/ forum / (archived) How the idea for A* originated
Thu Mar 19, 2009 4:06 pm
Wikipedia's entry on Sgr A* is surprisingly weak; all it really tells you is that it's at the center of the galaxy, and probably a black hole. A better source is the Max Planck Institute for Extraterrestrial Physics; they did the pioneering research mapping the positions of stars at the Galactic Center over a series of years that showed some of them orbiting around the position of the A* radio source at incredible speeds: up to 10% of the speed of light. Calculating from that, they were able to tell that there must be an object there with a mass in the magnitude of millions of times the mass of our own Sun, which can only be a black hole. They have a nifty animation showing the positions of the stars they calculated on this page:
EDIT 1/1/14: ^ That link no longer works; the page has been moved and revised:
The other good visual source is the Chandra X-Ray Observatory Center site operated by the Smithsonian Astrophysical Observatory for NASA. There's too much dust and gas blocking our view of Galactic Center for it to be observed visually by Hubble, for instance, but X-rays go right through that stuff, so Chandra gets some of the best pictures of the place. Here's their A* X-ray image gallery: ... /more.html
However, if it's concrete information and the latest research that you want on Sgr A*, the best and basically only source I was able to find is the fantastic archive of recent academic research papers on the Galactic Center that's maintained by the Los Alamos National Laboratory on Cornell University's arXiv ("Archive") server:
Scientific research papers can be a bear to read through if you aren't, like, an actual scientist (I'm still trying to figure out what the heck "rotational temperature" is, for instance), but if you're patient you can still get a good deal of real information out of them. Wikipedia's entry on the Galactic Center doesn't actually give you any idea of what conditions there are like (I should probably try updating that for them, but my Wikipedia editing to date has consisted of removing four-letter spam words from a few articles that I've just noticed by chance :p, so I really don't know how to add information according to Wikipedia's standards), so I had to turn to Chandra and lanl.arxiv papers for actual info. Some of the better things on A* I found so far, for instance: ... index.html

Quote: "Even during the flares the intensity of the X-ray emission from the vicinity of the black hole is relatively weak. This suggests that Sgr A*, weighing in at 3 million times the mass of the Sun, is a starved black hole, possibly because explosive events in the past have cleared much of the gas from around it."
"...huge lobes of 20 million-degree Centigrade gas (the red loops in the image at approximately the 2 o'clock and 7 o'clock positions) that extend over dozens of light years on either side of the black hole. They indicate that enormous explosions occurred several times over the last ten thousand years."

Quote: "strong circumstantial evidence that a dense swarm of 10,000 or more stellar-mass black holes and neutron stars has formed around Sgr A*"
"roughly one quarter of the gas is in a hot component at 200 K" ... 7479v1.pdf

Quote: "the GC clouds present a wide range of temperatures from ~ 15 K to ~ 150 K"
"the whole GC region is permeated by radiation with an effective temperature of ~35000 K" ... "relatively hot stellar radiation" ... 9271v1.pdf

Quote: "any significant heating of the molecular gas is therefore confined to an area ~4 pc from Sgr A*"


So basically, a radius of maybe 15 light years or so around the Galactic Center seems to be so inundated with radiation as to be pretty much a death zone. And even much farther out than that there are areas covered by vast clouds of hot gas that would fry you to a crisp. However, if you could avoid those (;)), and you didn't do silly things like put transparent windows on your space ship--which would allow cosmic rays and other radiation in that would kill you off much faster than the worst cigarette habit--as far as I can tell you'd still be left with plenty of star systems in very dense clusters around that ~15 ly death zone where you could have all kinds of interesting adventures and maybe even not die right away. =D


Back to how I got the idea, while link browsing on Wikipedia one day I happened across an article
with a really fantastic picture Hubble visible spectrum picture
image by NASA/ESA (source:
showing a stream of subatomic particles rocketing out from the galaxy Messier 87 (that yellow clump in the upper left) at a speed measurable as a significant fraction of the speed of light; this "relativistic jet" (so-called, I think, because as you approach the speed of light, observably strange things begin to happen--time slowing down for you relative to something moving slower, for instance--as first described by Einstein's Theory of Relativity) is 5000 light years long.
I found that completely mind-blowing. Relativistic jets are shot out of the centers of some galaxies due to interaction with the gravitational pull of the supermassive black hole at the galaxy's center. This got me thinking about how cool it would be to have stories about humans adventuring in these galaxies, and then I started thinking about the stories I would tell in that setting if I could: who would be there, how they got their, what their motivations would be, how they'd survive and get around, and so forth.
My first choice for a setting was a particular galaxy sort of close to our own with a cool name that I don't want to mention right now because I might still make a series out of it one day =D, but then I got to thinking about it and realized that it would be really hard to explain humans getting to another galaxy without faster-than-light travel, since they're millions of light years away.
I didn't want to resort to hypothetical science like faster-than-light travel, so I had to find another setting. I found or remembered reading that there's a supermassive black hole--Sagittarius A*--at the center of our very own galaxy, "only" 30,000 light years away, and I thought I could come up with a way--albeit unlikely--to explain humans getting there. Combined with the hand-drawn animated cinematic process I'd been using on the Matrix Online, that's where the idea for A* came from; it seemed to me that the hard-edged noirish nature of those black and white drawings would be a pretty good fit for such a harsh and desolate environment, where without a nice protective atmosphere to block or spread out radiation, you'll get really sharp shadows.
This also fit in with the visual design of space settings that had really impressed me in two movies I'd seen recently: The Chronicles of Riddick and then its (better) prequel, Pitch Black. And I just like the power of contrast that rough black and white drawings can contain: work in that vein by artists such as Frank Miller and Frank Frazetta has had a large influence on me--not to say that I consider my own efforts anywhere close to the great things they've produced. I also adore old black and white noir films by people like John Huston (The Maltese Falcon), Howard Hawks (The Big Sleep), and Alfred Hitchcock (I Confess).
Also I just liked saying "supermassive black hole," and A* is a pretty keen name too, once you cut off the clunky "Sagittarius" part. =D I may have picked up an affinity for crazy-sounding names like those while transcribing the text of the wacky space shooter Explosion Invincible Bangai-O. In A*'s terms, I figured that the people who'd ended up in this rough and dangerous civilization around the black hole wouldn't waste time--and might not even know about--romantic things like ancient (especially for them) Roman names, and would stick with highly functional names, which Sagittarius-less "A*" fits to a T.
By the way, I'm going to move this to the A* forum, since it's directly related to the webcomic.