What we know about dark energy can be pretty much summed up in these words: "We know that it dominates the universe. In fact, it comprises an estimated 73 percent of the universe, while so-called dark matter accounts for 23 percent, and matter of the familiar kind — the stars, galaxies, all known life — comprises only four percent." The speaker is David Lambert, a University of Texas at Austin astronomer and the director of UT's McDonald Observatory. And it has always seemed to Centauri Dreams that these numbers -- what we know and see of the universe is no more than four percent of the total -- should inspire a certain humility. Yes, we know more than those before us, but just how far we are from comprehending the nature of 'reality' seems obvious. There are real reasons to wonder whether the human mind is capable of ever understanding ultimate reality. Perhaps a quote from Martin Rees about the beginning of the universe is appropriate: "There are lots of ideas of what...

Any guesses as to what the most powerful event in the universe is? According to a team of NASA scientists working with breakthrough computer modeling techniques, it's the merger of two massive black holes. When the event occurs, gravitational waves muscle out from the collision site at the speed of light. Each such merger generates more energy than all the stars in the universe combined. John Baker at Goddard Space Flight Center is lead author of the paper, which appears in the March 26 issue of Physical Review Letters. Of course, although the modeling works (via the largest astrophysics calculations ever performed on a NASA supercomputer), one problem is that gravitational waves have yet to be detected directly. But there is reasonable expectation that that will change through observations from the Laser Interferometer Gravitational-Wave Observatory and the joint NASA/ESA Laser Interferometer Space Antenna, a proposed mission that should be able to do the job. Einstein's theory of...

The image below is merely a marker -- it leads to something far grander. For what you're looking at is a small part of a vast image of 'empty' space, made with over 64 hours of observations using the Wide-Field Camera on the 2.2-meter La Silla telescope in Chile. Rather than linking to a simple enlargement of this fragment, I've linked instead to a zoomable imaging tool set up by the European Southern Observatory, where you can roam the galaxies in any direction you please in what is called the Deep 3 Field. Image (click to use the zoom tool): Part of the Deep 3 Deep Public Survey field, showing the brightest galaxy in the field ESO 570-19 (upper left) and the brightest star UW Crateris. This red giant (upper right) is a variable star that is about 8 times fainter than what the unaided eye can see. An 'S'-shaped ensemble of galaxies is also visible in the lower part of the picture. Credit: European Southern Observatory. The Deep 3 field is located in what appears to the naked eye as...

What is 200,000 light years across, 153 million light years from Earth, and invisible to normal telescopes? The answer is, a newly-discovered 'dark galaxy', one of a number of new galaxies identified by a project called the Arecibo Galaxy Environment Survey (AGES). The enigmatic dark galaxy is located near NGC1156, a normal enough (though irregularly shaped) galaxy near the constellation Aries. Dark galaxies are made up primarily of gas and dark matter, making the job of finding them problematic. After all, without stars or other radiation sources, such a galaxy remains hidden from normal observation. But the AGES survey focused on hydrogen, for the interactions between hydrogen atoms in gas clouds within the galaxy create emissions at the 21 cm neutral hydrogen wavelength. Led by Jonathan Davies (Cardiff University), the AGES team used Arecibo's giant radio dish in conjunction with ground and space-based telescopes to pick up the dark galaxy's unique signature. Robbie Auld (also at...

Centauri Dreams follows studies about dark matter with great interest, given the mysterious nature of the stuff and the fact that it apparently has so much to say about how galaxies form. One way to get a handle on dark matter is to study the positions and velocities of stars in the galaxies themselves, thus learning what forces must account for them and how unseen matter may be affecting where they travel. A new study in this vein has now uncovered a 'river' of stars of considerable size that arcs over the disk of the Milky Way. "We were blown away by just how long this thing is," says Carl Grillmair, an associate research scientist at the California Institute of Technology. "As one end of the stream clears the horizon this evening, the other will already be halfway up the sky." Image (click to enlarge): On an evening in early April, the new stream rises 45 degrees from the eastern horizon, passing just under the bowl of the Big Dipper. The North Star Polaris is at far left."...

Inflation has always been hard to get one's thoughts around. If nothing can travel faster than light, then how can the universe itself have expanded from submicroscopic to astronomical size in mere moments? The solution -- that while nothing can move through space faster than light, space itself knows no such restriction -- is still unsatisfying, for we don't understand how inflation happens, or how it may still affect the accelerating expansion of today's universe. The best recent work on these matters has been done through analysis of data from the Wilkinson Microwave Anisotropy Probe (WMAP), using three years worth of observations of the cosmic background radiation. The temperature of that afterglow tells us much about the universe's age and how it developed, and WMAP can read such temperature fluctuations down to grades finer than a millionth of a degree. The new measurement gives us clues not only about that crucial first trillionth of a second, but also about how and when the...

