Firstly, yes it is true that this happened 26,000 years ago! More specifically, the event happened 26,000 years ago in our reference frame. There are other reference frames in which this event occurred two minutes ago or 5 million years ago. But generally these are not useful reference frames since the Earth's reference frame is not too different from the reference frame with respect to the center of mass of the Galaxy (we are not moving all that fast compared to the speed of light).
That said, as astronomers we are not particularly interested in dating precisely when the event happened. 26,000 years is a very long time in human history, but it's not very long on astronomical timescales. Not very much has changed in the Galaxy over the past 26,000 years, so we don't gain much by dating it at the time the event occurred (with respect to the Earth's reference frame, of course). Furthermore, we wouldn't even know exactly when it happened even if we wanted to! Our clocks are very precise here on Earth, but our distance measurements to most celestial objects are very fuzzy, particularly the further away you get. Because of this, these sorts of events are always referred to with respect to the year they were observed on Earth. (Thus, the most recent nearby supernova is known as 1987A because it was the first supernova observed in 1987.)
This all changes when you are studying more distant objects though! For very distant galaxies, we are now seeing things when the universe was considerably younger and things were much different. Then it becomes important to keep the event's age in mind. For these objects we will actually refer to their redshift. The redshift can be measured relatively well, and is related to the distance and age of the event via the Hubble constant and the acceleration parameter. Measuring these parameters is tricky and is a whole subfield of their own, so we usually stick with redshift as it is more related to things we can easily measure.
A final note on the paper itself. These observations were taken at Keck on Mauna Kea. There has been a lot of controversy around the construction of the Thirty Meter Telescope, so the authors actually acknowledge indigenous Hawaiians specifically in their paper:
> The authors wish to recognize that the summit of Maunakea has always held a very significant cultural role for the indigenous Hawaiian community. We are most fortunate to have the opportunity to observe from this mountain.
Which does miss the point -- whether it happened a billion years ago somewhere else or 2 seconds ago somewhere else, the effects of that event are being measured by us right now, meaning if it was gonna kill us, it would have happened now, not 26,000 years ago.
So to answer your question, no it is not possible for anything to affect us any faster than the universal speed limit of causality (that light happens to be able to hit).
See e.g.: https://en.wikipedia.org/wiki/SN_1987A
Not just that, but lights when it passes through a medium slows down depending on it's refractive index (speed of light in water is about 225 000km/h while in vacuum it's 300 000km/h). This is important distinction as recently we had an uproar when it looked like neutrinos are slightly faster than c (in the end, it was a measurement error).
You can observe effects of particles going faster than speed of light in a medium if you look at photographs of Cherenkov radiation.
How does a particle or its environment measure the particle's traversal of a truly empty space?
300 000 km per second
"Its exact value is 299,792,458 metres per second (approximately 300,000 km/s"
I read that as: Can something come along and snuff us out after we've observed the light wave component of the event, such as a shock wave of some sort?
That is the only way it can happen.
Probably. Why would points becoming more distant due to expansion of space be a counterexample to the speed of light being a limit on the speed of causal propagation? Spatial expansion doesn't move anything, so it can't propagate information.
Not that it matters, because the speed of light is still the limit: if they could influence us when they were closer, that would have happened by now.
It certainly moves matter-energy in different regions of space with respect to one another.
I know that's a weird explanation, so consider:
t0: S~~~>O U (shadow exists)
t1: S~~~~~~> U (shadow exists)
t2: S~~~~~~~~~>U (shadow !exist)
At time "t0", "U" thinks he's in the shadow.
At time "t1", "U" thinks he's in the shadow.
At time "t0", "U" thinks he isn't in the shadow, since the photons are now hitting him.
A similar calculation/thought-experiment can be done for shadows with "angular momentum", in case you think the tangential velocity of the shadow will exceed the speed of light.
t0: SO U1 (U1 in shadow)
t1: S~~~~~~~~~~>U1 (shadow leaves top first)
I didn't do the precise math, but I'm pretty sure the tangential velocity of the shadow along the dotted line won't be greater than the speed of light. The curvature of the "wave front" formed by the tips of the arrows ">" above will be lesser than the dotted line curvature, so the photons near the top of the diagram hit the dotted edge before the ones towards the bottom. This is because the source, S, takes time to move away from O.
