have an introduction, development, and conclusion. If you do not do it electronically, I am expecting a paper copy in class when we meet.


The sum total of your notes will be in a term paper. Whichever way you do it, I do not want copy and paste. If I find out, that your term paper was ripped off from a classmate, or other sources, I will subtract points appropriately.


You will write a mandatory five-page term paper on the book "The Universe Within", by Neil Shubin, due on the date noted on the class schedule. It is strongly recommended that you begin the paper early! A brief introductory abstract should summarize the contents to follow and the main focus of the paper is on the science content. More details will be provided in class.


Class Schedule and Attendance:


Be sure to do the textbook readings before the corresponding lecture so that you can ask any questions during the lecture. You are given 1 week to complete assignments, after the due date, you will lose points at 10% per day. Remember, in-class assignments cannot be made up and only ONE late assignment will be accepted for the entire course.


Attendance/Classroom Policy:


A passing grade is not possible without regular attendance and participation. Successful completion of in-class assignments is vital to your grade. Note that in-class assignments CANNOT BE MADE UP. At least one-half of all homework assignments must be completed or you may fail. In the event that your final grade is borderline, regular excellent class participation may make a difference. Students whose conduct disrupts the class will be asked to leave; repeated offenses will result in withdrawal from the class.


Course Objectives:


Upon successful completion of this course the student will be able to:


1. Apply scientific and mathematical reasoning to interpret observed phenomena.
2. Demonstrate a familiarity with the basic vocabulary and concepts in modern astronomy.
3. Describe the fundamental ideas of archeoastronomy.
4. Describe the motions of celestial bodies (moon, planets, stars) in the night sky.
5. Describe the electromagnetic spectrum, and its importance and use in astronomy.
6. Demonstrate an understanding of fundamental concepts used in modern astronomy including gravity, ground-and-space - based telescopes, and spectroscopy.
7. Describe the birth and structure of the solar system, including the Sun, the Terrestrial, and Jovian planets, the Asteroid and Kuiper Belts, and the Oort Cloud.
8. Describe the properties of and the birth, evolution, and death of stars, including types and processes.
9. Describe the properties and types of galaxies including dark matter.
10. Describe the current thoughts on dark energy, cosmology and extraterrestrial life.




Monday, May 27, 2013

Did the ancient egyptians record the period of the eclipsing binary Algol - the Raging one?

"Normalization allowed us to imitate the pattern of lucky and unlucky days, although we did not know the rules that were used to choose them. It gave us the Q⋆estimates and eliminated some of the unreal periods. The best idea of all was to test what happens after removing . This resulted in the 2.d850 period being the only significant real period and its significance increased. CC does not give explicit clues as to why AES assigned the prognoses with such regularity, but the  period differs by  from the current orbital period   of Algol. If this is indeed the reason for finding this periodicity in CC, then  should have increased about  since 1224 B.C."

arXiv

Sunday, May 26, 2013

Astronomers discovered ancient Egyptian observations of a variable star

Astronomers discovered ancient Egyptian observations of a variable star:

"The study of the “Demon star”, Algol, made by a research group of the University of Helsinki, Finland, has received both scientific and public attention. The period of the brightness variation of this eclipsing binary star has been connected to good prognoses three millennia ago. This result has raised a lot of discussion and the news has spread widely in the Internet."

'via Blog this'

Saturday, May 25, 2013

The Ascent of Man: why our early ancestors took to two feet - News and events, The University of York

The Ascent of Man: why our early ancestors took to two feet - News and events, The University of York:

 "A new study by archaeologists at the University of York challenges evolutionary theories behind the development of our earliest ancestors from tree dwelling quadrupeds to upright bipeds capable of walking and scrambling."

'via Blog this'

Up, Up and Away - NYTimes.com

Up, Up and Away - NYTimes.com:

"THE values of gold and silver have dropped like a stone in international trading markets. Coffee futures are hovering near a three-year low. But the price of one commodity has been rising as if it were lighter than air — and in this case, well, it is."

