One of the fundamental questions astronomers are trying to answer is: What is the Universe made of? Numerous lines of evidence show that the Universe is about 73 percent "dark energy," 23 percent "dark matter," and only 4 percent normal matter. Yet this answer raises further questions, including: Where is all the normal matter?
Astronomers call this dilemma the "missing mass" problem. They can see normal, baryonic matter -- protons, electrons, and neutrons -- when it forms luminous stars, or when it blocks starlight as huge, dark molecular clouds. And what they see totals only a fraction of the normal matter they know is out there.
Now, astronomer Fabrizio Nicastro of the Harvard-Smithsonian Center for Astrophysics (CfA) and colleagues have found evidence for the existence of a large reservoir of baryons in our Local Group of galaxies. This baryonic matter forms a warm fog surrounding and enveloping the Milky Way and its neighbors.
"Our research shows that this warm fog may hold as much as two-thirds of the normal matter within the neighborhood of the Milky Way," says Nicastro.
Finding The Missing Mass
Nicastro and his team looked at ultraviolet and X-ray wavelengths where the intergalactic fog absorbed light from distant sources like quasars and active galactic nuclei. They culled data from the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite to identify about 50 clouds, or fog banks, surrounding our galaxy in every direction.
Atoms in individual clouds absorb light at specific wavelengths, creating dark lines in the spectra of background light sources. The motion of a cloud shifts the wavelength of its spectral line due to the Doppler effect.
Nicastro's team used these spectral shifts to derive radial (line-of-sight) velocities for the clouds, giving clues to the clouds' locations and origins.
Those studies showed that the warm clouds were almost certainly part of the Local Group of galaxies, which is comprised of the Milky Way and Andromeda spirals, along with about 30 smaller galaxies.
Given the amount of material they detected using FUSE and NASA's Chandra X-ray Observatory, Nicastro and his associates infer that the warm fog in the Local Group contains as much mass as a million million (10^12) Suns.
This result shows remarkable agreement with the amount of matter needed to gravitationally bind together the galaxies within the Local Group.
A Relic Of Galaxy Formation
Theories indicate that the early Universe was filled with a nearly homogeneous mix of hydrogen and helium gas. Clumps of dark matter within this primordial soup acted as seeds for galaxy formation. Over several hundred million years of time, the force of gravity pulled together some of the Universe's normal matter to form galaxies holding billions of stars.
However, only about one-third of the Universe's baryonic matter was consumed. Much of it still floats between the galaxies, invisible except for the shadow it casts.
"Finding this leftover material provides further evidence that our theories of galaxy formation are correct and offers clues to the history of our own Milky Way galaxy," says Nicastro. "This discovery, combined with future research, also may help track dark matter because the intergalactic filaments of baryonic matter should connect the dark matter clumps."
This research was reported in the February 12, 2003, issue of the scientific journal Nature in a paper authored by Fabrizio Nicastro (CfA); Andreas Zezas and Martin Elvis (CfA); Smita Mathur (Ohio State University); Fabrizio Fiore (Osservatorio Astronomico di Monteporzio); Cesare Cecchi-Pestellini, Douglas Burke, Jeremy Drake, and Piergiorgio Casella (CfA).
Harvard-Smithsonian Center for Astrophysics
Subscribe To SpaceDaily Express
Rivers Of Gas Could Provide Part Of Universe's "Missing" Matter
Columbus - Feb 13, 2003
An Ohio State University astronomer and her colleagues have detected a type of hot gas in space that could account for part of the "missing" matter in the universe.
|The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.|