The Milky Way's black hole may spring to life in 2013 | Hacker News Reader

The Milky Way's black hole may spring to life in 2013

arstechnica.com

85 pointsevo_943 comments

Considering the lightyears involved, I assume this means we'll see it in 2013?

Was thinking the same thing. Depending on how you think about space-time it "is" happening 27,000 years go.

http://en.wikipedia.org/wiki/Milky_Way#Galactic_Center

Or rather, it is happening now 27k light-years away.

Presumably, yes. It would be odd for the astronomers to use two different temporal points of reference; time of observation is the only time that matters. Plus, any excitement on the part of astronomers would be super pointless if they had to wait another 24824 years to observe it.

From the point of view of a photon originating in that gas cloud, it was emitted by an electron in the gas cloud and absorbed by an electron in the telescope sensor at the exact same instant.

On the other hand it would be impressive if they correctly predicted it from 24-millenia-old data.

That's correct. But never forget the idea of a "now" is deeply tied to a "here".

Implying whatever happened so many thousand years ago will have an impact here at about the same time we observe it happening from here? (I.e. light coming from that time and direction arrives here at about the same time as whatever implication this has to us does.)

If so, what kinds of implications would this have to us? Is this quasar radiation merely an observable thing, or could it disturb communications or something along those lines?

Edit: no doomsday paranoia implied. :-)

I think that’s the implication, but it goes even further than you say: because of the relativity of simultaneity (see Wikipedia), there is no absolute yardstick of the timeline.

In other words, “it happened n years ago”, like “it’s happening right now”, isn’t defined by itself; it only makes sense for given values of here and there.

This comes out of special relativity and is closely connected with the fact that nothing, not even photons, can move faster than a certain speed.

It's interesting — this both appeals to my intuition and is hard for me to completely wrap my head around... I can see it but I realise that I don't naturally think like that.

Essentially, it's meaningless to say that two things are absolutely happening at the same time in different places. There is no such thing as "meanwhile, somewhere else". Or at best, it's a very limited model.

When we observe the light from an event is when it actually happens, from our perspective, for all intents and purposes. Kinda screws up our whole way of thinking, but this is how the universe actually works.

Think of it as the "egocentric" rule of astronomy: always describe things from the perspective of the observer (you), not from the perspective of the agent.

Can somebody explain why the black hole at the center of our galaxy is called "Sgr A*"? Is there some system behind the name or are astronomers just like programmers in naming stuff (it took me a while to figure out how to pronounce nginx >:().

That stands for Sagittarius A* http://en.wikipedia.org/wiki/Sagittarius_A*

Sgr is short for Sagitarrius, a constellation. If you mark off the boundary of Sagitarrius, Sgr A* would be in that region. The black hole itself does not have the name, but rather the radio source associated with it. (conjecture alert)I'm not sure where the * comes from, but I believe the A is associated with the fact that Sgr A is a super nova remnant. Supernova are typically named "SN [year] [alpha]" where [year] is the year discovered and [alpha] is an alphabetical character in order of discovery. A supernova remant wouldnt have a year associated, so i'm guessing it's given a constellation and then alphabetical marking.

Typically, astronomers have a mix of common names and many systematic naming schemes, but they get obsoleted when better instruments find darker objects. There was once a catalog of nebula called Messier with about 130 objects (M1,M2,..). We still use these designations, but suddely they found thousands more of these objects and had to rename using the New General Catalog, (NGC1,NGC2,NGC496). Even further the IC goes into many thousands.

For constellations, stars in each constellation are usually named alphabetically with greek chars in terms of their apparent brightness. Alpha Centauri is the brightest star, for example, in Centarus. Then there are common names like Polaris, the north star, whch is alpha ursa minoris.

> There was once a catalog of nebula called Messier

Hah, I'd sort of known what the Messier catalog was, but you inspired me to look at its Wikipedia page[1]. Apparently Charles Messier was looking for comets, and was tired of getting distracted by things that weren't comets. M1 is the Crab Nebula[2].

This amuses me.

[1] http://en.wikipedia.org/wiki/Messier_object [2] http://en.wikipedia.org/wiki/List_of_Messier_objects

It stands for "Signor A*", in order to show it proper respect. I'm glad to see that in this crude age, our astronomers still have class.

Could someone explain the implications of all this in laymen terms? Are we in deep shit?

No. From what I understand, any material caught in the accretion disk is merely funnelling down into the black hole's event horizon, i.e. the centre. It will not affect any orbiting bodies, such as our solar system, but it will make the black hole pseudo-visible to astronomers because the material in the accretion disk will admit some light.

It will add mass to the black hole though, right? So that will affect orbits, no? Or is that just so infinitesimally small that it can reasonably be ignored?

