[HN Gopher] Three of the oldest stars in the universe found circ...
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Three of the oldest stars in the universe found circling the Milky
Way
Author : belter
Score : 90 points
Date : 2024-05-15 16:40 UTC (6 hours ago)
(HTM) web link (news.mit.edu)
(TXT) w3m dump (news.mit.edu)
| rthnbgrredf wrote:
| > Interestingly they're all quite fast -- hundreds of kilometers
| per second
|
| I bet that the milky way could only capture these ultra fast
| moving stars because of dark matter.
| AnimalMuppet wrote:
| But they're in the halo. Can they actually be gravitationally
| bound at that distance at those velocities? Is even the
| (computed by other means) amount of dark matter enough for them
| to be captured?
| klyrs wrote:
| This echoes a thought I had recently -- stars traveling at
| relativistic speeds should look deceptively young due to time
| dilation. But while this is certainly speedy, mere hundreds of
| km/s isn't enough to significantly prolong the observed
| lifetime of a star.
| malfist wrote:
| > should look deceptively young due to time dilation
|
| That's not how we date stars. We typically date the star by
| it's metallic content. More non-hydrogen elements in it's
| spectrograph, then we know it's an older generation of stars.
| Starlevel004 wrote:
| > More non-hydrogen elements in it's spectrograph, then we
| know it's an older generation of stars.
|
| It's actually the exact opposite, but yes.
| pfdietz wrote:
| There's some weird caveats, like so-called "Lead Stars".
| These are aged stars with very large amounts of lead
| relative to other heavy elements. This happens because lead
| is the end nuclear of the so-called s-process, where
| neutrons are captured at a slow rate in large stars whose
| internal processes produce some neutrons by (alpha,n)
| reactions.
|
| In lead stars, there are so few seed nuclei (those metals)
| that each of the seed nuclei that are there can capture
| many more neutrons.
| jddj wrote:
| Does it matter in this context whether it's metals or tree
| rings or wrinkles around the eyes?
|
| It's all time, right?
| klyrs wrote:
| > It's all time, right?
|
| Sure, but we can measure time dilation between the peak
| of a mountain and the base of a mountain, due to the
| differing velocities. Time is relative!
| pdonis wrote:
| _> stars traveling at relativistic speeds_
|
| So far, to my knowledge, we have not observed any. As you
| note, hundreds of km/s is way too small to have any
| appreciable effect.
| ChrisGranger wrote:
| "The fastest star ever seen is moving at 8% the speed of
| light"
|
| https://www.space.com/fastest-star-ever-moves-8-percent-
| ligh...
| AnimalMuppet wrote:
| 0.08c translates into a gamma of 1.0032. That's not
| enough for relativity to be doing much...
| bloopernova wrote:
| How much relativity effects occur at 0.2c? A sci-fi book
| series I'm reading has warships unable to hit other ships
| if their relative velocity is above 0.2c. I was wondering
| if that was realistic.
| klyrs wrote:
| I found this to help me not sound completely ignorant in
| this thread
|
| https://www.omnicalculator.com/physics/time-dilation
| luyu_wu wrote:
| As the lorentz factor calculated above, not much! Time
| would only be dilated by that much, and length by the the
| same amount. It'd definetly be hard to hit something at
| that speed, but not due to relativity!
| chasil wrote:
| The stars that are going beyond our cosmological horizon are
| effectively traveling away from us faster than their light
| towards us.
|
| https://en.wikipedia.org/wiki/Cosmological_horizon
|
| "Or, more precisely, there are events that are spatially
| separated for a certain frame of reference happening
| simultaneously with the event occurring right now for which
| no signal will ever reach us, even though we can observe
| events that occurred at the same location in space that
| happened in the distant past.
|
| "While we will continue to receive signals from this location
| in space, even if we wait an infinite amount of time, a
| signal that left from that location today will never reach
| us."
