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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

#21

Post by pfdietz »

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.

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

#22

Post by kadoban »

caf wrote: post #8
api wrote: post #2

Primordial black holes are a fascinating topic. One of my favorite hypotheses is that "planet nine," a large possibly 1-5 Earth mass planet suggested by some orbital models to exist beyond Neptune and Pluto in the far outer solar system, may be a primordial black hole. If such a thing existed it'd be a black hole about the size of a billiard ball and would be extremely hard to detect. It would not emit Hawking radiat…

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?

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

#23

Post by [deleted] »

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.

[deleted]

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

#24

Post by dreamcompiler »

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?

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

#25

Post by vundercind »

gus_massa wrote: post #19
pixl97 wrote: post #18

Earlier quoted context omitted.

You toss off some mass as you pass the black hole and it gives a powerful boost.

Do you have a source for that?

Star Trek fans will recognize the name as that of a versatile light starship class often seen acting as science vessels.

https://en.m.wikipedia.org/wiki/Oberth_effect

FWIW I’ve read several explanations of why this works, including some confidently claiming that one or more of the others was wrong, and a couple of which kinda made sense as I was reading them, but not a one of them has made a lick of sense to me after I thought about it for a while. Despite all the attempts at understanding it, I still couldn’t tell you why it works (aside from “this math says it does” which is a shit answer)

[edit] the other thing you can do, even at the same time is:

https://en.m.wikipedia.org/wiki/Gravity_assist

But the specific effect in question seemed to be the Oberth Effect, given the mention of throwing off mass.

Gravity assist just relies on the body in question being really heavy and in (orbital, say) motion in some fashion that’s useful to you. Kinda “pulls” you along. You steal a negligible amount of energy from a huge body, which translates into some decent speed for your very-light spacecraft.

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

#26

Post by messe »

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?

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 receive a disproportionally larger increase in kinetic energy.

Because your potential energy falls off with distance to the black hole at the same rate regardless of the speed you're travelling at, your total energy upon escaping the black hole is much larger than it would be had you burned your thrusters outside its gravity well.

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

#28

Post by MeImCounting »

vundercind wrote: post #25
gus_massa wrote: post #19

Earlier quoted context omitted.

Do you have a source for that?

Star Trek fans will recognize the name as that of a versatile light starship class often seen acting as science vessels. https://en.m.wikipedia.org/wiki/Oberth_effect FWIW I’ve read several explanations of why this works, including some confidently claiming that one or more of the others was wrong, and a couple of which kinda made sense as I was reading them, but not a one of them has made a lick of sense to me after…

OK so I was totally confused by the Oberth effect and how it could possibly be and so did some research.

Now I have no idea why or how kinetic energy has a quadratic relationship with velocity, but it does. Something something work something something square of velocity, who knows. If someone could explain that to me like I'm 5 I would totally appreciate it.

But if we just take that as a given then we can develop an intuitive understanding of the Oberth Effect pretty easily if we remember that velocity is only relevant to a reference frame. So when you burn at periapsis (at top speed aka when youre closest to our black hole) your energy relative to the black hole is increased a lot more because for a given unit of fuel you add the same amount of velocity, and doubling your velocity is more than doubling your energy. That energy is what carries you up and away from the black hole and towards your apoapsis (or the stars)

It makes sense if we just pretend to understand why it is that somehow magically KE is proportional to the square of its velocity IDK

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

#29

Post by tsimionescu »

sandworm101 wrote: post #14
Loughla wrote: post #11

Earlier quoted context omitted.

I feel like if you were close enough for a gravity assist, wouldn't the tidal forces just tear the probe apart?

The tidal forces would be no different than using jupiter for an assist. You would still have the probe pass by at several thousand, several tens of thousands of kilometers. A close-in gravity assist may look better on paper, but the practicalities and speeds of such a thing are risky. One small error and the mission would be over quick, launched out at a radically incorrect trajectory.

Isn't the whole advantage that you could get much closer to the center of mass of the black hole compared to a planet, thus gaining much more kinetic energy per unit thrust, but also risking higher tidal forces?

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

#30

Post by tsimionescu »

Tostino wrote: post #12
Loughla wrote: post #11

Earlier quoted context omitted.

I feel like if you were close enough for a gravity assist, wouldn't the tidal forces just tear the probe apart?

Not necessarily. If you replaced the sun with an equivalent mass black hole, none of the orbits of the planets would change.

Sure, because none of the planets are anywhere near close enough to the sun to experience tidal forces. But if you were to approach the sun VS a sun-mass black hole, at some distance the difference would become noticeable through tidal forces (ignoring the massive difference in emitted radiation, of course).
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