Are elliptical galaxies influenced by a halo of dark matter? The theory has been accepted until recently through observation of the gravitational effects apparently caused by such matter. But 2003 findings (Romanowsky et al., Science 301, pp. 1696-1698) turned up little evidence for dark matter in such galaxies. Now a different explanation for those observations has surfaced, one that seems to rescue the dark matter concept. That's good news, because dark matter ought to be there. From a University of California at Santa Cruz press release: "A dearth of dark matter in elliptical galaxies is especially puzzling in the context of the standard theory of galaxy formation, which assumes that ellipticals originate from mergers of disk galaxies," added Avishai Dekel, professor of physics at the Hebrew University of Jerusalem and first author of the Nature paper. "Massive dark matter halos are clearly detected in disk galaxies, so where did they disappear to during the mergers?" The dark...

A strange blue light near the core of the Andromeda Galaxy promises to tell us much about black holes and the behavior of objects near them. First spotted in 1995 by the Hubble Space Telescope, the blue light was thought to emmanate from a single, massive star, or possibly an exotic source of energy that was little understood. But new spectroscopic observations show that the light is actually made up of 400 stars packed into a disk only one light year across. Now this is a very strange finding, for these young stars -- thought to be on the order of 200 million years old -- are revolving around the black hole at the center of Andromeda so closely that they should be torn apart. How could gas and dust coalesce to form stars in such an environment? Mysteries, of course, are just what astronomers like to find; they often lead to enough new data to revise earlier theories and produce more complete explanations. Image: This artist's concept shows a view across a mysterious disk of young,...

Astronomers have detected the most distant explosion ever observed, finding the afterglow of a gamma ray burst that marked the end of a massive star and the probable birth of a black hole. Named GRB 050904, the object's redshift is 6.29, pegging it as roughly 13 billion light years from Earth. The universe itself is now thought to be 13.7 billion years old, so the burst comes from the era when stars and galaxies had only recently formed. Gamma rays force astronomers to work fast. Most bursts are sudden events, lasting only about ten seconds, which is why alerts are sent out whenever NASA's Swift satellite detects one. But while the bursts are brief (and don't even penetrate the atmosphere), the afterglow of these mammoth explosions can linger long enough to be observed by instruments on the ground. Which is what UNC-Chapel Hill astronomer Daniel Reichart immediately set out to do. As telescopes around the globe locked onto the afterglow, Reichart's team was able to measure the...

What would give a neutron star the kind of push that would send it out of the galaxy at over 1000 kilometers per second? Nobody knows, but data from the Very Long Baseline Array, a system of radio telescopes spanning 5,000 miles with locations from Hawaii to the US Virgin Islands, have revealed just such an object, and have allowed astronomers to measure its motion with unprecendented accuracy. "This is the first direct measurement of a neutron star's speed that exceeds 1,000 kilometers per second," said Walter Brisken, a National Radio Astronomy Observatory astronomer. "Most earlier estimates of neutron-star speeds depended on educated guesses about their distances. With this one, we have a precise, direct measurement of the distance, so we can measure the speed directly," Brisken said. The star's speed translates to 670 miles per second, numbingly fast, but even at these speeds, an object like this would still take 1200 years to cross the 4.3 light years that separates us from the...

Getting an overview of our own galaxy is tricky work. After all, we live in one of its spiral arms, so we see through a swarm of surrounding stars that mask the true galactic shape. Astronomer Ed Churchwell at the University of Wisconsin describes the effort as an attempt to define the boundaries of a forest from a vantage point deep within the woods. But when it comes to stars, changes of wavelength can help. Working in the infrared, the Spitzer Space Telescope can see through intervening clouds of interstellar dust to the Milky Way's dazzling center. Churchwell and team's latest work is a survey of 30 million stars using Spitzer data that has revealed details about what the Milky Way looks like from the outside. The picture, as shown in the illustration, is a bit different than we had been led to expect. For cutting through the galactic center is what Churchwell calls a "long central bar." Other galaxies have been observed with stellar bars -- large bodies of gas, dust and stars....