| jajko wrote:
| Sun is moving cca 230 km/s around Sagittarius A*, so something
| even further from the center would have even higher speed if
| rotating at same speed (don't know if that's the trend in our
| galaxy, very much a tourist in astronomy)... doesn't sound that
| unusual unless its those 999km/s corner cases
| deciduously wrote:
| Except these stars are rotating the other direction
| ashes-of-sol wrote:
| Orbital velocity increases as you get closer to the middle,
| not the other way around.
|
| An example closer to home, our orbital velocity around the
| Sun is 29.8km/s. Mercury is 47.9km/s (on average, it actually
| varies throughout its orbit). Neptune is 5.4km/s.
| shrimp_emoji wrote:
| This doesn't apply to stars in the Milky Way. Unlike
| planets around a star, stars in the Milky Way don't follow
| Keplerian physics in their orbit around the galactic
| center.
|
| https://en.wikipedia.org/wiki/Galaxy_rotation_curve
|
| ```
|
| The rotational/orbital speeds of galaxies/stars do not
| follow the rules found in other orbital systems such as
| stars/planets and planets/moons that have most of their
| mass at the centre. Stars revolve around their galaxy's
| centre at equal or increasing speed over a large range of
| distances. In contrast, the orbital velocities of planets
| in planetary systems and moons orbiting planets decline
| with distance according to Kepler's third law.
|
| ```
| ck2 wrote:
| So a vaguely related question for an astronomy thread about our
| galaxy since smart people lurk here:
|
| If the center of most galaxies is a super-massive black hole,
| including the Milky Way, and most of those SMBH have relativistic
| jets with lobes throwing out particles near light speed
|
| 1. Have we detected such lobes in the milky way? why not?
|
| 2. If those particles are going near the speed of light yet have
| no reason to slow down unless captured, unlikely outside of their
| original galaxy, they are still going for billions of years? (wow
| if so!)
|
| 3. If some of those jets from other galaxies are pointed at earth
| and contain physical particles with mass near the speed of light,
| why don't they do measurable damage?
|
| reference: https://www.nustar.caltech.edu/page/relativistic_jets
| Dylan16807 wrote:
| They do do measurable damage!
|
| The amount we measure is extremely small because of how wide
| the beams are by the time they reach earth.
| AnimalMuppet wrote:
| I'm not an astronomer, and may or may not be smart.
|
| 1. I don't know; Google probably _does_ know.
|
| 2. Those jets aren't in a complete vacuum. They're running into
| galactic gas, of which, on a galactic scale, there is quite a
| bit.
|
| 3. Several reasons. One, they aren't a perfect "beam". They
| spread out. If you're a few billion years away, they spread out
| quite a bit in that distance. Then, to get to us, they go
| through their galaxy's gas, intergalactic space (not totally
| empty), our galaxy's gas, and finally our atmosphere. Each of
| those reduces the amount of radiation. Oh, yeah, our
| magnetosphere deflects charged particles, too.
| jwells89 wrote:
| For #3, I think I remember reading that the Sun's heliosphere
| (which contains the entirety of the familiar Solar System)
| also plays a role in cutting down what gets to Earth, but I
| may be misremembering.
| notaustinpowers wrote:
| > 1. Have we detected such lobes in the milky way? why not?
|
| Sag A* (our black hole in the center of the Milky Way) isn't
| considered "active" right now. We don't notice it gobbling up
| stars and gasses, which would be necessary for the jets to be
| possible. I remember back in 2020 or 2021 there was an article
| that we're noticing a jet from Sag A*, which we're still trying
| to understand why because we don't expect Sag A* to be active.
| It's also super difficult to monitor Sag A* since there is so
| much dense dust, gas, etc in the way between us and the SMBH.
|
| > 2. If those particles are going near the speed of light yet
| have no reason to slow down unless captured, unlikely outside
| of their original galaxy, they are still going for billions of
| years?
|
| Generally speaking, yeah, they are! If we're looking at photons
| though, they will eventually get red-shifted so much that
| they'll become infrared (invisible to us), until their energy
| is so low that it'll be near impossible to see without
| telescopes more powerful than anything we have right now.
