Milky Way's Black Hole a Gamma Source?

eldavojohn writes "A paper recently accepted for publication (preprint here) proposes a sound explanation for the source of the gamma rays that permeate our galaxy. The Milky Way's central object Sagittarius A*, widely believed to be a supermassive black hole, is now suspected to be the source. To test this theory, two scientists created a computer model to track the protons, flung outward with energies up to 100 TeV by the intense magnetic fields near the event horizon, as they make a random walk through the plasma environment. It can take thousands of years for them to travel 10 light-years from the black hole, where they collide with lower-energy protons to form pions. These decay into gamma radiation emanating from a torus-shaped region around the central object."

huh?

[mastershake_phd]

I thought the background gamma radiation was from the big bang and thus older than the galaxies?

Distribution of life?

[PIPBoy3000]

I wonder if that means that life is only possible near the outer arms of the galaxy? If you assume that gamma rays are a point source in the middle of our galaxy, what sort of radiation levels are you going to see closer to the center?

Do we know?

[pygmy_jesus]

I've been semi-interested in Cosmology/Astrophysics lately, and from everything I've seen and read so far, I've ascertained that we don't know much. Between dark matter, dark energy, gravity, black holes, big bang, etc. it seems like we just conveniently make up "stuff" to fit some model or equation. Do discoveries like this mean anything at this time considering there's no way to prove any of it?

Re:Distribution of life?

[Normal Dan]

There are already dangerous levels of radiation within our own solar system, however, we are protected by an atmosphere. I would imagine one of two possibilities. Any planet with the potential for life closer to the center of our galaxy would have enough shielding of some sort (either a thick atmosphere or a thick ocean) to allow life to form on almost any suitable location in the galaxy. The other possibility is, life can exist in high amounts of radiation, but it might not be life as we know it.

Re:Distribution of life?

[MollyB]

I'm no scientist, but as amateur astronomer and cosmology 'nut' I can say that even though the central portion (the "bulge") may have higher levels of radiation of all frequencies that would be damaging to life-as-we-know-it, the fact remains that out in the spiral arms of the galaxy there are many stellar nursuries (huge molecular clouds that occasionally have a shock wave pass through that can ignite new stars). These regions sometimes congeal a massive star which burns in a few millions of years rather than the multi-billion life our sun can expect. This star then explodes quite violently, and fries the surrounding neighboorhood, not only with electromagnetic radiation of many frequencies (gamma included), but would bombard nearby star systems with ionizing radiation (unhealthy stuff like the nuclei of iron, etc.) even if it is in the galactic suburbs.
So, maybe it is lucky it'd take about 30,000 years at the speed of light to get to the center; it is dangerous enough way out here, nevermind the comets and asteroids. 8)

Incorrect summary

[forand]

The summary makes it sound as though this is an explanation for the DIFFUSE gamma-ray emission seen in our Galaxy. This is not the case, the paper only discuss a source of gamma-rays observed to be spatially coincident with the Galactic center. Gamma-ray telescopes do not have high angular resolution so there is a possibility that the gamma-rays are not actually coming from the Galactic center in the first place. Finally this is not a new proposal. Proton acceleration near black holes is quite commonly discussed and accepted. Furthermore photo-pion production is a well known process that has been well measured in the lab. I think the real meat of this paper is that they are suggesting observations of emission associated with the black hole that we have observed gravitationally for a while now. This is the big news, not that the gamma-rays in our galaxy have been explained, not that protons make pions which decay into gamma-rays.

Re:Distribution of life?

[Dan Slotman]

Actually, other parts of the galaxy are farther from the milky way and other black holes. These arms, teeming with life, use gamma rays to communicate and travel. They haven't come calling since our arm is poisoned with radiation, making interstellar travel prohibitively dangerous!

High Radiation Life Forms

[Lord Balto]

Of course. Life evolves to fit the current conditions. In a high radiation environment, I can imagine a life form that takes advantage of the high radiation levels to rapidly mutate and evolve, increasing its chances of survival in a hazardous environment. Actually, there are plants on this very planet that for some reason have developed the abilty to mutate rapidly. The hawthorn for example. There was a point when there were hundreds of named species of hawthorn. Before the botanists realized the damned things were just mutating spontaneously.