Quasars remain a mystery in several key areas. These massive black holes that live at the center of distant galaxies are voracious, and we know that they can consume the equivalent mass of a thousand stars every year. Surrounded by rings of dust and gas, they light up as they pull in this material to become the fantastically bright objects we observe not just in visible light, but in infrared and x-ray light as well. And that's the problem. To get a count on how many quasars are out there, astronomers have measured the cosmic x-ray background, where quasars outshine everything in the universe. It should be possible to predict how many quasars there are using this method, but it doesn't seem to work. In fact, the estimated number derived from the x-ray background doesn't match the figures derived from x-ray and optical observations of known quasars. In other words, something is hiding many of the universe's quasars from our view. Now the Spitzer Space Telescope has used its infrared...

An object called CSL-1 may have a lot to say about the nature of the universe. The odd thing about this double source -- evidently a pair of galaxies -- is that both galaxies appear identical. They share a common redshift, a similar shape, and their luminosity profiles match that of two giant elliptical galaxies. Moreover, the spectra of the two components seem to be identical. Is this a double image of the same galaxy? If so, then something tantalizing is going on. String theory, the latest and still evolving explanation for how the universe works, says that there should be gigantic counterparts to the strings that make up the fundamental particles of matter. A single-dimensional string millions of light years in length -- think of it as a thread of energy -- is one prediction made by string theory, and CSL-1 may indicate the presence of just such a cosmic string. For a cosmic string would be so energetic that it would warp spacetime around it, with the effect that a string lying...

When theories aren't borne out by observation, the problem just may be the size of the dataset. As witness recent work on gravitational lensing, that phenomenon where light is distorted and magnified by the gravitational pull of galaxies and other matter as it makes its immense journey from distant quasars to the Earth. Such lensing has been observed for over a decade, but just how the light is magnified, and on what scale, has until now been an elusive question. And answers to it haven't seemed to fit the standard model of cosmology, one in which visible galaxies represent only a small part of the mass of a universe seemingly filled with dark matter. Now researchers from the Sloan Digital Sky Survey (SDSS) have been able to perform a large-scale study of such magnification, and their theories do gibe with the standard model. The team was able to measure the brightness of some 200,000 quasar sources and determine the precise magnification caused by gravitational lensing. The new...

Hard to believe that it was fully fifteen years ago today that the Hubble Space Telescope was placed into orbit from the Space Shuttle Discovery. Hubble's list of achievements has been outstanding, from detecting proto-galaxies whose light was emitted less than a billion years after the Big Bang to providing data that helped astronomers confirm the age of the universe, now calculated at some 13.7 billion years. And don't forget the extraordinary moments closer to home, such as the space telescope's views of comet Shoemaker-Levy 9, the famous 'string of pearls,' hitting Jupiter in 1994. Hubble's 700,000 images have provided views up to ten times sharper than any previous telescope could offer. The image above, a part of the Eagle Nebula, shows a tower of cold gas and dust being shaped by the light of hot new stars. It was taken with Hubble's Advanced Camera for Surveys (ACS), providing a picture so sharp that, at full resolution, the image could be blown up to the size of a billboard...

More on the 'fine structure constant,' that fundamental number that seems to be crucial to our understanding of electromagnetism, and therefore the way the universe works. Our recent story on Michael Murphy and his Cambridge team discussed findings from the Keck I telescope on Mauna Kea that suggested subtle changes to the value of the fine structure constant since the earliest era of the universe. But those findings remain highly controversial, as was apparent on Monday the 18th. That was the day that astronomer Jeffrey Newman (Lawrence Berkeley National Laboratory) presented data from the DEEP2 redshift project, a five-year survey of galaxies more than seven light years away. Speaking at the annual meeting of the American Physical Society (APS) in Tampa, Newman said his team's results showed no change to the constant within one part in 30,000. "The fine structure constant sets the strength of the electromagnetic force, which affects how atoms hold together and the energy levels...