New Scientist is running an interesting piece by Zeeya Merali on the the theories of George Chapline (Lawrence Livermore National Laboratory) and Robert Laughlin (Stanford University), which attempt to explain both dark matter and dark energy in a way that would revise our view of black holes. The duo and their colleagues have examined the collapse of massive stars in relation to quantum critical phase transitions in superconducting crystals. During such transitions, electron fluctuations slow down, suggesting what might happen on the surface of a collapsing star. From the article: [Chapline] and Laughlin realised that if a quantum critical phase transition happened on the surface of a star, it would slow down time and the surface would behave just like a black hole's event horizon. Quantum mechanics would not be violated because in this scenario time would never freeze entirely. "We start with effects actually seen in the lab, which I think gives it more credibility than black...

A new seven-pixel radio 'camera' installed on the 300-meter Arecibo radio dish two years ago this April has brought extraordinary new sensitivity to the huge radio telescope. Called the Arecibo L-Band Feed Array (ALFA), the system of detectors is being used to image large areas of sky at a much faster rate than before, while searching for tricky time-variable phenomena like pulsars. The latter are rapidly spinning neutron stars that are the result of supernovae. Where the Arecibo upgrade impacts interstellar flight studies is in what it may tell us about some of the most crucial subjects in cosmology. Stephen Torchinsky, who is the former ALFA project manager, has this to say: "ALFA is going to discover probably 1,000 new pulsars that we haven't seen yet," said former ALFA project manager Stephen Torchinsky. "The expectation is that we're going to find some exotic objects. We could use these systems to test the limits of the theory of relativity -- and at the most extreme cases, to...

The Hubble Space Telescope's new image of the Pinwheel Galaxy is worth lingering over -- the thumbnail below can only suggest its power, so do click on it to see a larger JPEG, and click here to gain access to still larger versions -- the fullsize original is 455 MB worth of data! The Pinwheel is spiral galaxy Messier 101; its image was assembled from 51 separate Hubble exposures along with elements from ground-based photographs. The final composite image in its glorious entirety works out to a colossal 16000 x 12000 pixels. If you do download the full original, you'll find all kinds of hitherto unseen objects. K.D. Kuntz at Johns Hopkins catalogued almost 3000 previously undetected star clusters in it. But to me this image is one of those perspective-makers that get us mindful, on days when we need it, of the scale of things cosmic. The Pinwheel is 170,000 light years across (that's close to twice the size of the Milky Way), and it contains about a trillion stars. The extraordinary...

About 440 million light years away in the direction of the constellation Aries is the source of a curious gamma ray burst. Curious because it lasted for nearly 2,000 seconds, while most gamma ray bursts last anywhere from milliseconds to tens of seconds. Moreover, the burst is dimmer than one would expect, which makes scientists believe we may be viewing the event off-axis, although there is no consensus on the matter as yet. Is GRB 060218 a new kind of explosion, a precursor to a supernova? The blast was detected on February 18, and since then satellite and ground-based telescopes have been focused on the area. There has never been a gamma ray burst detected this close to Earth -- in fact, this one is 25 times closer than the average. A team in Italy believes a supernova may be building here, while the European Southern Observatory's Very Large Telescope has picked up the kind of optical brightening that also suggests the supernova solution. Image: The collapsing star scenario that...

As if we needed another reminder of how much we have to learn about the galaxy, now comes word that an entirely new kind of cosmic object has been identified. Working with the Parkes radio telescope in eastern Australia, a multi-national team has found a type of neutron star that is all but undetectable most of the time, while occasionally releasing a single burst of radio waves. The time interval between bursts has thus far been observed to vary between 4 minutes to 3 hours. Detection of these objects -- called Rotating Radio Transients -- is a formidable challenge due to the sporadic nature of their emissions. "These things were very difficult to pin down," says Dr Dick Manchester, a member of the research team and a veteran pulsar hunter who works for CSIRO, Australia's Commonwealth Scientific and Industrial Research Organisation. "For each object we've been detecting radio emission for less than one second a day. And because these are single bursts, we've had to take great care...