|
| > 3. If some of those jets from other galaxies are pointed at
| Earth and contain physical particles with mass near the speed
| of light, why don't they do measurable damage?
|
| Space is a vacuum, but there are still things that can slow
| these particles down (loss of energy like photons, gravity
| wells from other massive objects, running into a spec of space
| dust, etc. Also, space is _very empty_ , and statistically,
| it's incredibly improbable that one of these jets could be
| aimed directly at us, while also being close enough to us, to
| cause damage. We do notice them though! They're powerful enough
| to get picked up by scientific instruments, but are not
| concentrated enough or powerful enough to cause damage to us or
| Earth.
| dylan604 wrote:
| > Generally speaking, yeah, they are! If we're looking at
| photons though, they will eventually get red-shifted so much
| that they'll become infrared (invisible to us), until their
| energy is so low that it'll be near impossible to see without
| telescopes more powerful than anything we have right now.
|
| Isn't the precisely what JWST is built for?
| notaustinpowers wrote:
| Even JWST has it's limits. There are some very, very, very,
| very old galaxies that are so red-shifted, JWST is only
| able to see them thanks to gravitational lensing amplifying
| the energy of the light. https://www.space.com/james-webb-
| space-telescope-distant-gal...
| PaulHoule wrote:
| When it comes to the "oldest stars" there is reason to
| believe that very early there were very big Population
| III stars that formed very quickly and burned out fast
| leaving nothing but black holes and there is hope JWST
| will see some.
|
| In general there are multiple recent observations that
| things seemed to happen much more quickly in the early
| universe than we expected so maybe what we think was the
| first 1 billion years was really the first 10 billion
| years or there is another big secret to be discovered in
| cosmology.
| hannasanarion wrote:
| > and most of those SMBH have relativistic jets with lobes
| throwing out particles near light speed
|
| This is not correct. Most SMBH do not have relativistic jets.
| The jets only form when the black hole is actively consuming a
| large quantity of matter.
|
| The Milky Way's SMBH Saggitarius A* is not actively eating
| anything, so it is not producing a jet.
| Conasg wrote:
| Those lobes have been detected in our galaxy, yes. There's a
| page from 2012 by NASA talking about it:
| https://svs.gsfc.nasa.gov/10918
|
| As I understand it, recent research suggests the last time our
| SMBH consumed enough matter to erupt was millions of years ago,
| so the lobes have cooled down and are difficult to detect.
| TheBlight wrote:
| FWIW, it's not clear that SgA* is actually a canonical black
| hole (nor that even such a thing truly exists in nature.)
|
| The EHT image is taken as confirmation but the accuracy of that
| technique has been called into question:
| https://arxiv.org/abs/2205.04623
|
| Edit: In response to the downvotes, here are 2 very good
| sources who at least argue against the existence of
| singularities and their event horizons.
|
| 1: https://arxiv.org/pdf/2312.00841
|
| 2: https://uncnewsarchive.unc.edu/2014/09/23/carolinas-laura-
| me...
|
| I don't know exactly when science discussion turned into rigid
| dogma enforcement but we are certainly in that era presently.
| sergent_moon wrote:
| I think some of the apparently dogmatic attitude is from
| exhaustion. Usually (I'm not implying you) someone calling
| commonly accepted science into question are just waiting for
| a moment to drop something about Jesus, or Chemtrails or some
| other nonsense.
| dekhn wrote:
| Neither of those are "very good sources". Further, they are
| basically mathematical modelling papers. We have a lot of
| experimental evidence about the nature of black holes. If you
| argument is just "black holes might not be a true
| singularity", well, nobody is strongly disagreeing with that,
| we just don't have evidence or good support for alternative
| models. People aren't being dogmatic, they just don't have
| any better models that explain the observations.
| TheBlight wrote:
| Laura Mersini-Houghton and Roy Kerr seem like very good
| sources to me. Are you familiar with their work? It seems
| not.
