[HN Gopher] Nasa's Roman Mission Will Hunt for Primordial Black ...
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Nasa's Roman Mission Will Hunt for Primordial Black Holes
Author : gmays
Score : 126 points
Date : 2024-05-09 22:33 UTC (2 days ago)
(HTM) web link (www.nasa.gov)
(TXT) w3m dump (www.nasa.gov)
| api wrote:
| 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 radiation (Hawking temperature still below the CMB),
| so the only thing it would emit would be when it encountered
| something and tore it apart. In that case you'd see X-rays, gamma
| rays, etc., but maybe only briefly. Only way to find it might be
| to model orbits accurately enough to predict its position and
| then look for gravitational lensing.
|
| If this companion object did exist it'd be a gigantic discovery
| of huge importance. It'd be within reach of probes, making it
| possible to study and even do experiments on to investigate
| things like quantum gravity. It could also be used in tight
| gravity assist flybys to accelerate probes to incredible
| velocities, maybe making interstellar probes a lot more
| practical. It'd be our very own way to yeet stuff to the stars,
| assuming these things could withstand insane g-forces (so
| probably not humans unfortunately).
| ryandrake wrote:
| > It could also be used in tight gravity assist flybys to
| accelerate probes to incredible velocities, maybe making
| interstellar probes a lot more practical.
|
| Would 1-5 earth masses really provide enough of a yeet to
| appreciably affect the speed of a probe? Jupiter is about 300+
| earth masses and we're not flinging probes out to stars using
| him.
| dooglius wrote:
| We did, Voyager 1 and 2 used Jupiter to get out of the solar
| system
| Sharlin wrote:
| And the Pioneers and New Horizons too.
| bigyikes wrote:
| You can get a lot closer to the center of mass of the black
| hole, which should drastically increase acceleration since it
| falls off with distance squared.
| gus_massa wrote:
| The satelite acelerates when it aproach the planet, but
| most of it is compensated when it goes away. There is a
| nice graphic in https://en.wikipedia.org/wiki/Gravity_assis
| t#/media/File:Voy...
| pixl97 wrote:
| You toss off some mass as you pass the black hole and it
| gives a powerful boost.
| gus_massa wrote:
| Do you have a source for that?
| vundercind wrote:
| 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.
| MeImCounting wrote:
| 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
| caf wrote:
| 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.
| kadoban wrote:
| 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?
| messe wrote:
| 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.
| HeatrayEnjoyer wrote:
| But you are still burning the same amount of chemical
| energy...
| ibeforee wrote:
| 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.
| perihelions wrote:
| It's super un-intuitive, but you're indirectly harnessing
| the gravitational potential energy of lowering your
| propellant into a gravity well and leaving it there. The
| overall orbital energy gain of the spacecraft can exceed
| the chemical energy of the fuel.
| lxgr wrote:
| Wow, that's an amazing intuitive explanation of "where
| the extra energy comes from" in an Oberth effect burn
| that I haven't heard before. Thank you!
| dotancohen wrote:
| 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.
| perihelions wrote:
| Your parent comment is the textbook definition of the
| Oberth Effect phenomenon. I think you've misread
| something.
| dotancohen wrote:
| I mean to say that the Oberth effect is one phenomenon,
| and that the lack of a feeling of acceleration is another
| effect.
|
| The Oberth effect itself is not responsible for the lack
| of feeling of acceleration during the assist.
| exe34 wrote:
| 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.
| ibeforee wrote:
| 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)
| dotancohen wrote:
| Black holes warp the spacetime around them, so your idea
| of distance is isn't really valid. Also the idea of time
| is warped as well, so the black hole doesn't quite just
| pass through your leg as you expect.
|
| Nor does the black hole "suck" anything in.
|
| What would happen from your perspective if such a black
| hole were to pass you at high velocity would be the same
| as if you were to pass the black hole at high velocity.
