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Physics + MathPhysics & Math

Scientists Detect 'Missing' Half of Universe's Normal Matter

ByAllison EckNOVA NextNOVA Next

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Scientists revealed the ligaments of the universe this week. For the first time, they’ve identified half of the normal matter in our universe that was predicted in mathematical models but not yet observed.

Now, two separate teams of scientists have discovered the missing baryons—particles like protons, electrons, and neutrons—that link galaxies together in hot, gaseous filaments.

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The Andromeda galaxy

Here’s Leah Crane, reporting for New Scientist:

Because the gas is so tenuous and not quite hot enough for X-ray telescopes to pick up, nobody had been able to see it before.

“There’s no sweet spot – no sweet instrument that we’ve invented yet that can directly observe this gas,” says Richard Ellis at University College London. “It’s been purely speculation until now.”

So the two groups had to find another way to definitively show that these threads of gas are really there.

Both teams took advantage of a phenomenon called the Sunyaev-Zel’dovich effect that occurs when light left over from the big bang passes through hot gas. As the light travels, some of it scatters off the electrons in the gas, leaving a dim patch in the cosmic microwave background—our snapshot of the remnants from the birth of the cosmos.

The teams used a stacking effect to accentuate the otherwise-dim space between galaxies. One group looked at 260,000 pairs of galaxies, while another analyzed over a million pairs. Both found evidence of gas filaments, and both teams’ data suggested that this matter is much denser than the mean of the normal matter in the universe.

The finding is a relief to many astrophysicists, since it confirms some of our most basic assumptions of how galaxies form. Dark matter , as opposed to normal matter, is still a cosmic mystery, but at least we’ve solved the question of where all of this previously-theoretical normal matter is coming from.