'via Blog this'

[1305.5482] Particle Physics in The United States, A Personal View

[1305.5482] Particle Physics in The United States, A Personal View:

 "I present my views on the future of America's program in particle physics. I discuss a variety of experimental initiatives that do have the potential to make transformative impacts on our discipline and should be included in our program, as well as others that do not and should not."

'via Blog this'

Friday, May 24, 2013

Giant band of galactic gas likely has dual origin : Nature News & Comment

Giant band of galactic gas likely has dual origin : Nature News & Comment:

 "Two satellites of the Milky Way contributed to the Magellanic Stream."

'via Blog this'

Rare View of Ancient Galaxy Crash Revealed: Scientific American

Rare View of Ancient Galaxy Crash Revealed: Scientific American:

 "Astronomers caught a glimpse of two star-forming galaxies as they collided 11 billion light-years away. The smashup could eventually produce one giant elliptical galaxy, researchers say"

'via Blog this'

Submerged structure stumps Israeli archaeologists

Submerged structure stumps Israeli archaeologists:

"TIBERIAS, Israel (AP) — The massive circular structure appears to be an archaeologists dream: a recently discovered antiquity that could reveal secrets of ancient life in the Middle East and is just waiting to be excavated."

'via Blog this'

A Fantastic Map of 500 Years of Meteorites Hitting Earth - John Metcalfe - The Atlantic Cities

A Fantastic Map of 500 Years of Meteorites Hitting Earth - John Metcalfe - The Atlantic Cities:

""I spent about 30 hours on the map," Pearce says. "It took me a surprisingly long time before I learned that 'metor' was not the correct spelling; I think there are still some typos in my code.""

'via Blog this'

The First Galaxies in the Universe (Princeton Series in Astrophysics): Abraham Loeb, Steven R. Furlanetto: 9780691144924: Amazon.com: Books

The First Galaxies in the Universe (Princeton Series in Astrophysics): Abraham Loeb, Steven R. Furlanetto: 9780691144924: Amazon.com: Books:


This book provides a comprehensive, self-contained introduction to one of the most exciting frontiers in astrophysics today: the quest to understand how the oldest and most distant galaxies in our universe first formed. Until now, most research on this question has been theoretical, but the next few years will bring about a new generation of large telescopes that promise to supply a flood of data about the infant universe during its first billion years after the big bang. This book bridges the gap between theory and observation. It is an invaluable reference for students and researchers on early galaxies.
The First Galaxies in the Universe starts from basic physical principles before moving on to more advanced material. Topics include the gravitational growth of structure, the intergalactic medium, the formation and evolution of the first stars and black holes, feedback and galaxy evolution, reionization, 21-cm cosmology, and more.
  • Provides a comprehensive introduction to this exciting frontier in astrophysics
  • Begins from first principles
  • Covers advanced topics such as the first stars and 21-cm cosmology
  • Prepares students for research using the next generation of large telescopes
  • Discusses many open questions to be explored in the coming decade



'via Blog this'

Avi Loeb: On the Importance of Conceptual Thinking Outside the Simulation Box


arXiv:1305.5495v1 [physics.hist-ph] 23 May 2013

Abraham Loeb
Institute for Theory & Computation
Harvard University
60 Garden St., Cambridge, MA 02138

ABSTRACT

Any ambitious construction project requires architects for its design and engineers who apply the design to the real world. As scientific research shifts towards large groups which focus on the engineering aspects of linking data to existing models, architectural skills are becoming rare among young theorists. Senior researchers should mentor qualified students and postdocs to think creatively about the big picture without unwarranted loyalty to ancient blueprints from past generations of architects.

“If you always do what you always did, you will always get what you always got.”
Albert Einstein

Too few theoretical astrophysicists are engaged in tasks that go beyond the refinement of details in a commonly accepted paradigm. It is far more straightforward today to work on these details than to review whether the paradigm itself is valid. While there is much work to be done in the analysis and interpretation of experimental data, the unfortunate by-product of the current state of affairs is that popular, mainstream paradigms within which data is interpreted are rarely challenged. Most cosmologists, for example, lay one brick of phenomenology at a time in support of the standard (inflation+Λ+Cold-Dark-Matter) cosmological model, resembling engineers that follow the blueprint of a global construction project, without pausing to question whether the architecture of the project makes sense when discrepancies between expectations and data are revealed.

