Moon Rising in New Zealand

Hello dear readers,
I am back - sort of.  I wanted to share this video of the full moon rising in New Zealand.  Read the info below the video.
http://vimeo.com/58385453

Palomar, and Some Final Thoughts

Hello all,
this is my final post (at least for now).  This will mainly be a reflection on the last quarter.  I'd like to start with our trip to the Palomar Observatory.  I have to say it's pretty impressive.  I wanted to be a bit more informative, but our tour guide gave A LOT of detailed information and I don't remember most of it.  I thought there would be more about actual astronomy.  Had I known there was going to be so much about behind-the-scenes detail, I would have brought a pen to take notes, so, sorry about that.  Some of it was interesting, like the making of the mirror and how it is cleaned.  Who knew smoothing and cleaning glass could be so difficult?  Check out the blog from one of my classmates: The Everlasting Symphony  He found a video of the process.  Some of the information is available on the observatory website.  The pictures don't do it justice, however.  The telescope is huge.  The best part of the tour was seeing inside the observing room.  It's too bad we couldn't be there while someone was observing something.  I am left with the hope that one day I will learn enough to be an astronomer (although after this class, I realize that is quite a lot) and maybe I can observe at Palomar, or someplace like it.
     I have always loved astronomy but now I am even more excited about it.  As the quarter progressed, I realized that I was spending more and more time on astronomy and soon I did not want to do anything else.  I have learned a lot in this class, but there is also a lot that I wish I had more time to understand better.  I realize now that astronomers are even more amazing than I previously thought.  So, I sadly say good-bye to the PHYS 111 class, but I may still add to my blog in the future if I have time.   I had some topics in the works that I never had time to post.  In the meantime, I leave you with this interesting website I found while at the Palomar website looking for information:  http://www.black-holes.org/.  Just hover the cursor over the circles then click on the topic of interest. 

Reversal of Earth's Magnetic Field

     Since the topic came up in class, I thought a post on the Earth's magnetic field would be appropriate.  As discussed in class, the magnetic poles have reversed in the past.  This happens on average every 200,000 to 300,000 years, although the last reversal was about 800,000 years ago and in geologic history there have been periods up to millions of years with no reversal.  These reversals do not happen instantaneously; the magnetic field lines become entangled and the poles wander.  Scroll down for a link to a computer simulation of this.  During this process, the field weakens temporarily (don't worry, this is not a problem) before the reversal happens.  It is unknown how long this reversal takes; all of the sources I have read so far estimate hundreds to tens of thousands of years.
      It is also unknown why the magnetic field reverses itself and why it happens so irregularly.  The reversals can be seen in the rock record, but there is no evidence to suggest why this happens.  In the computer model, the data was input into a supercomputer, and left to run, the computer model showed periodic reversals, which was an unexpected result.  See http://www.psc.edu/science/glatzmaier.html for more info and the computer simulation at the bottom of the page.  While the magnetic field does weaken during the transition, it does not completely disappear, and according to the USGS (see link in the references), it is not sufficient to cause mass extinctions.  If you are interested in a brief introduction about paleomagnetism and what the geologic record can tell us, read the next section. 

A Little Background and Interesting Facts

     In between the reversals, the magnetic poles are not completely stable; they wander, sometimes more than others.  A lava flow in Oregan indicates that for a brief period, magnetic north moved by about 6 degrees per day.  See http://www.psc.edu/science/glatzmaier.html for details.  Even now, the magnetic declination is changing slightly (declination is the difference between magnetic north and true north). 
     We know when the magnetic reversals happen by looking at the geologic record, lava flows for example.  Minerals in the lava that have magnetic properties align themselves with the magnetic field.  As the lava solidifies, the minerals crystalize with this orientation, creating a record of the magnetic field polarity.  Another, and very important, example of this record is the magnetic striping on the ocean floor.  At mid-ocean ridges, where the seafloor is spreading, magma rises to the surface, flows out symmetrically from the ridge and cools, with the crystals aligning themselves to the magnetic field.  This causes alternating stripes on the seafloor of normal and reverse polarity.  See the papers by Vine and Matthews (1963) and Vine and Wilson (1965) for detail.  This is the original research on magnetic striping and is heavily cited even in modern research.


