Brightest GRB ever!

Until the next one, at least. Read more about it here, and learn more about the Swift satellite by listening to this.

Description of January 7 Radio Show: Milky Way Galaxy

Long available here, below is a description of the January 7th episode of the radio show, where I continue the "Tour of the Universe" with a description of the Milky Way:

• Galactic Center and Galactic Plane - At the very center of the Milky Way, there is believed to a black hole which has a mass approximately a million or so times that of the Sun called Sgr A*. Pretty strong evidence for the existence of such an object comes from studying the orbit of stars very close to Sgr A* (link). Measuring the mass of similar black holes believed to be at the centers of other galaxies is much more difficult since there you can't resolve the orbits of individual stars. Other methods which have been proposed are the tightness of their spiral arms (link), the temperature of the hot, X-ray emitting gas surrounding the galaxy (if it is a galaxy without much ongoing star formation; link). Surrounding Sgr A* is a disk of stars including the Sun, referred to as the Galactic Plane. They stars orbits Sgr A*, and a new, precise measurement of the rotation of stars in the Milky Way was recently made using a particular class of pulsating stars called Cepheids - which have also been used to measure the distance to other galaxies (link). The spiral arms in the Milky Way are not believed to concentration of particular stars, but where a significant number of stars are born "at once" - which is why they appear brighter than other parts of the Milky Way and contain a vast majority of the most massive (and therefore, very short lived) stars in the Galaxy. There is evidence that our Sun has traveled a considerable distance from its birth site in the Milky Way. Since young stars are clustered along spiral arms, and young, massive stars are the dominant source of ultraviolet radiation in a galaxy, ultraviolet images like the one the Swift satellite recently made of M33 (link), are good ways of studying the spiral structure in a galaxy. Spiral arms, and other features of the galactic disks make the results of gravitational interactions between galaxies (link). The Milky Way also contains clusters of stars, the densest and oldest of which are called "globular clusters", which are believed to be stars formed at the same time out of the same cloud of gas. A recent study of the a particular globular cluster measured its age using three different methods and got three different answers - a bit of a puzzle (link). As discussed on a previous show, the most massive stars in the Milky Way are believed to end their life in a supernova explosions, which actually plays a very important role in the properties of the gas which fills the Galactic plane of the Milky Way. Recent Chandra and Very Large Array observations have discovered the remnant of the most recent supernova explosion in the Milky Way, believed to have occurred only 140 years ago (link). The material released in these explosion expand with a very high velocity, heating the surrounding gas to very high temperatures and compressing into a thin shell of material which make for lovely Hubble images - and very interesting science (link). The hot gas and cosmic rays produced in the interaction between the material ejected in a supernova and its surrounding might explain the flow of gas out of the Milky Way's Galactic Plane, and carve bubbles out of nearby cold gas as observed in the Tarantula Nebula in the Large Magellanic Cloud (link). This is believed to explain why clusters of young stars are often surrounding by "holes" in gas, though this is not the case for nearby dwarf galaxy IC 2574. In most galaxies like the Milky Way, ionized hydrogen is only found in the center of these galaxies, most likely the result of star formation occurring only in certain regions and not distributed uniformly around a galaxy (link). Spitzer observations of a nearby spiral galaxy M101 shows that organic molecules are only present towards its center and not its edges (link; image. In the Milky Way, most star formation is currently taking place near the center of the galaxy, but not so in M83 where GALEX recently observed star formation at the outer edge (link)
• Wednesday Morning Astronomer: I understand and don't necessarily disagree with his point in this article, but astronomers did not "cavalierly" come up with the idea of Dark Matter - it was first proposed to explain some observations in the 1930s I believe, did not gain acceptance for at least 30 years, and still bothers many people, dark matter has been "located" (though not yet explained), the every controversial "dark flow" observed in distance galaxy clusters might be due to an unknown force, but not one outside our universe but one important on distances greater than the speed of light times the age of the universe which defines the "observable universe." I know that is pretty subtle, but it is an important distinction.
• Calendar of upcoming Astronomy/Science events in the greater Poughkeepsie/New York City area.
• Globular Clusters and Galactic Halo: Outside the Galactic Plane there are dense concentrations of millions of old stars referred to as globular clusters. Recent observations suggest that, even though they are "only" 9-13 billion years old, the structure of stars inside globular clusters is still evolving (link). It is though the some globular clusters are actually the remnants of the centers of dwarf galaxies which have been absorbed by the Milky Way. Since such galaxies are also believed to have black holes at their center, the presence of a massive black hole (much more massive than the Sun) might be proof this occurring. Such a black hole might have been found in globular cluster Omega Centauri (link), which - unlike other globular clusters - also contains dust (link). A similar process might explain the large number of globular clusters in M87, the giant elliptical galaxy in the center of the Virgo cluster - it "stole" them from lower mass galaxies which got too close (link). By measuring the velocity of the stars in the halo of the Milky Way, the diffuse "cloud" of stars which surrounds the Galactic Plane, it is possible to estimate the total mass of our galaxy. A recent such measurement suggests a lower mass than previously estimated (link). How the Milky Way's halo got there is an open, and interesting question. The two possibilities are that the stars formed out of the same cloud of gas that collapsed to form the Milky Way, or that it is the remnants of galaxies which have merged into the Milky Way. Recent studies of the structure of the halo suggest the second possibility, as do the presence of streams of stars in the halos of two nearby galaxies (here). It is expected that there are stars in the vast empty space between galaxies, and astronomers are searching for them (link). Last, but not least, it appears that most of the mass of galaxies is not in stars, gas, or dust, but in "dark matter" - this mysterious stuff that has mass but doesn't seem to produce light. Dark Matter is present in the dwarf galaxies which orbit the Milky Way - in fact, one of these has the highest ratio of dark to "normal" matter of any known object (link), and the galactic plane might be enclosed in a larger disk of dark matter(link). The distribution of dark matter in a galaxy is not expected to be entirely smooth but contain clumps and streams (link) which might be measurable using the motion of nearby stars in the night sky. An alternative to dark matter is the Newton's equation for gravity is wrong on very large distances (called MOdified Newtonian Dynamics, or MOND), which can do a good job reproducing the orbit of dwarf galaxies around the Milky Way (link). There are many fewer known dwarf galaxies around the Milky Way than expected, a problem for our current understanding of galaxy formation, though possible solutions have been suggested (link)

