Milky Way galaxy: cloaked in a hot shroud? (Science News of the week).
Spacecraft observations indicate that a vast, unseen halo of hot gas envelops our home galaxy. Large enough that it literally could be brushing up against the Milky Way's nearest galactic neighbors, the halo may be the remnants of the primordial material that built the Milky Way, researchers reported this week.
Kenneth R. Sembach of the Space Telescope Science Institute The Space Telescope Science Institute (STScI) is the science operations center for the Hubble Space Telescope (HST; in orbit since 1990) and for the James Webb Space Telescope (JWST; scheduled to be launched in 2013). in Baltimore and his colleagues base their findings on observations of gas clouds known to be raining down on our galaxy (SN: 1/25/97, p. 55). His team examined 60 clouds at far-ultraviolet wavelengths, which for the first time, revealed the clouds' hot, outer edges.
Sembach's group used distant quasars Proper naming of quasars are by Catalogue Entry, Qxxxx±yy using B1950 coordinates, or QSO Jxxxx±yyyy using J2000 coordinates.
This page lists quasars.
A portion of the light spectrum not visible to the eye. Two bands of the UV spectrum, UVA and UVB, are used to treat psoriasis and other skin diseases. . En route to Earth, some of the quasar light passes through a gas cloud and is absorbed. Dips in the quasars' spectra recorded by the Far Ultraviolet Spectroscopic Explorer The Far Ultraviolet Spectroscopic Explorer, also known as FUSE, is a space-based telescope operated by the Johns Hopkins University Applied Physics Laboratory. (FUSE) satellite, which was launched in 1999, show that the absorption comes from oxygen atoms stripped of five of their eight electrons.
The energy required to strip away so many electrons suggests that as the clouds fall toward the Milky Way, they plow through an extremely hot gaseous medium, Sembach says. When the clouds encounter this high-temperature region, which cloaks the galaxy, their outer edges become extremely hot and atoms become highly ionized i·on·ize
tr. & intr.v. i·on·ized, i·on·iz·ing, i·on·iz·es
To convert or be converted totally or partially into ions.
The absorption dip indicates that the clouds barrel through the halo, known as the galactic corona, at 224 kilometers per second. Although the corona can't be seen directly, the energy it imparts to the clouds indicates it has a temperature of at least 1 million kelvins and weighs as much as 100 million suns, Sembach reported at a meeting of the American Astronomical Society The American Astronomical Society (AAS, sometimes pronounced "double-A-S") is a US society of professional astronomers and other interested individuals, headquartered in Washington, DC. in Washington, D.C.
The corona extends at least 150,000 light-years above and below the plane of our spiral galaxy. By comparison, one of the Milky Way's nearest neighbors, the Large Magellanic Cloud Noun 1. Large Magellanic Cloud - the larger of the two Magellanic Clouds visible from the southern hemisphere
Magellanic Cloud - either of two small galaxies orbiting the Milky Way; visible near the south celestial pole galaxy, lies about 170,000 light-years from Earth.
Other studies have shown that at least some of the infalling clouds contain fewer heavy elements than do gas clouds contained within the Milky Way. This suggests that the clouds examined by Sembach's team originate outside the galaxy. In contrast, a much smaller and cooler halo previously discovered by FUSE may have originated in the Milky Way.
The origin of the newfound halo fits with a theory, proposed by Leo Leo, in astronomy
Leo [Lat.,=the lion], northern constellation lying S of Ursa Major and on the ecliptic (apparent path of the sun through the heavens) between Cancer and Virgo; it is one of the constellations of the zodiac. Blitz of the University of California, Berkeley The University of California, Berkeley is a public research university located in Berkeley, California, United States. Commonly referred to as UC Berkeley, Berkeley and Cal and his colleagues, that the infalling clouds are leftovers from our galaxy's formation. As a huge reservoir of gas condensed con·dense
v. con·densed, con·dens·ing, con·dens·es
1. To reduce the volume or compass of.
2. To make more concise; abridge or shorten.
a. to build the Milky Way, its outer regions may have heated up, creating the high-temperature halo. Previous observations hint that some other galaxies also have hot coronas, which could be remnants of their own formation, Blitz notes.
If the Milky Way's halo is large enough, it may map out an even bigger halo of dark matter that's believed to surround our galaxy, Blitz notes. Dark matter--exotic, invisible material that would have clumped together much earlier in cosmic history than ordinary, visible matter did--may have served as the scaffolding for the gas and stars that became the Milky Way and all the other galaxies in the cosmos.
The new data could be the last that FUSE acquires for a while. The satellite shut down Dec. 10, 2001, after two of its four reaction wheels failed. Researchers are now trying to find alternative ways to steer it.