Re:Do we know?

[MightyMartian]

I think the rate of expansion is an awfully good example. The standard inflationary model does have a problem in that it doesn't predict the expansion rate we see. Scientists have two choices when the data and the model don't jive. They can either toss the model and start from scratch, or attempt to alter the model to reflect observations. The decision to do either is one based upon how well other predictions of the model perform. In the case of the inflationary model, other aspects of the theory do explain other observations very well, so while we know there's a problem, we also know that it isn't a problem that completely devestates the existing theory. It means that the theory is not complete, and so, rather than tossing the theory, cosmologists and physicists will seek to refine the model, and that's what they're doing.

I suppose someone who doesn't understand the fundemental process might find dark matter and the like to seem ad hoc solutions, but when you consider that the main theory involved (General Relativity) does such an incredibly good job of modeling most of the other phenomona we see in the observable universe, it seems more reasonable to invoke something, possibly unseen, that could be playing a part, rather than tossing out an entire theory.

Re:Water Bears

[khallow]

Hmmm, you got to wonder if that's a fortuitous coincidence or if that amazing ability to survive was spurred by something in their environment. Now that I think of it, any organism that can exist in an indefinite "cryptobiosis" [wikipedia.org] state (ie, when all metabolic processes stop for a possibly long period of time) would do better if it had some of the above properties. In particular, the ability to survive extreme genetic damage is necessary IMHO. Suppose humans had similar abilities. If I entered cryptobiosis say in an "average" North American location, I'd receive a whole body dose of perhaps 3 millisievert per year (maybe much less since I'm no longer breathing carbon 14 and radon). Since I'm in cryptobiosis, I have no ability to repair radiation damage, it's like I experience this huge pulse of radiation damage.

According to here [uic.com.au], every 100 millisievert results in a 5% boost (supposedly) in average life-time cancer rates, and 1000 or more millisievert is life threatening. So 30-40 years gives me a 5% boost in cancer rates and 300-400 years of cryptobiosis gets me up to 1000 millisievert. I can't survive roughly 3000 or more years (10 sievert which is automatically lethal) because I literally receive a fatal dose of radiation before I have a chance to repair it. We ignore that there may be other ionizing processes (chemical or thermal, for example) that would vastly shorten this time.

Re:Distribution of life?

[Artifakt]

There are definitely at lest one other self replicating molecule already known (RNA). RNA however has a much higner rate of copying errors, and lower error rates actually promote selection (down to a minimum - obviously zero errors means no selection at all, but even DNA is somewhere still well above the calculated ideal error rate for fastest selection).
        This seems somewhat counter-intuitive, but if you think of a species as a set with somewhat fuzzy boundaries, more errors mean the boundaries are fuzzier. More members of a species deviate farther from the average type. Since enough members of a species usually survive long enough that the avaerage organism reproduces once, most members are already pretty well adapted to their niche. Higher mutation rates therefore mean more members are ill adapted, so selection actually slows down because more species get out of balance and die out faster and more often without leaving a successor species. A higher mutation rate also means more organisms have 2 or more mutations, and since most mutations are negative, a swamping effect occurs, where possibly good mutations don't ever get a chance to be selected. A really high mutation rate means genes don't just find themselves increasingly surrounded by defective partner genes, they actually get a chance of being overwritten before they linger for enough generations to be tested.
        For sexually reproducing species, the chance of not being able to successfully breed with a given other goes up very quickly, etc, so sex becomes a less successful option than parthenogenesis, etc, and again selection slows down even more.
        Most biologists think RNA was once dominant on our planet, and that there were other replicators, more primative and having higher error rates, before RNA. It's possible that some of these are more optimal under other conditions, i.e. more or less radiation, heat, or in other atmospheres. It's also possible some codes that were never developed here on Earth have developed in other places.