|
|
|
M-31_V1, THE star in the Andromeda Galaxy that changed everything, Click on the arrow (just to the right of center) for a full resolution image (downloadable, 3.8mb) Click Here to see a close up, 10 arc minutes, field of view |
|
The point of this picture, was to see if I could capture a single star in another galaxy, far far away. The galaxy is Andromeda, (M31), our sister galaxy. An arrow in the picture points to THE star that Edwin Hubble noticed, that changed everyone's understanding of just how big the universe is. When Prof. Hubble compared this star in other photographs, he noticed that it was changing brightness with a regular rhythm and pattern, which meant it was a Cepheid Variable (see below). He was actually looking for just such a star, because already at that time, astronomers knew if a star changed brightness (magnitude) with a particular cycle, then it had a related, specific, light output, Sort of like knowing it had to be a 100 watt light bulb. It could not be a 50 watt bulb, just closer, or a 200 watt bulb, further away. So, if you have a "100 watt bulb" that appears really really dim, then it has to be really really far away. Once Hubble measured the brightness of this star, he could figure out how far away it was. He was stunned that the answer was that this particular star was at least a million light years away. Therefore too, M31 in which this star resided, had to be absolutely huge. Or in other words, what everyone thought was a proto-planetary disk, nearby, in our Milky Way, was way too big and way to far away to be anything but a whole other galaxy. And then, he realized that probably all the other presumed "proto-planetary systems" were almost certainly galaxies too. Can you imagine what it must have felt like to be the first person to come to this "cosmic" realization? And with the evidence to back it up too! What's more, ALL the other now transfigured "proto-planetary disks" are smaller than Andromeda, so probably, they were even More distant! This discovery forever reset our concept of the vastness of the universe. It took the biggest telescope in the world at that time, the 100" Hooker telescope near Pasadena Cal, a multimillion dollar telescope, to take the pictures Hubble examined back in the 1920's, (hardly 100 years ago). I wondered if an amateur like me with a mere 11" scope and a ten year old off the shelf DSLR camera could get a picture of that now famous, and very faint, and distant star. To my surprise, I can, and I did!! Its at magnitude 19, which is close to the limit of what is possible from my semi urban back yard. But with multiple 10 minute exposures, digitally stacked and enhanced, stars like this one can be seen, with just the equipment available to us amateurs today, at about the cost of a good fishing boat and trailer. CEPHEID VARIABLES, more about them Cepheid's, are giant, unstable, very bright stars. They are 30 to 80 times larger diameter than our sun, and can be as much as 10,000 times brighter. Which is why we (even I) can "see" them millions (2.5 in this case) of light years away. They pulse brighter and dimmer in stable cycles in repeating time frames. Some Cepheid's cycle in as little as one day and some take as long as two months. (M31_V1 is just over 30 days) Cepheid's are old, reddish and yellow stars, but in their prime, they used to be gigantic, brilliant blue stars. They've converted (fused) all their core hydrogen into helium, and have blown off a lot of their outer layers. What's left in the core is helium, with not quite enough surrounding mass (gravity) to squeeze (fuse) the helium into carbon, at least not at a steady rate. But there is enough mass to fuse some of the helium together from time to time. When the fusion happens, the explosive force (think atomic bomb, only much worse) pushes the surrounding mass away, and with the overburden pressure relieved, the fusion stops, but when the fusion stops the surrounding mass comes crashing back in, squeezing the core back together again to start the process over, and over, and over again. It can go on in a predictable rhythm for 10's of thousands of years. So that Dr Edwin Hubble could notice it, figure out and realize what it meant, tell everyone about it, and we all could come to the realization of just how big the universe is. And we could name a space telescope after him.
|
|
11" F10 Schmitt Cassegrain telescope (Celestron C11 HD Edge) on an Astrophysics (AP1100) tracking mount,
Canon 5D Mark II camera, at prime focus photos averaged together, then brightness and contrast enhanced to bring out the stars |