All Experts was the free question and answer service that for 19 years provided users with answers to their questions in a vast variety of subject areas from biology, medicine, geology, religion, politics, and psychology to astrophysics and physics. Since late 2004 I participated in the Astronomy forum - this before there was All Experts (it was known then as 'Experts Central') then three years later joined the astrophysics expert forum. Below I select some general questions from both forums that I had answered and which blog readers may find of interest. Enjoy!
1. Where would I look for an anti-matter galaxy or universe? (9/ 18/ 05)
Anti-matter is just the name given to matter which has its sub-atomic constituents (i.e. electrons, protons) reversed in electrical charge from normal matter. For example, normal hydrogen (matter) contains one proton (+ charge) for its nucleus, and one electron (- charge) whirling around it. Its counterpart, anti-hydrogen, contains one anti-proton (- charged) for its nucleus, and one positron, or positive electron (+ charged) whirling around it.
Interestingly, the behavior of such ‘anti-atoms’ would be subject to the exact same laws of quantum mechanics as its normal matter counterpart. Since absorption and emission of radiation would be governed by the same quantum rules, there would be absolutely no way to tell them apart in terms of the light we receive – say through a telescope. This means that on the basis of radiation received alone it is not possible to distinguish matter from anti-matter.
The only way for sure to tell an anti-matter galaxy exists, would be if it collided with a matter galaxy. In such a case, the two would mutually annihilate one another, leaving only energy behind. But a very great deal of energy!
However, it is wise not to get your hopes up for locating an anti-matter galaxy, star, or anything else. It appears that on the basis of some very complex experiments, to do with the ‘symmetry of sub-atomic particles, there is far more matter than anti-matter in the universe. Indeed, James Cronin, one of two physicists who won a Nobel Prize (in 1982) for a study of ‘symmetry violations’ believes the universe is overwhelmingly made of matter.
According to Cronin’s scenario, the early universe may well have been equally divided between matter and anti-matter, but this didn’t persist. Applying the results of his experiments – which showed an unequal rate of decay of K-mesons into pi-mesons, Cronin thinks the resulting asymmetry led to enhanced rates of matter production.
The end result is that any anti-matter is most likely in sub-atomic or at most simple atomic form. It doesn’t exist in as large an aggregate as a galaxy, and certainly not a universe.
2. Is it possible or conceivable to use black holes or worm holes to take a short cut through space-time and get to another distant part of the universe? (10/ 23/ 08)
For some time there has been speculation that black holes and white holes are connected to each other by what’s called a ‘worm hole’. The black hole as an object or ‘end’ where matter vanishes, and the white hole as a place where it re-emerges. (Some have opined that the distant bright objects called quasars are actually white holes). The general appearance of such a scenario is illustrated in Fig. 1.
In this diagram, the black and white holes represent equally open ‘rips’ in the fabric of space-time. The difference is that in the first matter is sucked in (by powerful gravity) and in the second it’s explosively blown out. The wormhole, meanwhile, represents the shortcut through space time linking the two.
One problem is that such a scenario or depiction is only believed plausible for a static black hole. Unfortunately, this type of black hole is not very realistic. After all, if a star is rotating when it collapses to form a black hole, it is doubtless going to be rotating (though much faster) afterwards. Hence, rotating black holes are far more plausible than static ones.
Could a rotating black hole work in place of the static one? Yes, but major problems would accompany this in terms of use for space travel. For one thing, it would no longer lead to one particular place in the cosmos, but to multiple places, at different times. This means there is no sure way to navigate to your destination through a wormhole. You could end up in a far different location to that you desired, or worse a totally different time.
Added to this, if black holes exist in the way general relativity leads us to suspect, it is doubtful they can be used as ‘gates’ to enter wormholes and get to another part of the cosmos. The reason is that the enormous gravitational pull exerted by a black hole would rend asunder any object in its vicinity. A space ship, therefore, would be ripped to shreds long before it could enter a black hole.
Finally, the whole theory of white holes has fallen more and more into disfavor. We now find that quasars, believed to be evidence for the white hole, could easily be the ejected cores of energetic galaxies. So, the same source that powers exploding galaxies, could also power them without invoking anything exotic like white holes.
It seems that it is better to enjoy (science fiction) tales of space ships taking shortcuts through worm holes for what they are, rather than projected plausible future scenarios.
There's absolutely no chance or possibility that the Sun will ever become a black hole. The reason is that it doesn't possess enough mass. In order to reach even minimal stage for an implosion leading to a 'collapsar' (neutron star, black hole etc) a star's mass needs to be at least 1.44 times that of the Sun. This was worked out decades ago by the Indian astrophysicist Subrahmanyan Chandrasekhar, and hence is called 'Chandrasekhar's limit'. Since there is no possiblity of the Sun ever becoming a black hole there is no need to worry over the Earth's fate in that regard.
4. What’s the worst thing the Sun could do to us? (3/ 19/ 12)
Probably, engulf the Earth and burn it to a cinder. This is basically a matter of physics. Right now, the Sun burns hydrogen in its center by fusing 4 protons to get helium. The energy released in the core nuclear reactions is enough to support the Sun’s outer layers of gas from collapsing and maintain a kind of balance. In this balance, the outward gas pressure produced by the released energy, equals the inward weight of the Sun’s layers.
The problems begin when the Sun uses up its store of hydrogen (protons) in the core. at that point, it will have to fuse the helium nuclei instead. Helium fusion produces less energy than hydrogen fusion. This means much more helium must be used, and this will raise the central temperatures as high as 100 million degrees. The increased core temperature in turn will cause the outer layers of the Sun to heat and expand. It's estimated that the expansion will be as much as three times the Earth’s orbital diameter or nearly 300 million miles. This will be enough to vaporize all the planets between Mercury and Jupiter. That includes Earth.
Fortunately, we don’t have to start worrying until the Sun’s hydrogen stores get down to only 10 percent of their current value. This will probably not be for another 4 to 5 billion years!
What about mammoth solar flares? See Fig. 2:
Well, it seems that there is a containment limit on their maximum (magnetic) magnitude which is set by the nature of the solar dynamo and how intensely its (toroidal) magnetic field can be "wound up" to spawn new sunspots in each cycle. Since flares are generally associated with large spots - especially delta class, we'd need to see them on the scale of about a quarter the solar radius in diameter to warrant a real fear factor. (For possible monster flares that might eviscerate the ozone layer or most of the Earth's atmosphere) . Thus far we haven't over recorded solar astronomy and there's little indication we ever will experience such an event, though it is best to say never say never!
No comments:
Post a Comment