The problem with researchers focusing on the engineering aspects of a prevailing paradigm rather than on questioning its foundation is that their efforts to advance scientific knowledge are restricted to a conservative framework. For example, cosmological data is often analyzed in the conservative mindset of a community-wide effort to reduce the error budget on measurements of the standard cosmological parameters. The cosmology community has become so conservative that when a discrepancy was identified recently between different methods for deriving Ωm and σ8 (using microwave background anisotropies sourced at redshift z ∼  and cluster abundance measurements at ) in the latest data from the Planck satellite, the mundane possibility of assigning a mass of 0.2eV to neutrinos is being debated as a wild deviation from the mainstream comfort zone. Deviations of this magnitude were trivial for previous generations of cosmologists who were debating the underlying physical principles that control the Universe while entertaining dramatic excursions from conservative guidelines.

Conservatism is possible today because we now have a standard cosmological model, which was not in place several decades ago. It is nevertheless disappointing to see conformism among young cosmologists who were born into the standard paradigm and are supposed to be least biased by prejudice. The experience resembles seeing the children of hippies from the 1960s transform surprisingly quickly into establishment executives. This phenomenon has its obvious reasons. The unfortunate reality of young astrophysicists having to spend their most productive years in lengthy postdoctoral positions without job security promotes conformism, as postdocs aim to improve their chance of getting a faculty job by supporting the prevailing paradigm of senior colleagues who serve on selection committees. Ironically, one might argue that an opposite strategy of choosing innovative projects should improve the job prospects of a candidate, since it would separate that candidate from the competing crowd of indistinguishable applicants that selection committees are struggling through.

The orthodoxy exhibited by young cosmologists today raises eyebrows among some of the innovative “architects” who participated in the design of the standard model of cosmology. Too soon after the enigmatic ingredients of the standard cosmology were confirmed observationally, they acquired the undeserving status of an absolute truth in the eyes of beginning cosmologists.

One would have naively expected scientific activity to be open minded to critical questioning of its architectural design, but the reality is that conservatism prevails within the modern academic setting. Orthodoxy with respect to mainstream scientific dogmas does not lead to extreme atrocities such as burning at the stake for heresy but it propagates other collective punishments, such as an unfair presentation of an innovative idea at conferences, bullying, and drying up of resources for innovative thinkers.

The problem is exacerbated by the existence of large groups with a rigid, prescribed agenda and a limited space for innovation when unexpected results emerge. In large groups, such as the Planck or SDSS-III collaborations, young cosmologists often decide not to challenge the established paradigm because other group members, and particularly senior scientists who are considered experts on the issue, accept this paradigm. If hundreds of names appear on the author list of a paper, the vast majority of them have limited space for maneuvers – like a dense swarm of fish in a small aquarium. The fact that letters of recommendation are written by few group leaders adds pressure to conform to mainstream ideas. True, some scientific goals require a large investment of funds and research time, but under these circumstances efforts should be doubled to maintain innovative challenges to mainstream thinking. It is imperative that individual scientists feel comfortable expressing critical views in order for the truth to ultimately prevail.

And there is no better framework for critically challenging a prevailing dogma than at the architectural “blueprint” level. Sometimes, a crack opens in a very particular corner of a dogma due to a localized discrepancy with data. But conceptual anomalies are much more powerful since they apply to a wide range of phenomena and are not restricted to a corner of parameter space. Albert Einstein’s thought experiments are celebrated stepping stones that identified earlier conceptual anomalies and paved the path to the theories of Special and General Relativity in place of the fixed spacetime blueprint of Isaac Newton. And before Galileo Galilei came up with his conceptual breakthrough, it was standard to assume that heavy objects fall faster than light objects under the influence of gravity.