Thank you very much listening, and please email or post below any questions, comments, or concerns you might have.

Description of December 31st Radio Show: Latest Astronomy News

Long available here, below is a description of the December 31st episode of this radio show, where I discussed the major Astronomical results to come out in December 2006. They were:

• Solar System News: Recent powerful solar flare produced both neutral and charged particles, first time neutral particles detected from such an event; ESA's Venus Express detects hydrogen leaving Venus's atmosphere from the day-side for the first time - gas appears to be result of water being broken down into hydrogen and oxygen in upper atmosphere, and might explain why there is so little water on Venus; NASA's THEMIS satellites detect the opening of a large hole in the Earth's magnetic field due to the interaction with a clump in the solar wind; NASA instrument on India's Chandrayaan-1 Lunar spacecraft measures changes in chemical composition of lunar surface on small physical scales (link, image); next NASA mission to the Moon, the Lunar Reconnaissance Oribter; completes major milestone before April 2009 launch (website); evidence for climate change on Mars resulting from regular changes in the tilt of its orbit around the Sun - deduced from studying patterns of rock layers in a large crater (link); results from ESA's Mars Express satellite suggests that peculiar light-toned deposits result on ground water bursts onto the surface (link); NASA's Mars Reconnaissance Orbiter completes primary mission (website), releases new 3D images of surface (link), and found evidence for carbonite on Martian surface which requires the past presence of neutral or basic water on Mars's surface (article); evidence that site of NASA's Phoenix Mars Lander is currently going through a "dry" phase; next NASA mission to Mars - the Mars Science Laboratory - delayed until late 2011 due to cost over-runs, delay expected to have implications for future planetary missions; ongoing debate whether future joint NASA/ESA Solar System mission should be to Jupiter's moon Europa or Saturn's moon Titan; recent flybys of Saturn's moon Enceladus by Cassini show continuing activity and of Titan show evidence for volcanos spewing ice in to this moon's atmosphere; Swift satellite detects X-ray emission from Solar System comets (link)
• Wednesday Morning Astronomer: Yes, an ice cream carton hurtling towards the Earth at 99% the speed of light would be a very bad thing (article); no, the astronomical theory for what Voorwerp might be is not an attempt to upstage the Dutch schoolteacher who found it, but is an attempt to understand a still very bizarre object (link); star formation in the universe is actually on a decline, and if the current thinking on the universe is correct, the ultimate fate is a starless night sky - a very depressing prospect indeed (link); and I think it is definitely a good thing that the more we look, the less we understand (link).
• Calendar of upcoming Astronomy/Science events in the greater Poughkeepsie/New York area.
• More News: Evidence that brown dwarfs form like stars not planets (link); up and coming sub-mm radio interferometer ALMA gets its first telescope; astronomers discover the two faintest brown dwarfs known (link); analog to young Sun identified by CoRoT satellite (link); turbulence in proto-planetary disk important in determining how planets form (link); Spitzer images massive stars destroying proto-planetary disks of their neighbors (link); Dutch undergrads discover first extrasolar planet orbiting a fast-rotating star (link); Hubble Space Telescope discovers carbon dioxide in the atmosphere of an extrasolar planet (link) and measure the size of a different extrasolar planet (link); proposal to look for moons around extrasolar planets through the "wobbles" they create in their orbits (link); new technique proposal to look for water in the atmosphere of an extrasolar planet; direct imaging of extrasolar planets is Science magazine's #2 breakthrough of the year; Kepler spacecraft - which will search for Earth-like planets around Sun-like stars - shipped to Florida (just launched last week!!!)

As always, please post below or email any questions, comments, or concerns you might have. Thank you for listening!

Interview with Dr. Neil Gehrels online

The interview with Dr. Neil Gehrels of Goddard Space Flight Center is now available for your listening pleasure. In this interview, Dr. Gehrels talks about Swift, an extremely successful satellite which was designed to study the gamma-ray, x-ray, and ultraviolet/optical emission from gamma-ray bursts (GRBs) and has been instrumental in furthering our understanding of what these mysterious explosions are. For more information on his research, Swift, and GRBs, check out:

• Homepage of Dr. Gehrels
• Main webpage for Swift, which also contains information on how it studies GRBs
• An introduction to GRBs courtesy of NASA

Hope you enjoy, and thank you very much for listening. Please email me, or leave below, any questions, comments, or concerns you might have. Thanks!