Forgetting, for the moment, the difficulties of storing anti-matter if you get your hands on it (while positrons and anti-protons are capable of being stored in magnetic fields, if you combine one of each to form an atom of anti-hydrogen, suddenly it's magnetically neutral and can't be restrained so easily), are they saying that a BLACK HOLE, with gravity so MASSIVE that it can pull in EVERYTHING, including LIGHT, is actually *releasing* anti-matter?

Seriously?

Is that saying that anti-matter is not affected by gravity, or, even cooler, it's affected in the opposite way to normal matter?

Seriously?

I was under the impression that this happened when one of a pair of virtual particles was sucked into the black hole, and the other escaped. 50% of the time the particle that escapes will be an antiparticle.

uses anti-electrons (positrons) to look inside the human body.

Antimatter was theorised by Dirac a long time ago.

It has been known how to create anti-matter since the early '90's with the first

first antimatter created at CERN in 1995. They created anti-Hydrogen. Admittedly this was of a very high energy and subsequently very difficult to study.

The first low energy anti-Hydrogen was created in 2002 by the ATHENA project at CERN.

OK, so you might get to other places using antimatter before you die. But when you get back your spouse, kids and mates will be long dead. Not my idea of a happy life.

But knowing how to produce it is half the problem, surely the annihilation would destroy where the ever it was happening resulting in a big hole of nothing? What would happen then? Would it act as a blackhole might? Would everything else close up around it, like cutting a hole in paper and then buching the rest of the paper around the hole?

Would you even want to test it?

"Nor is it clear how the antimatter gets away from such massive gravity fields, to drift about the Galactic core getting annihilated."

Isnt antimatter supposed to have a repulsion to gravity rather than the attraction of matter?

"DOCTOR!!! My brain hurts..."

Is it just me or does it seem like the whole "dark matter" biz was dreamed up because no "reputable scientist" wanted to admit they hadn't a clue?

And as for black holes, I thought that NOTHING, not even LIGHT, could escape a black hole. Did science change when I wasn't looking? It is commonly accepted that there is a "supermassive" black hole (roughly several million times Solar mass) at the center of our galaxy and that the ludicrous gravitational pull from same is largely what holds the galaxy together as a spinning mass.

Further out on the tangent: how many gazillions of years before the black holes gobble up all matter in the universe? And is that where my keys went?

If you have a fiction called Perseus, it needs a horse to ride. Hence, you invent a fiction called Pegasus. But what's a hero without a maiden. So, you invent another fiction called Andromeda. Hero and maiden, how to get them together? To fix that problem you have a "thought experiment" - what if maiden needs to be rescued (from terrorists is good)? Great idea, really "works". And so, another fiction called Medusa. E cosi' via.

The more you invent, the better it all looks. The more fictions you have, the easier it is to juggle them together. The easier it is to "modify the behaviour" of your fictions on an ad hoc basis if your audience starts picking holes in your story. The more time you invest in all this, the more reluctant you are to give up your fictions. Especially if someone keeps throwing a lot of money your way to keep inventing them.

Things used to be so different when scientists paid for their own researches. For one, there was no incentive to cheat yourself out of the truth.

Any rag that can have scientists "pooh pooh"-ing each other; and not "expecting so much unexpectedness"; in the same article, should get a Pulitzer Prize. Or a silver poopa-scoop. Perhaps you could explain which one you'd prefer..

Black holes have long been thought to be a source of antimatter in the form of Hawking Radiation. The theory goes that empty space is fizzing with pairs of virtual particles that ordinarily pop into existence and subsequently vanish again after a fleeting instant. If such a pair span a black hole's event horizon, however, one of the virtual particles will be gobbled up by the immense gravity. The other is at liberty to be whisked away by a magnetic field, and there's a pretty good chance that it will be an anti-particle.

If you really want to give a physicist a headache, ask him why our universe is overwhelmingly dominated by matter rather than by anti-matter. On a related note, a spinning cobalt nucleus will spontaneously spit out an electron (beta decay), but it's always in the same direction with respect to the spin. Spooky. God definitely favours one hand over the other in our universe, but how does he know which one is which? After all, there's no external reference. Definitely spooky.

