back to article Boffins: Antimatter comes from black holes, neutron stars

Topflight astrophysics boffins believe they may have cracked the tricky problem of how to make antimatter, which would be useful for many purposes: for instance powering relatively practical starships, or - of course - blowing up an entire planet in one go. However, it appears that making antimatter requires the possession of a …

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@everything comes in twos - offtopic and long

A spaceship could totally descend through the atmosphere like a skydiver and not experience the burning-up, but it would have to slow down first. The man in a balloon is 'orbiting' the earth geosynchronously, by virtue of being coupled with the atmosphere, and so he has no net velocity in the tangential plane (neglecting wind currents). He's held aloft by his balloon and when he lets go he falls straight down, as viewed from someone down on the planet.

An orbiting spacecraft isn't held aloft by a positive bouyancy and so it isn't really 'aloft' in the same way: it's actually falling (at least, being accelerated towards the centre of the planet) but also it's travelling at right angles to the path it would fall so fast that, in the time it takes to fall a small distance towards the planet it's moved past the planet by such an amount (think of right-angled triangles) that it's no further away from the planet's centre, but is a few millidegrees round the orbital path and travelling with the same speed in a direction at right angles to the line between it and the centre of the planet, which is the identical situation to above but for a small rotation, so the same thing happens again and you move a few more millidegrees. It's all one smooth motion, and as you're out of the atmosphere (mostly) there's very little friction to slow you down and you can maintain an orbit with no energy input for a long time (the moon does not have engines, as far as I know, although that would be very cool).

The height of the orbit determines the linear velocity of the object, which is very high (>>thousands of mph). This is why geosynchronous orbit (its linear velocity as it travels round the earth is such that it covers one rotation in 24 hours, in the same direction as the planet rotates and therefore staying above the same spot) is a certain orbital band (i.e. between this height and this height). BTW outside the atmosphere you aren't influenced by the planet's rotation and you can orbit the planet travelling the opposite way, or from pole to pole, but inside the atmosphere you get dragged around with the planet.

To lower the orbit relative to the planet you just decrease your linear velocity, and gradually you enter thicker and thicker atmosphere, which exerts more and more friction. If you want to land, you have to slow right down from thousands of mph to zero (relative to the rotating earth now so you have to account for that too but it's a smaller effect). If you're moving too fast then contact with the atmosphere generates huge friction (the force is linearly proportional to velocity and in the opposite direction) and you burn up. This is what happens to shooting stars and whatnot, and why the shuttle has the heat resistant pads.

So the skydiver starts at height z with no horizontal velocity and no vertical velocity, and as he falls he accelerates (-d2z/dt2 - negative and second order with respect to time). His parachute exerts a drag force (dz/dt - positive and first order with respect to time) which reduces the effect of the acceleration. He's still accelerating though, and the faster he goes the greater the friction force until it counteracts the force exerted by gravity. At this point he is no longer accelerating, but still travelling at speed. The size of the parachute determines this eventual speed, aka terminal velocity. You aim to have this low enough to be able to survive impact at that speed, so it's far too low for the frictional forces to burn you up (although if you're skydiving from high altitude you'd have to wait until you got into atmosphere to deploy your parachute, at which point you might be travelling faster than terminal velocity and would need to slow down to it, so it might be close).

The shuttle on the other hand is also at height z and with no vertical velocity but a lot of horizontal velocity which is enough to make it burn up in contact with the atmosphere, and it loses some of it by decelerating with its engine until it can take the atmospheric friction, at which point it sheds the rest of its velocity that way. If it does it right it will find itself flying through the sky like a plane, and it then stays aloft by aerodynamics and lands like a plane.

The difference between the two is the amount of energy they initially posess. They may be in the same place in the sky (for a moment at least) but they have very different inertias and it's the shedding of this inertia which generates the heat, as it's done by friction. The shuttle could slow down using engines instead but it would have to use twice as much fuel then, which would mean taking even more fuel in order to get it up there in the first place.

