Dark matter has to be made up of some sort of elementary particle, but we know astoundingly little about it. Its existence can be inferred from its necessary effects -- something we can 't see seems to be holding galaxy clusters together, because the gravity from the stars we do observe in them isn't sufficient to do the job. That makes gathering any evidence for dark matter's behavior -- indeed, for its very existence -- a crucial goal for astrophysicists. And today we have the strongest supporting evidence yet that dark matter is real. The work comes via the Hubble Space Telescope, used by a team of astronomers to locate what appears to be a ring of dark matter in the cluster ZwCl0024+1652, some five billion light years from our Solar system. The ring is 2.6 million light years across, and this detection appears to be unique. Says M. James Jee (Johns Hopkins): "This is the first time we have detected dark matter as having a unique structure that is different from the gas and...

We've seen recently how difficult it can be to pin down the age of a star. Even the Alpha Centauri system is problematic, with age ranges for Centauri A and B varying from slightly less than four billion years to as many as eleven (depending on which star we're talking about, and which of several methods was used for the calculation). But one thing that helps with stars that are older than the ordinary is the chemical composition of the star in question. "Surprisingly, it is very hard to pin down the age of a star," says Anna Frebel (University of Texas), "although we can generally infer that chemically primitive stars have to be very old." Frebel's work has led her to a star that is old indeed. It is HE 1523-0901, now pegged thanks to the work of Frebel's team at the astounding age of 13.2 billion years, meaning it would have formed not all that long after the Big Bang. The researchers were able to study radioactive elements in the star to create a precise calculation. A...

The thought that Eta Carinae, a star at least 100 times more massive than the Sun, is a ticking time bomb seems to infuse much of the coverage about the huge supernova recently observed by the Chandra X-ray Observatory. And you can see why. Big explosions are marketable, which is why it sometimes seems that one way to categorize many of today's movies is by how many cars were blown up during the making of them. When you're talking about something a hundred times larger than the typical supernova, you're going to get attention. What if a star 100 times the size of the Sun -- or larger -- goes off in our neighborhood? Adding to the comparison is the fact that the supernova, known as SN 2006gy, seems to have expelled a large amount of material before the catastrophe. Eta Carina also shows signs of expelling mass, and it's 7500 light years away, vs. the 240 million light years of SN 2006gy. Close enough to cause us problems? I don't know the answer, but it does seem clear that one result...

In light of yesterday's post on black holes and their role in spreading heavy elements through the cosmos, the news out of Los Alamos provides an additional fillip of controversy re these enigmatic objects. A research team led by Philipp Kronberg has also been looking at clouds in deep space and their association with black holes, though what Kronberg's team has identified is a distinctive object indeed. It's a cloud of plasma more than six million light years across, one that may provide evidence for the role of black holes in triggering cosmic rays. Here's Kronberg on the subject: "One of the most exciting aspects of the discovery is the new questions it poses. For example, what kind of mechanism could create a cloud of such enormous dimensions that does not coincide with any single galaxy, or galaxy cluster? Is that same mechanism connected to the mysterious source of the ultra high energy cosmic rays that come from beyond our galaxy? And separately, could the newly discovered...

One of the problems of explaining the universe we live in is the presence of heavy elements. After all, the cosmos was a simple matter right after the Big Bang, with hydrogen and helium its only ingredients. Creating the heavier elements required stars, the model being that their eventual death in massive supernova explosions scattered 'star stuff,' as Carl Sagan liked to call it, throughout the universe, leading to the wide range of elements we see today and, of course, to life. New research is adding black holes to that picture, seeing them as influential in spreading these same elements far and wide. The supermassive black hole at the center of the galaxy NGC 4051 is at the center of investigation. A research team led by Yair Krongold (Universidad Nacional Autónoma de México) has found that gas is escaping the black hole from a source closer to its Schwarzschild radius than previously thought. In the case of NGC 4051, that radius -- the point beyond which nothing can...

Cepheid variables are simply indispensable. It was Harvard's Henrietta Leavitt who, in 1912, discovered a relationship between the cycle of variable brightness in these stars and their luminosity. With a classic Cepheid, the longer the period of the star, the greater its intrinsic brightness. That sets up the method: Determine the period of the variable, check its apparent magnitude with the absolute magnitude corresponding to that period, and you can measure the distance. The relevant term is 'standard candle.' But put telescopes into space and you can refine these measurements, as studies of Cepheid variables with the Hubble Space Telescope have now shown. That's helpful because we'd like to know the Hubble constant -- the universe's rate of expansion -- as accurately as possible, and Cepheids are one of our best tools. To fine-tune the Cepheid method, a team from the University of Texas at Austin has directly measured the distance to ten Cepheid variables, using Hubble to trace...

When you can work with a deformable mirror that compensates for atmospheric distortions, wondrous things can emerge. The Gemini Observatory (Mauna Kea, HI) used such a system coupled with a laser guide star as reference to produce an image of fast-moving 'bullets' of gas and the wakes they leave as they move through molecular hydrogen in the Orion Nebula. Some 1500 light years away from Earth, this stellar nursery has much to teach us about the birthing of stars. What we're looking at appears to be the movement of clumps of gas that have been ejected from within the nebula by some kind of violent event. They're moving outward at about 400 kilometers per second, vast gaseous agglomerations roughly ten times the size of Pluto's orbit around the Sun. At the tip of each clump you can see the blue glow of iron atoms shock-heated by friction with the surrounding cloud. The long wakes of their motion appear as orange smudges in the image below. Image: This composite image at infrared...