All that mass is already orbiting (on a galactic scale) right on top of the mass. It'll affect our solar system's orbits in the same way that the sun moving a few microns affects them, I'd imagine.

The black hole is estimated around 4 million solar masses, the gas cloud around 3 earth masses.

So by "spring to life" the writer meant "we may, if we're lucky, finally see a glint of something". It's very exciting, yet the writer put it in terms that will scare the living hell of any uneducated person like me. Glad there's always HN.

I was thinking of the exact same thing.

It's ironic when a piece of writing tries to present you with factual information begins with a deceiving title, all in the name of attention grabbing.

The mass is already roughly there. One thing to bear in mind - if you replaced the Sun with a black hole of equal mass, planets wouldn't change orbits. It's the same gravity and centre of mass, just a different density/volume.

This is true for Newtonian gravity, but only approximately true for general relativity (or so I understand it).

This includes the effects of general relativity. As long as the mass is the same, the orbits of planets will remain the same.

According to wikipedia[1] the converse of the Shell Theorem is (nearly) true:

Suppose there is a force F between masses M and m, separated by a distance r of the form F = Mmf(r) such that any spherically symmetric body affects external bodies as if its mass were concentrated at its centre. Then what form can the function f take?

The form of f allows Newtonian gravity but not Einsteinian.

[1] http://en.wikipedia.org/wiki/Shell_theorem#Converses_and_gen...

Interesting. However, I would have thought that planets are far out enough that classical is accurate enough. This sort of thing is why I specified planets as opposed to orbits in general.

The key point there is "spherically symmetric". The Sun isn't. It bulges around its equator thanks to rotation, as does everything. That does have effects on planetary motion; an object in an inclined orbit spends a bit more time a bit farther away from a bit of the Sun's mass. Replace the Sun with a black hole of equal mass and you don't have that oblateness. The effect on planetary orbits would be very small, so macroscopically the Solar System would still be the same, just with very slight differences in orbital speeds and periods.

In addition to the other explanations given, it won't affect us presently because it already happened a long time ago.

If I send a slow, waddling mobster to go break your kneecaps, are you affected when I give the order or two weeks later when Guido knocks on your door?

Good point, I retract my comment :)

Only if gravity moves at the same speed as light, right? It sounds like we've been observing energy emissions (light) rather than directly observing it's gravitational impact on us.

Gravity has to move at the same speed as light. If it didn't it would cause time paradoxes.

Ah of course, a theoretical graviton being a massless particle. That's what I get for not having a wee Google first.

My understanding (note: I am not a physicist, this is not a physics lesson) agrees with ars, gravity has to move at the same speed as light.

In either case, the energy emissions potentially are enough, if they're directed at us and strong enough.

No.

But the accretion disk might appear visible to various instruments.

Basically, we will see the exact location of the black hole for the first time directly. Not the collapsar itself, of course, but the swirling disk surrounding it.

I wonder if they took time dilation into account when calculating the arrival date.

That may be about to change, however. Astronomers have spotted a cloud of gas with a mass about three times that of Earth that's on a trajectory that will have it pass close to Sgr A in 2013*

If this is for real, I am ridiculously humbled by the power of modern astronomy. It's pretty damned amazing to me that we have the ability to detect the location, dimension, and trajectory of a mere 3 earth-masses of thin, amorphous gas 27k light years away, in the noisiest and densest part of the galaxy.

Based on the Nature article abstract images it appears they were able to image the cloud using the VLT telescope. I got confused about L'-band for a second. Thought they were talking about L-band.

Feel free to correct me if someone has read the article.

[1] http://www.nature.com/nature/journal/vaop/ncurrent/full/natu...

[2] http://www.eso.org/public/teles-instr/vlt.html

[edited for mistake]

This is the public webcast of the ESO VLT on the issue. http://www.youtube.com/watch?v=YFLkewQIzoA&feature=youtu...

I'd just like to point out that seeing that cloud isn't actually nearly as hard as getting direct observations of planets around other stars. The cloud is very brightly lit by all the stars around it, and is far enough from other light sources that you can just point a telescope at it without needing any tricks. Contrast this to looking at much dimmer planets that are very close to very bright stars. And we've been able to do that for big enough planets since 2008.

This is absolutely shockingly awesome. (No I don't use these words often at all.) Based on the non-mainstream scientific evidence, the coming radiation has the power to completely reconfigure our DNA, and in fact all DNA/RNA on Earth's surface. This is what had been predicted by numerous ancient cultures including Mayans, and badly misinterpreted as the end of the world, or end of the times. If you don't happen to be a hardline mainstream scientist, I really recommend picking up this book, if for nothing else, then for all the absolutely shocking scientific research it references: http://www.amazon.com/dp/0525952047/

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