We always thought that the real impetus to the theory of 'dark energy' came from the discovery that the expansion of the universe seems to be accelerating. But an article in New Scientist points out that Allan Sandage (Carnegie Observatories, Pasadena) had studied evidence that might have led to the theory of dark energy way back in 1972. Sandage was working with 'peculiar velocities,' deviations in the normal rate of cosmic expansion caused by the gravitational pull between groups and clusters of galaxies. And he had seen that galaxies just outside the Local Group showed velocities that were below what was expected. Fabio Governato of the University of Washington has now plugged dark energy into a computer model of galaxy formation and finds that this force matches nicely with the peculiar velocities for galaxies in regions like the Local Group. The Sandage data plus the new computer model, it can be argued, point to dark energy. You can find an abstract of Governato's study, "The...

Ordinary (or baryonic) matter -- the stuff that you and I and Procyon are made of -- is outnumbered five to one by so-called 'dark matter,' mysterious stuff whose presence can only be inferred from the way galaxies rotate. Some galaxies rotate so fast that, if they were made only of ordinary matter, they would fly apart. So some stronger gravitational force must be involved, even though we can't see what's causing it. Now an international team of astronomers has found a valuable clue in the form of a galaxy that is all but invisible. VIRGOHI21 was found in the Virgo cluster of galaxies some 50 million light years from Earth, and is the first galaxy ever detected that is made up almost entirely of dark matter. Observed by radio telescopes at the University of Manchester and Arecibo (and later studied at the Isaac Newton Telescope in the Canary Islands), the galaxy contains a mass of hydrogen atoms a hundred million times larger than the Sun. The mass rotates, just like a galaxy, but...

Construction of the world's largest scientific instrument is proceeding in the frigid wastes of Antarctica. The initial deployment of what will become the IceCube neutrino telescope involved drilling a 1.5-mile deep hole into Antarctic ice, then installing 60 optical detectors in it that will detect the elusive particles. But that's just the beginning: IceCube demands 70 such holes and 4200 of the volley-ball sized optical detectors. The final telescope will take up a cubic kilometer of ice and capture particles from the edge of the visible universe. What makes neutrinos so interesting is their ability to travel vast distances without deflection or absorption; they seem to pass ghost-like through ordinary matter, and are unaffected by magnetic fields. "Neutrinos travel like bullets through a rainstorm," Francis Halzen, a University of Wisconsin-Madison professor of physics and the principal investigator for the project explains. "Immense instruments are required to find neutrinos in...

A star that apparently had a close encounter with the black hole at the center of the Milky Way is now speeding out of the galaxy at some 1.5 million miles per hour. That's the conclusion of astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA), who say the star is moving fast enough to have achieved galactic escape velocity. "We have never before seen a star moving fast enough to completely escape the confines of our galaxy," said co-discoverer Warren Brown (CfA). "We're tempted to call it the outcast star because it was forcefully tossed from its home." The star is catalogued as SDSS J090745.0+24507; it was apparently a member of a binary system before its close brush with the black hole. According to the scientists' scenario, the companion star was pulled into orbit around the black hole while the outcast star was flung on a trajectory that will take it out of the galaxy entirely. Image: Astronomers at the Smithsonian Astrophysical Observatory have discovered the...

When you hear the word 'baryon,' you can think of neutrons and protons, though the term really covers any subatomic particles that use the strong nuclear force for their interactions. We know a surprising amount about baryons in the early universe, including the fact that a large fraction of their number -- almost half -- cannot be accounted for by current theory. What happened to the missing baryons? A paper in the February 2005 issue of Nature may shed some light on the matter. Using computer simulations of galaxy formation, Fabrizio Nicastro of the Harvard-Smithsonian Center for Astrophysics and colleagues write that the baryons could well be contained in 'warm-hot intergalactic matter' (WHIM), clouds of gas out of which galaxies and galactic clusters first formed. This work was based on observations made by the Chandra X-ray satellite on the quasar Markarian 421 (located in Ursa Major, the Big Dipper). A key player in these investigations was Ohio State associate professor of...

In Blazing Speed: The Fastest Stuff in the Universe, Robert Roy Britt looks at recent studies of a form of matter that moves remarkably close to the speed of light. The material comes in the form of huge jets of hot gas that are ejected from a kind of galaxy called a blazar. Some of these jets attain speeds of 99.9 percent of the speed of light, according to a study presented at the recent AAS meeting by Glenn Piner of Whittier College in Whittier, California. Britt's article gives an overview of Piner's work, but dig deeper at Piner's Web site Quasar Research at Whittier College, where he explains the study's methodology, which used Very Long Baseline Interferometry. The technique combines data from widely separated telescopes to achieve the same angular resolution as a single telescope with a size equal to the maximum separation between the individual dishes. From a news release from Whittier: Blazars are active galactic nuclei -- energetic regions surrounding massive black holes...

