Slashdot Mirror
Deep in the Core
meehawl writes "A video of what is currently thought to be the closest star to the supermassive black hole at the centre of our galaxy. The star orbits the black hole in a highly elliptical orbit with a period of 15 years or so, but at its closest approach it swings within 17 light hours of the black hole (around three times the distance between the Sun and Pluto). In the video, you can see the star ricochet past its closest approach to the black hole. This slingshot effect enabled astronomers to further pinpoint the mass of the black hole, which is confidently estimated at 2 million suns or so. The mass observation, coupled with the size constraints observed, indicates the object at the centre of the galaxy is definitely composed of some exotically dense form of matter."
The http://arxiv.org/abs/astro-ph/0210426:linkedarticl e says the "enclosed point mass" (read: black hole) has a mass of 3.7 million solar masses, +- 1.5M solar masses. Not 2M solar masses, as the article summary indicates. For most people, myself included, this is a meaningless distinction, but in the interest of scientific accuracy, I thought I'd mention it.
High-speed Road Trip (18.000KPH)
Apparently you haven't studied these things. The universe is 13.7 billion years old, it takes light from even the nearest star years to reach us, the Earth's mass is only a fraction of Jupiter's, Jupiter's mass is only a fraction of the sun's, the sun's mass is only a fraction of some other stars that exist, and on and on. So the general idea is that a lot of the things in the universe are a lot bigger than you and me and our tiny planet. So if a star (and just think how much mass is in a star compared to you) orbits something in 15 years, you don't think it's just a bit interesting that it covers about half of its entire orbit in one fifteenth of the total time?
Esoteric reference.
According to the original paper from 2002, the star is nowhere near close enough to be "tidally disrupted", so it's just orbiting. (What it says is that even at closest approach, it's still 70x too far way.)
With all those stars whipping around, though, it wouldn't be hard to get the occasional star either entirely ejected, or potted right in. More usually, an orbit would be changed so that it approaches closely enough on each orbit to have a bit of mass (say, a trillion tons) stripped off, and gets used up over the course of a few thousand years. Of course at some point we wouldn't be able to see it any more, so there could be a bunch of those happening right now.
Probably most of the mass moving near it is non-radiating low-density plasma whose motion is controlled less by gravitation than by unimaginably intense electromagnetic fields. We see stars, but there's lots else going on in there we can't see.
Black holes don't have special sucking power... it's just normal gravity. Just as a planet can orbit a star, or a star can orbit another star, a star can orbit a black hole. It will behave exactly as if it were orbiting a planet of an equal mass, as long as it's going fast enough to maintain orbit.
The caveat is that if one gets too close to the black hole, within what is termed the 'event horizon', then there is no turning back. Not even light escapes (generally speaking -- Stephen Hawking would be a more appropriate speaker on the subject.) This star does not appear to be doing that since it's still orbiting, and we can see it.
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it takes light from even the nearest star years to reach us
Umm, 8 minutes, actually.
"We returned the General to El Salvador, or maybe Guatemala, it's difficult to tell from 10,000 feet"
Examples of the real images are readily available (from near-infrared speckle imaging). It would be a herky, jerky, incomplete mess to the general public, however, to make a video of the actual data, hence the rendered movie. You can see, in the zoom in, the data points of actual observations used to determine the orbit of the key star. Scientists aren't trying to hide a thing. They're just trying to present their results in the clearest, most comprehensible way. Give them some credit for that. Scientists hide very little, as a general rule. We usually have to beg people to listen. Slashdot is a nice exception.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
No, actually. http://en.wikipedia.org/wiki/Kepler#Kepler.27s_law s
Kepler's elliptical orbit law: The planets orbit the sun in elliptical orbits with the sun at one focus.
Kepler's equal-area law: The line connecting a planet to the sun sweeps out equal areas in equal amounts of time.
Kepler's law of periods: The time required for a planet to orbit the sun, called its period, is proportional to the long axis of the ellipse raised to the 3/2 power. The constant of proportionality is the same for all the planets.