References:

Information including computer simulation of magnetic reversal (can be played using windows media player)
 http://www.psc.edu/science/glatzmaier.html

This is an excellent, non-technical site with the same computer model, but the animation requires quicktime
http://www.pbs.org/wgbh/nova/earth/when-our-magnetic-field-flips.html

USGS sites
About magnetic reversals and mass extinctions
http://www.usgs.gov/faq/index.php?sid=54684&lang=en&action=artikel&cat=11&id=484&artlang=en

For everything related to the magnetic field
http://www.usgs.gov/science/science.php?term=677


Technical

Vine, F. J., Matthews, D.H.., 1963, Magnetic anomalies over ocean ridges, Nature, no 4897, p. 947-949

Vine, F. J., Wilson, J. T., 1965, Magnetic Anomalies Over A Young Oceanic Ridge Off Vancouver Island: Science, Vol. 150, p. 485-489

This is hilarious!

If you know the song, "Bohemian Rhapsody," performed by Queen and used in the movie, "Wayne's World" then check out this parody called "Calculus Rhapsody."  BTW, this is related to astronomy since astronomy uses physics and physics requires calculus, right? ;)

http://www.youtube.com/watch?v=uqwC41RDPyg

General Relativity Taught by Leonard Susskind

Hello everyone - I wanted to share a helpful video for anyone who is interested in general relativity.  If you didn't already know about this, Leonard Susskind teaches a course on general relativity at Stanford, and the entire course is available for free on youtube.  I have only had time to watch the first lecture (it is 2 hours) but so far I think he does a very good job.  I especially like his explanation of covariant and contravariant vectors and tensors at the end.  I have had one course in tensor calculus already, and I still mix up contravariant with covariant.  If you're not there yet, then this is a good preview.  I wish I knew about this video before taking that class.  I will definitely finish watching the rest before I get into a class on GR.

Note: this is the link to the first lecture - from there you can get to the rest by clicking on the related videos.
http://www.youtube.com/watch?v=JRZgW1YjCKk

A Precessing Pulsar!

The Vela pulsar is a well-known gamma ray pulsar and is one of the brightest gamma ray sources.  Data from the Chandra X-ray Observatory shows evidence of precession.  It is the first neutron star observed to precess.  The Fermi Large Area Telescope (LAT), which is in a 95-day orbit around Earth and scans the entire sky every three hours looking for gamma ray sources, observed and tracked Vela's position for 51 months and the images were used to make a movie showing Vela's position with time, which can be seen here: http://www.nasa.gov/mission_pages/GLAST/news/spirograph.html

The cause for precession is still unknown, but the Chandra scientists have two theories:

1. It has been distorted, possibly by its fast rotation and interaction of its crust with the superfluid core, and is no longer a perfect sphere.  Because of its density, even small distortions have a large effect.

2. The strong magnetic field is influencing the shape of the jet.  According to the Chandra team, "if the jet develops a small bend caused, by precession, the magnetic field's lines on the inside of the bend will become more closely spaced.  This pushes particles toward the outside of the bend, increasing the effect."

Some quick facts:
Vela is 12 miles in diameter.
It makes a complete rotation in 89 milliseconds.
The precession period is estimated at ~120 days.

References:

http://www.nasa.gov/mission_pages/GLAST/news/spirograph.html

From Chandra X-Ray Observatory http://www.chandra.si.edu/press/13_releases/press_010713.html

Hmm... Man-made Gravitational Waves?