The UK's new Wide Field Camera (WFCAM) has just begun operations at the United Kingdom Infrared Telescope site in Hawaii. WFCAM is designed to survey huge swathes of the sky at infrared (heat radiation) wavelengths, and should be able to work with deep sky objects as well as close brown dwarfs and other stars that, although relatively nearby, may have eluded detection. The 'survey' part of its job description means WFCAM is designed for a large field of view; no other infrared camera now operating can equal its range. The early results are spectacular. The two images shown here are among the earliest made by WFCAM. They focus on the area of intense star formation in the constellation Orion, some 1500 light years from Earth. To give you an idea of this telescope's range, the full images it made of this region are 3600 times larger than Hubble's infrared camera. By varying the type of infrared filters, the new camera shows thousands of young stars that would ordinarily be hidden by gas...

Back when I was a kid gawking at images from the Palomar telescope, it seemed that the only way to see farther and better was to build bigger mirrors. We've learned how to do that, of course, but new techniques from adaptive optics to space-borne coronagraphs have made it possible to see things never before revealed. The latest weapon in the astronomers' arsenal is to me the most fascinating; it's the use of computers to combine imagery and tease out new information. The National Virtual Observatory is a case in point, creating the tools needed to maintain interoperating databases. "In a few years it will be easier to "dial-up" a part of the sky than wait many months to access a telescope," according to the NVO's Web site. And now we've got this remarkable image of 30 Doradus, the Tarantula Nebula. 30 Doradus is located in the Large Magellanic Cloud some 170,000 light years from Earth. A small, irregular galaxy that orbits the Milky Way, the LMC seems to be a region of active star...

Astronomers at Paranal Observatory (Atacama, Chile) caught this impressive image of the spiral galaxy NGC 6118, which is located near the celestial equator, in the constellation Serpens (The Snake). Note the bright star-like object indicated by the arrow. This is Supernova 2004dk, first reported on August 1, 2004; it's a Type 1b or 1c supernova captured several days before maximum light. According to the European Southern Observatory, this kind of supernova is apparently the end of a massive star that lost its hydrogen envelope because of transfer of mass in a binary star system before exploding. Excuse the low-res image, but it's hyperlinked to a higher-quality one (click on the image). An ESO press release on several supernova photographs and associated findings is available. Image: A composite colour-coded image of the "grand design" spiral galaxy NGC 6118, at a distance of 80 million light-years. It is based on images obtained with the multi-mode VIMOS instrument on the ESO Very...

Recent analysis on more than 100,000 stars studied by the European Space Agency's Hipparcos satellite showed that about 20 percent of them within 1,000 light years are moving in unusual trajectories. Rather than circular paths around the galactic center, they're moving toward or away from the core. The cause: so-called 'density waves' that compress gas and have a hand in star formation; they also seem to be able to deflect normal stellar motions. But don't count on a stellar near miss to give us an easy way to go interstellar, at least not any time soon. The closest encounter with another star won't occur for another 1.4 million years, when Gliese 710 will pass within 1 light year of the Sun (some 70,000 AU, perhaps within the Oort Cloud of cometary debris). In any case, Gliese 710 does not appear to be one of the stars affected by galactic density waves; its motion around the galactic center seems relatively normal. Barnard's Star is approaching us as well, at a speed of 87 miles...

Very Long Baseline Interferometry combines data from multiple telescopes around the world. Once collated and compared, the data can be processed into images that exceed those available at any of the individual telescope sites. In fact, the resulting image has a resolution equal to that of a telescope as large as the maximum antenna separation. Now becoming available is the digital version -- call it e-VLBI -- where data from the various observatories are routed through the Internet and combined at a center in the Netherlands. The result: real-time long-baseline interferometry. No more waiting as data tapes are shipped around the world to be combined at a central processing facility, a wait that in the past has taken weeks or months. For more, see this Particle Physics and Astronomy Research Council page.

A team of Australian researchers has built an unmanned observatory high on an Antarctic plateau that may provide images nearly the equal of Hubble's. That's the word from Nature, where University of New South Wales associate professor Michael Ashley, co-author of the paper, described the capabilities of the new viewing site. The paper's lead author is Dr. Jon S. Lawrence, a postdoctoral fellow at the University of New South Wales. The location is known as Dome C, 3250 meters above sea level on the Antarctic Plateau, at latitude 75 degrees south. Among its favorable characteristics are low infrared sky emission, dry and extremely cold air, few clouds and low dust and aerosol content. The upshot: much less 'star jitter.' All of these factors make the site, which is 400 meters higher than the South Pole, far better for viewing than the location of instruments currently in place in Chile, Hawaii and the Canary Islands. Having established the superiority of Dome C, the team now argues for...

NGC 6543 is called the Cat's Eye Nebula; it was one of the first planetary nebulae to be discovered. This gorgeous view from Hubble shows that it is also one of the most complex nebulae ever studied. You're looking at a Sun-like star at the very end of its life, losing its outer gaseous layers to create concentric clouds in ways that are still mysterious. Each bright ring is actually the edge of a spherical bubble of gas. Hubble used its Advanced Camera for Surveys (ACS) to make this image.