When we talk about the diameter of the Milky Way, it's usual to cite a figure of about 100,000 light years. But the much more diffuse halo of stars surrounding the galaxy actually extends almost twice as far. You would expect to find more or less the same situation in other galaxies, but new observations of the giant galaxy M87 have turned up a surprising fact: Its halo of stars is much smaller than expected. It's true that the halo is three times the size of that around the Milky Way, but its diameter of a million light years is still much smaller than anticipated given the size of the parent galaxy. Mysteries like this seem just the thing for the weekend, so consider the possibility, raised in the paper on this work, that the truncated halo is the result of a collapse of dark matter in the Virgo Cluster, where M87 resides. The Virgo Cluster is approximately 50 million light years from us and contains hundreds of galaxies of all descriptions, including spirals like the Milky Way....

While we're thinking about space telescopes like the aging but potentially repairable Hubble, let's not forget the launch now scheduled for Thursday from the Guiana Space Centre in Kourou. The European Space Agency's Herschel instrument will be lifted into an orbit 1.5 million kilometers from Earth, stationed at the second Lagrange point (L2) so that Sun, Moon and Earth can all be hidden behind a sunshade to afford the instrument a clear view without disturbance from its celestial neighbors. Image: About 0.5 hours after launch, Herschel separates from the launcher upper stage and starts its cruise to L2 (the second Lagrangian point), situated at about 1.5 million kilometers from Earth. Credit: ESA/D. Ducros, 2009. Along with Herschel goes Planck, also scheduled for the L2 point (the two satellites will separate shortly after launch and reach L2 independently). Herschel is the largest infrared telescope ever launched, with a 3.5-meter primary mirror made of silicon carbide that is...

With all eyes on the mission to service the Hubble telescope, it's fascinating to see that technology created for the James Webb Space Telescope is going to be used to enhanced Hubble's Advanced Camera for Surveys (ACS). The particular Application-Specific Integrated Circuit, or ASIC, design in question mirrors that of the Webb instrument and also equipment recently installed at the 2.2-meter University of Hawaii telescope on Mauna Kea, where it is part of the Charge-Coupled Device (CCD) detection system. An ASIC is a small, specialized integrated circuit, and the one about to go into Hubble could be transformative. That's because new spectrographic instruments going into Hubble will work with the repaired and upgraded ACS instrument in the study of dark energy and distant galaxies, a truly enhanced imaging capability for the aging workhorse. The ASIC next goes into space on the Webb telescope, leading one to ponder what a repair mission to that instrument would look like. After all,...

Do rogue black holes wander through the distant outskirts of the Milky Way? A new theory suggests one way to find out: Look for small clusters of stars that should accompany such objects. The idea is that low-mass proto-galaxies with black holes at their center would have merged, creating a gravitational kick that would send the now larger black hole outward fast enough to escape the host dwarf galaxy, but not fast enough to leave the overall galactic halo. Image: This artist's conception shows a rogue black hole floating near a globular star cluster on the outskirts of the Milky Way. New calculations by Ryan O'Leary and Avi Loeb suggest that hundreds of massive black holes, left over from the galaxy-building days of the early universe, may wander the Milky Way. Fortunately, the closest rogue black hole should reside thousands of light-years from Earth. Credit: David A. Aguilar (CfA). The 'kick' comes from the emission of gravitational waves as the black holes merge, carrying away...

No one has ever seen an object further away than the one at the center of the image below. It's a gamma-ray burst known as GRB 090423, spotted by the Swift satellite on April 23rd and quickly observed by the Gemini Observatory and United Kingdom Infrared Telescope, both on Mauna Kea (Hawaii). The source is visible at longer wavelengths but disappears at the 1 micron level, all of which corresponds to a distance of about thirteen billion light years. Image: The fading infrared afterglow of GRB 090423 appears in the center of this false-color image taken with the Gemini North Telescope in Hawaii. The burst is the farthest cosmic explosion yet seen. Credit: Gemini Observatory/NSF/AURA, D. Fox and A. Cucchiara (Penn State Univ.) and E. Berger (Harvard Univ.) Spectacular, no? Numerous telescopes around the planet went on to observe the GRB's afterglow, allowing the infrared light's spectrum to confirm the highest redshift ever measured: z = 8.2. The object in question was probably a...

Three brown dwarfs with masses that push up against the boundary between star and planet have been identified in IC 348, a star-forming region some 1000 light years from Earth in the direction of the constellation Perseus. The dwarfs do not appear to be gravitationally bound to a star although they are bound by the cluster, and they're useful as we try to broaden our understanding of the mass distribution in newly formed stellar populations. Andrew Burgess (Observatoire de Grenoble) has this to say about the find: "There has been some controversy about identifying young, low mass brown dwarfs in this region. An object of a similar mass was discovered in 2002, but some groups have argued that it is an older, cooler brown dwarf in the foreground coinciding with the line of sight. The fact that we have detected three candidate low-mass dwarfs towards IC 348 supports the finding that these really are very young objects." Image: IC 348, the star-forming region where the brown dwarfs were...

