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Shuttle crew in training
Astronauts Soichi Noguchi and Steve Robinson go under water in the Neutral Bouyancy Lab's gigantic pool to practice spacewalk activities for the upcoming STS-114 return-to-flight space shuttle mission. (3min 45sec file)
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Visiting the Cape
The STS-114 return-to-flight space shuttle crew visits Kennedy Space Center to inspect Discovery and the new sensor boom that will look for orbiter launch damage. (2min 22sec file)
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Day of Remembrance
NASA pays tribute to those lost while furthering the cause of exploration, including the Apollo 1, Challenger and Columbia crews, during this Day of Remembrance memorial from agency headquarters on Jan. 27. (38min 58sec file)

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Shuttle's new inspector
The Orbiter Boom Sensor System is loaded into space shuttle Discovery's payload bay. The arm will be used to inspect the shuttle for damage following the return-to-flight launch. (4min 18sec file)
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Spacewalk highlights
The Expedition 10 conducts a successful spacewalk outside the International Space Station to mount a German robotic arm and Russian science package to the Zvezda service module's exterior. (5min 07sec file)
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Huygens science update
One week after the Huygens probe landed on Saturn's moon Titan, scientists hold a news conference to announce additional results and describe more pictures from the mission. (69min 02sec file)

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ISS spacewalk preview
The upcoming spacewalk by the International Space Station's Expedition 10 crew is previewed by NASA officials at the Johnson Space Center on Jan. 21. (25min 04sec file)

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Launch of Deep Impact!
A Boeing Delta 2 rocket blasts off from Cape Canaveral carrying NASA's comet-smashing probe called Deep Impact. This extended clip follows the mission through second stage ignition and jettison of the rocket's nose cone. (5min 37sec file)
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Press Site view
A camera located at Cape Canaveral's Press Site 1 location offers this view of the Delta rocket's ascent. (1min 24sec file)
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Lost and found: Chandra locates missing matter
CHANDRA X-RAY CENTER NEWS RELEASE
Posted: February 2, 2005

NASA's Chandra X-ray Observatory has discovered two huge intergalactic clouds of diffuse hot gas. These clouds are the best evidence yet that a vast cosmic web of hot gas contains the long-sought missing matter - about half of the atoms and ions in the Universe.


This illustration shows the absorption of X-rays from the quasar Mkn 421 by two intergalactic clouds of diffuse hot gas. These distant clouds (located 150 million and 370 million light years from Earth), are likely part of a predicted diffuse web-like system of hot gas clouds - the cosmic web - from which galaxies and clusters of galaxies are thought to have formed. Credit: CXC/M.Weiss
 
Various measurements give a good estimate of the mass-density of the baryons - the neutrons and protons that make up the nuclei of atoms and ions - in the Universe 10 billion years ago. However, sometime during the last 10 billion years a large fraction of the baryons, commonly referred to as "ordinary matter" to distinguish them from dark matter and dark energy, have gone missing.

"An inventory of all the baryons in stars and gas inside and outside of galaxies accounts for just over half the baryons that existed shortly after the Big Bang," explained Fabrizio Nicastro of the Harvard-Smithsonian Center for Astrophysics, and lead author of a paper in the 3 February 2005 issue of Nature describing the recent research. "Now we have found the likely hiding place of the missing baryons."

Nicastro and colleagues did not just stumble upon the missing baryons - they went looking for them. Computer simulations of the formation of galaxies and galaxy clusters indicated that the missing baryons might be contained in an extremely diffuse web-like system of gas clouds from which galaxies and clusters of galaxies formed.

These clouds have defied detection because of their predicted temperature range of a few hundred thousand to a million degrees Celsius, and their extremely low density. Evidence for this warm-hot intergalactic matter (WHIM) had been detected around our Galaxy, or in the Local Group of galaxies, but the lack of definitive evidence for WHIM outside our immediate cosmic neighborhood made any estimates of the universal mass-density of baryons unreliable.

The discovery of much more distant clouds came when the team took advantage of the historic X-ray brightening of the quasar-like galaxy Mkn 421 that began in October of 2002. Two Chandra observations of Mkn 421 in October 2002 and July 2003, yielded excellent quality X-ray spectral data. These data showed that two separate clouds of hot gas at distances from Earth of 150 million light years and 370 million light years were filtering out, or absorbing X-rays from Mkn 421.

The X-ray data show that ions of carbon, nitrogen, oxygen, and neon are present, and that the temperatures of the clouds are about 1 million degrees Celsius. Combining these data with observations at ultraviolet wavelengths enabled the team to estimate the thickness (about 2 million light years) and mass density of the clouds.

Assuming that the size and distribution of the clouds are representative, Nicastro and colleagues could make the first reliable estimate of average mass density of baryons in such clouds throughout the Universe. They found that it is consistent with the mass density of the missing baryons.

Mkn 421 was observed three times with Chandra's Low-Energy Transmission Grating (LETG), twice in conjunction with the High Resolution Camera (May 2000 and July 2003) and once with the Advanced CCD Imaging Spectrometer (October 2002). The distance to Mkn 421 is 400 million light years.

NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA's Office of Space Science, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Ares 1-X Patch
The official embroidered patch for the Ares 1-X rocket test flight, is available for purchase.
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Apollo Collage
This beautiful one piece set features the Apollo program emblem surrounded by the individual mission logos.
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Expedition 21
The official embroidered patch for the International Space Station Expedition 21 crew is now available from our stores.
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Hubble Patch
The official embroidered patch for mission STS-125, the space shuttle's last planned service call to the Hubble Space Telescope, is available for purchase.
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