Tags: 2011 Nobel Prize, Cosmological Constant, Dark Energy, Eastern Illinois University, EIU
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Tonight at 8:00PM, October 12, 2011 in Room 2153 Physical Science Building
Dr James Conwell will be giving a talk on this years Nobel Prize in Physics: The Accelerating Universe and “Dark Energy”
NEW PODCAST:What’s New With Supermassive Black Holes January 18, 2011Posted by jcconwell in Astronomy, Black Holes, General Relativity, Podcast.
Tags: 365 days of astronomy, blackholes, Eastern Illinois University, Podcast, Supermassive Black Holes
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Extreme Universe: The Most Massive Neutron Star October 27, 2010Posted by jcconwell in Astronomy, Extreme Universe, General Relativity, Neutron Stars.
Tags: most massive neutron star, neutron star, PSR J1614-2230
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Using the National Science Foundation’s Green Bank Telescope , astronomers have discovered the most massive neutron star ever, this discovery will offer profound insight on the limits of neutron stars and the nature of matter under such extreme conditions.
“This neutron star is twice as massive as our Sun. This is surprising, and that much mass means that several theoretical models for the internal composition of neutron stars now are ruled out,” said Paul Demorest, of the National Radio Astronomy Observatory (NRAO). “This mass measurement also has implications for our understanding of all matter at extremely high densities and many details of nuclear physics,” he added.
The neutron star, called PSR J1614-2230 contains twice the mass of the Sun but compressed down into pulsar that is smaller than 20 kilometer It is estimated cubic inch of material from the star could weigh more than 10 billion tons. I have two videos below with more details for you.
The first is about the Discovery
The second is about the Instruments
NASA Gravity Probe B July 19, 2009Posted by neogajrhscience in Astronomy, General Relativity, Space Craft.
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Amy Brown has her blog at: http://neogajrhscience.wordpress.com/
Gravity probe B is a NASA mission first proposed in 1959 that was launched into space April 20, 2004. The probe contained a very accurate tracking telescope, and 4 gyroscopes. Its purpose was to test Einstein’s general theory of relativity, by measuring the amount of warp Earth causes in its surrounding spacetime (the geodetic effect) and the amount that Earth drags its local spacetime along as it rotates (the frame dragging effect). Data collection from the probe was completed in August, 2005, and data analysis has continued to the current date.
History of the Gravity Probe B Mission
Albert Einstein proposed his theory of general relativity in 1916, which linked the concepts of geometry and time with gravity. Gravity, as we understood it from Isaac Newton, was an attractive force between bodies due to their mass. Einstein proposed that, instead, gravity was a manifestation of the warping of spacetime around a body, which is also related to the body’s mass. To visualize this warping of spacetime, imagine a bowling ball placed in the center of the fabric of a trampoline. The mass of the bowling ball will pull the fabric down, warping the fabric in three dimensions. The bowling ball, of course, is compared to any object in space, and the more massive the object, the greater the warp.
General relativity has stood up to several types of tests. One of these involves the observational evidence of the precession of the perihelion of mercury, which shifts at the rate of 43 arc seconds per century. After all other influencing factors have been accounted for, this shift is attibutable to the effect of general relativity from the mass of the sun. Another type of test shows that light from distant objects bends as it travels past massive objects, such as the sun. This has been measured both with visible light, and more accurately with radio waves. Gravitaional redshift is another method that has supported general relativity. This measures the energy and time difference in objects at different positions in relation to earth. GPS satellites must account for the difference in 38 microseconds per day from the height they are orbiting to the surface of the earth. While these and other tests have provided substantial evidence to support general relativity, the evidence is not as precise as physicists would like it to be. Scientists were striving to devise a way to test general relativity on a precision basis.
In 1959, Stanford Physics Departmment Chair Leonard Schiff and MITphysicist George Pugh both independently proposed testing general relativity using gyroscopes. Schiff went forward with the idea, bringing on board other Stanford professores William Little, William Fairbank, and Robert Cannon. Schiff, Fairbank and Cannon continued to research the idea from different angles, and this research led to a proposal to NASA in 1962. NASA adopted the Gravity Probe project in 1964, and Stanford remained the primary project base.
The idea behind Gravity Probe B was to construct a space probe containing gyroscopes aligned to a distant space object. The spacecraft would surroound the gyroscopes, allowing them to remain in freefall. As the spacecraft orbits the earth, any warping effect of the spacetime around the earth would cause a measurable orientation shift of the spinning gyroscopes. This was to be measured in regard to two effects: the geodetic effect, which is the simple warping of spacetime due to the earth’s mass, and the frame shifting effect, which is the effect caused by earth dragging spacetime along as it rotates.