Perhaps I'm just being stupid... but, why is this a mystery?

It's been long thought that anti-matter would show anti-gravity - isn't the fact that it seems to escape such huge fields actually proof of that?

It could also be the reason WHY we see it in such large quantities - if matter/anti-matter is oalescing from the energy within (theory goes that when energy coalesces it forms equal quantities of matter and anti-matter) the only thing that will escape to be 'seen' is that able to escape the gravitational field.... i.e. something with anti-gravity, anti-matter...

So then this is about "snatching" ?!? P.H.? angle?

since electrons used to make an article like this are negativle charged, and anti-electrons are positivley charged... Does this mean I we built a register out of anti matter it wouldnt be cynnical about everything?

If that's the case, I dont want to know!!!

It that as radiation, or anti-radiation?

Perhaps this is an oversimplification of the conundrum, but is it not possible that antimatter escapes high gravity environments because it has inverse properties to normal matter that would be drawn to black holes? Simply put, if gravity attracts normal matter would not antigravity be required to attract antimatter?

As I understand it, antimatter still has positive mass, so it is affected by gravity in exactly the same way as normal matter.

Nothing can escape from a black hole from within the event horizon - the boundary where the escape velocity required equals the speed of light. However, virtual particle pairs leading to Hawking radiation form at this boundary, so there would be no theoretical problem with one of the pair (which will be half antiparticles) being catapulted out of the region by electromagnetic effects (similar to the way particles are handled in particle accelerators).

Do the EM fields around black holes preferentially fire out positively charged particles? If so, it would explain the massive amount of positrons out there.

"when you get back your spouse, kids and mates will be long dead. Not my idea of a happy life."

Take the kids and mates with you. Leave the wife behind to handle your financial affairs. One way or another, it's a happy return.

The leather one with the anti-tweed elbow patches, thanks.

Please, can we call time on the amateur physicists so confidently sharing their complete misapprehensions?

@Jamie and others: No, it hasn't "been long thought that anti-matter would show anti-gravity". Anti-matter particles have reversed spin, charge, and other properties compared to their matter partner particle, but they have positive mass and respond to gravity in exactly the same.

As to how they escape Black Holes: the Black Hole is only inescapable to a classical approximation, i.e. Einsteinian gravity. When you take into account quantum effects, particles can escape from very close to the horizon. Particle/anti-particle pairs spontaneously appear then mutually annihilate in empty space all the time (go look up the Heisenberg uncertainty principle for why). If they happen to appear very close to the horizon of the Black Hole, one can fall in while the partner shoots off into space before they can annihilate again, creating the appearance that the Black Hole is emitting particles (both anti-matter and matter).

*sigh* I guess this is what happens when people learn their physics from Star Trek...

Nothing spooky at all.

"...how does he know which one is which?" is like asking "Thermos bottles keep hot things hot, and cold things cold. How does the thermos know?"

Both are ill formed questions.

A black hole has a region (the famous event horizon) below which nothing can escape, but AT the event horizon the virtual particles of space, which consist of pairs of particles - one normal and one anti-mater - instead of recombining and neutalising each other can have one member swept into the black hole while the other, being just outside, can escape. This happens all the time and the idea that it does happen is actually what bought Stephen Hawkings his place at the top table. In fact, it is called "Hawking Radiation".

If there is some reason why the anti-particle is the one that escapes more often then that would make a black hole a net emitter of anti-matter.

BTW, the black hole pays the price for all of this and if starved of new material, will eventually evaporate as a result.

Well, that's what they tell me anyway.

Oh, and anti-matter has mass just like normal matter so it experiences gravity, not anti-gravity.

Luther,

You make IT sound all so easy, which it would be whenever you can resolve the model of the infinitely large with the infinitely small for ITs Mutual Equilibrium. Money cannot buy it of course, but throwing money at IT allows you to bask in Reflected Glory .

Although don't be fooled into believing that "one should not increase, beyond what is necessary, the number of entities required to explain anything" .... http://pespmc1.vub.ac.be/OCCAMRAZ.html .... because one needs to be able explain everything surely.

