Trio of Big Black Holes Found in Galaxy Smashup

[CygnusX-1]

by Dr. Ken Croswell

Astronomers staring across the universe have spotted a startling scene: three supermassive black holes orbiting close to one another, two of them just a few hundred light-years apart. The trio, housed in a pair of colliding galaxies, may help scientists hunting for ripples in spacetime known as gravitational waves.

Link: ScienceNOW.

 

[Drakkith]

Nice. Hopefully we can find some more closer to home.

 

[SteamKing]

Nice. Hopefully we can find some more closer to home.

That's OK. I like to keep my black holes as far away as possible. Too many things can go wrong if they're nearby.

On the whole, I found the article in ScienceNow very confusing. First, the article mentions a couple of black holes orbiting one another although they are some 24,000 light years apart. Then, another pair of BHs is mentioned which are orbiting each other and are 450 LY apart. A third, previously described orbiting duo of BHs are some 24 LY apart. If these puppies attract each other strongly enough to orbit one another while separated by 24 LY, let alone 24 kLY, I want to be across the galaxy from them, or in another galaxy entirely.

Who knows? Maybe it's already too late, and the solar system is already orbiting a BH somewhere.

 

[Drakkith]

I think the article means that at first we thought it was just two black holes, 24 kly apart. Then, upon closer inspection, one of them was discovered to be a pair of black holes 450 ly apart. These two black holes are the 2nd tightest orbiting black holes, behind a pair that are 24 ly apart.

 

[mfb]

I think the article means that at first we thought it was just two black holes, 24 kly apart. Then, upon closer inspection, one of them was discovered to be a pair of black holes 450 ly apart. These two black holes are the 2nd tightest orbiting black holes, behind a pair that are 24 ly apart.

Right.

The trio is 4.3 billion light-years away, so it's completely safe for us :).

Who knows? Maybe it's already too late, and the solar system is already orbiting a BH somewhere.

It is hard to construct a scenario where this would happen without getting noticed. We orbit the center of our galaxy, where a massive black hole is a (small) part of the total mass, but I would not call that "orbiting the black hole".

 

[enorbet]

Do we have enough data to calculate when these will "collide" ? The mental image of a Black Hole Death Dance of an ever-tightening, ever-quickening spiral is just stupendous in every sense of the word and then some. Assuming we have data, is the Math equivalent to 2 bits of flotsam in a whirlpool, or is that altered by the fact that the force comes from "the flotsam" and not draining water?

 

[mfb]

For two orbiting black holes (or other isolated structures) in a completely empty space, it is easy to calculate the time they need to merge.

Assuming the 450 light years distance and 4 million years for an orbit are right and assuming the orbit is roughly circular with two objects of equal mass, the black holes have masses of 3 billion solar masses (calculation.

Plugging this into the formula for gravitational waves, we get a power of 5*10²³ W. That is a lot compared to powers we use here on earth, but tiny compared to their kinetic energy of 10⁵⁰ J. If you divide both numbers, you get a rough estimate of the mergin time: about 1 billion times the current age of the universe. Those black holes will continue to orbit each other long after all stars in the universe died, unless some other very massive object disturbs their orbit before.

 

[enorbet]

As much as a human mind can begin to comprehend such vast distances, I'm aware of the meaninglessness of my question as regards the 450 LY pair. I am more interested in the 24 LY pair and especially if there is some momentum vector from what I took to be "colliding" galaxies source, perhaps creating more of a spiral than a circling, stable orbit.

 

[mfb]

Neglecting gravitational waves and other objects, the orbits are always ellipses (for bound systems). There are no spirals.

Even for the 24ly-pair the timescale for gravitational waves is extremely long. Also keep in mind that the 24 light years are the minimal distance (the apparent distance as we just see two dimensions in the sky).

 

[CygnusX-1]

This discovery was just featured on the John Batchelor Show. You can listen to the program at http://www.johnbatchelorshow.com/podcasts/2014/07/01/third-hour .

 

[Borek]

Plugging this into the formula for gravitational waves, we get a power of 5*10²³ W. That is a lot compared to powers we use here on earth, but tiny compared to their kinetic energy of 10⁵⁰ J. If you divide both numbers, you get a rough estimate

I wonder how rough it is, taking into account power is changing as r^-5, so the process will speed up very quickly.

Definitely no chance for me to witness the merge, just curious.

 

[mfb]

Better than a factor of 10 - derivatives and integrals of r⁵ give factors of 5-6. As we are 9 orders of magnitude above the current age of the universe, that should be sufficient. We don't even know if the orbit is circular - if it is highly elliptical, I would expect a different result.