X-ray discovery points to location of missing matter

May 11, 2010
This artist's illustration shows a close-up view of the Sculptor Wall, which is comprised of galaxies along with the warm-hot intergalactic medium. Scientists used Chandra and XMM-Newton to detect the WHIM in this structure by examining the X-ray light from a distant quasar, which is represented in the inset to the upper right. This discovery is the strongest evidence yet that the "missing matter" in the nearby Universe is located in an enormous web of hot, diffuse gas. Credit: Spectrum: NASA/CXC/Univ. of California Irvine/T. Fang, Illustration: CXC/M. Weiss

Using observations with NASA's Chandra X-ray Observatory and ESA's XMM-Newton, astronomers have announced a robust detection of a vast reservoir of intergalactic gas about 400 million light years from Earth. This discovery is the strongest evidence yet that the "missing matter" in the nearby Universe is located in an enormous web of hot, diffuse gas.

This missing matter - which is different from -- is composed of baryons, the particles, such as protons and electrons, that are found on the Earth, in stars, gas, galaxies, and so on. A variety of measurements of distant and galaxies have provided a good estimate of the amount of this "normal matter" present when the universe was only a few billion years old. However, an inventory of the much older, nearby universe has turned up only about half as much normal matter, an embarrassingly large shortfall.

The mystery then is where does this missing matter reside in the nearby Universe? This latest work supports predictions that it is mostly found in a web of hot, diffuse gas known as the Warm-Hot Intergalactic Medium (WHIM). Scientists think the WHIM is material left over after the formation of galaxies, which was later enriched by elements blown out of galaxies.

"Evidence for the WHIM is really difficult to find because this stuff is so diffuse and easy to see right through," said Taotao Fang of the University of California at Irvine and lead author of the latest study. "This differs from many areas of astronomy where we struggle to see through obscuring material."

To look for the WHIM, the researchers examined X-ray observations of a rapidly growing supermassive black hole known as an active , or AGN. This AGN, which is about two billion away, generates immense amounts of X-ray light as it pulls matter inwards.

Lying along the line of sight to this AGN, at a distance of about 400 million light years, is the so-called Sculptor Wall. This "wall", which is a large diffuse structure stretching across tens of millions of light years, contains thousands of galaxies and potentially a significant reservoir of the WHIM if the theoretical simulations are correct. The WHIM in the wall should absorb some of the X-rays from the AGN as they make their journey across intergalactic space to Earth.

Using new data from and previous observations with both Chandra and
XMM-Newton, absorption of X-rays by oxygen atoms in the WHIM has clearly been detected by Fang and his colleagues. The characteristics of the absorption are consistent with the distance of the Sculptor Wall as well as the predicted temperature and density of the WHIM. This result gives scientists confidence that the WHIM will also be found in other large-scale structures.

Several previous claimed detections of the hot component of the WHIM have been controversial because the detections had been made with only one X-ray telescope and the statistical significance of many of the results had been questioned.

"Having good detections of the WHIM with two different telescopes is really a big deal," said co-author David Buote, also from the University of California at Irvine. "This gives us a lot of confidence that we have truly found this missing matter."

In addition to having corroborating data from both Chandra and XMM-Newton, the new study also removes another uncertainty from previous claims. Because the distance of the Sculptor Wall is already known, the statistical significance of the absorption detection is greatly enhanced over previous "blind" searches. These earlier searches attempted to find the WHIM by observing bright AGN at random directions on the sky, in the hope that their line of sight intersects a previously undiscovered large-scale structure.

Confirmed detections of the WHIM have been made difficult because of its extremely low density. Using observations and simulations, scientists calculate the WHIM has a density equivalent to only 6 protons per cubic meter. For comparison, the interstellar medium -- the very diffuse gas in between stars in our galaxy -- typically has about a million hydrogen atoms per cubic meter.

"Evidence for the WHIM has even been much harder to find than evidence for dark matter, which is invisible and can only be detected indirectly," said Fang.

There have been important detections of possible WHIM in the with relatively low temperatures of about 100,000 degrees using ultraviolet observations and relatively high temperature WHIM of about 10 million degrees using observations of X-ray emission in galaxy clusters. However, these are expected to account for only a relatively small fraction of the WHIM. The X-ray absorption studies reported here probe temperatures of about a million degrees where most of the WHIM is predicted to be found.

Explore further: When did galaxies settle down?

More information: These results appear in the May 10th issue of The Astrophysical Journal.

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2 / 5 (4) May 11, 2010

So theoretically speaking, could there be enough of this WHIM material that there would be no need for dark matter particles like neutralinos and axions? That would be interesting.
Shootist
1 / 5 (5) May 11, 2010
Quote the article, "This discovery is the strongest evidence yet that the "missing matter" in the nearby Universe is located in an enormous web of hot, diffuse gas."

Normal baryonic matter makes up the missing mass of the universe. Certainly Occam's Razor would suggest this result.
ForFreeMinds
1 / 5 (1) May 11, 2010
I'm confused. How can such low density material in the space between galaxies have temperatures of 100,000 to 10 million degrees? I thought it was cold in space far from stars.