Do that and you have a priceless Gift which Generates AI Life of ITs Own ...just as you inferred/shared. ...... although you do sound somewhat bitter as if you have compromised yourself for filthy lucre rather than compromising filthy lucre for yourself.

Blacks holes suck in everything that crosses their event horizon (yes, even light) but, and this is really cool stuff worked out by "Mr Brainbox", Stephen Hawking, they expel energy.

The energy is known as Hawking radiation. Black holes are always expelling this stuff (they're not entirely sure what it is yet) and may actually evaporate.

It could be that the two are related - the radiation being emitted by the black hole is causing, or may actually, positrons.

is just bent space, that's why a massless particle like a photon is affected by gravity.

Mass bends space, and anti-matter has a positive mass.

A black hole bends space to such an extent that any passing particle massless or otherwise, matter or anti-matter, virtual or real is bent along a path into the black hole.

It hurts my head too but I find all this stuff fascinating.

What I would like to know is why the Universe came out of the big bang with such a large entropy and what happens to that entropy should the universe collapse back into a singularity. We will have to wait for a sucessful theory of quantum gravity to answer that.

Oh and what in the Universe makes light move, instead of putting it's feet up with a nice cuppa and watching an episode of Star Trek.

"We expected something unexpected, but we did not expect this" This is redundant: "did not expect this" implies, actually demands, that "this" is unexpected. But the statement opened with "we expected something unexpected". So the statement reduces to "We expected something unexpected, but this is unexpected"! So I guess they got what they expected?

@Hang On...

Read your current (astro)physics. Steven Hawkins at el have shown that black holes radiate energy (and thus information) back into the universe and thus "evaporate" over an amount of time proportional to the size of the hole.

@"Nobody knows exactly how black holes and neutron stars make antimatter"

Tesseract. If you take a human in "hyperspace" and turn him 180deg to our "reality" before inserting him, he theoretically could come back with his heart on the right, etc...

Since it is possited that Black Holes (and to a certain extent neutron stars) warp the fabric of space-time (no ST references, thank you), it should not be a hard stretch to come to the conclusion that AM is simply matter which has been subjected to a "twist" when it came into close contact with the vent horizon of the object in question.

I'll collect my Nobel prize when I go get my coat.

Antimatter gets away from the neutron star or a black hole by means of anti-gravity. It is like melted butter and flat teflon pan theory, even if you wanted to keep the butter on the pan it would repel the teflon and leak out (known as escape velocity in physics), totally unexpected yet gastronomically beautiful.

The 'temperature' (i.e. rate of release of hawking radiation) is inversely proportional to the mass of the black hole. The black holes in question will be ancient, and very massive due to aggregation, and just generally having lots of mass to eat in the middle of the galaxy.

further there is no reason why holes would favour emitting anti matter over matter - indeed what is emitted should be pretty much governed by probabilities. There is nothing to stop the black hole emitting a double decker bus, and provided the universe lives long enough (it won't - or at least probably won't) then it even becomes likely.

So this very large emission of one class of matter over another may give the practical cosmologists something to get excited about, but the theoreticians are all going to be having some long nights (and get quite excited too of course).

Given the relatively high concentration of matter in that space it may be that warped space time affects the probability in favour of anti matter. Which is weird since the period when spacetime was most warped (1st second or so of the universe) seems to have massively favoured matter. All very interesting, if rather puzzling.

Oh, and Luther (and amanfrommars) - Occams razor is definitely being used here. Our current best theories are generally fairly internally consistent, and do not multiply entities unnecessarily. Luther - by all means have a go at a simpler one to explain the evidence. It has to be useful, and have some predictive power to count though (no 'because the flying spaghetti monster says so' types of thing)

"And as for black holes, I thought that NOTHING, not even LIGHT, could escape a black hole. Did science change when I wasn't looking? "

Yes, it did. A chap named Stephen Hawking was reponsible.

"are they saying that a BLACK HOLE, with gravity so MASSIVE that it can pull in EVERYTHING, including LIGHT, is actually *releasing* anti-matter?"

Maybe it is somehow radiated, like Hawkins radiation...

1. A black hole has strong gravity.

2. The 'empty' void is full of teaming pairs of particles that pop into existence randomly, and bump into each other and anihilate each other almost instantly.