Note that the wavefront formed by the photons moves radially outward from S, but ascii art is limiting.
There are similar things that appear to exceed the speed of light:
See "group" and "phase" velocities for similar things to the lighthouse.
Quantum entanglement works faster than light but cannot carry any information. As such the speed of causality (and implicitly of light) is still the real limit.
A. Earth is going to be hit by a super-mega-death laser focusing the entire power output of a star into a concentrated beam.
B. A long long time ago, a very dense moon was very far from a supernova. Unfortunately, far is relative, and so is speed in space. Specifically, relative to Earth, the moon is now traveling 5% the speed of light and is on a collision course.
In scenario A, there is no way for us to see this coming, because information also cannot travel faster than light. The light is what kills us.
In scenario B, it is theoretically possible to see this rogue-moon coming, since it is possible for light to reflect off of it and reach us before the moon does.
[EDIT] inverse square, that is. My bad.
It seems like the effect of that event could be felt only millions of years after the flash of light, no?
I have written a few things about dynamics on my blog, though (that was my subfield): https://joe-antognini.github.io/
Anyway, it's appreciated and this really was a great answer.
You’re right, that of almost any PhD I know (admittedly not that many) they are both able to explain what they have studied or written about clearer than any of the others I know.
The family loves when they both get talking about this theory and that, it makes for great conversation the rare times everyone is together.
Do we have other data like that? How far back does our record of Sgr. A[star]'s light curve extend?
Also, I gather that Sgr. A[star]'s rotational axis isn't normal to the mean galactic plane. And I presume that the axis precesses. Does it ever point near enough to the Sun to cause damage?
One fun coordinate system is Cosmic Background Radiation time. The CMB redshifts as the Universe expands, so the temperature of the CMB can serve as a clock. Anyone anywhere in the Universe can measure the average temperature of the CMB, and use that as their clock.
About Mauna Kea, I urge everyone to look into the issue in more depth before forming an opinion. There is a huge amount of disinformation being spread on social media, and the basic picture most media is painting is wrong. The Thirty Meter Telescope project has gone to great lengths to try to listen to the community, and to take religious and cultural concerns into account. These concerns had a big impact on both the location and the design of the telescope. The telescope site is father below the summit than the previous telescopes, so that it cannot be seen from most of the island. The entire optical design of the telescope was made to be super compact (F/1), which was a very risky technical decision, just so the telescope wouldn't be as tall. The internal clearances of the telescope within the dome are just 20 inches, barely allowing it to be serviced, for the same reason.
The sacredness of Mauna Kea is also much more questionable, within traditional Hawaiian religion, than activists are claiming. There's actually surprisingly little evidence that it was historically held to be anywhere near as sacred as TMT opponents claim. The Hawaiian creation story, for example, doesn't mention Mauna Kea. It's important to realize that the Hawaiian traditional religion was suppressed by the Hawaiian monarchy in 1819, which means that it is not easy to reconstruct nowadays. Many of the anti-TMT activists belong to a movement trying to bring the religion back to life, but what they claim about the religion does not necessarily reflect ancient beliefs. One thing that undermines their claims is the fact that pre-contact, native Hawaiians excavated the largest quarry in Polynesia on Mauna Kea.
There are, however, culturally significant sites on Mauna Kea that clearly should be preserved. There are ancient shrines and burial grounds, for example. The TMT site was chosen to be as far removed from such sites as possible. There are also places where modern "cultural practitioners" (ironically enabled by the observatory access road) carry out their practices, and TMT does not significantly disturb these practices.
One thing I didn't mention above that's important in all this is the Hawaiian independence movement. Many of the leaders of the protest movement view the State of Hawaii as illegitimate, and believe that the Hawaiian Kingdom is under illegal occupation by the United States. The telescope is a great symbol to rally in opposition to. If the State of Hawaii doesn't exist, what right does it have to grant permits for construction on Mauna Kea (yes, this is an argument that TMT opponents repeatedly made during the legal proceedings that eventually approved the TMT's permit)?
For me, that was a surprising bit in your comment. I don't understand how it can be true (5 million years in the future, sure, but the past?). Can you give an example or explain?
Say we're both on Earth 26,000 years ago. You stay on Earth and I shoot off at C/2 in a direction away from the SMBH. You wait 26,000 years and then see the flare. How long do I wait in my own reference frame before I see the flare?