|
| A "black hole" implies a singularity behind an event
| horizon not even light can escape from. There isn't any
| proof that such a thing exists in nature. You're correct in
| saying that we see the indirect gravitational effects of
| something that doesn't fit any model our imaginations have
| conjured up to date except for "black hole." That doesn't
| mean it's clear that black holes are a real thing.
| wizzwizz4 wrote:
| > _You 're correct in saying_ [...] _a real thing._
|
| This is, indeed, how science works. "All models are
| wrong", as they say. I'm not sure what you're trying to
| push back against.
| TheBlight wrote:
| That would be perfectly lovely for me if that was
| actually the attitude of most people weighing in on these
| discussions. But in practice, when it's insinuated that a
| more beloved sci-fi model may perhaps be
| incorrect/incoherent it's met with people being upset
| that it's being pointed out.
| wizzwizz4 wrote:
| Because you're _insinuating_ it. If you said right-out
| "while black holes are the best model we have so far to
| describe our observations, they might not actually be
| real", people would just give you funny looks for stating
| the obvious.
| cthalupa wrote:
| Kerr's paper is quite specifically about not believing in
| singularities, not about not believing in black holes. It's
| hardly a controversial opinion in the science community to
| believe that singularities in black holes are an artifact of
| our incomplete mathematical representation of how gravity
| works. That is not the same as suggesting that black holes or
| event horizons don't exist. Kerr's solution to the field
| equations involves two event horizons to begin with, and his
| argument in the new paper is based on Kerr black holes and
| explicitly talks about event horizons in multiple places.
|
| I'm very confused as to why you believe that paper provides
| significant argument as to why calling SgA* a black hole
| would be jumping the gun.
| colechristensen wrote:
| >3. If some of those jets from other galaxies are pointed at
| earth and contain physical particles with mass near the speed
| of light, why don't they do measurable damage?
|
| When they hit Earth (from these kinds of jets and other
| sources) they're cosmic rays. But it isn't a whole beam of
| them, it's individual particles way up near light speed. We can
| detect them, they can flip bits in computer memory, but they
| don't do a lot of damage because even at their speeds, a single
| proton, electron, or two or more protons as a bare nucleus
| still doesn't have a particularly large amount of energy on a
| human scale.
|
| https://en.wikipedia.org/wiki/Cosmic_ray
| ChrisMarshallNY wrote:
| _> are still intact today_
|
| I would suggest, instead, that _we can still see their light_.
|
| They may have popped their clogs, long ago, and we would not have
| known, as we're seeing their old videotapes.
|
| There's something called the "Cosmic Event Horizon," or somesuch.
| It's the distance from us, that we'll never be able to see,
| because it is more than 13.8 billion light-years away, and we'll
| never see anything beyond.
|
| Every time I think about the distances and scales of the
| universe, I get a headache.
|
| _[EDITED TO ADD] I wasn 't talking about the nearby stars, and
| neither were they. That quote was talking about distant, red-
| shifted galaxies._
| colechristensen wrote:
| If they're circling the Milky Way, they are close, in a cosmic
| sense.
|
| The milky way is only 100,000 light years across.
|
| Stars of a certain small size will also continue shining for a
| trillion years.
| ChrisMarshallNY wrote:
| Yeah, it's interesting that folks seemed to take offense at
| what I said. It's really pretty much exactly what you'd hear,
| from any astronomer (which I'm not, but one of my favorite
| shows is _How the Universe Works_ ).
|
| Not all stars are created equal. Blue giants may only live a
| few billion years, while red dwarfs will last practically
| forever.
| colechristensen wrote:
| These are 13 billion year old stars that are only 30,000
| light years away, that's like one part in 40,000 of how
| long they've lived. They are most certainly still there
| shining. Is just incorrect to be pedantic about there light
| being there but maybe not them.
| ChrisMarshallNY wrote:
| That was a rhetorical statement. It's a "Here, there be
| dragonnes" type of thing. We say stuff like that,
| hereabouts, all the time. My statement was incredibly
| mild, compared to some of the crazy stuff people say,
| here.
| colechristensen wrote:
| Shrug, unnecessary pedantry is indeed a theme around
| here, I try to resist the urge but am guilty of it myself
| from time to time.