I wouldn't dream of trying (nor would I be able) to explain string theory -- for a popular treatment of that, see Brian Greene's The Fabric of the Cosmos (Knopf, 2004). But I do know that ideas like string theory and supersymmetry arose to help us unify the world of quantum mechanics and that of general relativity. Extreme energies can unite electromagnetism and the weak force (think radioactive decay). The next generation of particle accelerators may unify both with the strong force (atomic nuclei bonding). But where will we get the energies needed to explore the unification of the quantum world with gravity? The answer may come from outside the galaxy. Researchers at Northeastern University and the University of California, Irvine think that deep space neutrinos colliding with protons can release energies that test string theory. The notion is being examined in the AMANDA project, a neutrino detector at the South Pole. Although few high-energy neutrinos have been detected so far,...

The first data from the Radial Velocity Experiment (RAVE) have just been released, marking the first of what promise to be numerous contributions from this extraordinary project. The study of dark matter in particular will be immeasurably enhanced by this spectroscopic survey that measures the radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity) of up to one million stars near the Sun. The new data cover the first year of RAVE's operations at the Anglo-Australian Observatory (New South Wales). Using the 'six degree field' multi-object spectrograph on the 1.2-m UK Schmidt telescope there, the team can get spectroscopic data on 150 stars at a time. Thanks to RAVE, we now have data on line-of-sight motions of 25,000 stars, along with a rich lode of information on their brightness and color. And here's an interesting note: one of the astronomers working on RAVE is George Michael Seabroke, whose great-great-grandfather, George Mitchell Seabroke,...

As physicist Clifford Johnson notes in a Cosmic Variance post, Sunday the 29th was the anniversary of a powerfully symbolic event. As Johnson says: "On January 29th 1931, Edwin Hubble took Einstein up Mount Wilson to see the famous 100 inch telescope where Hubble had done at least two revolutionary things (with the aid of Henrietta Leavitt's remarkable work on variable stars): (1) He demonstrated that the Milky Way Galaxy, where we live, is not the entire universe, but just one of many galaxies, and (2) He confirmed (ahem, not discovered) that the universe was expanding and (with Humason…who started out as the janitor at the observatory) quantified it in what we now call "Hubble's Law". And don't miss Johnson's wonderful Walk Up Mount Wilson, complete with photographs, further background and the story of a wonderful morning hike. For a man who long resisted writing for a weblog (and for eloquent reasons), Johnson's posts have become simply indispensable.

What would fling a star out of the galaxy at over 1 million miles per hour? Warren Brown (Harvard-Smithsonian Center for Astrophysics) and colleagues have some thoughts on that, based on their own and other studies in Europe that have so far identified five stellar exiles, a group now called 'hypervelocity stars.' "These stars literally are castaways," says Brown. "They have been thrown out of their home galaxy and set adrift in an ocean of intergalactic space." Brown's team went after galactic escapees in a targeted manner, using computer models that showed such stars would be forced into their current trajectories by interactions in the galactic core. The idea is this: a binary star swings too close to the black hole at the galaxy's center. Its gravity tears the duo apart, in the process capturing one of the stars and ejecting the other one at high velocity. Evidence exists not only in the exiled stars themselves but in the other half of the binary pairs that once contained them;...

Catching up on news from the recently concluded American Astronomical Society meeting, I want to be sure to mention RAVE -- the Radial Velocity Experiment -- which is an all-sky spectroscopic survey of as many as a million stars passing near the Sun. Observations of stars in other galaxies show that only dark matter can explain their movement since there is not enough visible mass to keep them gravitationally bound. Early results from RAVE confirm that dark matter dominates the mass of the Milky Way as well. The survey will help to firm up our picture of the Milky Way's own dark matter and, by extension, its mass. "One important early application of RAVE aims to measure just how much stuff there is in our Milky Way galaxy — the collection of stars, gas and dark matter that is the home of our sun," said Rosemary Wyse (Johns Hopkins). "Newton's Law of Gravity allows us to figure out from the orbital motions of stars how much mass is holding them together. Faster motions need more...

If you go back 35 years, what we now call 'dark matter' was even more controversial than it is today. What was the stuff, if it really existed, and should we consider it a dim version of what we see around us elsewhere in the galaxy? Or was it something truly exotic, not yet explicable but traceable in the effects it had on galactic evolution? Whatever it was, we seemed to need it to explain a key observation: stars in the outer regions of the galaxy move faster than they ought to based on the observed mass of stars in the Milky Way. Today we still don't know what dark matter is, but an intriguing new study again reminds us of its extensive influence. As reported at the ongoing meeting of the American Astronomical Society, the Magellanic Clouds -- a pair of galaxies that orbit the Milky Way -- seem to be interacting with the galaxy's dark matter, creating a previously observed warp in the galactic disk. Using a new map of hydrogen gas emissions, researchers have found that the motion...