American Astronomical Society

What is on this page?

• Spitzer's Milkyway - Spitzer Captures Stellar Coming of Age in Our Galaxy
• Hunting Supernova - Hunting the Last Galactic Supernova and Anticipating the Next
• Girl Scout Day - National Air and Space Museum
• MESSENGER - MESSENGER's Flyby of Mercury

Current Event Links:

• Astronomical League - Astronomical Leagues Weekly Astronomy Guide
• SpaceWeather.com - News and Information about the Sun-Earth environment

Spitzer Captures Stellar Coming of Age in Our Galaxy

MISSION NEWS-June 03, 2008 NASA Article

More than 800,000 snapshots from NASA's Spitzer Space Telescope have been stitched together to create a new "coming of age" portrait of stars in our inner Milky Way galaxy.

The image depicts an area of sky 120 degrees wide by two degrees tall. It was unveiled today at the 212th meeting of the American Astronomical Society in St. Louis, Mo.

"This is the highest-resolution, largest, most sensitive infrared picture ever taken of our Milky Way," said Sean Carey of NASA's Spitzer Science Center at the California Institute of Technology, Pasadena, Calif. Carey is lead investigator for one of two teams responsible for the new picture. "Where previous surveys saw a single source of light, we now see a cluster of stars. With this data, we can learn how massive stars form, map galactic spiral arms and make a better estimate of our galaxy's star-formation rate," Carey explained.

Because Earth sits inside our dusty, flat, disk-shaped Milky Way, we have an edge-on view of our galactic home. We see the Milky Way as a blurry, narrow band of light that stretches almost completely across the sky. With Spitzer's dust-piercing infrared eyes, astronomers peered 60,000 light-years away into this fuzzy band, called the galactic plane, and saw all the way to the other side of the galaxy.

The result is a cosmic tapestry depicting an epic coming-of-age tale for stars. Areas hosting stellar embryos are identified by swaths of green, which are organic molecules, called polycyclic aromatic hydrocarbons, illuminated by light from nearby newborn stars. On Earth, these molecules are found in automobile exhaust and charred barbeque grills, essentially anywhere carbon molecules are burned incompletely.

The regions where young stars reside are revealed as "bubbles," or curved ridges in the green clouds. These bubbles are carved by the winds from young starlets blowing away their natal dust. The starlets appear as yellow and red dots, and the wisps of red that fill most bubbles are composed of graphite dust particles, similar to very small pieces of pencil lead.

Blue specks sprinkled throughout the photograph are individual older Milky Way stars. The bluish-white haze that hovers heavily in the middle two panels is starlight from the galaxy's older stellar population. A deep, careful examination of the image also shows the dusty remnants of dying and dead stars as translucent orange spheres.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA.

Hunting the Last Galactic Supernova and Anticipating the Next

MISSION NEWS-May 14, 2008 NASA Article

A supernova is a spectacular event. It can outshine the optical light from an entire galaxy, and with the help of big ground-based telescopes, it can be seen across more than half the Universe. At least one of the supernovas in our galaxy was so bright it was visible to ancient astronomers during the day. All of this light comes with a tremendous amount of energy, which has a big impact on the supernova's home galaxy, by heating and pushing gas around, pumping out new elements and creating exotic objects in the form of neutron stars and black holes. Supernovas are vital not only for the life of a galaxy, but the life in a galaxy. They may have helped trigger the formation of the Sun and the planets, and they disperse many of the elements critical to life, like the iron in our blood and the oxygen that we breathe.

How Often Do Supernovas Explode in Our Galaxy?

Given the incredible power of supernovas and their importance, you might think that astronomers have an excellent understanding of how often they explode in our cosmic backyard, the Milky Way galaxy. They don't. Mostly, they have given up on looking at our own Galaxy to estimate what its supernova rate is. Instead, they count the supernovas in a bunch of other, more distant, spiral galaxies that have about the same mass as the Milky Way. This is a bit like working out the average medical history of people with your size and assuming that it applies to yourself. A doctor would insist on a physical, but astronomers can't make demands of the Universe.

