HowDoWhy

A galaxy is a massive collection of stars gravitationally bound around a common central core. It is believed that most, if not all galaxies have at their core a super massive black hole - a black hole coming in at hundreds of thousands or billions times more massive than our own Sun.

Speaking of our own Sun, you can imagine a galaxy to be a super-sized solar system. Rather than a few planets orbiting a single star, a galaxy contains billions or hundreds of billions of stars orbiting a single or multiple black holes.

Galaxies come in different shapes. Most folks think of the classic spiral galaxy shape as shown in the spectacular image taken by the Hubble Space Telescope to the left, but galaxies can also be found in elliptical shapes ranging from nearly spherical to highly elongated and even ring shaped morphologies. Some lack much definable shape at all. This is usually due to “collisions” or interaction with neighboring galaxies.

Galaxies tend to cluster together in groups forming beautiful strands and webs throughout the universe. Our own local group contains 30 or more galaxies. Galaxies can also be incredibly big. The most recent observations of the Andromeda Galaxy, our nearest Spiral neighbor and largest member of our local group, put the count at some 1 trillion stars.

You might also be interested to know that the Andromeda Galaxy and the Milky Way Galaxy (the galaxy we call home) will someday merge into a giant elliptical galaxy. We are drawing towards each other at a pace around 60-90 miles per second. But with Andromeda almost 4.5 light years away, the merger isn’t expected to go through until sometime in 2.5 Billion AD. You might not want to bother waiting in line for good seats.

From some of my previous posts you know that objects don’t just have size, they have mass. A three-foot diameter ball of loosely packed feathers, for example, has far less mass than a three-foot diameter ball of lead. But if you keep compressing feathers into that three-foot sphere, keep squeezing and squeezing them in, you’ll eventually have as much mass as the lead sphere. Once the two spheres are of equal mass you only need to squeeze in one more feather and, suddenly you have a three-foot sphere of feathers that is more massive than the three-foot sphere of lead.Now imagine you have an unimaginably powerful feather-squeezing gizmo and could keep squeezing in feathers. If you kept squeezing them in, your feather ball would become more and more massive. Eventually it would be so massive that it would have measurable gravity. Sooner or later it would become so massive that you could walk around on it just like the Earth but not as large.

Because your feather squeezing gizmo is so powerful you’d keep squeezing feathers in until the sphere had as much gravity as the Sun, then more than the Sun. Eventually it would have so much mass and its gravity would be so powerful that even light would bend a little when it passed too close to it. And after that? Well, it would become so massive that anything, including light, would fall right into it and be unable to escape if it passed too close.

And just like that, you’d have created a black hole. A black hole is simply an object of so much mass that its gravity prevents the escape of anything, even light. Black holes of varying mass exist at the center of many galaxies (including our own, it is believed) and in the space beyond. They are formed by the death of very large stars or by the joining of enough mass (in the form of stars, gas and other matter until the inward gravitational pull of the object exceeds any outward forces imparted by spin or (in the case of stars) by the energy of fusion. At this point, the object collapses in size until an unbelievable amount of mass is compressed into an unimaginably small area of space.

When you think about black holes you’re actually thinking about two things - the object or mass in the middle and the area of influence that object exerts. (though both are depicted in the image to the left, remember they’d both actually be completely invisible until you get out to the event horizon). The area of influence can be further broken down into two components - the event horizon and everything outward beyond the event horizon out to a point where the gravitational effect is no longer notable (represented by the green fog). We’ve already described the mass in the middle. It is simply all the matter (gas, rocks, ice, feathers, squirrels or anything of sufficient quantity) that has been packed together until it is massive enough to have an area of influence that prevents the escape of everything, including light.

If you could measure out from the edge of the massive object, there is a sphere of space-time. If an object passes far enough away from that sphere of influence at a constant speed as in the image to the left then it has every chance of continuing on its path without even noticing the effects of the black hole. Super sensitive instruments might read a subtle fluctuation in gravity in the direction of the hole. Perhaps a subtle course correction might be required. But the point is, despite its awesome power, even a black hole has limits. The primary weapon in its arsenal, gravity, dissipates over distance.