Out near the end of the Big Dipper's handle is a strip of sky the width of two full moons that looks all but empty to the naked eye. But take a closer look, as the ongoing AEGIS survey is doing across the electromagnetic spectrum -- from radio and infrared through visible light up to the x-ray regions -- and you'll find more than 150,000 galaxies. AEGIS is examining galaxies up to 9 billion years back in time. The name stands for the All-wavelength Extended Groth Strip International Survey, and when I first wrote about it, I didn't have this link to the nineteen papers about the survey that will appear in the Astrophysical Journal Letters in the spring. What's exciting about the survey is its sheer breadth -- no other region of the sky this large has been examined quite so intensively. Cosmologist Jeffrey Newman (Lawrence Berkeley National Laboratory) puts it this way: "We have looked at this patch of sky with every possible telescope, at wavelengths covering nine orders of magnitude...

By analyzing a carefully selected set of 544 distant galaxies, researchers are beginning to learn how galaxies take their mature forms, becoming the glorious objects we see today. Sandra Faber (University of California at Santa Cruz), puts it this way: "We are now well on our way to seeing how galaxies evolved over the last half of the age of the universe. This work is not over, but the outlines of a theory are emerging." The galaxies in question weigh in with redshifts in the range of 0.1 to 1.2, which translates to 'look-back' times of between 2 and almost eight billion years. These adolescent galaxies are far more disordered than nearby ones, but it turns out that the relationship between a galaxy's mass and the orbital speed of its stars and gas is consistent over different types of galaxy and over billions of years of galactic evolution. In other words, the more massive a galaxy is, the faster the stars and gas inside it move. That analysis includes a 'dispersion component' that...

With all the press being given to the Large Hadron Collider under construction at CERN, it's interesting to see that the black hole believed to exist at the Milky Way's center -- the object called Sagittarius A* -- seems to be going it one better. The LHC will be able to accelerate protons to seven trillion electronvolts. But Sgr A* evidently slings nearby particles even more energetically, reaching the 100 trillion electrovolt level. Not bad for an object considered to be relatively inactive compared to black holes in other galaxies, and one explanation for the hugely energetic gamma rays streaming from that part of our galaxy. The study in question, reported in Astrophysical Journal Letters, sees the black hole as a cosmic particle accelerator, a region where powerful magnetic fields push particles to extraordinary energies. At play is the interstellar gas extending roughly ten light years from the black hole. Fuvio Melia (University of Arizona) calls Sgr A* "...one of the most...

If dark energy is pushing the universe apart at an accelerating clip, when did its effects begin to be felt? One way to study that question is through the Cosmic Microwave Background, whose infinitesimal variations in density and temperature give us an idea of what was happening a scant 400,000 years after the Big Bang. We should be able to find information in the CMB about how dark energy affected the formation of galaxy clusters by comparing CMB evidence against what we see in these clusters today. And that makes 'first light' at the National Science Foundation's South Pole Telescope a noteworthy event. The 75-ft tall telescope has been under assembly and testing since November, and its February 16 test run was a success. Now the pole's cold, dry air will allow long-term Earth-based study of the CMB with little interference from water vapor. The Sunyaev-Zeldovich effect, which distorts CMB radiation as it encounters the gases in intervening galaxy clusters, will help scientists...

The night sky has always been a kind of time machine, allowing us to look farther into the past the deeper we look into space. But the heavens are also a time machine in another sense -- by looking carefully, we can find stellar systems in almost every stage of development. We recently saw an example in the Helix Nebula, an object that suggests what our Solar System may look like in five billion years, after the Sun has gone into its red giant phase and then collapsed into a white dwarf. Now have a look at the Sun as it may have been five billion years in the other direction, back when it was coalescing out of its own primordial materials. The Pillars of Creation image taken by Hubble has become iconic, a majestic, breathtaking vista of a star-forming region in M16, the Eagle Nebula. Below, we see a Hubble image of the Pillars overlaid with Chandra X-ray Observatory data showing infant stars being born. Note the bright x-ray sources, most of which are young stars. Much harder to see...

Understanding dark matter, a major goal for cosmology, comes down to figuring out how normal matter interacts with its mysterious counterpart. A vital part of this work may be the objects called dwarf spheroidal galaxies, surely among the most bizarre agglomerations every observed. For current thinking (based on mass-to-light ratios) is that a dwarf spheroidal may be a galaxy composed almost entirely of dark matter. And if that's hard to imagine, consider the problem of researchers trying to observe such objects. A dwarf spheroidal is all but devoid of gas and contains few stars, its normal (baryonic) matter having been stripped away by interactions with larger galaxies. In fact, these ghostly galaxies seem to need larger galaxies in their proximity to form, according to new work by Stelios Kazantzidis (Stanford Linear Accelerator Center), Lucio Mayer (Swiss Federal Institute of Technology) and collaborators. Working with supercomputer simulations, the Kazantzidis team constructed a...