Orbital mechanics are quite complicated, cause you've got two reference frames (one being the rotating planet, the other being the nonrotating surface of the planet's volume), two coordinate systems (rectangular works at small distances like manchester to london but spherical works better for orbits), and a gradual boundary between them, where teh atmosphere thins to next to nothing, and two very different inertia levels, the difference between them being determined by the gravitational pull of the planet and thus ultimately by its mass (escape velocity is a measure of the difficulty of getting off a planet of a certain size that comes from this difference in energy levels). To calculate orbits and burn times you need to factor all this in - I suppose it must be like sailing, where the world is divided into two half-spaces, each with a different vector field of instantaneous force vectors (wind currents and sea currents). The boundary between the two fields is more defined than in orbital mechanics though.

I would get my coat but I don't need one as my hull is impervious to atmospheric effects.

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Coat

I'm impressed, guys (and gals)

Less than 24 hours after El Reg reports an obscure cosmological discovery, 50 comments have been posted grappling with the possible explanations. Many of these are from people who seriously know what they are talking about. Several comments contain very good short descriptions of Hawking radiation and how it can lead to the "evaporation" of black holes, and speculating about mechanisms which might, just, explain how a black hole might spew out a cloud of anti-protons.

OK, a few made mistakes. A few thought that anti-matter behaves differently to "normal" matter under gravity, for example, but this was soon corrected in the debate.

This is what science is all about. We might never know "the truth" but we can get closer and closer to it with better and better theories, by debate based upon observed evidence (Popper!).

We seem to be mercifully free of creationism and intelligent design (CID) in this discussion. The CID squad are fairly relaxed about cosmology: the big bang fits some versions of their superstitions quite nicely. You need to point out that homo sapiens shared a common ancestor with the apes about 7 million years ago to make them go ape-shit. (Pun intended!)

There are (regrettably) theocratic states where the level of knowledge of advanced physics and cosmology shown in this discussion would be unimaginable.

I suppose I had better attach the "get my coat" logo to this posting and hunker down for the CID counter-blast.

Thanks for a great on-going discussion.

Pete

(Retired university lecturer. BTW, your standards of English grammar and spelling are still abysmal; please read your Lynn Truss! :-)

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Anonymous Coward

@Acidbass

Way to make a simple answer complicated !

What's wrong with :

A spacecraft is moving really fast in order to stay up in space and not fall due to gravity.

A skydiver is just falling straight down.

The atmosphere causes the heating on re-entry because of friction (difference in speed between atmosphere and spacecraft)

The skydiver isn't moving fast enough to cause excessive friction and so doesn't heat up.

Blackbird (US spy plane) did cause enough friction to heat up, but did not go into space.

So the one word answer is "speed".

To go deeper, you could come straight in slowly and avoid the re-entry burn in a space ship, but you would need to carry extra fuel to slow the ship down first, which due to cost, isn't done, and causes extra safety worries.

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Happy

So what is it?

CAT: So, what is it?

KRYTEN: I've never seen one before -- no one has -- but I'm guessing it's a white hole.

RIMMER: A _white_ hole?

KRYTEN: Every action has an equal and opposite reaction. A black hole sucks time and matter out of the universe: a white hole returns it.

LISTER: So, that thing's spewing time back into the universe? (He dons his fur-lined hat.)

KRYTEN: Precisely. That's why we're experiencing these curious time phenomena on board.

CAT: So, what is it?

KRYTEN: I've never seen one before -- no one has -- but I'm guessing it's a white hole.

RIMMER: A _white_ hole?

KRYTEN: Every action has an equal and opposite reaction. A black hole sucks time and matter out of the universe: a white hole returns it.

LISTER: (Minus the hat.) So, that thing's spewing time back into the universe? (He dons his fur-lined hat, again.)

KRYTEN: Precisely. That's why we're experiencing these curious time phenomena on board.

LISTER: What time phenomena?

KRYTEN: Like just then, when time repeated itself.

CAT: So, what is it?

They all stare at him.

CAT: Only joking.

LISTER: (Suddenly upright, and minus his hat, again) Okay, so it's decided then. We consult Holly.

CAT: Hey, wait a minute -- I missed the discussion!

RIMMER: (Suddenly on the bench, where the CAT used to be sitting) We all did.

KRYTEN: (Suddenly on the table previously occupied by LISTER) Time is occurring in random pockets. The laws of causality no longer apply. An action no longer leads to a consequence.

CAT: (Back on the bench) So, what is it?

KRYTEN: I think we've experienced this period of time before, Sir.

CAT: Only joking.

KRYTEN: And that one. Since we're no longer affected by the laws of causality, we can override these time jumps if we concentrate.