My guess intuitively is that time dilation and the extra distance cancel out and I still wait exactly 26,000 years (no matter how fast I go), but I'd have to dig out my old physics textbook to figure it out properly. Also, what happens if instead I shoot off towards the SMBH? Or at 90 degrees? I'd obviously see the flare sooner in my reference frame, but how much?
It seems like there's a general rule that, by moving, you can decrease the time until you see events (at least those communicated by light) but you can never increase it.
Only 2 minutes would have passed for the SMBH in your frame of reference (but 52k years would have passed for earth in your frame of reference)
It hasn't happened yet in reference frames around the Large Magellanic Cloud, right?
The only reference frame that could see it and then measure and calculate it as having happened after today would be one travelling faster than c relative to us.
From what I understand, no one ever moves (fast, slow, whatever) compared to the speed of light from their own reference point.
The speed of light is always the same for all observers from their own reference point, so how do you reconcile those statements?
This is significant for observing external events and correlating phase shifts to figure out distances.
Eg. Things in the external universe may appear to happen extremely quickly.
It’s actually very important.
Regardless of how fast you appear to be moving in your own frame of reference, the speed you’re travelling in absolute terms affects what you observe externally (and specifically with regard to how fast you are moving compared to what you observing)
Time dilation is relative between you and some other reference frame. All the "stuff" in the universe nearby is (fairly) static, so we can say we are not moving fast, but it's still relative to the stuff around is.
It's similar to how the laws of physics are symmetrical under translation and rotation, but the presence of matter around us means the surface of the earth is not the same as the surface of the sun.
So, while we might use the CMB as a standard reference frame, the laws of physics should not.
If we didn't have any CMB radiation floating around to measure, everything would probably work exactly the same. Maybe you could measure all the motion of all the matter in the visible universe and measure the motion of the "center" relative to us.
There is no such thing. You always have to compare your speed to something else. Speed is calculated relative to something else. Relativity.
My point was that if we (the solar system) were travelling as a considerable portion of the speed of light, then we would experience time dilation, which would significantly affect our observations of the external universe.
So... it's fine.
I mean, you're basically right; speed isn't absolute, and it's wrong to refer to your speed relative to the CMBR as 'absolute'.
...but, well... I think it's fair to say 'The speed of light is constant in all frames of reference, so why [insert question here]...' is a very fair, and common question. 'Everything is relative' isn't an answer, it's just a platitude.
Isn't this wrong? Surely we would say that, in our reference frame, the event happened precisely when we observed it happening. That's what "frame of reference" means: it's whose clock we use to say when an event occurred.
To see this another way, suppose you saw two events at the same time, one two light-years away, and the other one light-year away. In your interpretation you would call those events simultaneous. Simultaneous events cannot affect each other in any reference frame. But if the two events were in a line, the light from the first event could have triggered the second.
Yes, I would say that those events occurred at the same time in my reference point, while also recognizing that we can't say in an absolute sense that they were simultaneous. Isn't that the point of relativity of simultaneity?
The whole point of relativity is that events do not occur at the exact moment they are observed, because light has a finite velocity. The fact that light's finite velocity is the same in all reference frames is what causes reference frames to tilt their spacetime angle according to their velocity.
It's the same as saying the Y component (height) of a line segment changes if you rotate it. The length of the line is the spacetime distance, the height (Y component) of the line is time, the x component is spatial distance, and the angle of the line depends on the relative velocity of the observer.
The event occurred is 26,000 light years away, we date it as having occurred 26,000 years ago.
How is it that a location that's closer, say 10,000 light years, would have dated the event to 26,000 ago rather than 10,000 light years?
ds^2 = dx^2 + dy^2 + dz^2.
In Special Relativity, you define a quantity called the spacetime interval:
ds^2 = -(c*dt)^2 + dx^2 + dy^2 + dz^2.
You treat time as a 4th dimension, and take it into account when calculating distances. Notice that this interval can be negative (the metric is "semi-Riemannian"). "Events" (locations in 4D spacetime) can only be causally connected (one can influence the other) if the spacetime interval separating them is negative (this is equivalent to saying that no information can ever propagate faster than light).
The key is that all non-accelerating observers agree on the spacetime interval between any two events. The spacetime interval between two events is the only solid distance you can give. The time interval by itself depends on the observer's reference frame (you've probably heard of time dilation). So too does the spatial distance (length contraction). But time dilation and length contraction behave in such a way that the spacetime interval remains constant.