The idea that the Moon was formed through the impact of a Mars-sized object with the early Earth (the 'big whack') has gained credibility over the years. Call it 'Theia,' a hypothetical planet that may have formed in our system's earliest era. And place it for argument's sake at either the L4 or L5 Lagrangian point, where the gravitational influences of other developing planets like Venus may have destabilized its orbit, accounting for the subsequent impact. It's an interesting notion that helps us to understand why the Moon has such a small iron core. In the early Solar System, both Theia and Earth would still have been molten, so that heavier elements like iron sank into their cores. The effect of the impact, say Princeton University's Edward Belbruno and Richard Gott, would have been to strip away primarily the lighter elements on the outer layers of the two planets, providing the building blocks for the Moon. Image: The Lagrangian points of the Earth-Sun system (note the James...

More on Saturday's supernova story, which was truncated both because I was wrestling with a flu bug but also because I needed to verify that the supernova under study at the Weizmann Institute of Science (Israel) was the event -- SN 2005gl -- examined in Nature this past week. A quick response from the Institute's Avishay Gal-Yam confirmed the identity, which means we have more to say about this unusual observation. Located some 215 million light years from us, SN 2005gl is striking on several counts, not least of which is that the blast of a supernova generally covers up all evidence of what the star once was. What Gal-Yam and co-author Douglas Leonard (San Diego State) discovered is that the Hubble Space Telescope had an image of the galaxy containing the progenitor star as it appeared eight years before it exploded. Moreover, the star stood out, being one of the brightest and most massive in the host galaxy. Image: Eight years later: A 2005 Keck Adaptive Optics Image of the event,...

A star on the verge of exploding is an exceedingly useful thing. Identify it through a telescope and you can examine its telltale behavior before and after the event, in the process learning whether our existing theories about neutron star and black hole formation are supported by observation. We've seen stars on the order of twenty solar masses go into supernova mode, their internal elements becoming heavier and heavier through the progress of nuclear fusion. Iron is the result, but at stellar center the iron breaks down into protons and neutrons, causing an internal collapse and a supernova flash that causes the star's outer layers to be blasted into space. The core, meanwhile, mutates into a neutron star, its radius reduced to a matter of ten or so kilometers. All of this occurs more or less as theory describes, but until recently, we hadn't had the chance to study a larger 50 solar mass star in its supernova agonies. A black hole should result. Avishay Gal-Yam (Weizmann Institute...

I, for one, would like to be in on the detection of gravitational waves. They flow naturally from the theory of General Relativity and ought to be out there, but none have ever been directly detected. What might make finding them easier would be a spectacular event, such as the merger of a pulsar and a neutron star or a black hole, an event that should cause a huge emission of gamma rays in its final moments. Short-period binaries are the ticket -- find them and you have the chance to test General Relativity to high degrees of precision. Some 200,000 volunteers have already signed up for the EINSTEIN@Home project, which searches for gravitational waves from rapidly spinning neutron stars. The project is now looking for volunteers for its new search, one that will use home computers to analyze data gathered at the Arecibo Observatory in Puerto Rico in the hunt for binary radio pulsars. This is jazzy stuff, another opportunity, like SETI@Home and the Galaxy Zoo, for those of us with an...

We've often speculated here about how many stars exist in the Milky Way. Earlier estimates have ranged from one hundred billion up to four hundred billion, with a few wildcard guesses in the range of one trillion. The number is still, of course, inexact, but recent work has led to a serious misunderstanding of the subject. As reported in this earlier post, Harvard's Mark Reid and colleagues have discovered that the Milky Way is likely to be as massive as the Andromeda galaxy, which means that it could have the mass of three trillion stars like our own Sun. Does that mean that the Milky Way contains three trillion stars? Absolutely not. I'm seeing the three trillion star number popping up all over the Internet, and almost reported it that way here when I first encountered the work. The misunderstanding comes from making mistaken assumptions about galactic mass. Reid used the Very Long Baseline Array to examine regions of intense star formation across the galaxy, a study the scientist...

Take a look at NGC 4565, a spiral galaxy seen edge-on. Spiral galaxies viewed at this angle often show dark dust lanes, the result of dust from dying stars mixing with interstellar gas. We've discussed the problem of interstellar dust in terms of objects moving at relativistic speeds between stars, but recent quasar studies are showing us that entire galaxies may expel dust to distances of several hundred thousand light years. In terms of the NGC 4565 image, that would be ten times farther than the visible edge of the galaxy. Image: Spiral galaxies seen edge-on often show dark lanes of interstellar dust blocking light from the galaxy's stars, as in this image of the galaxy NGC 4565. The dust is formed in the outer regions of dying stars, and it drifts off to mix with interstellar gas. Credit: Sloan Digital Sky Survey (SDSS-II). The astronomers who did this work talk of intergalactic space being filled with a haze of fine dust particles, a haze that can be examined by analyzing light...