So, why is it so hard to directly estimate the supernova rate in our galaxy? A big problem is that most of the supernovas in our galaxy should be very faint in optical light - and some effectively invisible - because their light is blocked by dust and gas lying in the Galactic plane. For example, the most recent supernova in the Galaxy (as measured in Earth's time frame [see sidebar]) is estimated to be about a trillion times fainter, optically, than it would have been without the veil of dust and gas. This makes the difference between it being visible with the naked eye and only being visible using a deep observation with a very large telescope.

Another problem for estimating the Galactic supernova rate is that supernovas in galaxies like ours are thought to occur about once every 30 years. But, if you want to see the bright flash from a Galactic supernova explosion using an optical telescope, you're probably in for a much longer wait, since the supernova needs to be relatively close to the Earth to avoid being obscured by lots of dust and gas. The last one definitely seen by historical astronomers occurred over 400 years ago (Kepler's supernova remnant) well above the plane of the galaxy.

Astronomers have estimated the Galactic supernova rate by extrapolating from these historical ones easily seen in the local part of the Galaxy to the obscured population in the entire Galaxy, but the correction factor is large and uncertain. It's clear that we've missed a lot of supernovas in the Galaxy in the last 2000 years - what's unclear is how many we've missed.

One way to count how many have been missed is to use X-ray and radio observations to peer through the dust and gas, and observe the remains of supernovas. These supernova remnants emerge a few decades after a supernova and last for thousands of years, and are bright in X-rays and radio waves. (The most recent update of a catalog of Galactic supernova remnants lists 265 objects.)

However, it is difficult to estimate the age of a supernova remnant, as with many objects in astronomy. The Galactic supernovas that occurred less than a few hundred years ago are most promising for estimating accurate ages, because expansion can be measured. Looking at how quickly something is expanding allows one to estimate how long it has been expanding.

Just the detection of one recent, obscured supernova in our Galaxy is exciting for starting to find these missing supernovas, since the previous youngest supernova remnant, Cas A, was known for over 50 years. Given the huge advances made in observational astronomy over the last ten or twenty years, that's a long time. Inspired by the successes of Cas A and G1.9+0.3, astronomers will be keen to continue finding evidence for recent supernovas in our galaxy by looking for expansion of remnants.

Another reason for excitement is that because no other remnant in the Galaxy is known to be as young, G1.9+0.3 offers a great opportunity to study the acceleration of cosmic rays, the dispersal of elements and the generation of X-ray and radio emission in unprecedented detail.

Since much work remains to be done, we cannot properly test yet whether a Galactic supernova does explode every 30 years or so. But, assuming it does, there's a decent chance one will go off in the career of a young astronomer and an obvious question arises: will such a supernova be detected today no matter where in the Galaxy it explodes? The answer depends on what sort of supernova it is. If it's a supernova generated by the collapse of a massive star, the flash of neutrinos caused by the explosion will definitely be seen by detectors on Earth no matter where it occurs in the Galaxy.

A neutrino flash was detected from Supernova 1987a, which occurred in a nearby galaxy. But, if it's a thermonuclear explosion of a white dwarf, a so-called Type Ia supernova, then it's much less clear whether it would definitely be detected. However, most supernovas are caused by core-collapse events, so there's still a decent chance that a Galactic supernova will be caught in action in the next few decades. When it does, it will be one of the biggest stories in modern astrophysics.

GIRL SCOUT DAY

NATIONAL AIR AND SPACE MUSEUM UDVAR-HAZY CENTER March 22, 2008 Article

Girl Scouts of the Nations Capitol program at the National Air and Space museum. First est 3125 girl Scout Guests, over 13,000 of the general public. Another wild day of public outreach. First thing was we had to do was spread out our activity tables. We had so many people trying to do/see/observe etc that the Fire Marshall said we were a hazard (never had one of our astronomy programs declared a fire hazard before, first time for everything I guess).

The American Astronomical Society had set up 4 activities and the Westminster Astronomical Society Westminster Astronomical Society had set up 5 activities. The AAS had set up "Guess The Meteorite", "The World of Diffraction", Building a Spectroscope" and "Building a Pluto Model". WASI had; "Seeing through Alien Eyes and Decoding Secret Messages, How our Atmosphere Protects Us (used as a game) including UV beads, How we find Planets around other Stars", the always a favorite "Pocket Solar System" and looking through my telescope at the moon (OK so it wasn't the real Moon, but it was a really nice picture we stuck to a walk way clear on the other side of the building-NOTE the Air and Space Museum frowns on Sticking things on their property-SORRY).