Therefore, as Hawkins proposed, at the edge of a black hole, when a pair pops into existence, occasionally one half of the pair gets dragged in by the black holes gravity, and the other doesn't. Leaving one extra particle in the universe. Therefore black holes appear to emit radiation.

Well thats the jist of it. So maybe something like this could be going on. Or maybe not. But what's said in the article doesn't necessarily mean that anti-matter isnt affected by gravity.

isnt it fact all things always have two parts, man,woman,light/dark,gravity,antigravitiy.

if black holes frow out more anti-gravity parts than gravity parts then do white holes do the opposit pull in anti-gravity particals and expel gravity particals as you might expect if equal and oposit in all things is scientificly true?.

"Oh, and anti-matter has mass just like normal matter so it experiences gravity, not anti-gravity."

again i wonder , if its not anti-gravity then what is anti-gravity, the above being true, it most exist as most anti-mass surely?.

OT

something else that bugs me, if the guy that went up to near space in the 60s(a few K above him)in that baloon and jumped out, without lots of friction making him burn up , why cant a space ship come in from slightly above his highest point (that few K)and that does have lots of friction and burns VERY hot.

why cant they come in/through at near zero speed and so not generate much friction as the .sky diver did just below them years before.

it just bugs me as i cant get any real satisfying answer.

Not that this article has much to do with Dark Matter, but here goes:

Dark Matter *has* been verified several times in the last few years. Initially, it was just a "guess" to plug a newly-discovered hole in current theories. But knowing that it might be out there, astronomers started looking for clues to its existence. Eventually, by design and by serendipity, they found it.

Google it for yourself, I'm too damned lazy. But you can start with www.badastronomy.com, they had something on these discoveries a few months back.

Dark Energy is currently in the same status as Dark Matter was initially. It plugs a hole in the theory. It might turn out like DM did, and reveal clues to its existence. Or it might not exist at all, and some other theory will be needed to "plug the gap".

As others have implied: "It's better to say nothing and be thought a fool, than to open your mouth and remove all doubt." i.e. keep your arrogant ignorance to yourself.

Light has seen all the episodes of Star Trek many times and is belting around the Universe looking for new ones.

Simple when you think about it really.

was the only way to explain why the universe is expanding faster rather than expanding slower or collapsing that being proven then dark energy must exist.

"...how does he know which one is which?" is like asking "Thermos bottles keep hot things hot, and cold things cold. How does the thermos know?" Both are ill formed questions.

Absolutely not. Your question is a trivial concern over thermodynamics. My point is that we live in a chiral universe and nobody knows why left or right dominates at the weak nuclear force level, in a similar way that matter dominates over antimatter. Further, to say that something is left or right *always* requires some frame of reference (transmit a TV show to an alien civilisation for example and the only way they will show it the right way round is if the movie shows a known star field or something that violates charge-parity or the like). Since the universe only has itself as a frame of reference, the only thing you can say about "left" is that it is not "right".

More about CP Violation and problems of symmetry at http://en.wikipedia.org/wiki/Cp_Violation

you can get anti matter to power a ftl of close to spaceship at a black hore, but you need a ftl ship to go and get it as they are far away.

That is useless

by stuffing a proton beam, OK quite a dense twenty-six gigaelectronvolt proton beam, onto a (cooled) 3mm diameter by 150mm long copper wire that had about *200*kilo*amps* flowing through it. Said wire dumped all sorts of junk out of the backend, some of which were Antimatter. A bit of filtering, magnetic meandering, concrete, boron and we had a beam of antiprotons. The team did this from 1981 onwards and got the Nobel Prize for physics in 1984 - but mostly for the clever faster than light beam antiproton beam densifier technology (Stochastic Cooling) which allowed the Antiproton Accumulator machine to feed the Super Proton Synchrotron and evince the W & Z intermediate vector bosons.

It was the Low Energy Antiproton Ring that first planned to decelerate an 3.5GeV/c pbar and see if, at rest , it floated UP or DOWN when acted upon by gravity. Hi Tim!