Aside from the gravitational wave connection, this doesn't really have much to do with astronomy, but it is something interesting to think about.  While I was reading up on gravitational waves for my last post, I came across a paper published in the journal Systemics, Cybernetics and Informatics titled, "The Utilization of High Frequency Gravitational Waves for Global Communication."  According to this article, and references therein, high-frequency means anything greater than 100 kHz.  As the title says, the authors claim that it is possible to generate and detect high-frequency gravitational waves for communication.  If you read my previous post, then you know that gravitational waves that have any potential to be detected require massive compact objects, such as neutron star or black hole binaries orbiting each other, and even then they are weak and our most advanced interferometers have not yet detected them.  So how can it be possible for us humans to generate gravitational waves that we can detect?  Interestingly, the authors, Robert and Bonnie Baker, claim to demonstrate theoretically that high-frequency gravitational waves can be generated using superradiance, which uses micro electromechanical systems (MEMS) technology.  According to the authors, some detectors (receivers of the GWs) have already been built, but they do not yet have the required sensitivity.  The authors conclude that, "the utilization of modern MEMS technology and a doublehelix array of them would allow for the construction of a HFGW generator or transmitter involving superradiance that exhibits sufficient strength to transmit HFGW signals globally.  This is possible even though the conversion rate of EM power to GW power is exceedingly small and, like EM radiation, the GW signal power falls off as the inverse square of the distance."  I know nothing about this technology, and I did not understand a lot of the details, but they seem to have some compelling arguments.  However, I still find myself wondering if this is really possible.  Assuming that what the authors propose in theory can be built and works in reality, what about the cost?  Will this ever be practical?  Something to think about.

Source:

Baker, R., Baker, B., Systemics, Cybernetics and Informatics, Utilization of High Frequency Gravitational Waves for Global Communication, Cybernetics and Informatics, 2012 Vol. 10 - number 5

Gravitational Waves

     In a previous post I briefly mentioned the Laser Interferometer Gravitational-wave Observatory (LIGO) designed to detect gravitational waves (GWs).  I want to expand on that and give an update on the status of GW detectors, especially LISA, but I thought it best to first include a discussion of GWs.  There is a lot to say about this, and I'm trying to keep it as short as possible, so I appologize if I don't cover something thoroughly.  For this reason, I have added extra links to easy-to-read sources in the list of references.  So what are GWs and why do we care? 
     GWs are ripples in spacetime, much like ripples in water, that are caused by the acceleration of compact, massive objects and propagate at the speed of light.  They differ from the electromagnetic (EM) waves we currently use to observe the universe in that the EM waves propagate through space, but GWs are perturbations of spacetime itself (see this website: http://www.ligo.org/, which has a 7.5 minute video that shows very good computer simulations with a brief description of GWs as well as LIGO).  So, while EM waves experience attenuation due to scattering and absorption through matter, GWs travel through matter with little attenuation.  The problem is that they are very weak and so are difficult to detect.  They are predicted by Einstein's General Relativity, and in 1993 Hulse and Taylor found indirect evidence for GWs with a radio pulsar (they got the Nobel prize for this), but so far none have ever been directly observed.  And this is why we care about them. 
     Direct observation of GWs would prove general relativity.  According to Kip Thorne (1997) it would potentially allow for high-precision tests of GR, determination of Hubble's constant and the cosmological constant and a better understanding of the objects that cause them, such as neutron stars and black holes(more on this in the next section).  Aside from compact objects, GWs would have also been produced from the Big Bang and so, like the Cosmic Microwave Background Radiation (look up WMAP for further info) that permeates the universe, GWs should also permeate the universe.  This is referred to as the gravitational wave background, or GWB.  So where observation by WMAP of the microwave background allowed astronomers to observe the early universe within hundreds of thousands of years after the Big Bang, direct observation of GWs would allow astronomers to observe the universe only seconds after the Big Bang.

                       Sources of GWs
     As mentioned above, GWs are produced from the acceleration of compact, massive objects.  These objects are primarily neutron stars(NS) and stellar mass black holes(BH).  A neutron star is one of the possible end stages of a star.  It is the result of the collapse of a giant star after fusion has stopped.  As the core collapses, protons combine with electrons to form neutrons, and what remains is a dense neutron core.  If it is less than 3 solar masses, it remains a neutron star, otherwise it collapses into a black hole.  These objects can come in binary systems: astronomers look for NS-NS binaries, NS-BH binaries and BH-BH binaries since it is known that these should produce GWs.  These are what land-based interferometers such as LIGO are trying to detect.