The people had so much fun that the parents had to make the kids leave our area to see the rest of the museum and other activities.

Highlights were:

(AAS Programs) Misty L trying to keep track of the Diffraction Glasses, Susan K making Pluto models, Alycia sitting on the floor making spectrograph's, Mike M trying to fool the GS in the Meteorite game, Ed W explaining the different views of a galaxy to someone who was having trouble understanding what a galaxy was, Cassy-Susana-Margaret-Hashima laughing and having fun with all the kids...

(WASI Programs) Salvi M explaining about our atmosphere in his best Russian to a couple of girls from Russia, Sergi M handing out Litho's, trading cards, to everyone who stopped at one of our activities, Stephen R doing the pocket solar system with a bunch of giggling girls, John B trying to do the same thing with help from his 6 yr old son, Dave L trying to find the moon when the kids moved the scope, and Ian S and Tony G discussing how many planets there were with a VERY smart and stubborn 13 year old girl (she almost had them convinced there were no planets according to the IAU definition).

Between both groups we went through 15 rolls of register paper, 21 Spitzer Calendars, 37 pairs of Diffraction Glasses, 200 good neighbor lighting sheets, 400 secret message sheets, 700 Planet Quest stickers, 800 posters, 1000 JUNO postcards, 2900 lithographs, 5500 book markers, 15 pencils, 12 sodas and a box of chocolate donuts. All in all another great day was had by all.

P.S. If you ever get a chance to do something like this DO IT!

MESSENGER

MESSENGER Mission News January 17, 2008 NASA Article

Just nine minutes after the MESSENGER spacecraft passed 200 kilometers (124 miles) above the surface of Mercury, its closest distance to the planet during the January 14, 2008, flyby, the Wide Angle Camera (WAC) on the Mercury Dual Imaging System (MDIS) snapped this image. The WAC is equipped with 11 different narrow-band filters, and this image was taken in filter 7, which is sensitive to light near the red end of the visible spectrum (750 nm). This view, also imaged through the remaining 10 WAC filters, is from the first set of images taken following MESSENGER's closest approach with Mercury.

The image shows Mercury's surface as seen from a low viewing angle, looking over the surface and off the limb of the planet on the right side of the image. The cratered terrain in the image is on the side of Mercury unseen by spacecraft prior to this MESSENGER flyby. This scene was imaged at multiple viewing angles as MESSENGER sped away from Mercury, and these multiple views of the same surface features from different perspectives and in different colors will be used to help understand the properties of Mercury's surface.

MESSENGER Reveals Mercury's Geological History

Shortly following MESSENGER's closest approach to Mercury on January 14, 2008, the spacecraft's Narrow Angle Camera (NAC) on the Mercury Dual Imaging System (MDIS) instrument acquired this image as part of a mosaic that covers much of the sunlit portion of the hemisphere not viewed by Mariner 10. Images such as this one can be read in terms of a sequence of geological events and provide insight into the relative timing of processes that have acted on Mercury's surface in the past.

The double-ringed crater pictured in the upper right of this image appears to be filled with smooth plains material, perhaps volcanic in nature. This crater was subsequently disrupted by the formation of a prominent scarp (cliff), the surface expression of a major crustal fault system, that runs alongside part of its southern rim and may have led to the uplift seen across a portion of the crater's floor. A smaller crater in the upper left of the image has also been cut by the scarp, showing that the fault beneath the scarp was active after both of these craters had formed.

The MESSENGER team is working to combine inferences about the timing of events gained from this image with similar information from the hundreds of other images acquired by MESSENGER to extend and refine the geological history of Mercury previously defined on the basis only of Mariner 10 images.

This MESSENGER image was taken from a distance of about 18,000 kilometers (11,000 miles) from the surface of Mercury, at 20:03 UTC, about 58 minutes after the closest approach point of the flyby. The region shown is about 500 kilometers (300 miles) across, and craters as small as 1 kilometer (0.6 mile) can be seen in this image.