
Milky Way’s Black Hole Just Flared, Growing 75 Times as Bright for a Few Hours - cyanbane
https://www.universetoday.com/143150/milky-ways-black-hole-just-flared-growing-75-times-as-bright-for-a-few-hours/#more-143150
======
antognini
Former astronomer here! A lot of the comments here are about how this event
occurred 26,000 years ago. I thought it would be useful to describe how we
think about these things in astronomy.

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.

~~~
MichaelApproved
> _(we are not moving all that fast compared to the speed of light)_

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?

~~~
wokwokwok
If we (sol / earth) were moving at a speed significantly closer to the
(absolute) speed of light we would experience significant time dilation.

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)

~~~
roywiggins
The thing we are at rest (ish) relative to is the cosmic microwave background.
That's why we aren't moving that much relative to the rest of the universe, on
average.

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.

~~~
mirimir
Huh. So could one use that as a standard frame of reference?

~~~
philipov
Yes and no. The laws of physics do not pick out a preferred frame of
reference, and they should be symmetrical under lorentz transformation, but
the fact that we live in a cosmological universe starting with a big bang
breaks that symmetry in practice.

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.

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melling
I didn’t realize until recently that supermassives and classic black holes are
formed differently.

[https://en.wikipedia.org/wiki/Supermassive_black_hole](https://en.wikipedia.org/wiki/Supermassive_black_hole)

It’s also fun to remember that this event happened 26,000 years ago.

~~~
kickopotomus
> 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[1].

[1]:
[https://en.wikipedia.org/wiki/Timeline_of_human_prehistory](https://en.wikipedia.org/wiki/Timeline_of_human_prehistory)

~~~
DecoPerson
So a photon emitted/reflected by some human weaving a basket may have just
interacted with the Milky Way's supermassive black hole!

~~~
bouncycastle
...and a gamma ray burst from some distant galaxy that will strike Earth
sometime in the future causing a great catastrophy could have already happened
while the human was putting on the finishing touches on the basket.

------
codeddesign
It seemed that the pulse jumped for about an hour. Obviously this happened
thousands of years ago, but would that be a literal hour? How much time is
lost/bent in transit?

~~~
delecti
We're moving _around_ it, but we aren't moving very fast (relative to c), and
our relative distance from it isn't changing much. The duration shouldn't be
much different despite the distance.

~~~
krasin
That makes an assumption that the flare was unidirectional. If it's a beam, it
could be that Earth was in the beam for an hour, but its duration is anything
(like, 1M years)

~~~
toxicFork
This is something awesome to consider. Perhaps we only passed through the
beam. Perhaps the beam itself was rotating.

------
gillesjacobs
Here is the researcher's visualization of the near-infrared flaring activity:
[https://twitter.com/i/status/1160368687590727680](https://twitter.com/i/status/1160368687590727680)

------
thelittleone
It's amazing given the lifespan of celestial entities that we can witness such
significant change in such seemingly human time scales (2 hours).

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:

0.00000069197080291971 seconds. 0.00069197080291971 milliseconds.
0.69197080291971 microseconds.

~~~
simonh
I think a better comparison is to the size of the region in which this event
occurred. For the event to appear to last only 2 hours to us, it can't have
occurred in a region more than 2 light hours across. That's only 14
astronomical units, less than the diameter of the orbit of Saturn. There are
stars bigger than that.

------
human20190310
It's awesome when a natural phenomenon matches a timescale that a human being
can witness, rather than taking centuries or more.

We get to see the whole show.

~~~
zwkrt
There is a neat physical argument that was made back when quasars and the like
were just being discovered. Basically if the flash of brightness only lasts an
hour, then you can argue convincingly that the source of the flash must be
less than a light-hour across. The faster the flash, the smaller the bound on
the size of the phenomena. This is what lead people to realize that quasars
are wildly energetic but necessarily very small

------
fermuch
I think this video does a great job at describing what happened, how, and the
theories of why.

[https://youtu.be/Or8O_b7F640](https://youtu.be/Or8O_b7F640)

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?

------
broth
Out of curiosity, is it possible that some cataclysmic event in the universe
happened thousands of years ago that has yet to reach and potentially affect
Earth?

~~~
ypcx
I'm also interested. And adding to the question: Is it possible that this
particular flare-up may be a forward echo of such an event? I.e. have we
observed this happen before in other parts of the Universe?

~~~
randie63
It would need to travel faster than light

------
MFLoon
Can any astronomers comment on if we are in any danger of getting blasted with
gamma radiation or other black hole excretions?

~~~
NikkiA
Any such radiation would have arrived with the light of the black hole
flaring. The fact that you're alive to read this implies that nothing fatal
happened.

~~~
luc4sdreyer
Maybe some people did die, it's a bit too early to tell if it killed, say ten
people. It's probably very unlikely though.

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.

~~~
kabdib
X-class flares from our sun are 10E32 or so ergs. The black hole flares were
roughly 10E35 ergs, about a thousand times more energetic but they are about a
billion times farther away than our sun. Apply N^2 law and . . .

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.

------
softwarelimits
What software are these people using for the fantastic animations?

Is there an established framework for astrophysics that allows to work on a
high level to produce these nice visuals?

------
agumonkey
What are the chances that cosmic events of this kind could affect Earth ?
say.. ironically massaging atmospheric state and climate change ?

~~~
shkkmo
There is evidence they have:

> 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. [1]

[1] [http://nautil.us/issue/22/slow/the-secret-history-of-the-
sup...](http://nautil.us/issue/22/slow/the-secret-history-of-the-supernova-at-
the-bottom-of-the-sea)

------
jeffdavis
Seems odd that it would be a hunan-timescale event. Why not a few microseconds
or a few million years?