To see heat, you'd better be cold. In space, at least, because when you're looking in infrared wavelengths, the heat of your instrumentation can overwhelm the image you're trying to get. Infrared light is hugely useful, especially when it lets us see through clouds of dust to what lies beyond. Take a look at the image below, which penetrates the dust to show stars in the center of the Milky Way. I ran into it thanks to a post on QUASAR9 and have been musing about spacecraft cooling ever since. Image: A mosaic of many smaller snapshots, the detailed, false-color image shows older, cool stars in bluish hues. Reddish glowing dust clouds are associated with young, hot stars in stellar nurseries. The galactic center lies some 26,000 light-years away, toward the constellation Sagittarius. Credit: Susan Stolovy (SSC/Caltech) et al., JPL-Caltech, NASA. The Spitzer Space Telescope, which caught this image with its infrared cameras, has to be cooled to near absolute zero (-459 degrees...

Looking at the beautiful swirl of a spiral galaxy, it's hard to imagine how much we're not seeing. But current studies indicate that dark matter in a typical galaxy outweighs the stars in it by ten to one. That's the conclusion of astronomer Michael Strauss (Princeton), who has been working on how the dark matter halos of such galaxies cluster. Combine those calculations with the visible information provided by quasars and you can say something about the mass of the halos. This is fascinating work indeed, using Sloan Digital Sky Survey data that reveal quasar superclusters divided by vast regions of empty space. The quasars themselves are bright concentrations of gas falling into supermassive black holes at the center of galaxies. And it's clear they're embedded in massive concentrations of dark matter. Says Strauss: "We can't observe the dark halos directly, but we know from theoretical calculations how they should cluster with one another. By measuring the clustering of the...

With its Wide Field Planetary Camera 2, Near Infrared Camera Multi-Object Spectrograph (NICMOS), and Fine Guidance Sensors still operational, the Hubble Space Telescope isn't exactly blind. But the loss of the Advanced Camera for Surveys would be a serious one, and the bad news is that the next servicing mission, scheduled for mid-2008, probably won't be able to fix the problem. ACS lived out its five year operational life but dazzling vistas like the Ultra Deep Field make us yearn for more. Hubble's other instruments are still doing good science. Recall that the UDF itself is actually made up of images from the ACS and NICMOS, leading Centauri Dreams to believe that many observational programs will go forward after adjusting to the change in instrumentation. As always, we make a virtue of necessity, a phrase first recorded by Chaucer that resonates even now in the realm of deep space exploration. Meanwhile, we receive more positive news from the testing of the James Webb Space...

It took six years to develop the design for the 'microshutters' that will fly aboard the James Webb Space Telescope. They will work with its near infrared spectrograph to screen out light from foreground objects. The advantages are enormous: The Webb telescope will be able to adjust its light mask with exquisite precision, something that previous technologies could not achieve to anywhere near this level of performance. We're talking thousands of tiny shutters -- 62,000 to be exact -- each measuring 100 by 200 microns, arranged in four identical grids. They'll function in front of an eight million-pixel detector, allowing only the light from the specific areas under observation to reach the instrument. Moreover, the new technology greatly widens the efficiency of the instrument in terms of observational time. Says Harvey Moseley (principal investigator for the microshutter at GSFC): "The microshutters provide a conduit for faint light to reach the telescope detectors with very little...

The mammoth black hole Sagittarius A* isn't the only interesting thing near the center of our galaxy. The European Space Agency's Integral observatory, working with gamma rays, tracks about eighty high-energy sources in the area. About ten of those closest to the galaxy's center had faded when Integral performed a series of observations last April. A mysterious force? Hardly. "All the sources are variable and it was just by accident or sheer luck that they had turned off during that observation," says Erik Kuulkers of ESA's Integral Science Operations Center. Fair enough, and useful for astronomers, who were able to use the sudden quiet to look for still fainter sources, and to set limits on the brightness of the x-ray binaries involved. These consist of two stars orbiting each other, one a normal star, the other a collapsed object -- a white dwarf, neutron star or black hole. The compressed star pulls off gaseous material from its companion, heating it to a million degrees...

Most stars in the universe were evidently formed in stellar nurseries like the Tarantula Nebula, shown in the spectacular image below. I've been wanting to shoehorn this item into our pages for a couple of weeks now but always wound up having it preempted by other news. Nonetheless, this look at the complex known as 30 Doradus is well worth pondering as we move into a new year of interstellar studies. It's based on data collected through four filters using the Wide Field Imager on the European Southern Observatory's 2.2-m instrument at La Silla (Chile). Image (click to enlarge): One square degree image of the Tarantula Nebula and its surroundings. The spidery nebula is seen in the upper-centre of the image. Slightly to the lower-right, a web of filaments harbours the famous supernova SN 1987A. Many other reddish nebulae are visible in the image, as well as a cluster of young stars on the left, known as NGC 2100. Credit: Observations carried out by João Alves (Calar Alto, Spain),...