Conceptual work is often undervalued in the minds of those who work on the details. A common misconception is that the truth will inevitably be revealed by working out the details. But this misses the biggest blunder in the history of science: that the accumulation of details could be accommodated within any prevailing paradigm by tweaking and complicating the paradigm. A classic example is Ptolemaic cosmology, a theory of epicycles for the motion of the Sun and planets around the Earth that survived empirical scrutiny for longer than it deserved. A modern analog is the conviction shared by mainstream cosmologists that the matter density in the Universe equals the critical value, Ωm = 1. This notion dominated in the 1980s and the early 1990s for nearly two decades after inflation was proposed, a period during which discrepancies between data and expectations were assigned to an unknown “bias parameter” of galaxies even when data on the mass to light ratio on large spatial scales indicated clearly that Ωm ∼ 0.3 as we now know to be the case. Today, when discrepancies between the observed distribution of dark matter inside galaxies and theoretical expectations for cold dark matter halos are revealed, these discrepancies are commonly brushed aside as being due to “uncertain baryonic physics” even in dwarf galaxies where the baryons make a negligible contribution to the overall mass budget. Similarly, when a hemispherical asymmetry in the power spectrum of temperature fluctuations of the cosmic microwave background was reported a decade ago, it was quickly dismissed by mainstream cosmologists; this anomaly is now confirmed by the latest data from the Planck satellite but still viewed as an unlikely (< 1% probability) realization of the sky in the standard, statistically-isotropic cosmology. Given that progress in physics was historically often motivated by experimental data, it is surprising to see that a speculative concept with no empirical basis, such as the “multiverse”, gains traction among some mainstream cosmologists, whereas a data-driven hypothesis, such as dark matter with strong self-interaction (to remedy galactic scale discrepancies of collisionless dark matter), is much less popular.

The most efficient way to simplify the interpretation of data is to work at the meta-level of architecture, similarly to the helio-centric interpretation developed by Copernicus in the days when the Ptolemaic theory ruled. An engineering project which aims to study the strength of rods and bricks might never lead to a particularly elegant blueprint for the building in which these ingredients are finally embedded. In the scientific quest for the truth, we also need architects (theory makers), not just engineers (theory implementers/testers).
Some argue that architects were only needed in the early days of a field like cosmology when the fundamental building blocks of the standard model, e.g., the inflaton, dark matter and dark energy, were being discovered. As fields mature to a state where quantitative predictions can be refined by detailed numerical simulations, the architectural skills are no longer required for selecting a winning world model based on comparison to precise data. Ironically, the example of cosmology demonstrates just the opposite. On the one hand, we measured various constituents of our Universe to two significant digits and simulated them with accurate numerical codes. But at the same time, we do not have a fundamental understanding of the nature of the dark matter or dark energy nor of the inflaton. In searching for this missing knowledge, we need architects who could suggest to us what these constituents might be in light of existing data and which observational clues should be searched for. Without such clues, we will never be sure that inflation really took place or that dark matter and dark energy are real and not ghosts of our imagination due to a modified form of gravity.

It is true that numerical codes allow us to better quantify the consequences of a prevailing paradigm, but systematic offsets between these results and observational data cannot be cured by improving the numerical precision of these codes. The solutions can only be found outside the simulation box through conceptual thinking. For example, observations of X-ray clusters are currently being calibrated at the percent level using hydrodynamic simulations as a precise tool for inferring cosmological parameters. However, important physical effects that may influence the temperature and density distribution of the hot intracluster gas, such as heat conduction, thermal evaporation, and electron-ion temperature equilibration, are left out of these simulations despite the fact that the Coulomb mean-free-path of protons in the outskirts of clusters is comparable to the cluster radius.

Conceptual thinkers are becoming an extinct species in the landscape of present-day astrophysics. I find this trend worrisome for the health of our scientific endeavor. In my view, it is our duty to encourage young researchers to think critically about prevailing paradigms and to come up with simplifying conceptual remedies that take us away from our psychological comfort zone but closer to the truth.

I thank Richard Ellis, Ido Liviatan, Robb Scholten and Josh Winn for helpful comments on the manuscript.

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