Thursday, April 9, 2009

Flying saucer galaxy!

Hubble spies invading saucer from space!

Hubble image of spiral galaxy NGC 7049
Click to Brobdignagify.

OK, it’s not an alien spaceship. But Holy Haleakala, what a gorgeous galaxy! It’s NGC 7049, a kind of hybrid galaxy, one that is part disk (like our spiral Milky Way) and part elliptical. These types of galaxies are fairly rare. They are shaped like disk galaxies — a flattened disk surrounding a central bulge — but have almost no gas compared to a normal spiral galaxy. It’s the gas that makes spiral galaxies obvious to the eye. As gas orbits the galactic center in a disk, odd gravitational instabilities build up, creating spiral-shaped traffic jams in the disk. Gas piles up there, collapses, and forms stars. The stars light up the gas, and from a few dozen million light years away, you see a gorgeous spiral galaxy.

But NGC 7049 is not gifted with gas, so the disk is fuzzy and featureless… almost. This galaxy does have a ring of beautiful dust lanes circling the center, which is unusual even for these types of galaxies! We see the dust in silhouette because it absorbs light from stars, blocking the starlight behind it. It takes a considerable quantity of dust to absorb that much light, which is weird– dust is usually formed when there’s lots of star formation. But without gas, NGC 7049 can’t make new stars, and so there shouldn’t be much dust. What gives?

My first thought when I saw this picture was that the galaxy must have recently eaten a smaller galaxy and taken on all its dust. And it turns out that may very well be the case. Studies of these types of galaxies shows that some do have gas, but in some cases the gas is orbiting the galaxy in the wrong direction, the opposite direction as the stars do. That’s a sure sign that a smaller galaxy got too close, collided with the larger galaxy, and finally merged with it. In some of those events the geometry of the collision with smaller galaxy will yield a counter-rotating block of stars, gas, and dust.

So that’s probably what happened to NGC 7049. And now, a few hundred million years later, we reap the benefit of being able to see this spectacular and lovely galaxy.

Original here

Is a Death Star Poised for Final Supernova Detonation Aimed at Earth? Astronomers Say "Maybe"

Death_star Australian astronomers have been studying an intergalactic assassin poised to wipe out life on Earth. Maybe. Observations indicate that cosmological curiosity WR104 may be a killer - and we might be the victim.

The pretty pinwheel that makes the system so distinctive is now know to be a combination of two stars - a blue star orbiting the Wolf-Rayet 104. Note that the "Wolf-Rayet" name is the astronomical equivalent of a beeping red LCD countdown reading "0:01" - it's a swollen star getting ready for final supernova detonation. At the moment its fusion reactions are blasting its own photosphere off into space, where the blue companion orbits and illuminates the material, creating a seriously impressive spiral over twice the size of our solar system.

We have a perfect view of this pinwheel pattern, since the spiral is at right angles to us, in the same way a man being held at gunpoint has a perfect view of the little hole the bullets come out of. And the gun is over twenty-five times the size of the sun. When a binary system collapses into a black hole, which astronomers call 'coalescence' (a euphemism which makes 'heated debate' a valid description of World War II), it can release a gigantic burst of gamma rays. Gamma rays are the ultimate high energy electromagnetic radiation, and while the burst lasts less than two minutes it can contain more energy than the entire mass of the sun converted into energy by E = m c^2. You'll notice that the mass of the sun and the speed of light, c, are extremely large numbers.

On the upside we'll never see it coming. The EM-burst travels the speed of light so the only warning we'd have is dying - which most people will accept is a little too late. The dinosaurs certainly did (some scientists believe historical mass extinctions were caused by similar intergalactic "life reset button" gamma bursts). Even better, this Earthicidal explosion may have already happened with the lethal radiation already speeding its way right at us. On the other hand, the big boom might not happen for hundreds of thousands of years - and might do so without a peep of gamma radiation.

The combination of science and philosophy is a challenging field that many don't bother with, but this is a strong motivation to start. If you could die tomorrow, how would you like to live today?

Posted by Luke McKinney.

Original here