Can this explain the rotation characteristics of galaxies?
thermodynamics
3.9 / 5 (7) May 11, 2010
ForFreeMinds: The vacuum they are talking about (6 protons per m^3) is extremely "hard." Under those conditions the particles (atoms and ions) are moving ballisticaly (meaning they do not bump into each other). They were ejected from supernovae and other extreme events and started with high speeds (the equivalent to being very hot). So, they can retain their high temperature (high speed). However, if you were there, you would freeze very quickly because you would radiate energy away and very few atoms or ions would hit you so your body would have a net cooling effect since your radiation would greatly outweigh the heating of a few atoms impacting you.

I have no idea how you are relating this to the rotation of a galaxy.
Shootist
not rated yet May 11, 2010
I'm confused. How can such low density material in the space between galaxies have temperatures of 100,000 to 10 million degrees? I thought it was cold in space far from stars.

Can this explain the rotation characteristics of galaxies?


somebody will pop up soon and 'yell', The Electric Universe!
Shootist
1 / 5 (3) May 11, 2010

I have no idea how you are relating this to the rotation of a galaxy.


The gas is everywhere and apparently of sufficient mass to help explain the insufficient mass paradox that led everyone to search for stuff that isn't there.
PinkElephant
5 / 5 (8) May 11, 2010
Normal baryonic matter makes up the missing mass of the universe. Certainly Occam's Razor would suggest this result.
No. The article even specifically states, in its FIRST PARAGRAPH, that:
This missing matter - WHICH IS DIFFERENT FROM DARK MATTER [emphasis added] -- is composed of baryons, the particles, such as protons and electrons, that are found on the Earth, in stars, gas, galaxies, and so on. A variety of measurements of distant gas clouds and galaxies have provided a good estimate of the amount of this "normal matter" present when the universe was only a few billion years old. However, an inventory of the much older, nearby universe has turned up only about half as much normal matter, an embarrassingly large shortfall.
All this does, is reconcile measurements between very distant galaxies, vs. nearby galaxies, in terms of total mass content. It does not address any of the issues that imply the existence of dark matter.
thermodynamics
3.9 / 5 (7) May 11, 2010
ForFreeMinds: Now I understand what you were trying to say. You thought that that this plasma might be dark matter. The problem is that it is made up of baryons and there was a "missing" batch of baryons expected based on the Big Bang and the standard model. Only about half of the baryons that are expected were accounted for. Now they have found a goodly fraction of those that were missing. However, it is still an order of magnitude too small to make up for the dark matter that is being chased by a number of physicists. All baryons are only expected to be about 5% of the universe. About 23% is supposed to be dark matter and the remainder is dark energy. So, even finding the missing baryons (to add up to the approximately 5%) does not bring it close to the expected mass of dark matter needed to hold things (such as galaxies) together.
PinkElephant
4 / 5 (4) May 11, 2010
...needed to hold things (such as galaxies) together.
"It surrounds us and penetrates us. It binds the galaxy together." - Obi-Wan Kenobi

An unintentionally pithy turn of phrase, perhaps?

Or maybe the Force is what physicists are pursuing. (In which case, someone ought to warn them to stay away from the Dark Side...) Time to bust out the microscopes and go hunting for those midi-chlorians... =D
ForFreeMinds
3 / 5 (2) May 11, 2010
Thanks to the many of you for responding to my question. I was referring to the galaxy rotation curve http://en.wikiped...n_curve, and the idea that there is a substantial amount of matter far from the center of the galaxy which causes the velocity of stars far from the center to be the same as stars much closer to the center.
Caliban
3 / 5 (2) May 11, 2010
How does this fit with the recent discovery that the deep sky surveys were off by a factor of 10 in reckoning the number of visible distant galaxies(published here recently)?
Do the two combined equal the magic number, or are we now operating with an excess?
thermodynamics
2.3 / 5 (3) May 11, 2010
Caliban: Great question. I believe the article you are referring to is:

http://www.physor...597.html

What this is saying is that it has been expected that there would be more galaxies out at the distance of redshift 2.2 and greater than could be seen. However, that just means that they could not see those faint objects before but they expected them to be there based on the local count of galaxies and the theory of galaxy formation. If they had been missing then the assumptions about locality and formation would be wrong. However, they found them with better telescopes. This is not missing mass, it was just not visible expected mass. Each of those galaxies is expected to be held together by dark matter just like our local galaxies and clusters are (theoretically). So, this does not explain away the local behavior of galaxies and clusters which are the basis for the idea of dark matter.
Ravenrant
1.3 / 5 (3) May 12, 2010
Normal baryonic matter makes up the missing mass of the universe. Certainly Occam's Razor would suggest this result.


I agree, this is the most likely answer. My second guess would be we don't know all the physics yet. I think the least likely answer is dark matter, non-baryonic.
Skeptic_Heretic
5 / 5 (3) May 12, 2010
Just to clear this abstract up for a few of the people above:

What we think about matter distribution:

4.6% Observable "Hard" (or "Hot")Baryonic Matter(everything we can see due to radiation)
1.4% Unobservable "Cold" Baryonic Matter (like the above article describes)
24% non-baryonic Dark Matter
70% Dark Energy

Now these measurements above and observations from both mentioned articles bring our level of certainty that the Baryonic matter we can't find, within that 6%, is there. As the abstract said, this has NOTHING TO DO WITH DARK MATTER. This is refining our preception of the Baryonic matter content distribution only.

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