Scientists figured out years ago that there was nowhere near enough matter in our Local Group of galaxies to create enough gravity to keep them from flying apart. Our Local Group consists of our own Milky Way Galaxy, the Andromeda Galaxy, and several dwarf galaxies. They reached the same conclusion regarding all of the galaxy clusters in the observable universe.
Realizing that something must be holding them together, they deduced the existence of a form of invisible matter and called it dark matter. There must be a lot of it because, to account for the stability within galaxy clusters, approximately 73% of the universe must be dark matter. Think of it as a kind of matrix or web within which galaxies form and develop.
Ordinary matter which makes up the stars, planets, and all visible objects in the universe, including ourselves, only makes up about 4% of the universe.
The rest, or about 23% of the universe, is another theoretical concept called dark energy, which exists in deep space in the regions between galaxy clusters. It causes space to expand, which explains why space is expanding between the galaxy clusters.
One problem with the theory of dark matter is that there should be more dwarf galaxies in our Local Group than have been observed. Last year, at the annual American Astronomical Society meeting in Seattle, Dr.Sukanya Chakrabarti from the University of California at Berkley presented her theory that they are present, but basically rendered invisible to us by dark matter and she proposed to look for evidence of their presence using radio telescopes to analyze disturbances in the vast clouds of hydrogen gas at the farthest reaches of the Milky Way. Her idea is similar to attempting to find a boat by searching for its wake.
Using the method, Dr Chakrabarti found a set of ripples that indicate a comparatively huge satellite galaxy, 260,000 light-years from the centre of the galaxy.
The satellite – dubbed Galaxy X in deference to the 19th-Century discovery of Neptune that named it Planet X – should weigh between three and 10 billion times as much as the Sun, about a hundredth as much as the Milky Way itself.
Now all that remains is to confirm it. That will have to wait until Dr Chakrabarti’s collaborators are granted time to use the Spitzer Space Telescope.
This year, at the annual meeting in Austin, a team of scientists from the Canada-France Hawaii Telescope presented four palm-print size images taken during different seasons of the year, each showing a region of space more than a billion light years across.
Together, they represent the images of more than 10 million galaxies, whose light gives the only hints of the large-scale structure of dark matter.
“Light coming toward us from a distant galaxy is bent by the gravity of a lump of matter in the middle,” explained Catherine Heymans of the University of Edinburgh.
“Einstein’s theory of general relativity tells us that mass bends space and time, so when light comes toward us through the Universe, if it passes some dark matter, its light gets bent and the image we see gets bent and distorted,” Dr Heymans told the meeting.
“Dark matter is leaving its signature on the images of very distant galaxies.”
As the evidence for dark matter begins to add up, it seems to be only a matter of time before scientists finally detect a particle of dark matter. Perhaps, the Large Hadron Collider will git ‘r done next year.