                      Searching for GWs
Gamma Ray Bursts  

     Gamma ray bursts are associated with extreme core collapse and are also thought to result from a the merging (or coalescence) of a NS-NS binary or NS-BH binary, which should produce stronger GWs, so many astronomers believe that using gamma ray bursts is very promising (Abadie et al., 2012).  In fact, some believe that with the next generation of GW observatories we should be able to directly detect and observe GWs within the next decade unless the theory is fundamentally flawed (Wen, 2011).
     There is one other promising source of GWs for future detectors, and that is the detached whited dwarf binary J0651 +2844.   According to Hermes et al. (2012), it is the loudest non-interacting binary in the mHz range, and that makes it an excellent verification source for future missions aimed at the direct detection of GWs.  Hermes et al. (2012) also report that it is "the shortest period detached compact binary and the cleanest system to observe at optical wavelengths for orbital decay due to gravitational wave radiation."  According to general relativity, any system emitting gravitational wave radiation should lose energy through this radiation.  J0651 has a 12.75 minute orbital period and the orbit is decaying at a rate of about -0.31 s/yr, which is within the limits of what is predicted by general relativity.
 
Pulsar Timing Arrays

     A less expensive way to detect GWs than building giant interferometers is to use pulsars.  Pulsars are rapidly rotating, highly magnetized neutron stars.  The strong magnetic field accelerates electrons to high velocities and produces radiation in radio, optical, x-ray and gamma wavelengths and this radiation travels out along the axis of the magnetic field, like a beam, that appears to observers on Earth like a pulse as the star rotates.  They are ideal for use in detecting GWs because of their precision timing.  They are the most stable natural standards of astronomical time and give us a unique opportunity to detect the low-frequency GWB (Potapov, 2010).  GWs distort the EM signals produced by the pulsars, causing fluctuations in the times of arrival.  When many pulsars are observed over time, patterns in the fluctuations can reveal gravitational waves.  This collection of pulsars is called a pulsar timing array. 
                             

                       More on GW Detectors
LIGO is what is known as a Michelson interferometer that consists of two observatories, one in Washington and one in Louisiana, and each is connected to a corner station by L-shaped arms.  I highly recommend this website, http://www.ligo.org/.  LIGO is designed to detect GWs from 40 Hz to several kHz, with maximum sensitivity at 150 Hz.  Virgo is an Italian GW obsrvatory similar to LIGO.  Neither has been able to detect GWs yet.  Improvements to both, called Advanced LIGO and Advanced Virgo, are in progress that would increase the sensitivity by a factor of ten.  Advanced LIGO is scheduled to be fully operational by 2014 and Advanced Virgo by 2015.  The Laser Interferometer Space Antenna (LISA) is a space-based interferometer designed to detect GWs in a frequency range of 10^-4 to  10^-1 Hz.  It began as a joint NASA-ESA project and is supposed to be the best chance to observe GWs from the Big Bang.  They have been planning it for quite some time, and according to the NASA website, should have been operational by now.  Unfortunately, there were funding issues (and possibly other problems) that caused delays.  NASA has not updated their website so keep in mind that if you visit the pages pertaining to LISA, it is incorrect.  Other websites of unknown reliability also claim LISA will be operational in the near future, but according to the ESA's contact person, Oliver Jennrich, LISA will not be operational before 2027.  I have been interested in this project since I learned about it several years ago, so I am quite disappointed that it is still so far from completion.

NOTE: I realize I tried to put a lot of information here so I highly recommend looking through my source list.  The Kip Thorne link is especially good for detailed information without being too technical; in particular, try reading the introduction and section 4 (about the interferometers and GW detection).  It discusses clearly and in detail some things I only touched on. 

References:

LIGO
General: http://www.ligo.org/ 

For fun: http://www.einsteinathome.org/ (similar to SETI, you can allow your computer's idle time to help with the search for spinning neutron stars to detect GWs)

Technical: https://www.advancedligo.mit.edu/overview.html

LISA 

general info: Oliver Jennrich - ESA contact
              ESA website LISA mission homepage: 
http://www.rssd.esa.int/index.php?project=LISA&page=index

Specs and technical:

http://www.rssd.esa.int/SYS/docs/ll_transfers/LISA_Science_Requirements.pdf

Gravitational waves and pulsars:
general info

  NASA website:     http://imagine.gsfc.nasa.gov/docs/features/topics/gwaves/gwaves.html
         http://imagine.gsfc.nasa.gov/docs/science/know_l2/pulsars.html  
  Square Kilometre Array:

http://www.skatelescope.org/the-science/gravity-einstein-pulsars/pulsars-gravitational-waves/

