“Half The Universe’s Matter Was Missing. Astronomers Just Found It.”

Her er en interessant video , der viser at man – sandsynligvis ? – har fundet den manglende “matter” i den synlige del af universet, som man teorisk forventede, men ikke kunne finde

Taget herfra

A new analysis of the sky has finally confirmed where the missing half of the Universe’s visible matter has been hiding.

In the space around galaxies, it lurks as huge, invisible clouds of ionized hydrogen. Normally, this would be impossible to see – but a large international team of astronomers and astrophysicists has developed a technique that reveals its hiding places, out there in the darkness amidst the stars.

Survey programs confirm the missing half of the Universe’s material takes the form of an intergalactic mist of hydrogen expelled farther from the active cores of galaxies than anybody previously thought.

“We think that, once we go further away from the galaxy, we recover all of the missing gas,” says astronomer Boryana Hadzhiyska of the University of California, Berkeley and Lawrence Berkeley National Laboratory.

“To be more accurate, we have to do a careful analysis with simulations, which we haven’t done. We want to do a careful job.”

Normal, or baryonic matter, makes up around 5 percent of the matter-energy distribution of the Universe; the rest is dark matter (27 percent) and dark energy (68 percent). Dark matter and dark energy are a whole other thing, but the Mystery of the Missing Baryonic Matter is one that has vexed scientists for decades.

The problem is that we simply don’t know where a large proportion of it is. Hydrogen makes up around 90 percent of the Universe by atoms, and 73 percent by mass; so a large chunk of the missing baryonic matter is hydrogen. Scientists estimate that we’ve misplaced more than 50 percent of the Universe’s hydrogen.

Hydrogen in space can glow, as is the case with the Orion Nebula, but has insufficient density and irradiation to achieve brightness in intergalactic space. (NASA, ESA, M. Robberto (STScI/ESA) and the Hubble Space Telescope Orion Treasury Project Team)

Hydrogen in space can be ionized by radiation, causing it to glow faintly, but in the space between galaxies, the gas is too diffuse, and the glow too faint, for this to be easily detectable.

But there’s more than one way to look for an invisible cloud of hydrogen. One method that has been gaining traction is by looking at changes in the light behind it – the cosmic microwave background, the fossilized ‘first light’ in the Universe that permeates the cosmos.

“The cosmic microwave background is in the back of everything we see in the Universe. It’s the edge of the observable Universe,” says cosmologist Simone Ferraro of Lawrence Berkeley National Laboratory. “So you can use that as a backlight to see where the gas is.”

As this light travels through diffuse clouds of ionized hydrogen, it can be brightened or dimmed as it scatters off electrons in the gas. This is called the kinematic Sunyaev-Zel’dovich effect. As you can probably imagine, though, the cosmic microwave background is really faint and hard to see too.

Image of the cosmic microwave background. The circles indicate spots where ionized hydrogen has scattered the radiation. (ACT; Louis et al)

So, the solution is stacking. You take a bunch of observations and lay them on top of each other in stacks to emphasize really, really faint features. The researchers did this for more than a million glowing red galaxies within a radius of 8 billion light-years of the Milky Way.

Their results showed that the halo of hydrogen wrapped around these galaxies is much larger than we thought. It also offers the tantalizing possibility that the haloes are much larger than even this survey was able to detect.

Taget herfra