The idea of the probe was a simple one, but the technology required was not. More than a dozen new technologies had to be developed to make the probe work, and this took over 30 years to accomplish. The spheres that make up the four gyroscopes hold a guiness world record as the roundest objects ever made, and required the invention of new manufacturing techniques to complete them. They are made of quartz, refined to be homogeneous to within two parts in a million, and the sphericity is accurate to within 3 ten millionths of an inch. The spheres are coated with superconducting niobium.
The gyroscopes are housed within a suspension system that is only 32 microns larger in radius than each gyroscope. Also attached to the housing is a SQUID magnetometer, which measures the tilt of the gyroscope spinning within as its magnetic field interacts with the sensor. The satellite itself contains a nine foot long dewar (a large thermos) to contain the superchilled helium necessary to maintain the correct temperature to have the superconductive gyroscopes work properly.
In order to combat the small amount of heat that would enter the dewar, a special plug had to be designed to allow helium condensate to seep out into the outer layer.
In the late 1970’s and early 1980’s, the probe underwent a changeover form a research project to a flight mission project. Lockheed Martin was brought in to help with the design. It wasn’t until the late 1990’s, however, that the project was brought directly to NASA as a definite flight program. It took nearly seven years to work out all the bugs. Gravity Probe B was launched into orbit on April 20, 2004.
In a nutshell, the spacecraft that took over thirty years to design and launch was going to test the general theory of relativity. The spacecraft contains a tracking telescope. This telescope is pointed at a distant star, IM Pegasi, as a guide star. A quasar would be the desirable tracking object, but the telescope would not be able to stay focused on one, so IM Pegasi was used, and its position would then be compared to a distant quasar during data analysis. Once the telescope locks onto the position of the guide star, the gyroscopes are caused to sart spinning, and their alignment is matched to the alignmnet of the telescope. As the gyroscopes continue to spin, and the spacecraft orbits the earth, electrical signals between the gyroscopes and sensors in their housings are measured and sent back ot earth as raw data.
After the succesful launch, Gravity Probe B was in orbit 642km above the Earth. Before the probe could begin collecting data, a four month period of initialization and check out was accomplished. This period was supposed to be shorter, but several problems had to be corrected or accounted for before data collection could begin. One problem was that the spacecraft had trouble tracking the starfield due to the roll of the craft. Another problem was the loss of two of the sixteen helium thrusters. Setting the gyroscopes to spinning and aligning their spin axes with the guide star also caused some delay. The gyroscopes were expected to spin at a faster rate than they actually were spinning, so many adjustments and calculations had to be made on the ground to achieve alignment. One further delay during initialization occured whern the probe passed over the Earth’s south pole, and was bombarded by proton radiation from the sun. The delay was caused by one of the spacecraft’s computers going down and having to be rebooted after the proton bombardment. Because the initialization phase took quite a bit longer than anticipated, the decision was made to allow the data colection phase to be shortened. The spacecraft continued to send data until August 15, 2005. The remaining six weeks until the helium was depleted and the mission was ended on September 29, 2005 were spent claibrating and testing the equipment on the spacecraft.
Scientists associated with the Gravity Probe B mission have been analyzing the data since 2005. In the ideal scenario, every instrument on the spacecraft would have performed without complication, and staightforward data would have been provided. Some of the systems on the probe functioned very well. The dewar and the telescope performed exactly as expected. Unfortunately, the gyroscopes did not. The spheres themselves did spin extremely predictably, but the magnetic fields that they produced as they did so have been difficult to analyze. The spin axes of the gyroscopes were effected by the torque of the spacecraft, and scientists have been trying to account for the data anamolies by identifying and quantifying them. In terms of the two phases of data, the geodetic effect jumped out obviously, even from the raw data. The measurement of the warping of space around earth was calculated by the data to be within 1% of the predicted 6606 milliarcseconds/year. It is the measurement of the frame-shifting, however that is more effected by the data problems. NASA has closed the project, but other funding sources are allowing the data analysis to continue. Scientists with the project predict that with further analysis, they will be able to get the frame shifting data to within 3 to 5 percent of the expected 39 milliarcseconds per year.
The Legacy of Gravity Probe B
Regardless of the scientific outcome of the Gravity probe itself, the thirty year life of this research and space flight mission has provided the world with valuable benefits. Ninety seven students received PhDs at Stanford and other universities working on this project. Technologies developed for the spacecraft have been used in other applications, such as the optical bonding and fused quartz technologies used on the gyroscopes. Photo diode detector technology has helped to improve digital cameras for all of us. The porous helium plug developed for Gravity Probe G has been used in other cryogenically sensitive missions such as IRAS and COBE. Further, the attitude control technology in the spacecraft led to more accurate (1 centimeter) GPS now being used for automatic aircraft landing and automatic precision farming. Scientists and teams associated with Gravity Probe B have won several awards, including the 2005 NASA group achievemnet award given to the whole team. Gravity Probe B will remain into the future as one of the most memorable NASA missions in the history of the space program.