  1993 Nobel prize info: http://cosmictimes.gsfc.nasa.gov/online_edition/1993Cosmic/nobel.html

Technical:
Abadie, J. et al., ApJ, 760:12 (18pp), 2012 November 20

SEARCH FOR GRAVITATIONAL WAVES ASSOCIATED WITH GAMMA-RAY BURSTS DURING LIGO SCIENCE RUN 6 AND VIRGO SCIENCE RUNS 2 AND 3

doi:10.1088/0004-637X/760/1/12

Hermes, J.J. et al., 2012, RAPID ORBITAL DECAY IN THE 12.75-MINUTE BINARY WHITE DWARF J0651+2844

arXiv:1208.5051 [astro-ph.SR]

Potapov, V. A. (2010). Timing of millisecond and binary pulsars and search for the low-frequency gravitational waves.

AIP Conference Proceedings, 1206(1), 231-236.

doi:10.1063/1.3292528
 

Thorne, K.S., "Karl Schwarzschild Lecture: Gravitational Radiation - A New Window Onto the Universe," in Reviews in Modern Astronomy, 10, ed. R.E. Schielicke (Astronomische Gesellschaft, 1997), pp. 1-28.  http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1997RvMA...10....1T&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf

 

Wen, L., Detecting gravitational waves and their electromagnetic counterparts

International Journal of Modern Physics D

Vol. 20, No. 10 (2011) 1883–1890

DOI: 10.1142/S021827181101989X

An Update and Additional Links

     First, I want to appologize for not posting or responding to comments for a while due to a health issue.  Also, I discovered some errors in a previous post after reading comments; I have updated that post.  Thanks to those who left comments.  For those who wanted to check out some lectures by Kip Thorne, here are some links that I found quite useful: 

http://www.its.caltech.edu/~kip/scripts/lectures.html - lectures for the general public (so it says) as well as for physicists and astronomers

http://elmer.caltech.edu/ph237/  - Course on gravitational waves taught at Caltech complete with course materials and homework.

A real post is coming soon; I just wanted to put this info out while I finish research for my next topic.

Explanation of ILRT's

The LA Times reported this weekend that astronomers can now explain intermediate luminosity red transients (ILRTs).  ILRT's are stellar bursts whose luminosities are between novae and supernovae.  They appear very red and are short-lived (STSCI).  Previously, some astronomers theorized that they result from two stars in a very close orbit that temporarily share a common envelope, referred to as a common envelope event or CEE, but there was no direct evidence (STSCI, Ivanova et al.).  Because CEE's are short-lived, astronomers thought it was improbable they would ever directly observe one, but in the paper by Ivanova et al., published Thursday in the journal Science¹, they propose a direct observational signature of a CEE, and these observations are in agreement with computer simulations based on the previous theories. 

I recommend the STSCI website provided below.  It provides more information than the LA Times article (also included), but is less technical than the paper published in the journal.  The paper has supplemental material available in the online version of Science.  This so far seems slightly more understandable, but it is very long.  It does have some cool computer simulations.  I have provided the link for that as well.

NOTE: if you have trouble accessing the supplemental material, you may need to be on campus or sign in to vpn through the UCR Libraries.  I also provided a link to view all the sources cited - some of them are free to download, so you don't have to sign in.

¹Identification of the Long-Sought Common-Envelope Events

N. Ivanova et al.

DOI: 10.1126/science.1225540

Science 339, 433 (2013)

Supplemental material and computer simulations: http://www.sciencemag.org/content/suppl/2013/01/23/339.6118.433.DC1

Space Telescope Science Institute (STSCI):  https://blogs.stsci.edu/newsletter/2011/11/21/miniworkshop-on-the-astrophysics-of-intermediate-luminosity-red-transients/

Click this link to see the LA Times article:  http://www.latimes.com/news/science/sciencenow/la-sci-sn-common-envelope-events-20130124,0,1637211.story?track=rss 

List of sources cited in the journal:  http://www.sciencemag.org/content/339/6118/433.full.html#ref-list-1