| From your perspective, you would begin orbiting that
| object, carried along with it. So would all the matter
| near you. But it would be matter, not objects, as the
| tidal forces would spaghettify all objects very quickly.
| pavel_lishin wrote:
| Depends on the size of the hole. If it's small enough,
| all you might get is one long bruise due to tidal/gravity
| effects, without losing a single atom of your body
| Loughla wrote:
| I feel like if you were close enough for a gravity assist,
| wouldn't the tidal forces just tear the probe apart?
| Tostino wrote:
| Not necessarily. If you replaced the sun with an equivalent
| mass black hole, none of the orbits of the planets would
| change.
| tsimionescu wrote:
| 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).
| jebarker wrote:
| I'd like to see a simulation of what that would look like.
| I mean, if by magic the sun was replaced with an equivalent
| mass black hole in an instant would anything be visible
| from earth before the inevitable freeze?
| utensil4778 wrote:
| From Earth's perspective, you wouldn't see anything
| interesting except for the sun vanishing.
| Gravitationally, all that matters is the absolute mass,
| so all the dynamics of the solar system stay the same.
|
| A black hole of 1 solar mass has a radius of something
| like 3km. Totally invisible from Earth. You probably
| wouldn't even see any gravitational lensing. All we would
| see is the sun there one moment, and then nothing the
| next.
|
| Life on Earth would continue for a while, but the planet
| would eventually freeze over.
|
| So, nothing interesting. The sun vanishes and then some
| time later you freeze and/or starve to death.
| sandworm101 wrote:
| 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.
| tsimionescu wrote:
| 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?
| sandworm101 wrote:
| On paper yes, but doing so also reduces the time for the
| burn. Probes have very low-thrust engines. Even during a
| jupiter slingshot they barely have time to accellerate
| much on thier own. Often they do not bother, relying
| totally upon the grav assist to accellerate. The danger
| too of a closer approach is that something gets
| miscalculated. Get too close and an inevitable tiny
| misalignment will throw you onto a wild unwanted
| trajectory. There is no gps out there. Knowing exactly
| where and how a probe is moving isnt easy.
| sandworm101 wrote:
| At that size, very few things would ever get close enough to be
| torn apart, let alone fall in. We should look for objects
| suddenly changing course ivo the potential black hole.
| perihelions wrote:
| - _" In that case you'd see X-rays, gamma rays, etc., but maybe
| only briefly."_
|
| One speculative possibility is that we could find a
| _continuous_ gamma annihilation signal from its dark matter
| halo,
|
| https://arxiv.org/abs/1909.11090
|
| https://hn.algolia.com/?query=What%20If%20Planet%209%20Is%20...
| breckenedge wrote:
| 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.
| stainablesteel wrote:
| it sounds a lot like it now that i read this, large dispersed
| amounts of antimatter that apparently doesn't give off light
| yet has massive gravitational pull
| nullserver wrote:
| https://youtu.be/qy8MdewY_TY?si=NVZzWJSFXl4EATRK
|
| Good video on topic
| ccgreg wrote:
| Antimatter has the same electrodynamic properties as matter.
| pfdietz wrote:
| 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.
| exe34 wrote:
| Spicy nuggets.
| NegativeLatency wrote:
| > preferentially segregated into a dense phase of hadronic
| matter
|
| Sounds interesting, where can I read more theories about
| this?
| pfdietz wrote:
| Here's a recent (2021) paper on the idea:
| https://arxiv.org/abs/2105.08719
|
| It has the nice feature of explaining why the density of
| baryons and the density of dark matter are not too
| different. Naively, there's no reason to expect the two to
| be anywhere close to each other. It also offers an
| explanation for the observed matter-antimatter asymmetry in
| the universe.
|
| Don't believe any theory until it's been well tested.
| dreamcompiler wrote:
| 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?
| at_a_remove wrote:
| 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.
