Second Black Hole at the Center of the Milky Way

Tsalg pastes "A second black hole lurks at the centre of our Galaxy, according to astronomers who have watched a cluster of stars spinning around it. Just three years ago, astronomers confirmed that the Milky Way revolves around a supermassive black hole, called Sagittarius A*, which is about 2.6 million times more massive than the Sun. But now a much smaller black hole, just 1,300 times our Sun's mass, has been found orbiting about three light years away from its supermassive cousin. placing it intermediate between the relatively small (stellar mass) black holes in the Milky way Galaxy and the supermassive black holes found in the nuclei of galaxies."

Comments

i read....

[Anonymous Coward]

...a security hole instead a second black hole on the first glance. I guess im getting paranoid.

Contradictory?

[dshaw858]

I thought that the goin theory was that at the center of each galaxy lay a black hole, which created the "spiral" effect (such as the one that we see in the Milky Way's "arms"). Does this contradict current knowledge, or is our galaxy just a fluke?

- dshaw

Re:Contradictory?

[Profane MuthaFucka]

That would be a movie effect, not reality. The spiral arms of the galaxy are a density wave propagating through the stars and dust of the galaxy's disk. Think of how sound can be described as a density wave propagating through the air. Same thing.

Re:Contradictory?

[Ayaress]

What the other poster said. But even if things where like you said, this is a 1600 solar mass black hole orbiting a 2.6 million solar mass black hole at a distance of 3 light years. At galactic distances, they can be approximated as a single 2.6016 million solar mass object. It's just not big enough to matter in that respect.

Re:Contradictory?

[CheshireCatCO]

There is (according to current understanding) definately a density wave there. Read Binney and Tremaine's "Galactic Dynamics", for example. While it's certainly true that stars virtually never collide, they don't have to to propogate a wave. Their mutual gravity binds them together quite nicely. (We see the same sorts of behaviors in Saturn's rings, incidentally. The rings are also collisional, but self-gravity is what lets most of the waves propogate.)

If the arms rotated because of the stellar orbits, you can easily see that the arms would be wound up beyond recognition by now. So that clearly doesn't work. (It's referred to as the "winding problem" in astrophysics.)

By the way, I'm pretty sure that sound waves aren't consider "density waves". The latter are driven by gravity, sound waves are pressure waves.

Re:Contradictory?

[Profane MuthaFucka]

Density waves don't need to be limited to just inelastic collisions. Look at traffic on a highway, in a traffic jam. You've got density waves there too, and no collisions, hopefully.

In a galaxy, gravity is the binding force. Imagine every star in the galaxy as a physical ball. And for simplicity's sake, imagine that it's connected to all it's neighbors by a spring. That spring is gravity. Now, move the sheet of interconnected stars that you've just made. Bingo, you have density waves.

Re:Contradictory?

[anubi]

One thing that has been puzzling the hell out of me...

If the "big bang" theory is correct, and the entire universe emanated from a point -

Where did all this rotational inertia come from???

I guess the primordial point we supposedly came from was spinning?

Is it likely that "black holes" can be spun up so much from ingesting incoming rotational inertia that they become unstable and sling themselves apart... aka, the "big bang"?

I am not a cosmologist, or even a cosmetician as far as that goes, but I often ponder on why everything I see seems to be spinning.

Re:Contradictory?

[Ckwop]

Do we have any way of knowing if the universe as a whole is rotating? Or if it is, in what plane and how fast?

One of the key axioms of Cosmology is that of isotropy. No matter which way you look the universe looks roughly the same. This has been a very successful conjecture and many a cosmologist wouldn't like to throw that principle away without a fight.

I'm no expert at cosmology but my immediate thought is that material would spread out along the plane of rotation like dust does with newly forming stars. Therefore we'd expect to see more stars in single plane than elsewhere in the sky.. which isn't true.

Of course, the rotation could just be very slow but I think it's unlikely.

Simon.

black hole collision

[i_should_be_working]

any astronomers know what to expect to see when two black holes collide? we have pictures of stars colliding or ripping each other apart. we have ones of whole galaxies colliding. but what about black holes?

Re:black hole collision

[Carnildo]

If black hole "A" combines with black hole "B", the resulting black hole will have a greater mass, and thus a larger event horizon.

Re:black hole collision

[benhocking]

And some very interesting gravity waves will be generated!

Re:black hole collision

[chenzhen]

Actually this is a pretty tough problem to solve. The computation was attempted by several leading numerical relativity institutions some years ago, but met with no success. The professor I work for is currently building up a code that will hopefully someday be able to handle the binary collision problem.