The long and the short of it is that time intervals are observer-dependent.
I can't imagine that they would say that!
I'm sure that you mean the equivalent of 24,000 BC in our reference frame, after Lorentz transformation. Not that they would likely even know about us, or manage the transformation.
This is bloody confusing.
Or know when ours was supposedly born?
This can happen for instance with extreme differences in relative velocities. Someone else can probably show an example with the math, but a key concept here is the that distances also change when you move real fast or are in a deep gravity well.
Clocks here on Earth currently read May 13th, 2019. And you can conclude that we observed the event on May 13th, 2019. We believe the black hole is approx. 26,000 light years away. Thus we know the light took 26,000 years to reach us. So we say the event took place around 23,981 BC.
We have 3 events here:
A. A clock on Earth reading May 13th, 2019
B. Light from the black hole flare reaching Earth
C. The black hole flaring
We can say that A and B occurred simultaneously in all reference frames (they occurred at the same location and at the same time). C did not occur simultaneously with A or B in any reference frame (except perhaps, debatably, that of something moving at the speed of light).
Are you sure that we are in the same reference frame? I’m willing to accept that you started a fairly short journey at some appreciable fraction of C, turned around and gave just recently arrived back home, but I’m going to need some proof.
The same is true regarding the black hole flare. Except that we are not only learning about it now due to negligence, but because we, with all current knowledge in physics we have and also our technology, we don't have a way to see what's happening right now. But say an astronomer finds a wormhole and points their telescope to it. They could know about things that will only be visible by everyone else in 26,000. Time to invest in those black hole futures.
This is a Lorenz geometry definition of reference frame, not an everyday sense of “frame of reference”
If I call my friend at 7:30am and tell him, does that mean the person was murdered at 7:30am?
It’s also fun to remember that this event happened 26,000 years ago.
This is one of my favorite (but also the most daunting) things about space. It is so awesome (and bizarre) that we can essentially observe the past. In this case, the event occurred sometime around when humans were figuring out how to make baskets.
No, the averages ignore input order. Reality is order dependent.
The past is the only thing we can observe!
In situations on the universal scale, it is incredible to know that no matter what, we will only be able to see the distant past (thousands to millions of years) for most other celestial bodies.
Would the statement stand if it were updated to say, "The (presentMoment - latency) is the only thing we can observe"?
Perhaps "experience" instead of "observe" would have fit better - although, experience by definition is only in the present, otherwise it would be a memory.
Then a counter argument might be: everything is memory, even the current moment being experienced. I suppose that sliver of "now" might be infinitesmal, approaching zero..
The info has to take time to travel.
1. You have a collection of black holes that formed from stars in a very dense cluster at the nucleus of the Galaxy early in its life that all merged to form an intermediate mass black hole, which then grew into a SMBH.
2. An intermediate mass black hole formed directly from the direct collapse of a large gas cloud and then grew into a SMBH.
But even the better known case of the formation of stellar mass black holes is still not well understood!
Based on my limited understanding of cosmology, wouldn't the gas first form a star, and not form a SMBH until the star's nuclear reaction became too weak?
Tweet from the author saying this, in case anyone else was looking for a citation:
A reference frame is a coordinate system. Usually with 3 space-like coordinates and a time-like coordinate we call "time". That last coordinate is what gives meaning to "now" between two distant places. But this meaning entirely depends on the reference frame chosen.
In Special Relativity, there are special reference frames called "inertial reference frames". From these we can easily calculate elapsed time for any particular path through space-time.
In General Relativity it is harder - there are generally no inertial reference frames to be found. But we can still do the same calculation using tensor math and something called "the metric". You can actually do the same thing with special relativity, however the metric is dramatically simpler in an inertial reference frame so people usually take the easier approach.
The various measures of "curvature of space" are measurements of how quickly any attempt to describe space-time an inertial reference frame will be wrong. Just as the curvature of a ball makes it impossible to properly describe its surface as a flat plane. (Mathematically this description is very precise.)
Now in a low gravity situation, we can find inertial reference frames that are approximately a match. The almost inertial reference frame where the distant galaxies are moving straight away from us is the one we usually implicitly think of. In that reference frame, this light was emitted 26,000 years ago. But you can pick a reference frame that gives literally any answer that you want.