Adam Goldstein must be living right. Here's a grad student (University of Alabama, Huntsville) who's on his first day on the job working with the Fermi Gamma-ray Space Telescope. He's given the task of monitoring the Gamma-ray Burst Monitor (GBM) instrument, which routinely detects bursts, about one a day. This time, though, when the phone rings, it is to flag a burst like no other, 700 times longer in duration than the average. We already knew that GRBs were exotic events. Many astronomers believe that they occur when, out of its nuclear fuel, a massive star collapses into a black hole, creating jets of material that interact with gaseous debris previously shed by the star. But this one, detected in mid-September last year, was a true behemoth, with a red shift pegging its point of origin as twelve billion light years from Earth, in the constellation Carina. GRB 080916C turns out to be the most powerful gamma-ray event ever detected. Image: GRB 080916C's X-ray afterglow appears...

Just how common are brown dwarfs? The answer is still up for debate, for stars like these (with masses less than 0.05 that of the Sun) are so small that they do not burn hydrogen, and as they age, they become more and more difficult to detect. But we'd like to know more, especially in understanding our local interstellar neighborhood. Red dwarfs are common throughout the galaxy, and we know that they can support planetary systems and even worlds in the habitable zone. Is it possible that brown dwarfs are even more numerous than red dwarfs? Asking questions like these takes us into what is known as the initial mass function (IMF), which involves the number of stars versus their masses at the time of their formation. The place to study the issue is a star forming region like the one shown in the image below. This Subaru Telescope composite shows the W3 Main region, about 6,000 light years away in the constellation Cassiopeia. A region like this is helpful because the majority of stars...

A familiar scenario from the early universe is getting a tune-up. It's long been believed that cosmic dust was first produced by supernovae, becoming the essential building block for the formation of planets. New work using the Spitzer Space Telescope suggests a second mechanism that complements the first. So-called 'carbon stars,' stars late in their lives and similar to red giants but containing more carbon than oxygen, may have played as significant a role as supernovae themselves. The work focused on the carbon star MAG 29, some 280,000 light years away in the Sculptor Dwarf galaxy. Says Albert Zijlstra (Jodrell Bank Centre for Astrophysics): "All the elements heavier than helium were made after the Big Bang in successive generations of stars. We came up with the idea of looking at nearby galaxies poor in heavier elements to get a close-up view of how stars live and die in conditions similar to those in the first galaxies." Image (click to enlarge): The star MAG 29, shown in...

Finding something unexpected adds immeasurably to the pleasure of doing science. Yesterday we looked at an anomalous transient in Boötes, one that has already spawned a number of theories to explain it. Today let's look at some of the radio noise that pervades the cosmos, and an intriguing experiment that discovered more of it than expected. The story makes this writer marvel again at how the universe continues to change the game. I like how Philip M. Lubin (UCSB) puts it: "It seems as though we live in a darkened room and every time we turn the lights on and explore, we find something new. The universe continues to amaze us and provide us with new mysteries. It is like a large puzzle that we are slowly given pieces to so that we can eventually see through the fog of our confusion." Indeed. Lubin is on the team behind the NASA balloon-borne experiment called ARCADE (Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission), which discovered this particular static back in...

We continue to follow the American Astronomical Society's meeting in Long Beach with fascination. This has, indeed, become AAS week in these pages. But amidst the news of brown dwarf discoveries, a more massive Milky Way than previously thought, and asteroids around white dwarf stars, the story of a genuine mystery stands out. Such a mystery is the optical transient known as SCP 06F6, a flash of light picked up by the Hubble Space Telescope back in 2006. Have a look at the images below: Image: This pair of NASA Hubble Space Telescope pictures shows the appearance of a mysterious burst of light that was detected on February 21, 2006. The event was detected serendipitously in a Hubble search for supernovae in a distant cluster of galaxies. The light-signature of this event does not match the behavior of a supernova or any previously observed astronomical transient phenomenon in the universe. Credit: : NASA, ESA, and K. Barbary (University of California, Berkeley/Lawrence Berkeley...

On my walk this morning, I was musing about the ongoing AAS meeting in Long Beach when I found myself having one of those epiphanies that seem to open a window into the heart of things. The day was unusually warm but gusts of wind tossed the trees and low clouds laced with rain scudded past. And suddenly I was no longer walking along a quiet street but became aware that I walking a planet within a star system, within a cloud of stars, and that by being made up of elements from those stars, I was in some sense an expression of that universe as it observed itself. It's hardly an original notion, but the sense of it was palpable, an almost physical awareness that translated something known factually into something experienced. It was spurred by the recent news that the Milky Way is fifty percent more massive than we thought, maybe the twin of the Andromeda Galaxy. Increasing our sense of scale adds to the grandeur. The punch of the Fermi Paradox comes from the sheer size of galaxies --...