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Nasa’s Roman Mission Will Hunt for Primordial Black Holes

nasa.gov

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Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#31

Post by exe34 »

pfdietz wrote: post #21
breckenedge wrote: post #3

I really want primordial black holes to turn out to be the missing antimatter from the Big Bang, but I don’t think that could ever be tested. And of course a mechanism for this would probably need new physics since antimatter interacts the same as normal matter wrt gravity.

There were suggestions that the antimatter-matter asymmetry is because antimatter was preferentially segregated into a dense phase of hadronic matter, like quark matter nuggets. This would be interesting because if such nuggets could be found and captured, they'd be a potential source of energy by annihilation with ordinary matter.

Spicy nuggets.

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#32

Post by exe34 »

kadoban wrote: post #22
caf wrote: post #8

Earlier quoted context omitted.

Assuming you don't go so close that tidal effects tear the probe apart, the g-forces should only be those imposed by the probe's thrusters firing during the assist. When the thrusters aren't firing it's just in free-fall.

Hm, that can't be how that works, can it? How do you get any extra velocity then if there's never any acceleration beyond what your thrusters provide?

If you sit on a merry-go-round, and spin it very fast, you feel the "centrifugal force" trying to keep you in an inertial frame. That's because you're having to hold on to the ride. If you're in a spacecraft in orbit around Earth, you don't feel the force keeping you in a circular motion, because both you and the craft are experiencing the same force.

The worse thing about going past a blackhole would be tidal forces, which would exert differential stretching to your craft and you. I don't know the numbers for a blackhole that small. Also you'd need to aim very precisely - if you miss, it's a long way round to get back there and if you aim too well, it might take a chunck out of your craft and your left foot.

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#33

Post by [deleted] »

messe wrote: post #26
kadoban wrote: post #22

Earlier quoted context omitted.

Hm, that can't be how that works, can it? How do you get any extra velocity then if there's never any acceleration beyond what your thrusters provide?

It's called the Oberth Effect. In short, in Orbital mechanics, burning your thrusters deeper within a gravity well, results in a greater increase in kinetic energy than burning them further out. This is because momentum ~ v, while kinetic energy ~ v^2. If you're travelling faster—as you would be as you approach the black hole and fall deeper and deeper in your orbit—then you can expend to same amount of momentum to r…

[deleted]

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#35

Post by HeatrayEnjoyer »

messe wrote: post #26
kadoban wrote: post #22

Earlier quoted context omitted.

Hm, that can't be how that works, can it? How do you get any extra velocity then if there's never any acceleration beyond what your thrusters provide?

It's called the Oberth Effect. In short, in Orbital mechanics, burning your thrusters deeper within a gravity well, results in a greater increase in kinetic energy than burning them further out. This is because momentum ~ v, while kinetic energy ~ v^2. If you're travelling faster—as you would be as you approach the black hole and fall deeper and deeper in your orbit—then you can expend to same amount of momentum to r…

But you are still burning the same amount of chemical energy...

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#36

Post by at_a_remove »

dreamcompiler wrote: post #24
breckenedge wrote: post #3

I really want primordial black holes to turn out to be the missing antimatter from the Big Bang, but I don’t think that could ever be tested. And of course a mechanism for this would probably need new physics since antimatter interacts the same as normal matter wrt gravity.

What happens when an antimatter black hole collides with a matter black hole? We'd see gravitational waves but no photons, right? Would the grav waves reflect the tremendous energy release somehow?

No.

The "no hair theorem" states that black holes preserve exactly three numbers: mass, charge, and angular momentum. Baryon number, lepton number (as you would see in antimatter) are not conserved, the information is lost.

And, no, antimatter does not have negative mass, in any of the three contexts (mass-energy equivalence, inertia, and gravitational).

Therefore, a black hole fed entirely by antimatter would be indistinguishable from a black hole fed entirely by the equivalent matter.

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#38

Post by ibeforee »

HeatrayEnjoyer wrote: post #35
messe wrote: post #26

Earlier quoted context omitted.

It's called the Oberth Effect. In short, in Orbital mechanics, burning your thrusters deeper within a gravity well, results in a greater increase in kinetic energy than burning them further out. This is because momentum ~ v, while kinetic energy ~ v^2. If you're travelling faster—as you would be as you approach the black hole and fall deeper and deeper in your orbit—then you can expend to same amount of momentum to r…

But you are still burning the same amount of chemical energy...

Wikipedia says:

In terms of the energies involved, the Oberth effect is more effective at higher speeds because at high speed the propellant has significant kinetic energy in addition to its chemical potential energy.[2]: 204 At higher speed the vehicle is able to employ the greater change (reduction) in kinetic energy of the propellant (as it is exhausted backward and hence at reduced speed and hence reduced kinetic energy) to generate a greater increase in kinetic energy of the vehicle.

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#39

Post by ibeforee »

exe34 wrote: post #32
kadoban wrote: post #22

Earlier quoted context omitted.

Hm, that can't be how that works, can it? How do you get any extra velocity then if there's never any acceleration beyond what your thrusters provide?

If you sit on a merry-go-round, and spin it very fast, you feel the "centrifugal force" trying to keep you in an inertial frame. That's because you're having to hold on to the ride. If you're in a spacecraft in orbit around Earth, you don't feel the force keeping you in a circular motion, because both you and the craft are experiencing the same force. The worse thing about going past a blackhole would be tidal forces…

I was wondering that actually if the hole goes through your leg does it leave a hole or does your whole body get sucked in.

I imagine it is the whole body unless you are travelling really fast at the time. Like near speed of light.

Because the gravity outside the event horizon will still be crazy strong going out for several km (earth is a good comparison in the gravity is still fairly strong about 6000km from the centre)

Re: Nasa’s Roman Mission Will Hunt for Primordial Black Holes

#40

Post by dotancohen »

messe wrote: post #26
kadoban wrote: post #22

Earlier quoted context omitted.

Hm, that can't be how that works, can it? How do you get any extra velocity then if there's never any acceleration beyond what your thrusters provide?

It's called the Oberth Effect. In short, in Orbital mechanics, burning your thrusters deeper within a gravity well, results in a greater increase in kinetic energy than burning them further out. This is because momentum ~ v, while kinetic energy ~ v^2. If you're travelling faster—as you would be as you approach the black hole and fall deeper and deeper in your orbit—then you can expend to same amount of momentum to r…

The phenomenon described is not due to the Oberth effect.

What would be happening would be that the human in the spacecraft, and the spacecraft, are accelerating at exactly the same rate because they are accelerating due to gravity. Thus, the human feels no pressure accelerating him (no outside force acting upon him) from e.g. his seat. And his internal organs feel no pressure accelerating them from each other. They (the craft and the human and all his internal organs) are in free fall together and feel no forces acting upon them despite the whole system (craft-human-organs) being accelerated to tremendous velocities.

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