The information contained in this article was obtained form the following sources:
Measuring the Black Hole July 9, 2009Posted by jcconwell in Black Holes, General Relativity, IYA 2009, Podcast.
Tags: blackholes, EIU, IYA 2009, Podcast
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Today’s podcast at 365 days of Astronomy is about measuring those mysterious objects, Black Holes. Usually you think about the tidal forces of a Black Hole ripping and compressing anything falling in until it’s so hot, about 10 million K, that it emits x-rays.
In today’s pod-cast sponsored by the EIU Physics Department learn how radio telescope aid our knowledge of these dark objects. Go to:
The first observational proof of General Relativity May 31, 2009Posted by jcconwell in Astronomy, General Relativity.
Tags: General Relativity
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Ninety years ago, on May 29 1919, Sir Arthur Eddington led a expedition to test the new theory of gravity, Einstein’s General Theory of Relativity.
Einstein first proposed his General Theory of Relativity in 1915. It describes how any massive object, such as the Sun, creates gravity by bending space and time around it. Everything in that space is also bent: even rays of light. Consequently, distant light sources, behind the massive object, can appear in a different position or look brighter than they would otherwise.
If you look at pictures of clusters of galaxies from the Hubble space telescope you’ll see this effect as gravitational lensing. It’s the distortion of distant background galaxies as their light passes through the gravity of a cluster.
Back in 1919 they did not have the sensitive digital cameras that could see these faint streaks. So in 1919, the Royal Astronomical Society (RAS) launched an expedition to the West African island of Príncipe, to observe a total solar eclipse and prove or disprove Einstein’s General Theory of Relativity. They were to measure the deflection of the position of stars very close to the sun, the object that has the biggest gravity in the solar system. In order to measure the dim stars so close to the sun they need a solar eclipse that would block out the sun’s glare to make the dim stars visible.
“This first observational proof of General Relativity sent shockwaves through the scientific establishment,” said Professor Ferreira. “It changed the goalposts for physics.”
It also made Einstein an instant worldwide celebrity, something that the special theory of relativity in 1905 did not. Thanks to X’s blog for pointing this out.
Gravitational Waves and LISA January 11, 2009Posted by jcconwell in Astronomy, Black Holes, General Relativity.
Tags: blackholes, Gravitational Radiation, LIGO, LISA
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The AAS meeting in Long Beach this week had many nifty displays. My favorite, since I’m biased toward general relativity, is the LISA display. LISA stands for Laser Interferometer Space Antenna. Here I am in front of the full scale model of one of three proposed LISA satellites.
Now you may wonder why you want an orbiting gravitational wave satellite, especially since we have LIGO (Laser Interferometer Gravitational-Wave Observatory) already taking data. The answer is in the sensitivity diagram below
In order to make gravitational radiation you need to have an accelerated mass. The biggest masses with the largest accelerations are colliding black holes and neutron stars. Since most actual collisions are thought to be between orbiting bodies, the frequency of the radiation is related to the orbital frequency = orbits/second.
Now black holes seem to come in two classes. First, stellar mass black holes, created in massive core collapse supernovae. These black holes are around 10 solar masses and have a radius of 30 kilometers (18 miles). The greatest amount of radiation comes just as the two black holes are touching, or merging. The orbital velocities are about the speed of light. and the time to complete one orbit is
(orbital circumference) / velocity = .0006 second
or a frequency of 1600 orbits/second. This about the peak frequency for the radiation from this type of collision. In the diagram above, this frequency band is where LIGO was designed to be the most sensitive.
But there is a second class of black holes, the supermassive holes. These giants are from a million to several billion times the mass of the sun. They seem to form the core in most galaxies, and so when galaxies collide and merge, two orbiting monster black holes will release copious amount of energy. The good news is you can detect this from much further away than the merger of the smaller black holes. The bad news is the frequency.
A two million solar mass hole has a radius of 60 million kilometer and a circumference of about 380 million kilometers. In this case the period for the holes to orbit around each other is much longer
(orbital circumference) / velocity = 126 seconds
or a frequency of .008 orbits/second. A very low frequency, too low to detect on Earth, due earthquakes and seismic activities. This is where the frequency band where LISA comes in and why you need it in space rather than on Earth.