Since light has zero mass, it can move at the speed of light. Anything moving at that speed experiences infinite time dilation. Since movement requires time, light cannot be moving, so therefore exists at the point of origin and point is destruction simultaneously, even if these points are 15 billion lights years apart. Therefore, photons are not fast, just very long.

@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.

The question is more "Is there more anti-matter than matter forming?"

Virtual electron-positron pairs are constantly forming from the quantum vacuum. There should be an equal chance of the electron or the positron being the one captured.

Unless there is something to favour the electron being the one captured...

Very small mass difference (theyre always described as being the same)

Negative Charge being attracted to the Black Hole

Preference for electron spin direction

or something to favour the positron being repelled/ejected away from the hole

I can't imagine the particle density in the vacinity of a black hole is as low as "empty space" so you'd expect all the positrons to have a chance to annihilate

Maybe spinning black holes eject electrons one way and positrons the other?

"We expected something unexpected, but we did not expect this" is a contradiction in terms. If they did not expect what they got (2nd clause), it was unexpected and therefore expected (1st clause). But I was expecting a Spanish Inquisition pun... And an SI icon would be fitting...

OT re reentry from space: The parachutist was not in orbit. For the Space Shuttle to be in orbit around the Earth, it must be accelerated to something like 25000 km/hour (or miles/hour??). When it comes back down, it's hitting the atmosphere at something like this speed, which results in a lot of friction and heat. They can't come straight in, they have to skim the surface and bounce back a few times to get the speed down to where they can handle the friction... I saw a NASA guy heat up a tile with a blowtorch, then touch it with his hand - it wasn't even warm (I touched it too).

Since all black holes rotate and the interstellar medium has material in it (mostly hydrogen), is there a possibility that a static charge builds up around the black hole by simple friction? Would that account for -ve particles being sucked in in preference to +ve?

Hmmmm.

So antimatter does the opposite of matter.

And nothing can escape the pull of a blackhole.

Then that means antimatter will do the opposite to everything else meaning it CAN escape a blackhole?

As black holes (probably) have very strong magnetic fields and may be rapidly spinning, that would be enough to send positrons and electrons escaping at the event horizon in opposite directions. If the density of matter nearby is low enough, a significant proportion might make it far enough away to form clouds of particles?

@everything comes in twos:

Someone's been watching too much Red Dwarf again, haven't they?

"if black holes frow out more anti-gravity parts than gravity parts then do white holes do the opposit pull in anti-gravity particals and expel gravity particals as you might expect if equal and oposit in all things is scientificly true?."

Tsk Tsk.....

@ Mike Bell

"Further, to say that something is left or right *always* requires some frame of reference (transmit a TV show to an alien civilisation for example and the only way they will show it the right way round is if the movie shows a known star field or something that violates charge-parity or the like)."

Of course, making the assumption that the biology of the alien civilisations' viewing apparatus (eyes) is made up the same way as us, and can see the same wavelengths of light as us? With the level of biodiversity that we see within our own humble sphere, (and I'm thinking along the lines here that canines/felines see different wavelengths of light to humans, they can see movement of light on a TV screen, but not the definitive shapes (I'm sure I read that somewhere...)) who's to say that the aliens can even see what's being transmitted? Not that I'm booboo-ing your comment, just that sometimes assumptions can thow an idea so far off course.

Right, got that out of the way.

Where is the Paris Hilton angle?

Antimatter has opposite CHARGE to matter not negative MASS, so no antigravity for you trek fans.

The charges on atomic/subatomic particles are not the same as magnetism, which for atomic particles is based on spin (and for molecules also based on dipole moment) so anti-hydrogen is no more magnetically neutral than an antiproton, moreover a magnetically neutral element could not be held in a magnetic field. Sorry to piss on your chips, chaps.

I also imagine that the discovery of interstellar antimatter will not lead to laser swords, time travel, hovering skateboards, teleportation, warp drives or the possbility of finally meeting and having sex with humanoids sporting an amazing variety of different shaped latex foreheads and eyebrows.

