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...