RIMMER: Look, the only way out of this is to consult Holly.

CAT: (Snaps fingers) I'll go with that.

KRYTEN: Gets my vote.

LISTER: Okay, so it's decided then. We consult Holly.

KRYTEN: Ah, I think we've just encountered the middle of this conversation!

CAT: So, what is it?

LISTER: Ooh, someone punch him out.

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Explanatory power of scientific myths

If you RTFA, it seems at bottom to be about nothing much at all: an asymmetry in the positron distribution is alleged to correspond to "a region in which there are believed to be a lot of binary star systems containing neutron stars or the even more outrageous black holes". But binaries, neutron stars (and black holes, of course) are supposed to be everywhere - what is the (statistical) strength of the alleged correlation? Is someone staking a pole in the ground here, or merely waving a flag about as a warning-off to others? This in turn seems to be nothing more than the astronomical equivalent of seeing a white patch in the sky and deciding to call it "fog".

Entertaining as all the shed-loads of speculations riding on top of that might be to Reg (not to mention Nature) readers, it is entertainment that costs serious money. Ignoring that every man, woman and child in the UK is now effectively invoiced for £1000+ over Northern Rock, it is not even remotely gladiatorial fun - and the Romans didn't go to the Colliseum to see a vocal contest between crowds of gladiators' supporters. That is simply not distracting enough.

There are no black holes. They are a fuck up of the mathematics. http://www.geocities.com/theometria/index.html.

Facts of observation need explanation - not an ever-burgeoning totem pole of figments of the imagination, each mythic ancestor propitiated with offerings from the faithful, and demonstrating its fertility by sprouting a hierarchy of ever more fabulous progeny, all imbuded with previously unsuspected magical powers.

This is what advancement in scientific theories has come to - not the power to explain a broader domain of facts, but power pure and simple, power as dominion, power reified and made anthropomorphic. My black hole trumps your neutron star - the pot is mine. (My "field" is bigger than your "field". My "forces" are stronger than yours. We imagine science is purely descriptive, but the centrifugal attraction of figurative language lures ever Siren-like). Ultimately another conflation of synechdoche with metonymy. Yet it curiously mirrors inverted many other features of society.

The causes of black holes are on this planet, and are growing more potent and threatening. We need an invasion of Tim Burtons.

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Flame

Here is a more complete explanation

For those who think that the matter/anti-matter interaction will destroy everything

mass of an electron/positron 9.10938188 × 10-31 kilograms.

E = M C^2

M = 2 x 9.10938188 × 10-31 kg ~ 18.22 x 10-31 kg

C = 300,000 km/s (rounded)

C^2 = 90,000,000,000 (9 x 10^10)

E = 1.6398 x 10-16 kg/meters (if I have my units correct)

This is : ~16.5x10-16 newton/meters, or ~12.16x10-16 Ft/lb (for us 'Mericans)

A fruit fly produces more force flapping a wing.

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Black hole -

is a large gravity 'well', true not even light can escape the gravitational pull - BUT - just as every other object of mass - the force of gravity drops off in inverse proportion to the square of the distance from the source.

g = GM/D^2, where G is the gravitational constant.

The point at which the gravity field of a black hole is reduced too, or reaches (depending on your point of view) a required escape velocity equal to the speed of light is called the Schwartzchild Radius, or Event Horizon. Matter at this point or closer to the gravitational source of a black hole can not escape. Any distance farther from the gravitational source, and it is possible for matter to escape the gravitational field of a black hole.

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How could a black hole/neutron star produce anti-matter.

1- possibility is, as has been stated before - the "vacuum pressure" of empty space produces virtual particle pairs - near a large gravity field, or potentially near a large enough magnetic field, the particle pairs can be separated, rather than being able to join back together and interact. One 1/2 of the pair enters the Event horizon for example.

2- would be Hawking Radiation - Black holes can evaporate (at least according to Steven Hawking). Hawking radiation is particle emission by a black hole, nothing I can find - quickly - indicates what form this particle would take. If the particle emitted is anti-matter, then it could escape the local area of the black hole along the magnetic field lines.

Both black holes, and neutron stars will have BOTH large gravity fields (duh) and magnetic fields.

