What’s the biggest thing you can’t see that is still closest to you?
We can’t be the first ones to notice this. You’ll need patience with the following, as it really constitutes a short course in galactic black hole physics. It’s not hard to understand – just long. From The Pearl of Great Price, Abraham, Chapter 3:
1 And I, Abraham, had the Urim and Thummim, which the Lord my God had given unto me, in Ur of the Chaldees;
2 And I saw the stars, that they were very great, and that one of them was nearest unto the throne of God; and there were many great ones which were near unto it;
3 And the Lord said unto me: These are the governing ones; and the name of the great one is Kolob, because it is near unto me, for I am the Lord thy God: I have set this one to govern all those which belong to the same order as that upon which thou standest.
For decades, astrophysicists have believed that most if not all galaxies must have black holes at their centers. There is just too much “stuff” floating around, moving way to fast, way too close to other “stuff” for it not to all merge due to gravity and orbit-decay. They already knew about white dwarfs and neutron stars – that bigger and bigger original stars give way to more and more dense “final states.” You can actually “see” one neutron star by its rapidly oscillating magnetic field. It’s like a radar beam sweeping over you as the neutron star spins ~1000 times a second. The signal is coherent, which means that the neutron star must be smaller than the distance light can cross in that amount of time – less than 10 kilometers. Calculations show that a teaspoon of neutron star “stuff” would weight tons on Earth – that is, if you could transport and then somehow weigh it.
Hmmm. What happens if you throw in a lot more “stuff” into the mix – what would you get? Must be something denser (see the Newton paragraph below) – and it will be a real glutton for all the smaller stars and gas and dust whizzing around it. Because of tidal and magnetic drag on the highly conductive material, the individual orbits will decay. Matter will spiral inwards. Annnnnd… I…. Gotcha!
With each cumulative new addition, the neutron star becomes larger and denser, until finally it has curved space so strongly that light can no longer escape it. By definition, it’s now a black hole. Matter spiraling into it is trapped.
For almost as much time as they’ve known about the idea, astronomers have diligently sought proof of a black hole at the center of OUR galaxy. They chose it because it’s closer than other galaxies, so it should be easier to image. However, on the face of it this would seem to be a daunting task, as a black hole, by definition, radiates nothing – no mass, no light, no signal can escape its event horizon. Remember from a previous chapter that black holes are really dark gray and fuzzy (but not cuddly). However, there ARE some indirect ways that we might see one. As in almost all of science, we figure things like this out only by indirect means (Eisenhauer, et al, 2003) – just as we figure out gospel truths by indirect means.
One way to “see” a black hole indirectly is to map stars close to the galactic core. “Our” black hole actually has a name these days: Sagittarius A*, pronounced “Sagittarius A-Star” or just abbreviated Sgr A*. It lies in a corner of a bright region in the center of the Sagittarius Constellation, in the center of our Milky Way. This bright spot was designated “Sagittarius A” by astronomers as the first bright apparent star classified in that constellation centuries ago when they first looked at it. To them, Sagittarius A looked like any other star, but they were using cruder telescopes than the ones you give your kids these days for Christmas. (That nearly worthless toy-store ‘scope? Galileo would have drooled over it.) As bigger and better telescopes became available, it turned out Sagittarius A was a whole lot more than a single star.
A very short course in basic orbital physics:
Thanks to Newton, we know that the gravitational force between two masses is equal to a constant (the “G” mentioned in the chapter on the Anthropic Principle) times one mass, times the other mass, all divided by the square of the distance between the geometric centers of the two masses. Whew, that’s a mouthful. Perhaps you can understand why physicists really prefer to say things in “equation” instead of in English. A quick translation (I didn’t use translate.google.com to do this) gives: F12 = G * M1 * M2/r * r. In shorthand this can be concentrated further to F=GMm/r2. This is important, because a star named “S2” close to the center of Sagittarius A has been tracked since 1992 as it moves in a fast, very tight orbit in the center of our galaxy. (http://www.solstation.com/x-objects/s2.htm). In the vernacular, that sucker is really rippin’: it orbits in an ellipse about 5 by 10 light-days across in about 15 years. Days and years here make it seem trivial until you remember the speed of light is 300,000 kilometers (~186,000 miles) per second. This star is moving so fast that it makes the huge nearby stars look like icebergs with a dolphin zipping around nearby – if a dolphin could move at the speed of sound. S2 orbits around something that can’t be directly seen – but because of that equation above, the unseen mass of “our” Black Hole can be measured, and it’s huge: about four million Suns’ worth of “stuff.”
A very short course in basic electromagnetic physics:
If matter is being drawn down into the monster, it will be accelerating because of that 1/r-squared part of the equation: the shorter the distance, the stronger the pull on it, and the faster it goes. In fact, it becomes seething plasma as it falls in, because the calculated forces are truly humongous (try dividing anything by a distance squared that approaches zero – it’s like magma expanding and accelerating up a volcano’s throat to a spectacular explosion, with ash distributed eight states away, like Mount St Helens in 1980). Such a seething cauldron of accelerating matter will radiate: electrons accelerating in a magnetic field give off electromagnetic energy at wavelengths proportional to the radius of curvature of their ever-tightening spiral motion inward. That’s a complicated set of words but think instead of a tether ball spiraling into the pole – a good place not to leave your head. The event horizon of a black hole in a busy galactic center, in fact, should be shrieking at all wavelengths. The closer to the event horizon, the stronger the pull and the higher the energy – and the higher the frequencies, all the way up into hard gamma radiation. You need a number followed by lots of zeros to describe the energies involved. It’s hard to see the screaming-edge source because of all the stars, gas, dust, and junk in between Sgr-A* and Earth – and it’s also a long way away to “look” (about 26,000 light years away) to see anything.
Back to the matter at hand:
Astronomers are a persistent lot, and eventually they figured out that certain longer wavelengths can get past all that dust and junk and be picked up by Earth-based radio-telescopes. (They settled on a rather atypical radio wavelength of 1.3 millimeters – not that far from what your cell-phone uses. They chose this wavelength for several reasons, including because it’s not a cell-phone-band frequency.) If you can get a rich enough billionaire to pay for it, you can get a big enough array of radio-telescope dishes, spaced far enough apart on the Earth, to get a pretty darn good radial resolution. Think: seeing the shape of a coin located a football stadium distance away. The shrieking edges of Sgr A* can more or less be made out this way. Its diameter is no greater than 44 million kilometers – probably a lot less. This is about one-half the size of Mercury’s orbit around our Sun. Now, fit four million Suns into that volume – and then step back, or scream as you are gobbled up.
In 2004, astronomers were astounded to find evidence of a much smaller (1,300 Solar masses) invisible object orbiting the 4-million-Solar-mass Sgr-A* black hole – a sort of mini-black hole orbiting the BIG black hole (Ghez, et al, 2005). This object resides in the center of a cluster of seven massive stars, which orbit it. Astronomers have also identified a number of additional giant stars that circle around in the near vicinity of Sgr-A* (the “lumbering icebergs”).
Now read verses 2 and 3 of the third chapter of Abraham again. Does this ring a bell? Note that this is not saying that God resides in, or near, a black hole. However, you would have to agree that there are a number of remarkable coincidences here. There are also some amazing physical processes taking place in the core of our galaxy. Abraham hints rather broadly at a vastly greater understanding than I think most people recognize, and certainly more than a humble shepherd could possibly have known on his own.