~~~
PopePompus
The time scale is set by the orbital period of the innermost stable circular
orbit (ISCO
[https://en.wikipedia.org/wiki/Innermost_stable_circular_orbi...](https://en.wikipedia.org/wiki/Innermost_stable_circular_orbit)).
That period depends on the spin of both the black hole and the accretion disk,
but the possible orbital periods range from 4 to 54 minutes for our galaxy's
supermassive black hole. The period is proportional to the black hole mass, so
for a really big black hole like the one in M87, the period is weeks long.
That's part of the reason why the EHT imaged the M87 black hole, but has not
produced a Sgr A* image - it takes many hours for the EHT to gather the data
to produce an image, and Sgr A* is not stable on that time scale. It's like
taking a long exposure of a foot race. But M87's black hole can't change much
in a few hours.

------
logfromblammo
So if the light from this event took 26 kyear to reach us, how long until the
"om nom nom" sound reaches at least a Voyager probe in the interstellar
medium?

Well, supernova shockwaves can travel at up to 0.1c, so at best another 234
kyear. Keep your microphones ready.

------
chiph
Could this additional energy affect any stars near it -- possibly causing them
to nova?

~~~
philipov
To the best of my knowledge, stars go nova because they have finished their
fuel, and they can no longer sustain fusion once they begin fusing iron. It
seems unlikely that being hit by a shockwave would trigger that. If it
stripped away a lot of fuel, it would probably cause the star to go the route
of a white dwarf rather than explode, right?

------
pts_
Why link to ad blogs instead of the actual study
[https://arxiv.org/abs/1908.01777](https://arxiv.org/abs/1908.01777)?

~~~
shkkmo
The article has significantly different and more approachable content that
explains the context of the paper. It also has a link directly to the paper at
the bottom.

------
redm
I'm always amazed at the amount of information and details astronomers can get
from such a blurry little picture. It puts our galaxy's size in better
perspective.

------
hirundo
Remember when Beowulf Shaeffer took the Long Shot to the galactic core and
discovered that it was exploding and would wipe out life in Known Space, so
the Puppeteers moved their planets to parts unknown?

Could this flare be a foreshock of that? It'd be nice to have some time to
settle my affairs.

------
auslander
Could it be one of the Voyagers?

------
roywiggins
I like to play Bingo with comments on science stories:

\- "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"

------
korijn
[Removed poor joke, no one thinks it's funny and it's attracting downvotes..
Please stop hurting my karma. I can't delete this post anymore either. Sorry.]

~~~
iamgopal
Why multiply by 2 ?

~~~
chimeracoder
OP is hypothesizing that an event happened on earth which emitted something
traveling at the speed of light[0], traveled some distance, then interacted
with some object which emitted something else[1] which traveled back to be
observed on Earth. Hence, double the distance between Earth and the black
hole, because it's traveling twice.

I'm not sure exactly what OP is implying though.

[0] light, radiation, information, etc.

[1] ie, reflected, or caused some reaction

~~~
Izkata
> I'm not sure exactly what OP is implying though.

The destruction of Atlantis?

~~~
saalweachter
Atlantis is usually put at "just before history" \-- Atlantis was destroyed
and then their survivors did all the impressive stuff around the world like
building the pyramids and Stonehenge, so around ~5000 years ago.

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.

------
sixtypoundhound
The Eye of Terror Pulsed... :)

------
quickthrower2
The word "Just" is bending my mind! I guess it means we Just saw it, but it
probably happened a while ago.

~~~
crooked-v
From our perspective, it was 26,000 years ago - though for some takes on
physics, it's easier to intuitively understand if you say "now, with a
26,000-year lag time on rendering updates".

~~~
IggleSniggle
I prefer “now, from something 26000 years away”

------
furdnacity
Doesn't look like I can comment on this article or contact the author, but
there is a typo.

> SO-2 made it’s closest approach about a year before the flaring observed in
> May 2019.

Should be its not it's

~~~
Udik
It's a lost battle.

~~~
quickthrower2
Innit a lost battle.

------
gumby
Um, shouldn't the headline say 25 Ky ago? It didn't "just" flare, unless
"just" means "happened to for no known reason" which I suppose is a legit
interpretation.

~~~
Insanity
The flare "just reached us" is the way this should be understood.

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

~~~
gumby
> 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.

~~~
tiborsaas
Interestingly the reverse is true for Earth events. I a mail gets delivered 75
years later, then it's news :)

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cosmotic
If a black hole is of brightness 0 (by definition), then 75 times that is
still 0. They are probably referring to something happening just outside the
event horizon and thus something that is not actually the black hole and just
a phenomenon caused by the black hole.

~~~
Causality1
Even if there were no external matter in the vicinity of a black hole, its
brightness would still not be zero thanks to Hawking radiation.

~~~
roywiggins
Nobody's observed Hawking radiation, so we don't know for sure.

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.

~~~
causality0
Hawking radiation has been observed in multiple experiments.
[https://arxiv.org/abs/1009.4634](https://arxiv.org/abs/1009.4634)
[https://www.nature.com/articles/s41586-019-1241-0](https://www.nature.com/articles/s41586-019-1241-0)

~~~
Ma8ee
Neither of those observations are from black holes.

~~~
Causality1
That is not the claim I addressed. He said Hawking radiation has not been
observed. I provided citations that it had.

~~~
roywiggins
It's been observed in the same way that magnetic monopoles have been observed:
physical analogs have been built, but nobody has observed an actual magnetic
monopole.

"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.

~~~
causality0
The claim that black holes are perfectly black is subject to those same
constraints.