Once separated, the magnetic fields will draw the particles apart. Electrons, as we should all know, have a negative charge - hence will be drawn toward one pole of the magnetic field, and Positrons (as we should be able to guess from their name and the fact that they are anti-particles to an electron) are positively charged and will be drawn toward the other pole.

Being very light and in very large magnetic fields, these particles will very quickly accelerate to speeds and energies needed to escape.

Most likely, the escape path will be along the rotational axis of the object - as this is usually where the magnetic poles also lie.

Hope this helps.

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Re: Positron just a reverse Electron @Gordon Ross

"@Aubry You are indeed correct. Give yourself a silver start. However, you could have earned yourself a gold star if you'd also mention that it is proposed that a postitron is actually an electron traveling backwards in time."

I already did in a comment to a previous article (you can do a search on El Reg if you really want). I even went so far as to point out that *theoretically* the entrie universe could be made up of a single photon bouncing back-and-forth through time. ^_^

Do I get my gold star now? Please?

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@Retired university lecturer (aka Peter Mellor)

>> We might never know "the truth" but we can get closer and closer to it with better and better theories, by debate based upon observed evidence (Popper!).

Slick use of quotes.

Because without them the truth of that statement is unknowable, except by assuming that Popper! was a God-who-Never-Lied (the evidence for this is underwhelming). It would also be tautological - truth is the product of better theories, but better theories are merely those which produce better truth. Round is nice for wheels, but circular reasoning is not much use in finding out what is really true, or what is really a better theory. In terms of social praxis (aka following the money), it implies "just keep on with the funding, and we'll find the bastard one day - right now we need a bigger telescope/cyclotron/office/remuneration package to do that". Shades of the hunt for OB-L there. Perhaps a telescope/etc big enough to let us read the labels on energy packets, then we can all unambiguously distinguish Hawking radiation from the fake designer goods (e.g. the radiations the Alien Greys are pumping at us from their orbiting spaceships)? So those quote marks are disingenuous - tantamount to admitting that science funding is a racket played on the public.

OTOH they really should be around "closer", don't you think. Does "closer" mean we will not know that we've got to the truth until like we're on top of it, perhaps having just fallen over it and sprawling (in agony or in ecstasy)? As I said figuratively, resort to figurative meanings to justify science makes the activity indistinguishable from that which say promotes totem pole enlargement (literally or figuratively) because they would then be so much closer to the Spirit in the Sky - or of course to those Alien Greys. But people with less curiosity about the natural world but with the same values of self-adulation have already mapped that semiotic structure onto their own bodies - and the surgeons are standing by. (In Rome wannabe PHs boast that Daddy has promised to pay for a boob job if they pass their exams). And natural scientists still wonder why they have trouble getting their message across...?

Not enough competition, one suspects. It's time to spread physics funding wider. And ensure the research can get published. And is made accessible. As for "getting the message across", forget your PhD in physics, this is the Media-Information Complex you're fishing in now.

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J
Coat

I saw, 57 comments...

...and wondered, what on Earth (or in the galactic centre) are so many people commenting on a story like this one?

Then it dawned on me: it must be the Trekkies!

But the important thing, and I suspect nobody has said it (can't be bothered to read it all): I want my anti-matter-powered flying car NOW!

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@luther blisset

"But people with less curiosity about the natural world but with the same values of self-adulation have already mapped that semiotic structure onto their own bodies"

I'm just guessing that your education was more sociological than scientific?

Your weltansanchauung discloses logical and verbal convolution and thereby a mode of cogiatation which is more phrenology-related than contemporary science-based, unless aforesaid science is contemporary with a pre-diluvian era. And the hippopotami wearing pink tutus in Disney's Fantasia also provide an equally striking and relevant metaphor, so this is worth including in the semantic and logical melange of mental regurgitation we are indulging in.

Aren't we clever?

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Silver badge
Alien

Truth Seekers ... Virtual Time Travellers?

"As for "getting the message across", forget your PhD in physics, this is the Media-Information Complex you're fishing in now."

Aka the Ministry of Flexible Truth, Luther? After all, it is only always a Temporal Convenience left unchallenged and/or triumphant against a challenge but it is always relative to the Past and for the Future we can easily imagine anything we would like to be True and create facts to fit around it ...... but with all due care and attention that they also remain imaginative rather than having any substance in historical fact lest it be a fabrication dreamt up to suit a covert agenda.

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