But that reference frame is a bad description of the experience of timelines for fast moving objects, or what is happening in deep gravity wells. However that is fine, since from that reference frame we can predict exactly what the experience of those timelines will be, and our predictions turn out to be correct.
In other words, you can say "26,000 years ago from Earth's perspective", but it isn't the definitive answer for everything in this galaxy, and it definitely isn't the same answer for the rest of the universe.
I am struggling to guess exactly what you mean by that. Could you clarify? Is the first part of the quote (up to "have") just a statement about coordinate charts? If not, and it helps with the clarification, I know how SO+(1,3) (and more particularly the one-parameter SO(1,1) boost subalgebra of O(1,3)) relates to the gauge symmetry of massless |helicity| >= 1 particles and flat spacetime, and I'm pretty sure you do too.
Here is the conversation I frequently have in intro physics if relativity is included (it is this particular very common misconception I was trying to point out):
student: "So, time is relative because light(information) has a finite speed. Therefore, if a star at distance 1kly explodes 1k years ago, for us it happens today?"
me: "No, it is a bit more subtle. What you have said is true both for sound and light, but we do not talk about 'sound' theory of relativity, so there must be something more to light. Time is relative because light(information) has a fixed finite speed in all inertial reference frames. The star exploding and we observing the star explode are two different events. The time between these two events is measurable, it is 1k years in our reference frame for instance." (and then I go into how the space-time-interval is the thing that is constant, how these two events are always in the same order, how only in the reference frame of the photon they happen at the same time, how in another reference frame it might be 1year or 1M years, etc).
Then start with simply rescaling the coordinates on the timelike axis. Nothing changes but the labels. The same thing if we simply rescale the spacelike axis. We can measure in parsecs, lightyears, lightseconds, metres, and so on; on the time axis we can use seconds or fortnights or kiloyears and the but for the coordinate labels the diagram does not change. Then demonstrate a translation by sliding the timelike axis down so that the timelike origin is last week, last year, next year, and so on; demonstrate a spacelike translation by sliding around the origin on the spacelike axis. Again, invariance is manifest. We can do both types of translation at once, and put the origin on the exploding star instead of on the Earth. All we're changing is the labels associated with the events (and the labels for points along the intervals).
One can also show that a rotation of the coordinates also only changes labels, not relative locations -- this is where a pair of transparencies, or one paper one transparent layer works well. It might be handy to have the rescalings handy on transparencies so you can show that you can freely mix coordinate rescalings and translations and rotations, and the (literal!) underlying picture remains invariant in the face of all of these.
This opens up at least four interesting types of discussion: (1) if we calculate out the light's interval it's 0 (thus "null"). Any segment of the null path from exploded star to detector is also itself lightlike between the two ends of the segment, so dS^2 is still 0. What gives? (Answer: using a set of coordinates lets us deal in coordinate-based distances; and for extra credit we could talk about arbitrary parametrization, affine-parameter style); (2) why are the slopes of the different explosion products different, or why is the interval timelike for the non-light material?; (3) what do boosts do to coordinates?; (4) coordinates representing a moving observer with the origin always fixed on itself leave the underlying picture invariant but suggests kinematics and dynamics; and (5) a contrast between a "conventional" observer that remains at spatial zero but which "evolves" along the timelike axis compared to the same observer against a different set of coordinates.
For extra credit, explicitly distinguish between types of Lagrangian and Eulerian observers that differ only in their choices of systems of coordinates as in (4) and (5), even as the underlying picture of events remains identical for all observers.
This leads us into a block universe picture, where we have (classical or quantum) fields filling the whole of spacetime -- completely everywhere -- with arbitrary sets of coordinates imposed on portions of the spacetime used to describe field-values as (a) "objects" like worldtubes and instantaneous snapshots giving us something like a classical extended object; (b) dynamical laws that in a block universe picture simply predict the field-values (or "objects") at at a coordinate-location in spacetime
given some set of field-values at another location in spacetime ; (c) the "conventional" splitting of the block universe into 3+1 spacetime, but showing that the split is as arbitrary as any choice of system of coordinates because we can e.g. rotate a set of Cartesian coordinates differently for relatively boosted "conventional" observers.
