SOFIA

Well, I posted a link to an editorial essentially blasting NASA's SOFIA project. Here is an article describing all the pretty impressive science it will hopefully accomplish. Enjoy!

Runaway star

Thanks to a nice little quirk in gravity (which actually NASA and ESA routinely use to send satellites to other planets in the Solar System), a small object orbiting a more massive one can get a big boost to its speed. Well, the most massive object in the Milky Way is the black hole at is center - Sgr A*. And it can accelerate stars to ridiculously high velocities. Well, some of these stars have been found - including one which should have exploded long before it reached its current location in the galaxy even with its high velocity. Go here and here and here to read more about how it survived its trip.

How old is the Milky Way?

Maybe a better answer will be coming soon. Go here to read how particle physics might help.

The dusty Milky Way

Even though it was launched to study the Cosmic Microwave Background, Planck also detected emission from warm dust since they emit light at the similar wavelengths. Go here to check out an amazing image it has made of "nearby" dust in the Milky Way. Enjoy!

The History of Globular Cluster Terzan 5

one of the oldest, densest, and most massive collection of stars in the Milky Way. Go here for more information.

The Milky Way's neighbors

In addition to M31 (Andromeda galaxy), orbiting the Milky Way are a collection of small, irregular galaxies which likely had lost gas and stars to the Milky Way's gravitational attraction when they get too close. Go here for some new, pretty pictures of one of the galaxies that may form the building blocks of the Milky Way's halo.

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 3rd Radio Show: Black Holes

Long available here, below is a description of the 2008 December 3rd episode of this radio show with focused on black holes. On this program, I discussed the following:

• Black Holes: Black Holes are objects believed to be so dense that light can not escape if it gets to close (i.e., past the "event horizon"). Additionally, its gravity is so strong that material that makes up a black hole can not arrange itself into a structure that can withstand its own gravity, so this material is thought to collapse into a point. But if one can't see too close to a black hole, how does one know? Well, it the above is correct, that black holes should not have a surface, unlike a neutron star. If a neutron star or a black hole is close enough to a normal star, its gravity is so strong that it will rip material off the surface of the normal star and cause it to fall on itself. This process is called "accretion", and as discussed previously on this radio show by Dr. Tod Strohmayer, this has process have been observed for many neutron stars and black hole candidates. In the case of a neutron star, this material will pile up on the surface of the neutron star, and this pile will got hotter and denser until it is so hot and dense that the hydrogen in this material fuses into helium, releasing a burst of heat and light which is observable by X-ray telescopes such as the Rossi X-ray Timing Explorer. One would not expect such bursts from material falling onto a black hole - which is more massive than a neutron star - since their is no surface for the material to collect. These X-ray bursts have been detected from neutron stars (for example this link), but not from any black hole candidates. Therefore, even there seems to be evidence that black holes indeed do not have surfaces. Additionally, black holes appears to have a mass either a few times that of the Sun (called "stellar-mass black holes"), or millions to billions times that of the Sun - like the black hole believed to reside in the center of our galaxy, the Milky Way (called "super-massive black holes"). Why there seems to be a lack of black holes with a mass between these two extremes (for example, a thousand solar masses) isn't known. One possibility is that such black holes exist, but reside in the middle of globular clusters where they would be hard to detect. A recent survey of globular cluster RZ2109 did not find such a black hole, suggesting that if this was correct they are extremely rare (link). Studies of the super-massive black holes suggest that their may be an upper-limit to how massive they can be, around 10 billion times that of the Sun (link). Since black holes do not have any structure, they are often thought to be some of the simplest objects in the universe (really!) - according to Einstein's theory of General Relativity, in order to completely describe the properties of a black hole you need to know its mass, its spin, and its electric charge (and real black holes in the universe and expected to have zero electrical charge). If so, stellar-mass black holes and super-massive black holes should accrete matter the same way - as observed for black holes in the nearby galaxy M81 (link). As mentioned before, it a normal star passes too close to a black hole, the black hole's gravity will cause material from the star to fall towards, and eventually fall inside, the black hole. As this material falls towards the black hole, it gets hotter - so hot that it produces a lot of X-rays. By looking at the periodic flickering of this light, it is possible to estimate the mass of the black hole. This was recently done for one black hole in the Milky Way, at they estimate a mass of just 3.8 times that of the Solar Mass, the lowest mass black hole known (link). Periodic flickering has also been observed from the super-massive black holes in the centers of other galaxies, and can be used to estimate their mass as well. This was done for galaxy RE J1034+396, which has a mass a million times that of the Sun (link). What causes the light from gas falling into a black hole to flicker is not known, but a recent study of the visible light flickering and X-ray light flickering from a Galactic black hole suggests that its magnetic field plays an important role (link). As mentioned before, there is a super-massive black hole in the center of our galaxy called Sgr A*, and material falling into this black hole also produces regular flares of light (link). In fact, there is evidence that, around 300 years ago, it produced a flash of light so bright that today we are seeing some of the light reflecting off molecular clouds near the Galactic center (link). A major goal of astronomers today is to make an image of light coming from the event horizon around a black hole. The best chance to do this is using radio telescopes to observe Sgr A*, and radio astronomers have gotten down to only 3 times the expected size of the event horizon (link 1, link 2). It is possible to use to orbits of objects around black holes to test general relativity (GR), just as one does this with neutron stars. This was recently done for the two black holes believed to be orbiting each other in center of galaxy OJ 287, and the time between the closest approach of these two black holes agreed with what GR predicts. The material that flows into a black hole is believed to form a disk (called an "accretion disk") around the black hole before it passes the event horizon. Quasars are believed to be galaxies where the optical light of this disk shines much, much brighter than all the stars in the rest of the galaxy. If so, the spectrum of the quasar - how bright the quasar is at different colors - should resemble that of a disk. This is hard to measure in great detail since the light at some colors is absorbed by material between the Earth and the galaxy, but a recent study suggests that it does (link). Additionally, for some unknown reason, the presence of gas flowing into the black hole is often associated with the presence of gas flowing AWAY from the black hole with very high velocities (>60 million mph). Astronomers at UCSC and University of Florida recently observed this outflow turn on around a quasar (link). Sometimes this very collimated outflow (called a "jet) is pointed directly at the Earth, in which case the galaxy is called a "blazar." Recent radio observation of a blazar suggest that these jets are powered by the magnetic field of the black hole (link). Quasars come in very different varieties, with one class recently observed to produce many more X-ray than previously thought to be possible (link). The presence of very, young stars around super-massive black holes like Sgr A* strongly suggest that stars can form in the accretion disk around them (article, link 1). Optical observations of these accretion disk have also detected weird optical filaments around them, suggesting this gas is confined by a weak magnetic field possibly generated by the black hole (link). While all galaxies are currently thought to have a super-massive black hole in their center, very few galaxies are quasars. Why some galaxies are quasars are most are not is unknown, but it is though that quasars are the result of two galaxies recently merging together.
• Calendar of upcoming Astronomy / science events in the greater Poughkeepsie / New York City area.
• Wednesday Morning Astronomer:
• News:

