GREENBELT, MD - A new skymap has been produced that allows astronomers a powerful tool to study and more accurately juxtapose the various celestial objects that comprise the known universe. And it comes about because of mysterious objects in the farthest flung reaches of space called quasars.
Quasars are remote deep-space objects that are typically "...brighter than a billion suns", according to Dr. Chopo Ma of NASA's Goddard Space Flight Center. (Not million....BILLION!) Many scientists believe these objects are powered by giant black holes that constantly feed on nearby gases. Gas trapped in the black hole's powerful gravity is compressed and heated to millions of degrees. In theory, this is the "engine" giving off intense light and/or radio energy that is the signature of quasars. This is what makes them detectable from earth.
Most quasars lurk in the outer reaches of the cosmos, over a billion light years away. They are so far away and so distant as to be almost unfathomably distant - distant enough to actually appear stationary to us. (For comparison, a light year, the distance light travels in a year, is almost six trillion miles. Our entire galaxy, consisting of hundreds of billions of stars, is about 100,000 light years across.)
To put this in prospective, I like to mention a simple exercise in terms most can associate, like say ones wife's ability to shop. Let's suppose you are the beneficiary of a rather large endowment from an unknown benefactor. It comes to you with certain terms and restrictions: you are to receive one million dollars, but, in order to receive it, your wife must go out and spend it each day at the rate of one thousand dollars a day.
My wife is very creative, and I have no doubt of her ability to accomplish the task.
But if this were presented to you just so, your wife would return after three and a half years with hand outstretched, saying, "Honey, I need more money." Such is the case for a number of one million.
But if the sum was a billion, well gentlemen, we would not see our wives again for three and a half CENTURIES.
Suffice it to say, these objects we call quasars are very far away indeed.
This makes them the ideal candidate for the Global Positioning System (GPS). GPS satellites send signals to a receiver in your GPS navigator, which calculates your position based on the location of the satellites and your distance from them. The distance is determined by how long it took the signals from various satellites to reach your receiver.
The system works well, and millions rely on it every day, but what tells the GPS satellites where they are in the first place?
"For GPS to work, the orbital position, or ephemeris, of the satellites has to be known very precisely," said Dr. Chopo Ma of NASA's Goddard Space Flight Center in Greenbelt, Md. "In order to know where the satellites are, you have to know the orientation of the Earth very precisely." http://www.floridatoday.com/article/20091029/BREAKINGNEWS/91029030/1007/rss06
Thus a collection of remote quasars, whose positions in the sky are precisely known, was used to form a map of celestial landmarks in which to orient the Earth in space. The first such map was completed in 1995. It took a team of scientists over four years to make using painstaking analysis of observations on the positions of about 600 objects (mostly quasars, but the specifics of that is the subject of another article). This first map was called the International Celestial Reference Frame (ICRF), and it paved the way and allowed GPS technology to come into its own.
Dr. Ma led a three-year effort to update and improve the ICRF map. Scientists call this map ICRF2. It uses observations and reference points of approximately 3,000 quasars, making it five times more detailed and specific than the first map. This new skymap (ICRF2) was officially recognized as the fundamental reference system for astronomy by the International Astronomical Union (IAU) in August, 2009.
The making of such a map is not easy. Despite the brilliance of quasars, their extreme distance makes them too faint to be located accurately with the conventional telescopes we are all familiar with. (I am referring here to the ones used by most amateur astronomers that use optical light - the light that we can see - to create an image visible in the eyepiece.) Instead, a special network of radio telescopes is used not unlike the ones in the movie 'Contact' with Jodie Foster. This network is called the Very Long Baseline Interferometer (VLBI).
The larger the telescope, the better its ability to see fine details. This is what is called spatial resolution. A VLBI network coordinates all of its observations to get the resolving power of a telescope as large as the network. VLBI networks have spanned continents and even entire hemispheres of the globe, giving the resolving power of a telescope thousands of miles in diameter. For ICRF2, the analysis of the VLBI observations reduced uncertainties in position to angles as small as 40 microarcseconds.
What can we relate those "uncertainties" to in everyday terms? Let's say that for all practical purposes, this new system allows us to resolve an object on the pavement in Los Angeles, California about the thickness of a 0.7 millimeter mechanical pencil lead, and to clearly determine its dimensions and characteristics when viewed from Washington, D.C.
"The ICRF maps are not only useful for navigation on Earth; they also help us find our way in space -- the ICRF grid and some of the objects themselves are used to assist spacecraft navigation for interplanetary missions, according to Ma.
Despite its usefulness for things like GPS, the primary application for the ICRF maps is astronomy. Researchers use the ICRF maps as driving directions for telescopes. Objects are referenced with coordinates derived from the ICRF so that astronomers know where to find them in the sky.
Also, the optical light visible to our eyes is only a small part of the electromagnetic radiation produced by celestial objects, which ranges from less-energetic, low-frequency radiation, like radio and microwaves, through optical light to highly energetic, high-frequency radiation like X-rays and gamma-rays.
Astronomers use special detectors to make images of objects producing radiation our eyes can't see. Even so, since things in space can have extremely different temperatures, objects that generate radiation in one frequency band, say optical, do not necessarily produce radiation in another, perhaps radio. The main scientific use of the ICRF maps is a precise grid for combining observations of objects taken using different frequencies and accurately locating them relative to each other in the sky." http://www.nasa.gov/centers/goddard/news/topstory/2009/icrf2.html