| woopsn wrote:
| Fascinating mission. I don't understand how microlensing events
| resulting from primordial black holes can be differentiated even
| statistically, given that they "can't be formed by any known
| physical process", but in any case it's exciting to discover
| there's much more of something up there than we knew. Even if
| they are "just" rogue planets.
| api wrote:
| We have a variety of ways to make insanely precise measurements
| of light to the point of counting photons. I'm guessing that
| factors into being able to detect microlensing.
| hyperific wrote:
| NASA in the title should be all capital letters as it's an
| acronym and not a name.
| jdminhbg wrote:
| Depends on where you live:
| https://proofreadingpal.com/proofreading-pulse/writing-
| guide....
| ibeforee wrote:
| nasa.gov is the domain here
| ralferoo wrote:
| As a Brit, I've never noticed NASA spelt Nasa before, and I'm
| on the fence about Unesco, not because I recall seeing it
| title-caps, but because it doesn't look offensive to me.
|
| That said, when I googled for the title-caps variants of both
| words, I saw the Guardian, Independent and Times all used it
| for Nasa, but only the Guardian and Times seem to use it for
| Unesco. There was also a page from the NYT that used Unesco,
| so a counter example from the US, but even the UK government
| pages refer to it in all caps, as do most other UK articles.
|
| I certainly find it a weird generalisation that "UK English"
| (sic) prefers title-caps, as we tend to like our abbreviated
| names and pretty much always use all-caps when every letter
| comes from a separate word, and only title-caps when we use
| runs of letters from each different word - quango (quasi-
| NGO), Bakerloo (Baker St-Waterloo), Beeb (compared with BBC),
| Lib Dems, etc. We also have a few things that aren't
| consistent for government things - Defra (always used to be
| DEFRA, but they seem to have rebranded), MOD (always caps),
| Ofqual (=Office of Qualifications, always title case), Ofcom
| (=Office of Communications, now seems to officially be title
| case, but always used to be OFCOM), UCAS (University and
| Colleges Admission Scheme, always all-caps), etc.
|
| Maybe the stylistic choice is based on how pronounceable it
| is as a word, but whatever I don't think there are any hard
| and fast rules!
| LegionMammal978 wrote:
| U.S. newspapers have a tendency to convert abbreviations to
| title case, even when everyone else uses all-caps. For
| instance, I've only ever seen "Covid-19" written in
| newspapers: everyone else always used "COVID-19", "COVID",
| or just "covid", or "the coronavirus".
| kristianp wrote:
| Launching by May 2027. Was hoping it would be sooner, given the
| presence of this article, but it seems they drip feed them out
| gradually.
|
| https://science.nasa.gov/mission/roman-space-telescope/
| chefkd wrote:
| question for the initiated: why do space agencies divide their
| resources and attention between different projects? Wouldn't it
| make sense to focus first on making the moon and it's resources
| accessible kind of like airplanes then systematically expand to
| Mars, asteroid belt, and so on instead of spreading out too thin
| without conquering the closest
| macintux wrote:
| Purely speculative:
|
| - Betting everything on a single huge project is risky. You
| wait for years for completion, and if some critical part of the
| project costs more/takes longer than expected (much like
| Artemis today) you risk achieving nothing at all.
|
| - Small, cheap projects that don't bankrupt the agency if they
| fail, when they succeed, generate ongoing positive PR and
| scientific results. NASA famously promoted this concept after
| one or two expensive projects had problems (of course, not
| famously enough that I remember more details).
|
| - Some of those smaller projects are critical, like climate
| monitoring. You can't just set aside those sorts of tasks for a
| literal moonshot.
|
| - Smaller projects contribute towards the big ones: NASA has
| given SpaceX a fair bit of money over the years that is paying
| off with Starship and Artemis.
| mrcwinn wrote:
| What the heck is "Nasa"? Not the sword I'll prefer to fall on,
| but even if you're in the UK, let's honor that this organization
| is in the United States and they self-describe as "NASA."
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