If the object flies closer to the black hole then its direction of travel might be influenced. It would, in effect, be pulled towards the black hole rather than traveling forward in a straight line. It might even be slowed a bit until it escaped the gravitational influence assuming it is applying constant force.

An object (a rocket, for example) has two choices to minimize the influence of the black hole it passes near. It can increase its speed to limit its time in the black hole’s gravity well or it can increase its distance from the gravity well as in the first example.

Fly too close, though, and the object might be captured by the black hole’s gravitational influence. It might then be held in a permanent orbit around the black hole, not falling in but not escaping. If it could increase thrust, it might escape. If it ran out of fuel, it is doomed to eventually fall past the event horizon. Once it falls past the event horizon, all bets are off. Remember, that current theory holds that nothing can move faster than light. Since even light is incapable of finding its way back out from the inner side of the event horizon, no rocket or spaceship could either. The event horizon is where the black hole begins to appear black. That’s because light can’t escape to reach our eye so, effectively, nothing from that point inward appears to exist.

Black holes are some of the strangest things you can find in space. Physics gets really weird when you throw black holes in the mix. A black hole literally warps both space and time. If you’re interested in reading more about black holes, super massive black holes, or micro black holes, eat a good breakfast, get plenty sleep the night before and make sure you bring your thinking cap with you. Then go to Ted Bunn’s absolutely wonderful FAQ about black holes and read until your brain hurts.

If you have flash enabled, I also strongly recommend visiting ThinkTechnologies.com and enjoying a very well put together flash presentation on the bizzare nature of black holes.

We’ve already answered in a previous post that the Sun is the closest star to the Earth, but when most people ask this they’re really asking, what is the closest star to the Sun. The closest star to the Sun is Proxima Centauri at 4.2 light-years away.

Interestingly, most folks often think of Alpha Centauri as the nearest star but there are two misconceptions there. First, Alpha Centauri is actually a binary pair of stars rather than one star. They are known as Alpha Centauri A and Alpha Centauri B. Second, while nearly as close as Proxima Centauri, the Alpha Centauri pair are slightly further away at 4.3 light-years.

Other interesting facts about these stars:

• The Centauri group is believed to actually be a triple star system, with Alpha Cent A and B orbiting each other and Proxima orbiting in a massive circle around the two of them.
• Alpha Centauri A is about 1.2 times the size of the Sun.
• Alpha Centauri B is about .86 times the size of the Sun.
• Tiny Proxima Centauri is only 1.5 times the size of Jupiter but 150 more massive.
• Proxima Centauri is barely massive enough to ignite its hydrogen. Much smaller and it would have been a failed star known as a Brown Dwarf.

You might be surprised to know that a light-year is just one normal Earth year long (a Julian year of 365.25 days)! Confused? Think of it this way, a light-year isn’t a measure of time, but a measure distance within a certain amount of time (a year).

If you’ve kept up with all my other posts on space, you’ll know that distances get pretty big in space. Even within our own solar system, common units of measurement start to break down and become impractical. We’ve discussed the use of the Astronomical Unit as a compensation for the vast distances in our own solar system, but when you move beyond our solar system and start working with the distances between stars, even the AU stops being practical. Enter the light-year which quite simply uses the distance light travels in one year as a means of measuring things that are really far apart.

Our previous post gave the speed of light as 186,282 miles per second (and some change). To determine how far light travels in one year, multiply 186,282 by 60 to get a Light-minute of 11,176,943.82 miles per minute. Now multiply that figure by 60 to get a light-hour of 670,616,629.2 miles per hour. Multiply that figure by 24 to get a light-day of 16,094,799,100.8 miles per day. Finally, multiply that figure by 365.25 and you wind up with a light year which is a measure of distance covering roughly 5,878,625,371,567.2 miles per year.

So how does that stack up in our solar system? To reach each of the planets and Kuiper Belt objects like Pluto it takes light leaving the Sun:

• Mercury - About 3 minutes
• Venus - About 6 minutes
• Earth - About 8 minutes
• Mars - About 12 ½ minutes
• Jupiter - About 43 minutes
• Saturn - About 1 1/3 hours
• Uranus - Just shy of 3 hours
• Neptune - A bit over 4 hours

At 4.583 billion miles from the Sun (at maximum distance) it takes light from the surface of the Sun a little under 7 hours to reach Pluto.