 Essentially, this is pulling in the idea that initial values need not be in the relative past for a spacetime-filling IVP solution to obtain! Indeed, undermine the idea that we are evolving initial values in time, rather than extending some set of values outwards from a kernel. Any thought of time evolution can be cured by remembering that one should as a matter of course at least briefly consider all sorts of messed up coordinate charts on top of the underlying block picture. One is simply preferring to work with one static chart for purely personal reasons (which may include the ease with which an intended audience may follow the path to a set of results).
> 1year or 1M years, etc.
Here I would like to believe that "M" means "Martian". Or perhaps "Mercury". :D But those would correspond with a coordinate rescaling rather than a boost.
So doesn't it make sense that it only became part of reality yesterday ? And therefore to say that it happened yesterday. The famous supernova of 1572 AD also very much didn't happen anywhere close to 1572 AD.
If we would take a snapshot of the Universe VM spacetime at the current moment at the start of the event, the "now" in time would have to correspond to the current state for every other location if you want it to be useful and not only intuitive.
But this is where paradoxes come in because the black hole, stationary from in its frame of reference, would still experience 26,000 years and not see you arrive until then. From my understanding, general relativity solves this paradox with de-acceleration causing the one who was traveling at the speed of light seeing the rest of the universe's clocks' speed up.
So technically, your clock would have not moved 26,000 years forward, but other's would have.
Special relativity solves this fine (there is no paradox in it for that particular thought experiment), no need to involve general relativity. There is nothing paradoxical about the observer near the center of the galaxy not seeing you until you are near, because you are traveling at speed almost as great as the speed of the information carrier (the light you emit if we are talking about space, or the sound you make if we are talking about something on Earth). So you actually do not even need relativity to explain the "they do not see us coming". You do need relativity to explain the fact that to you all of this took only a blink of an eye.
This makes me think of lone sad CMB photons, who accidentally stop by hitting an atom and cannot even recognize a tiny bit of the universe they remembered since. A spark moment, and they lost everything to billions of years.
Or is it just the first collision ever that stops them and they just happen to miss every last particle in outer space for 13 billion years perhaps.
Wouldn't it have occurred much less than 26,000 years ago from the perspective of the black hole due to time dilation caused by the difference in gravitational potential of the blackhole compared to us?
Things that far away just don't move fast.
Does that mean, same duration within nanoseconds? milliseconds? seconds? minutes?
It was "a couple hours", so without doing too much more math than that, it was probably the same duration here and there within "a couple minutes". I'm more than comfortable calling that the "same" duration in conversational terms, but I would expect it's not the same duration within nanoseconds, as we're accelerating relative to Sgr.A* (rotationally).
I'm not familiar with spacetime, and was curious for a sense of scale here. A couple of minutes difference sounds quite significant to me (though I agree I'd conversationally call it "about the same").
But yes, space is way more enormous than most people (including myself) can wrap their head around. Spacetime warping is also hard to really get, I understand it conceptually but I can't really picture it.
Things moving less than about 15% of the speed of light experience less than 1% time dilation, and for comparison, we're moving around the center of the galaxy at 0.2% of the speed of light.
One of the wildest things to me is that GPS satellites have to compensate for time moving slightly slower because they're moving so fast around the earth, and also time moving slightly faster because they're further from the gravity of earth.
So, it just happened, and the light took about 26,700 years to reach us, assuming nothing happened to it on the way (which is a bad assumption, even just because there's a lot of stuff between here and there, but especially considering it originated from a severely warped spacetime).
The milky way galaxy is estimated to be ~13.7B years old. The black hole was brighter for a 2 hours. That event, as a percentage of the milky way's age represents: 0.00000000000001666500016665%.
As a comparison of what that represents as a unit of time in an average human lifespan (79 years) it equals:
We get to see the whole show.
Is there an object massive enough to make the black hole emit that amount of light, but which is not bright enough to be detected by our equipment?
More importantly, there is a very wide spectrum of danger between death and no effect, especially when you consider things like cancer. I assumed that was the point of the grandparent's question.
The amount of radiation you received from the Sagittarius flares is almost indescribably tiny. Many, many orders of magnitude less than the cosmic ray background radiation that we already live with. If you didn't have a sensor pointed right at the BH, you wouldn't be able to distinguish it from the noise.
Sure it could always happen at any time, that's not a very useful thing to say. More interesting is what this event teaches us, if anything.
