[ExI] missing matter found, maybe

[Damien Broderick]

[This is a fairly coarse-grained journalistic report, but maybe 
interesting anyway...]

<http://www.cosmosmagazine.com/news/3451/large-chunk-missing-universe-found>

Large chunk of missing universe found
Wednesday, 19 May 2010

by Meghan Miner
Cosmos Online

Scientists using two X-ray telescopes have found evidence for the 
'missing matter' in the nearby universe. This matter is made up of hot 
diffuse gas, which is known as WHIM (warm-hot intergalactic medium). To 
get this result, researchers analyzed X-ray light from a distant quasar 
that passed through a 'wall' of galaxies about 400 million light-years away.


SYDNEY: A large chunk of missing matter - theorised but never before 
measured - has been discovered as a vast smear of extremely hot 
intergalactic gas 400 million light-years away.

In order for the predominant theories about the formation and evolution 
of the universe to hold true, a certain amount of matter should be 
present; but large amounts of it have long remained elusive.

Now an international team of astronomers have found most of the missing 
matter, pinpointing its location using two different X-ray telescopes.

Clues to how galaxies formed

"We didn't just find a 'lost & found' item in the cosmic baryon budget," 
said Taotao Fang of the University of California at Irvine and lead 
author of the paper in The Astrophysical Journal, "our findings provide 
important clues to the question of how galaxies formed and evolved.

"The missing matter we found are the leftovers from the early galaxy 
formation process," said Fang

The missing matter has long been hypothesised, and some of it has even 
been spotted before; but previous observations did not uncover the full 
extent of this massive gas cloud.

Higher temperatures

"What [previous studies] found is the missing matter at lower 
temperatures ... about 10-20% of the total missing matter," said Fang. 
"What we found are missing matter at higher temperatures and account for 
the majority 80 to 90% of the missing matter."

By using two X-ray telescopes, instead of one visible light telescope as 
in previous studies, the exact location of the missing matter could be 
calculated and the results were more robust.

The X-ray telescopes that captured the images identifying the location 
of the missing matter are housed on NASA's Chandra and the European 
Space Agency's XMM-Newton - which has a command centre in Perth, 
Australia. Both orbital observatories that have been in space since 1999.

High-energy waves

X-ray telescopes detect different aspects and temperatures of light than 
visible light telescopes. "Just like when we use our eyes or an X-ray 
machine to look at a person, we see different 'aspects' of this person," 
said Fang.

By using X-ray telescopes scientists are able to observe radiation 
produced by different physical processes, such as high-energy waves 
emitted from particles that have extremely high temperatures like 
explosive forces, large gravity forces and magnetic fields.

In this case, astronomers looked for high frequency waves around a 
supermassive black hole, which - because of the size and pull on the 
area around it - generates huge amounts of X-ray energy.

Sculptor Wall

In the same line-of-sight as this black hole is a structure called the 
Sculptor Wall, which stretches tens of millions of light-years across, 
and is home to thousands of galaxies and a large portion of the newly 
found matter.

The matter, which is different from dark matter, is in a form known as 
'Warm-Hot-Intergalactic-Medium' (WHIM), a diffuse gas 'reservoir' with 
an extremely low density- about six protons per cubic metre- a possible 
explanation as to why it evaded earlier detection.

In comparison, the interstellar medium between stars in our own galaxy 
has about a million hydrogen atoms per cubic metre.

Composed of baryons?

The missing matter is likely composed of baryons, particles such as 
protons and electrons that are found through out our Solar System and on 
Earth. The baryons are leftover from galaxy formation processes and were 
then enriched by materials ejected from galaxies later.

These findings confirm the current theory about the formation and 
evolution of the universe and will help in further modelling of these 
processes in greater detail.

A very cool result

"This is a very cool result," says Geraint Lewis an astronomer at the 
University of Sydney, "but when I say cool, I mean exceedingly hot, like 
the temperature of these gasses.

"It's nice to see someone make a prediction and to find that the stuff 
is actually there ... we need to have a census of all the matter in the 
universe," he added.

According to astronomers' estimates, more matter is still missing, and 
to find it, suggests Fang, we'll need to develop new technology - a 
telescope with higher photon sensitivity.