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back to article Stars spotted dancing superfast tango around black hole handbag

Astroboffins have found a star whipping around our galaxy's central supermassive black hole so fast that it completes a circuit in just 11.5 years, which could help test Albert Einstein's theory of relativity. Keck Telescopes on Mauna Kea, Hawaii, observing the galactic centre The orbit is the shortest known orbit of any star …

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Anonymous Coward

Yay!

Science: Amazingly massive large number.

Creationists: 0

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Re: Yay!

I must have missed the bit where the article mentioned opposition from creationists...

Can't we admire the wonder of the universe without using it as a chance to insult each other's beliefs?

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Megaphone

Re: Yay!

"Can't we admire the wonder of the universe without using it as a chance to insult each other's beliefs?"

No. Every new scientific discovery should be openly paraded as more evidence against mindless superstition. How else will the virus of superstition ever be extinguished? By continuing to believe it some sort of virtue that deserves admiration and respect?

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Childcatcher

Re: Yay!

"Can't we admire the wonder of the universe without using it as a chance to insult each other's beliefs?"

I can demonstrate scientifically (at least to my satisfaction) that god exists. Notice I use a small g because god is not anthromorphic. However, emphatically, I do not believe in religion. Religions are created by men for men and all religious text are written by men not God. Let me give you a nice recent example - Scientology. I will avoid mentioning the text starting with K because that will just get me death threats. You see what religion does to people.

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Silver badge

sucked into the event horizon?

Sucked into singularity maybe? AFAIK, the event horizon is like our horizon here - a boundary beyond which you can't see anything.

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Re: sucked into the event horizon?

Not quite - if you were to get a step ladder your horizon would be (a little) further away and if you're in a balloon then your horizon is still further away. You're ability to see things is determined by the presence of a straight-line path from the object to you.

With a black hole the event horizon is fixed in size (until more mass is sucked in to increase the mass/ size of the black hole which will in turn create a large event horizon) so no matter what your position there will be a limit beyond which it is impossible to see anything closer to the black hole itself.

The effect of a black holes' gravity is felt at different strengths at different distances - the event horizon is simply the distance from the black hole at which the gravity is more powerful than light (ie gravity is pulling space-time fast enough that even photons can't make progress) so it's impossible to see anything, even though it still exists in some form.

A straight-line path form the object to you might exist, but since light cannot get to your eyes you will never see it.

ttfn

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Silver badge

Re: sucked into the event horizon?

"With a black hole the event horizon is fixed in size ... so no matter what your position there will be a limit beyond which it is impossible to see anything closer to the black hole itself."

That is until you fall below what used to be the EH - for you that limit (event horizon) will move as you fall and will always be some distance below you (until the singularity eats you) even though for people outside you'd be long gone.

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Facepalm

Re: sucked into the event horizon?

Once an object has crossed the event horizon no "straight-line path [from] the object to you" exists. (Although a path might exist from you to the object...) But that's okay,because you never see the object cross the horizon.

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Re: "straight-line path"

Good luck finding a straight line around here, what with all the curved four-dimensional spacetime here abouts. Perhaps you could substitute the notion of "geodesic" instead?

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Headmaster

Re: "straight-line path"

This brings me to criticizing the use of "SUCKED". Nothing is being "sucked" (in, out, or off) as this implies acceleration. Disregarding tidal effects, the star is free-falling. Nobody would say that the International Space Station is "sucked" by planet Earth.

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Headmaster

Re: sucked into the event horizon?

> for you that limit (event horizon) will move as you fall and will always be some distance below you

What? I don't think so. The event horizon is crossed (by you, freefalling observer) once all the sky has collapsed into a single blueshifted point directly overhead, with all the rest being black. From that point on "the singularity" is no longer "where" but "when", it becomes your immediate head-butting future. The event horizon has been left behind. It is quite literally your past.

Greg Egan puts it like this:

“Yes! The centre of the hole lies in our future, now. We won't hit the singularity face-first, we'll hit it future-first — just like hitting the Big Crunch. And the direction on this platform that used to point towards the singularity is now facing ‘down’ on the map — into what seems from the outside to be the hole's past, but is really a vast stretch of space. There are billions of light years laid out in front of us — the entire history of the hole's interior, converted into space — and it's expanding as we approach the singularity. The only catch is, elbow room and head room are in short supply. Not to mention time.”

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Silver badge

Re: sucked into the event horizon?

I think not. There won't be any blue shifted collapse to a point - all you should see is that the area of black which was below you is still below you and is growing larger. On the visible horizon of that black you will see a glowing edge from all the light behind the horizon that gets refracted towards you by gravitational lensing. Up above you will see the universe pretty much unchanged, only distorted to the extent your speed of free fall approach relativistic levels. Down below you can even see stuff which has fallen through the EH just before you did, it will never quite reach the ever falling EH from your point of view.

All that will apply, of course, only if you happen to fall into a black hole massive enough to have its Schwarzschild radius larger than the radius where the tidal forces become lethal. Otherwise you will be dead long before you even reach the EH.

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Silver badge

Re: sucked into the event horizon?

But that's wrong. Any lightray projected outwards from your eye excepts the ones going "straight up" will intersect the event horizon at some point. I.e. everything will be black except for a single point. Similarly, if you are at 3M radius, the event horizon will look like a flat infinite expanse.

Fun's here: http://gregegan.customer.netspace.net.au/PLANCK/Tour/Tour.html#BHVIEW I'm sure there are others.

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Silver badge

Re: sucked into the event horizon?

But the light I see is not projected out of my eye! :-) It is coming in and nothing about the EH prohibits the light from outside to follow me as I fall towards the central mass. However, no light bouncing off me can reach above the apparent EH for the outsider. That's why for them I would slowly spatter into a flat blob on the surface of the "blackness", dim and red shift into oblivion, while I would still see their puzzled faces and only the fact that they've stopped responding to my signals will indicate to me that I've fallen beyond the point of no return...

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Joke

Re: "straight-line path"

Nobody would say that the International Space Station is "sucked" by planet Earth.

Not unless they were writing some particularly surreal NASA slash fanfiction.

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Silver badge

Re: sucked into the event horizon?

@Destroy All Monsters - I looked at the site you mentioned. It appears quite good (I have not gone through the mathematics myself). The Java app is nice too.

It confirms what I was saying (which made me quite happy :-) ) and it also explains the reason for the difference in our opinions, namely: Our observer was free-falling but you were looking at effects modelled from the point of view of a stationary observer. If you switch the app from the default "stationary" to "free-falling" you will see the difference.

P.S. If you turn the line of sight to point sideways it looks spectacular as you move towards the hole!

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Anonymous Coward

So, just how wide is the black hole and just how fast are the suns traveling to be able to go around it in 16/11 years? I'm curious if they are already going a large fraction of light speed.

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Anonymous Coward

Velocity

The paper mentions "velocities of up to ∼10,000 km/s" so about 1/30th speed of light.

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The last I read, Sgr A*'s radius was definitely less than 1AU (distance from here to the sun), with a mass of 4E6 times the sun's.

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Joke

Holy Crap!

Earth is shooting giant yellow lasers at the Milky Way!

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Coat

Re: Holy Crap!

But where are the sharks?

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Mushroom

Re: Holy Crap!

Or, the Milky Way is shooting us.

Run!

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Coat

Astronomers are looking in the wrong places

I'm sure a bit of googling would help them find a lot of vids of two stars dancing the black-hole tango.

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Devil

Spaghetti of gas

Sounds like what happens when you eat high fiber spaghetti.

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Angel

Re: Spaghetti of gas

We found Him, blessed be his Meatballs, r'Amen!

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