There’s a press release today that a team of astronomers have found a good chunk of what we’ve been trying to find:

“After an extensive search, astronomers say they have definitely found half of the universe’s missing normal matter in the spaces between galaxies.

Astronomers have long known that the amount of matter we can see doesn’t match up with what’s actually there. Normal matter (which includes galaxies, stars and us) makes up only about 4 percent of the universe. This type of matter is also called ‘baryonic’ because it is made of baryons (protons, neutrons and other subatomic particles).

The missing part of baryonic matter has largely escaped detection because it is too hot to be seen in visible light but too cool to be seen in X-rays. Dubbed the ‘intergalactic medium,’ or IGM, it extends essentially throughout all of space like a cosmic spider web.”

Read the full article here.

Do note that this missing matter is not the “dark” matter that people have been imagining existing in large quantities for some time now. Whatever the dark matter actually is, it’s not the sort of normal matter (baryonic) that we’re familiar with (stuff made up of protons or neutrons – or stuff that has an electrical charge). If it was made up of that non-exotic material we’d be able to detect electro-magnetic radiation from it, and it wouldn’t be “dark”.

Note too that this discovery only now accounts for about 4% of the total gravitational effect that is observed. The dark matter that we can’t “see” is thought to provide the rest of the missing gravitational “charge”.