Past Interview: Prof. Allyson Sheffield (Vassar College)

Already available, here is my interview with Prof. Allyson Sheffield of Vassar College on her research on determining the origin of the "thick disk" of the Milky Way. I didn't get a chance to discuss this on my January 7th radio show where I covered the Milky Way, so I thought it might be of interest. Hope you enjoy!

January 7th radio show: The Milky Way

Now available here is the January 7th episode of this radio show, where I do my best to describe and cover all the latest news of the different components of the Milky Way - starting with million solar mass black hole at the center to the diffuse, large "halo" of stars which surrounds the Galactic disk where the Sun resides. Hope you enjoy, and as always, any and all feedback is appreciated. Thank you for listening!

Hubble Image of the Galactic Center

The near-infrared camera on the Hubble Space Telescope recently took this picture of the Galactic Center, and it looks absolutely gorgeous. For a zoomable version of this image (which is definitely worth looking at), go here. Enjoy!

Description of September 10th Radio Show: Milky Way Structure and Galaxy Formation

Already available here, below is a description of the September 10th edition of this radio show. On this program, I discussed:

• Calendar of upcoming Astronomy / science events in the greater Poughkeepsie / New York City area.
• Interview with Prof. Allyson Sheffield of Vassar College.
• News: Phoenix Mars Lander begins analysis on deepest soil sample to date (link) as well as makes some puzzling measurement regarding humidity on the Martian surface; amateur astronomers see Perseid meteor shower hit the Lunar surface; ESA's Rosetta spacecraft flies by astroid (2867) Steins - sees chain of craters, rotation, and overall diamond shape (link); Cassini detects ring arcs around two moons of Saturn (link); NASA awards contract to S.C. Jones Services, Inc. to get rid of pests at Kennedy Space Center; NASA building "Solar Ultraviolet Magnetograph Investigation" to measure the strength of the magnetic field at the outer edges of the Sun; NASA developing a new space equiptment rack for "Zero-Gravity" flights; NASA delays launch of Space Shuttle Atlantis to October 12 and launch of Space Shuttle Endeavor to November 12 due to bad weather - media viewing of equipment to be flown on Atlantis for installation on Hubble Space Telescope set for Sept. 10; launch of ESA's GOCE satellite delayed due to rocket problems; NASA to hold media briefing on September 25th on Lunar Exploration plans; mirror blank produced for Large Synoptic Survey Telescope (link); NASA produces 50th anniversary art book - information here; NASA announces new Carl Sagan postdoctoral fellowship to study extra-solar planets - information here; NASA issues a challenge to high school and college students to describe a future supersonic airliner - information here - as well as a new aeronautics competition - information here; Swift to announce new gamma-ray burst findings today; Custer Institute to host 30th annual Astronomy Jamboree and Conference October 3rd and 4th.
• Milky Way Structure and Galaxy Formation: It is currently believed that all galaxies, including the Milky Way, formed by the merging of smaller galaxies together - an this process is ongoing. If this is correct, there should be evidence for this in the Milky Way today - as discussed by Prof. Sheffield at the beginning of this show. A recent survey of satellite galaxies of the Milky Way, small galaxies which are in the process of merging into our galaxy, discovered that they all have roughly the same total mass (stars + dark matter) - regardless of how many stars they have. This implies something strong about the formation of these galaxies or the properties of dark matter - astronomers are still not sure which (link). Evidence of previous mergers is also in "streams" of stars - stars with similar orbits and chemical composition - in the halo of the Milky Way. There are many questions regarding the structure of the Milky Way - including how many spiral arms there are, since two of the spiral arms that were thought to be there have apparently disappeared (link).

Hope you enjoyed and, as always, any and all feedback is appreciated. Thank you very much for listening!

Interview with Prof. Allyson Sheffield now online

Available here is my interview with Prof. Allyson Sheffield of Vassar College on the relationship between the present structure of the Milky Way and its formation. For more information on her research, check out her webpage, or email me a question, or leave a comment below. Hope you enjoy, and thank you for listening!