| ChrisMarshallNY wrote:
| I suspect that a number of folks didn't realize where the
| quote came from.
|
| They were talking about distant galaxies, not the
| relatively nearby stars.
| Starlevel004 wrote:
| > They may have popped their clogs, long ago,
|
| Nearly every single star we can see in the entire Laniakea
| supercluster is still shining today.
|
| The universe is big, but stars live for a really long time.
| cvoss wrote:
| > still shining today
|
| It's an interesting quirk of these discussions of events at
| relativistic scales that it's very hard to precisely speak
| about what we mean whenever we reference time.
|
| For all of us "here", who are within non-relativistic
| distance of each other, "today" is a meaningful point in
| time. But what does our "today" mean for that far-away star?
| I think you are trying to articulate that, if the star is X
| light years away from us, after X years from "today" we will
| still be receiving light that has traveled from the star to
| "here". But you might instead mean that if a traveller were
| to depart from "here" "today" at near relativistic speed,
| when he arrives at the star he will find it still shining
| "there" at "that time".
|
| But notice those are definitely not the same data point about
| the star. The first data point will arrive here in X years to
| show us the star was still shining X years previously. But
| the traveler will collect the second data point (almost
| immediately for himself, by the way) and may find the star
| dead. This can happen if he and the star's last light cross
| paths in flight.
| dhosek wrote:
| My favorite thing along these lines is a question from my
| undergrad special relativity textbook:
|
| A pole vaulter carrying a 40m pole is running at a speed
| such that to an observer, he appears contracted by 1/2. He
| runs through a barn of length 20m and the doors at each end
| of the barn are closed simultaneously.
|
| But to the pole vaulter, the barn appears contracted by 1/2
| and thus appears to be 10m long to him. What does he see
| when the doors are closed?
| dhosek wrote:
| Of course, just by virtue of context in this discussion,
| the answer is kind of given away.
| Starlevel004 wrote:
| > It's an interesting quirk of these discussions of events
| at relativistic scales that it's very hard to precisely
| speak about what we mean whenever we reference time.
|
| No it isn't. This is a stupid psued talking point.
| ChrisMarshallNY wrote:
| Depends on what type of star.
|
| The only stars that have never been observed to die, are red
| dwarfs.
|
| I think blue giants are the shortest-lived ones.
|
| Ours is in the middle. I think they give the Sun about four
| billion more years.
|
| BTW: That was a rhetorical statement. The issue is, we don't
| actually know what's going on, today.
| ErigmolCt wrote:
| Wow... discovering some of the oldest stars in our galactic
| neighborhood is a remarkable thing
| marcosdumay wrote:
| Shouldn't they be distributed everywhere?
|
| Finding some close to us is just expected.
| actionfromafar wrote:
| Aren't some galaxies older than other.
| Sharlin wrote:
| Indeed. And there should be plenty of them, given that a
| large fraction of all stars (evidently including these three)
| are K-type orange dwarfs slightly smaller and cooler than the
| sun. They last tens of billions of years on the main
| sequence, burning their hydrogen at a leisurely pace. A large
| majority of stars born back then should still be alive and
| kicking long after the sun is gone.
| labrador wrote:
| They should name them the Father, the Son and the Holy Ghost
| bufferoverflow wrote:
| Considering there are 200 to 1000 billion galaxies (based on what
| we can see), the odds of that is not just astronomically low,
| it's basically impossible.
|
| Which tells you that the method for determining the age of stars
| is wrong.
| alexander2002 wrote:
| (Disclaimer: I am not an expert) In my humble opinion, because
| the black hole calculations and other important proven
| scientific equations must have taken into account the age of
| stars, the age of a star could be imprecise but not outright
| wrong.
| SiempreViernes wrote:
| They have just dropped the qualifier "known" from the title, as
| in it should be read "Three of the oldest _known_ stars found
| in our galaxy ".
|
| We obviously don't know the age of each and every star in the
| entire universe, calm down dude.
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