Wilkinson Microwave Anisotropy Probe: Mapping the Early Universe

Click here to ho to our page on radiometers

Click here to go to our page on radio astonomy

The Wilkinson Microwave Anisotropy Probe (WMAP) was a satellite-based telescope designed to look deep into space (and thus, far back in time) to measure the universe.  Launched in 2001, WMAP was stationed near the second Lagrange point (L2) of the Earth-Sun system, a million miles from Earth in the direction opposite the sun. This location means it is always in the same position relative to both the Earth and the Sun. From there, WMAP spent the next nine years measuring the cosmic microwave background radiation and mapping out tiny temperature fluctuations across the universe.. 

Here's some detail directly from the NASA site (https://map.gsfc.nasa.gov/mission/)

The WMAP instrument consists of a set of passively-cooled microwave radiometers (connected to radiator panels with metal straps) with 1.4 x 1.6 meter diameter primary reflectors to provide the desired angular resolution. Measuring the temperature of the microwave sky to an accuracy of one millionth of a degree requires careful attention to possible sources of systematic errors. The avoidance of systematic measurement errors drove the design of WMAP:

  • The instrument has five frequency bands from 22 to 90 GHz to facilitate separation of galactic foreground signals from the cosmic background radiation.
  • WMAP is a differential experiment:  WMAP measures the temperature difference between two points in the sky rather than measuring absolute temperatures.
  • An orbit about the Sun-Earth L2 libration point that provides for a very stable thermal environment and near 100% observing efficiency since the Sun, Earth, and Moon are always behind the instrument's field of view.
  • A scan strategy that rapidly covers the sky and allows for a comparison of many sky pixels on many time scales.

View a live 3D model of the Observatory!


So after all that, what did they discover? You can stop reading now if you beleive the universe is 6,000 years old....

The universe is 13.77 billion years old, with a 1% margin of error. By combining the imagery from the nine years of observation, tNasa was able to make a map of what the unverse looked like at the very beginning.  The image below shows temperature fluctuations (shown as color differences) across a range of range of ± 200 microKelvin that correspond to the seeds that grew to become the galaxies.

Credit: NASA / WMAP Science Team

The first stars came into being when the universe was about 400 million old.

The universe is mostly energy, not matter.  And only 4.6% of it is made up of atomic matter, the kind we know here on Earth. The rest of the matter is "Dark Matter" (that is, it has gravity but doesn't emit light) and the rest of the universe (71%) is "Dark Energy" - a form of anti-gravity that is the source of the expansion of the universe. 

Detailed Studied of Temperature and Polarization in the CMB
Credit: NASA/WMAP Science Team / PNG(17 Kb) PNG(46 Kb) PDF(598 Kb)


What's next?

The James Webb Space Telescope, currently scheduled to launch in 2021, is a large infrared telescope that will head out to the same Lagrange Point (L2) to orbit the sun at about a million miles away from Earth. The plan, according to NASA, is to "study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System."  Quite an undertaking!

By the way, the Wilkinson here does not refer to our old friend and MW101 Hall-of-Famer Ernest Wilkinson , but rather to David Todd Wilkinson, a cosmologist from Princeton. We aren't sure if they were related at all.


WMAP's "baby picture of the universe" maps the afterglow of the hot, young universe at a time when it was only 375,000 years old, when it was a tiny fraction of its current age of 13.77 billion years. The patterns in this baby picture were used to limit what could have possibly happened earlier, and what happened in the billions of year since that early time. The (mis-named) "big bang" framework of cosmology, which posits that the young universe was hot and dense, and has been expanding and cooling ever since, is now solidly supported, according to WMAP.

WMAP observations also support an add-on to the big bang framework to account for the earliest moments of the universe. Called "inflation," the theory says that the universe underwent a dramatic early period of expansion, growing by more than a trillion trillion-fold in less than a trillionth of a trillionth of a second. Tiny fluctuations were generated during this expansion that eventually grew to form galaxies.

Remarkably, WMAP's precision measurement of the properties of the fluctuations has confirmed specific predictions of the simplest version of inflation: the fluctuations follow a bell curve with the same properties across the sky, and there are equal numbers of hot and cold spots on the map. WMAP also confirms the predictions that the amplitude of the variations in the density of the universe on big scales should be slightly larger than smaller scales, and that the universe should obey the rules of Euclidean geometry so the sum of the interior angles of a triangle add to 180 degrees.


WMAP has also provided the timing of epoch when t


Among the satellite’s new findings is that 73% of the universe is in the form of dark energy, while only 4% is in the form of ordinary, baryonic matter.

WMAP (formerly MAP) – named after David Wilkinson of Princeton University who was a pioneer of cosmic background studies and who died last year – has an angular resolution some 40 times better than that of its predecessor, the Cosmic Background Explorer (COBE). This improved resolution enables it to resolve temperature fluctuations in the 2.73 K background radiation of only millionths of a degree.

By combining the new data with other kinds of measurements, the WMAP team can say that this radiation dates back to 380,000 years after the Big Bang, and that stars first ignited 200 million years after the Big Bang. The new results also imply that the universe is 4% baryonic matter, 23% cold dark matter and 73% dark energy in a form more like a cosmological constant than a negative-pressure energy field. The WMAP satellite is also able to measure the polarization of the radiation, and this has provided new evidence for inflation in the early universe. The results have already ruled out a “textbook example” of a particular inflation model.


Author : Brenda

Source : https://map.gsfc.nasa.gov/