One of the major problems is that programs crash pretty quickly when the evolution develops a singularity. A good method for avoiding this is called excision, where the singularity is removed from the grid and replaced with boundary conditions. This was recently implemented in my advisor's group and applied to the binary neutron star problem. At the end of the evolution, a black hole forms, so it doesn't seem like there are too many steps before a full black hole collision is possible.

Re:black hole collision

[chenzhen]

On second thought I shouldn't say no success. There have been successes in computing special, less physical cases, for example in treating the stars as frictionless dustballs not possessing magnetic fields. But these features are very important in determining the rotation structure of stellar fluids, and are probably essential in modeling the physically correct binary merger. The general problem remains to be solved, and the goal is to figure out what physical processes produce gravitational waves, so that we know what to be looking for experimentally.

Here are some visualizations of previous merger simulations:
1
2

Re:black hole collision

[Tablizer]

Actually this is a pretty tough problem to solve. The computation was attempted by several leading numerical relativity institutions some years ago, but met with no success.

Just divide by zero......twice :-)

Re:black hole collision

[scoser]

And here's a distributed computing project to detect such gravity waves: http://www.physics2005.org/events/einsteinathome/

Tithing

[AtariAmarok]

"black holes are a popular myth like god"

So, if you give money to a church, it goes to God; and if you pay taxes to government, it goes down a black hole?

Stars ripping each other apart.

[AtariAmarok]

we have pictures of stars colliding or ripping each other apart

See this link for more information and pictures. I particularly like the one where Andre Agassi knocks Tiger Woods' kneecap out of the arena.

So, is it just a coincidence

[CodeWanker]

that when I flush a toilet the water looks like a spiral galazy as it goes down the sewer? Sounds like God leaned on the handle.

What are the odds

[Anonymous Coward]

that my immediate guess, that it's the remains from a swallowed dwarf galaxy, is correct?

Re:What are the odds

[Ayaress]

Excessively low, I should think. Only 1300 solar masses. Even a tiny dwarf galaxy would be millions of solar masses. Also, they tend to get torn apart rather than crushed in the process of being "swallowed."

Re:What are the odds

[Anonymous Coward]

And the black hole that they might have in their center?

awesome

[Striker770S]

just think, we wont get sucked in unless we are actually aiming to do so, otherwise we will just revolve around the black hole. so its nothing to get worried about, and by the time the black holes do collide(if they actually do), it will be many years until the effects are felt here on earth, and by that time we will blow ourselves up.

Re:Scary

[FooAtWFU]

A few words of reassurance.
Remember, a black hole doesn't have any magical sucking power. It's just gravity. If a star collapsed into a black hole, its gravitational pull doesn't get any stronger. It's still the same mass, it's just a lot denser. Contrary to what science fiction shows will tell you, it won't start "sucking in" anything that the star it collapsed from wasn't already "sucking in".

Now consider how often you see planets and stars collide. You ever hear about it? Even when two galaxies run into each other, they tend to just fly apart into a rather incoherent mess instead of individual stars going anywhere- due to gravity, orbital mechanics, density, all that.

Remember: space is very, very, very, unimaginably big. I believe in the book Einstein's Universe (excellent explanation of relativity, including some stuff on black holes, for the nonexperts) they discussed the density of matter which would be required if the universe were to reach a steady state, not expanding or contracting, and they came up with a ballpark figure of about a baseball-size mass every cubic light year (pun optional), and went on to say that current observations of the universe indicated that this seems to be much more than actually exists.

Re:Is this a big surprise?

[Tsalg]

That this is a surprise depends on whom you ask. The real issue here is to understand how those huge f**off multi-billion solar mass black holes form. And so far there had not been such high-quality evidence for anything in between a stellar-mass black hole formed by a single massive star collapse, and those monsters in the middle of galaxies.

So those who think that they come from mergers of solar-mass BHs are comforted. There's also those who say that in no way those monsters had enough time to form by such a slow process. Read for instance Spin, Accretion and the Cosmological Growth of Supermassive Black Holes. Formation of supermassive black holes in turn is likely to have an impact on star formation rate in galaxies, another highly speculative area.

The other original thing here is that evidence for intermediate BHs in other galaxies comes from 1) luminosity measurements, which is a much more biased method than speed measurements of stars gravitating around it (to measure star velocities you have to be able to resolve them, which is only possible in relatively nearby objects) and 2) objects that were not in small clusters like here.

Death and Taxes

[RobertB-DC]

[T]hey calculated from the movement of the seven stars that they must be orbiting an intermediate-mass black hole, called IRS 13E, which spirals around Sagittarius A* at about 280 kilometres per second.

Is it just serendipity that this object, into which everything goes and never comes back, is named after an Earthly agency to which similar attributes are often ascribed?