After years of “close” estimates, the speed of light was nailed down to 299,792.458 kilometers per second or 186,282.397 miles per second in 1983. Previous estimates came surprisingly close to the mark given how difficult it must be to put a limit on something as fast as light. We also know that the speed of light is a constant (which will become important if anybody ever asks me about relativity). It’s also important to understand how fast light moves as it will become a relevant measure of distance in subsequent posts.

Some facts about light:

• It takes light leaving the surface of the Sun a little more than 8 minutes to reach the Earth.
• It takes light traveling from the center of the Sun about 1 million years to reach us. Not because it is moving any slower but because the Sun is so densely packed that a particle of light keeps getting bounced around rather than traveling in a straight line as it moves from the center outward.
• If you watch somebody bounce a basketball or clap their hands from far away, you’ll notice that the sound of the ball or clap is out of synch. That’s because the light that allows you to see the action of the clap or bounce travels MUCH faster than the actual sound of the event.
• A beam of light is made up of all the colors of the rainbow.
• Your eye sees colors because an object absorbs some of the color of light and reflects others. A lemon absorbs the yellow spectrum of light more poorly than other colors so you see a lemon as yellow because yellow is what is reflected off the lemon and towards your eye.

Measuring the dimensions of our solar system brings up a question of preference. Are you interested in the diameter from the Sun to the outermost planet? To the innermost edge of the Kuiper Belt? To the outermost edge of the belt? To the Oort Cloud? Would you fully grasp the true scale even were I to answer any of the above? Likely not. Distances and scale in the solar system are so tremendous that, unless you create a physical model, you’ll never really understand just how large an area we’re talking about. Maybe we should put it all into perspective when we’re done.

Most of us think of the solar system as the sun and its planets so we’ll make that our first measure of distance. As mentioned in a previous post - Weren’t there 9 planets? What happened to Pluto? - Pluto has lost its planetary status so that makes Neptune the furthest planet from the Sun at about 2.79 billion miles or 30.07AU. AU stands for Astronomical Unit and is a means of measurement already discussed in my post - What is an Astronomical Unit. Remember, that’s a radial distance (from the center to the edge). The diameter of the solar system as measured to the outermost planet is twice the radius or 5.58 billion miles (60.14AU).

But the solar system isn’t just limited to its planets. There are also the Kuiper Belt objects such as Pluto. These have been measured in as close as 31.7AU and as far out as 48AU. The general inner edge of the Kuiper Belt is accepted as 30 AU (closer in than even Neptune’s elliptical orbit) and as far out as 50 AU. In miles, that equates to 2.79 billion miles and as far out as 4.65 billion miles.

But why stop there? The real edge of our solar system, where the Sun’s gravity loses dominion over its surroundings, is the Oort Cloud. The Oort Cloud is estimated to reside in a sphere about 18 trillion miles out from the Sun. That’s 18,000,000,000,000 miles or 193,548.38 AU. Think about that… if you made the trip from the edge of the Sun to the Earth and some wise guy in the back seat shot off his mouth and convinced everybody to, “just keep driving till we hit the edge of the solar system,” you’d have to repeat the trip you just made over 193.5 thousand times more before you reached your destination.

Well, there you have your straight forward numerical answers but, as I implied before, wrapping your head around what those numbers really mean is just impossible without some kind of example or model. So if you’d like some common examples, read on! Continue reading »

Well I suspected things would run long and they have. There’s simply so much out there and so many good questions about space that I’m going to continue the project into this week before changing topics. Even then I’ll have just scraped the surface and will have to come back from time to time to add another few posts on space-related questions.

I only have one more post (for now) on the solar system which will be going up shortly. It’s a long one but I recommend you read through to the end because the distances I’ll be covering and the examples I’ll give to make it more digestible are simply staggering. Hope you enjoy and remember to come back every day or two to see what’s new at HowDoWhy. For a taste of what’s coming up, I’ll be talking about galaxies, the universe, light, black holes and alternate dimensions for the rest of the week.