* An undetected high velocity object
* Radation bursts
The thing is that since space is so big, we would have to be extremely unlikely to get hit. If a radation burst was directional it would still be like blindly throwing a dart and hitting a bullseye 24,000 light years away in this case.
I believe it's possible for our Sun to emit a solar flare large enough to kill us too (this is far more likely then radiation from a blackhole killing us because its magnitudes closer).
I liked this analogy, so I felt inspired to calculated the odds. Particularly: the percentage of the "sky" (celestial sphere) that is covered by the Earth from Sagittarius A* 's perspective. That's equal to the two dimensional projection of the Earth onto a 26000 ly sphere around Sagittarius A*.
cover% = π x (6371km)^2 / (4 x π x (26000 x 9.46 x 10^12 km)^2) x 100%
= 1.677 x 10^-26 %
"If you had a model of Saturn that was a meter stick wide (3 feet), its rings would be about 10,000 times thinner than a razor blade!"
Is there an established framework for astrophysics that allows to work on a high level to produce these nice visuals?
> Based on the concentration of Fe-60 in the crust, Knie estimated that the supernova exploded at least 100 light-years from Earth—three times the distance at which it could’ve obliterated the ozone layer—but close enough to potentially alter cloud formation, and thus, climate. While no mass-extinction events happened 2.8 million years ago, some drastic climate changes did take place. 
Well, supernova shockwaves can travel at up to 0.1c, so at best another 234 kyear. Keep your microphones ready.
Could this flare be a foreshock of that? It'd be nice to have some time to settle my affairs.
- "it was actually X thousand years ago"
- "it's actually false color, why can't we see what it really looks like"
- "surely this means quantum FTL communication works"
- something casually eugenic
and recently, with the Mauna Kea stories, there's a guaranteed "who do these bozos think they are, science is more important than anything"
A very interesting idea!
Although I don't think that the black hole cared much of those few photons from earth.
Expanding it, how long until my hand waving could cause a strong enough "butterfly effect" for an observable cosmic phenomenon to occur beyond our solar system?
A million years? 100 million?
Edit: Thank you for your comment. Just keep it! Sometimes people here are just a bit quick to judge. It's amazing to think humans could have affected such a monster at all, no matter how little. Even for a handful of photons worth.
My rough estimate says around 9 years, and 3 months.
The essence of chaos is that effects grow exponentially with time. For example with weather, errors in measurement lead to roughly an order of magnitude in errors in measurement every 3 days. Going from the scale of a single atom to the scale of a star is about a range of 10^60. At that rate of exponential growth means that in 180 days, which is 0.5 years a single atom out of place leads to a different outcome for things like solar flares.
Therefore a photon from your hand moves one atom on Alpha Centauri about 4.367 years later. A half-year later it causes the difference between a solar flare being there or not. Then 4.367 years later it comes back here. And the result is that in roughly 9 years and 3 months, one photon from your hand could have caused a visible change in another star.
I'm not sure exactly what OP is implying though.
 light, radiation, information, etc.
 ie, reflected, or caused some reaction
The destruction of Atlantis?
You're looking at something more like 50,000 years ago, so something like the Toba population bottleneck (which probably didn't happen 70,000 years ago).
The cleansing of saidin in the previous turning of the Wheel, might work.
> SO-2 made it’s closest approach about a year before the flaring observed in May 2019.
Should be its not it's
Or well, we _just_ discovered it.
But I guess it would make the title less appealing. Who would read "black hole flared 25000 years ago for 1 hour"? :P
"We Looked Back In Time 25,000 Years and You Won't Believe What We Saw"
"We Just Learned One Of The Last Things That Happened Before The Neanderthals Died Out and It Was Amazing"
Fortunately science is slightly more immune to clickbait titles than other topics. Though only slightly.
So it's possible it could be the black hole itself, but it could be a disruption in close proximity.
Anyway, it's not obvious to me that the edge of a black hole is the event horizon. The event horizon is mostly empty space too. Maybe it's the ergosphere, which can be further out. Since a black hole is just a region of space, the boundary is sort of arbitrary.
"Nobody has observed a magnetic monopole" is still true, even if systems that behave like quasi-monopoles have been built.
My conclusion (that we can't know for sure that black holes produce Hawking radiation) only makes sense if I was talking about observing actual Hawking radiation rather than analogs, which I was.