One of the Stephen Hawking books I read, explained the phenomenom of Hawking Radiation. If you apply a quantum approach to the analysis of gravitational effects close to a black hole's event horizon, Heisenberg's uncertainty principle states that nor the position nor the speed of a particle can be precisely determined. In the conditions of extreme gravitational warps close to a singularity (an area where the laws of physics are rather unpredictable), a particle MAY exceed the speed of light limit for a very short amount of time (just enough to allow it to escape). That breaking the light barrier implies that the particles travel BACK in time, is an expected outcome since all paths that approach a singularity end at singularity itself. Remember extreme gravity does funny things to the laws of physics. This could be complete bollocks of course, Hawking himself admitted that he wasn't sure this was the correct explanation and that a quantum theory of gravity has not been developed yet.

Anti-matter behaves EXACTLY like matter, follows gravitational warps (its attracted by gravity), is affected by electromagnetic fields, and is affected by the strong and weak nuclear forces to both radiate and form atoms. Negative energy, however, behaves in an opposite fashion than natural energy. Negative energy can be created by hermetically closing off a region between two perfectly flat plates, extracting ALL particles and cooling the whole system to absolute zero. Because the region between the two plates is hermetically sealed from the outside universe and it is at absolute zero, the net energy between the plates is zero. However because of the Heisenberg uncertainty principle, the virtual particles that are created both between the plates and outside of them, create an energy deficit inside the plates. The virtual particle pressure outside the plates is greater that inside the plates which causes the system to have a negative energy state. Negative energy anti-gravitates but if you expose the fictional box, to the Earth's gravitational field, it will still fall down (the earth's field is still greater than the anti-gravity field). The above effect is called the Cassimir effect, and was theorized by Dutch physicist Hendrik Casimir and was used by Kip Thorne in the scientific basis for the movie, Contact. The effect has been experimentally tested and the Casimir force was detected.

British boffin, Paul Davies wrote about this in his book "How to Build a Time Machine".

This

Is it possible that the combination of matter and anti-matter does not result in total destruction but actually produces Dark Matter. That might explain why there is so much of it floating around undetected. It might also explain why we in the 'matter reality' see so little of the 'anti-matter reality'.

In a universal Big Bang event it seems conceivable that a huge proportion of the 'proto-matter' was split up into what we regard as matter and its opposite, anti-matter. When the two aspects meet they fuse back together to form the original proto-matter or what we regard as Dark matter.

Or is that too obvious?

"The charges on atomic/subatomic particles are not the same as magnetism... a magnetically neutral element could not be held in a magnetic field"

- until the charged particle starts moving relative to the magnetic field, which it must in this case due to gravity if nothing else. This being the principle behind the generation of aurora on Earth and the electric motor.

This used to be taught at GCSE as the left hand rule, but obviously physics education isn't what it used to be.

Of course the magnetic field around a black hole may not do anything other than concentrate the particles at the 'poles', as with the Earth's field. But initially at least positively and negatively charged particles would experience forces in opposite directions.

Dark matter is this generation of astronomers' Vulcan and, like Vulcan, it explains the observed results very nicely and can't be detected. And like Vulcan, it can't be detected because ain't there. In a third parallel with Vulcan, I'd bet the real reason comes from relativity or some other modification to gravitational theory.

The properties of anti-matter are reversed, but NOT mass.

Eg: Electron: Spin: 1/2 Electric charge: -e Mass: Me

Positron: Spin:-1/2 Electric charge: +e Mass: Me

Properties such as Strangeness, Charm, Spin, Charge, Topness, Bottomness, are reversed but mass is always conserved.

This is why a Messon (Such as a Si Messon) A combination of a Charm - Anti-Charm quarks has a mass of 3.1GeV/C^2 (and not Zero).

Looking at Gravity from general relativity it is a curvature in spacetime by matter or energy which means particles follow Geodesics (trajectories) which are the shortest routes (Like straight lines in flat space) this means they're falling in space not transfering force like electromagnetic interactions (photons) between them.

And If you look at it Quantum Mechanically then the whole process involves gravitons, lets wait for them to confirm the existance of these before we start conjuring up anti-gravitons which would mean Messons don't exist.

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.

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! :-)

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.

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.

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.

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.

----------

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.

----------

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.

"@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?

>> 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.

...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!

"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?

"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.