Andromeda: Beauty And The Beast
/ sciencereason ... The Hidden Universe (Episode 1): Andromeda - Beauty and the Beast.
This is the Hidden Universe of NASA's Spitzer Space Telescope, exploring the mysteries of infrared astronomy with your host Dr. Robert Hurt.
In Greek Mythology, the Princess Andromeda was sacrificed to appease a sea monster's appetite. But astronomers are learning that the Andromeda Galaxy is less the spiral beauty and more the voracious beast.
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At a distance of 2.5 million light years, Andromeda is still the closest spiral galaxy to our own Milky Way and was considered to be nearly its twin. In fact, Andromeda, or M31, is over twice as large, holding about a trillion stars.
Traditionally astronomers thought it was a classic spiral galaxy with graceful, tightly wound arms. This was based on how spirals typically appear when seen from the edge. But from this perspective its just plain hard to see whats going on in the disk. The stars are all jumbled together with the dust lanes that trace the spiral arms.
This is where the infrared eye of NASAs Spitzer Space Telescope can help sort things out. When viewing galaxies at infrared wavelengths, the dust lanes glow. Spiral arms and other structures are easy to see.
Spitzers view of Andromeda is nothing short of spectacular. In the shorter wavelengths from the IRAC instrument we see both the stars and dust lanes in sharp detail. At longer wavelengths seen by the MIPS detector, the starlight mostly fades letting us study the warm dust directly.
Without the confusion of stars, we see Andromeda is missing one pretty common element of most spiral galaxies: the spiral! Stretching the image to simulate what wed see from above, its clear that most of the dust in this galaxy lies in a ring, not in arms at all.
What happened to the arms? The smoking gun, or rather speeding bullet, can be seen near the disk of Andromeda. Known as M32, this small satellite galaxy seems to have had a big impact. Astronomers have deduced that about 210 million years ago, while dinosaurs ruled the Earth, M32 plunged through Andromedas disk.
Computer simulations show that such an encounter will disrupt spiral arms. Theyll morph into rings like gravitational ripples in a galactic pond. The simulations very closely match the dusty rings we see today.
Combining the infrared view of Spitzer with the ultraviolet light captured by NASAs Galaxy Evolution Explorer offers yet another perspective. The disrupted ring and irregular splashes of the hottest young stars highlight the ongoing disruption in Andromeda. While M32 has for now ruined a beautiful spiral, its own fate is sealed.
Greek mythology, rather stereotypically, recounts that daring Perseus rescued Princess Andromeda from the big, scary sea monster. But in a case of scientific role reversal we see the Andromeda galaxy is no helpless appetizer but a devouring beast itself. There are signs that its already gobbled up other small galaxies, claming their stars as its own. M32 will be the next snack, but the main course is yet to come.
In as little as 5 billion years, about the life expectancy of our sun, Andromeda and the Milky Way will likely collide. Our own Galaxy will merge with the larger Andromeda after a pretty spectacular show. Perhaps we need the rescue!
It just goes to show that appearances can be deceiving, in both pizzas and galaxies. Looking at either from a new perspective, like Spitzer has done with Andromeda, can yield interesting, and even tasty, surprises.
• http://www.spitzer.caltech.edu/
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