All posts for the month July, 2010

A New Mars Map from the Mars Odyssey

A screen grab of a zoomed-in portion of the THEMIS mars map. Click to enzoomify. Courtesy NASA/JPL and THEMIS team, University of Arizona.

Well, this is cool.  You can browse the most-accurate map of Mars, created by images from the mars Odyssey spacecraft, at your leisure at the click of a mouse.

The map consists of nearly 21,000 images from the Thermal Emission Imaging System ( THEMIS). This is a  a multi-band infrared camera on Odyssey built and tended by researchers at Arizona State University’s Mars Space Flight Facility in Tempe, in collaboration with the folks at NASA JPL.  This work has been an eight-year-long project.  The were smoothed, matched, blended and cartographically controlled to make a giant mosaic.
So, check out the link above. You can pan around the images, zoom in quite closely, and almost get a feel for “being there” on the Red Planet. At full zoom, the smallest surface details are 330 feet wide.

Carina’s Starry Nebulous Beauty

The hot Wolf-Rayet star WR 22, part of the Carina Nebula's population of hot, massive stars. MPG/ESO La Silla.

Astronomers have their favorite places to study in the cosmos — places they return to again and again.  They do this not just because the places look pretty or are easy to spot.  Some places in the cosmos just command our attention because they have SO much going on and can teach us a great deal about processes like starbirth and star death.

Such is the case with the Carina Nebula. It lies a few thousand light-years from Earth and contains regions of starbirth, one very eye-catching example of incipient star death, and a lot of gorgeous clouds of gas and dust that are stellar nurseries.  Astronomers used the European Southern Observatory’s Wide-Field Imager to zero in on a very bright, very unusual star called WR 22.  It’s a Wolf-Rayet star, a rare and very massive (some 70 times the mass of the Sun) object that is shedding its atmosphere into surrounding space — contributing to the rich collection of recyclable star materials in the Carina Nebula. WR 22 is actually one member of a double star stystem.

WR 22 fronts a backdrop of glowing hydrogen and other gases. Heat and intense ultraviolet radiation from stars such as this one causes those clouds to light up. If the radiation is intense enough, it can eat away at the clouds.   This leaves less material to create new stars, resulting in a sort of cosmic cannibalism by the massive stars already in existence.  In the not-too-distant future, WR 22 will probably evolve to become what’s called a luminous blue variable star, and then spend much of its remaining time going through different phases of hydrogen and helium burning before dying as a Type Ic supernova.  Their future is a pretty standard one for stars of their mass and type.  But, since there are only a few hundred known Wolf-Rayet stars such as WR 22, they are objects that astronomers watch as much as possible, returning to them often to chart their progress down their evolutionary sequences.  For the rest of us, we get to peer over the shoulders of astronomers who study these babies — and we get to marvel at the gorgeous scenes in which these stars appear.

Hyper-Velocity Star Wanders in the Wrong Neighborhood

An artist's conception of a star getting the boot from the Milky Way Galaxy. Courtesy: STScI

What happens when a little group of stars traveling together through the galaxy find themselves in the wrong neighborhood? If it’s the hyper-velocity (meaning super-fast, moving at 2.5 million kilometers per hour, or three times the Sun’s velocity through space) hot blue, supermassive star  HE 0437-5439, then the scenario is one worthy of a TV detective show.

It’s one that astronomers have pieced together, like CSI technicians at a cosmic crime scene.  The only evidence they have is the star itself.   It’s hot, massive, and blue.  It’s at least 100 million years old, since that’s how long it would take for such a fast-moving object to travel out along the trajectory it has been following from the center of the Milky Way. By all rights, a 100-million-year-old star this massive should have burned out by now. Instead, there it is, speeding away from something that happened to it.

The most likely explanation for the star’s blue color and extreme speed is that it was part of a triple-star system traveling happily along through the galaxy. At some point it wandered in the wrong place. That started a gravitational billiard-ball game with the galaxy’s monster black hole. And, where three stars were first involved, one got sucked into the black hole and the other two merged to create the hot, massive star that then got the gravitational kick out of the galaxy.

This concept for imparting an escape velocity on stars was first proposed in 1988. The theory suggests that the Milky Way’s black hole should eject a star about once every 100,000 years. And so, here is HE 0437-5439, a supermassive blue star that should be dead by now, but instead it’s blasting away from the Milky Way, having once been the leftover pair of stars given the boot by a gravitational assist from the unlucky third member of the triplet as it was devoured by the black hole.

As the remaining pair rocketed away, they went on with normal stellar evolution. One of the pair wa a massive star and it puffed up to become a red giant. Eventually, it enveloped its partner. The two spiraled together and eventually merged into the superstar “blue straggler” we see today.

So, as they say on one of the CSI episodes on TV: what’s the evidence? How can we know what happened hundred million years ago and to such a massive star?  Based on the speed and position of HE 0437-5439, the star would have to be at least 100 million years old to have journeyed from the Milky Way’s core. Yet its mass — nine times that of our Sun — and blue color mean that it should have burned out after only 20 million years — far shorter than the transit time it took to get to its current location.

To solve the puzzle of a massive star traveling so fast away from the core of the galaxy required a number of observations to chart the star’s path. It was first discovered by the Hamburg/European Southern Observatory survey in 2005.   HE 0437-5439 was then observed by the Hubble Space Telescope, which charted the star’s position in 2009. Astronomers then compared that position with positions calculated in the images taken in 2006. They could figure out its trajectory, which took it very near the core of our galaxy. The rest of the story is based on deducing the mass of the star and then using stellar evolution to come up with a plausible scenario of how such a massive star could end up where it is, traveling so fast.

There are more of these high-speed stragglers to study, and astronomers may likely find that some of them also wandered where they shouldn’t have, suffering a similar fate to the progenitors of HE 0437-5439. Stay tuned!