When dealing with measurements on an orbital scale, you have to think big. As my previous astronomy posts have shown, the distances are vast. Though humans see and use numbers like million, billion and trillion all the time, our brains have a tough time conceptualizing what those numbers really translate to. How often, for example, have you held a million individual items in your hands? Or seen them in a room?

Yankee Stadium, for example, has a seating capacity of 57,545 people. If you’ve ever watched a game there you know what a “sea of people” looks like. Everything blurs into a cloud of colors. From a distance you might be able to take the whole scene in but it’s pretty staggering when you realize that the blurry mass of “things” sitting in all those seats are all individual people.

Well, to get to 1 million, you’d need more than 17 fully packed Yankee stadiums. Now think on an astronomical scale. The distance from the Sun to the Earth measures just shy of 93 million miles. If every person in Yankee stadium were a mile tall, you’d need 1616 filled stadiums worth of mile-tall humans lying head to toe to stretch from the Sun to the Earth.

So you can see that the numbers game in space doesn’t do well when we try to measure using things we can conceptualize. Even measuring from the Sun to the Earth is hard to grasp using common terms and, in the grand scheme of things, the Earth / Sun distance isn’t even all that big compared to other stuff in our solar system. Enter the Astronomical Unit or AU.  

The Astronomical Unit serves as a convenient measurement for things within our solar system. It is simply the average distance from the Earth to the Sun. So, one AU translates to about 93 million miles (92.9558 million miles to be exact). If one astronomer were speaking to another about a spaceship currently halfway between us and Jupiter, they’d say it’s about 2.1 AU from Earth. If their friend from the botany department strolled by and asked them what the heck 2.1 AU mean, our astronomer friend would quickly translate that to about 195 ½ million miles.

What is this question doing in the middle of my Week of Astronomy? Well, stay with me and you’ll find out! Kathleen of Virginia asked this one, maybe as a hint to her husband?

Kathleen – Black diamonds, also known as Carbonado, are indeed rare in the same sense that any gem is relatively rare compared to, say, a chunk of granite. But they aren’t that expensive. In fact, a comparably sized white diamond running about 1 carat would set you back 10 times as much as the black variety. Factors that reduce the price of black diamonds are its generally porous nature (think sponge-like without being soft), their 100% opaque color and the fact that they are “artificially enhanced” by color treating to hide their natural imperfections.

Black diamonds match the mood of their color in that they are mysterious things. They don’t form in the traditional places where white diamonds are found. In fact, they are only found in Central Africa and Brazil. Elements of their makeup have led researchers to theorize that black diamonds didn’t form on (or in) the Earth but, instead, arrived here from space! One theory suggests that they were spawned by the traumatic death-throes of a giant star, the explosion of which compressed material into the gems. In the early and traumatic days of our solar system some 4 billion years ago, this same material rained down on our planet. Our own star was born from the remnants of such an explosion as evidenced by the relatively high level of heavy elements in our solar system. We do know that diamonds form in space and they have been removed from samples of rock that have struck the Earth, but these tend to be tiny compared to carbonado.

Speaking of diamonds in space, one theory explained at PBS’s NOVA holds that Uranus and Neptune may produce so much pressure and heat in their atmospheres that abundant methane in the clouds actually rains down on the planetary core as diamond! Experiments conducted by scientists have actually shown it’s possible. Visit NOVA and read more about it.

If you are interested in purchasing black diamond jewelry, I’d like to recommend Bell Jewels. Their wonderfully helpful staff contributed to some of the information in this article and their selection is beautiful.

With all this talk about stars, planets and moons in previous posts, it’s about high time I mentioned a solar system. A solar system is exactly what the name implies - the system associated with a sun (star). Our own solar system contains 8 planets. We once had nine but the planet Pluto was downgraded as discussed in some previous posts - Weren’t there 9 planets? What happened to Pluto? and What is a planet? There’s actually more to a solar system than the planets, though. The greatest influence on a solar system is that from which it begets its name - the star. The star is the center around which everything else in a solar system is built. It “binds” everything together and influences everything that surrounds it.

You can imagine a solar system starting as a mass of gas and elements. Nothing is really cohesive but since every bit of matter has a tiny bit of gravity, things are gradually attracted to one another. Eventually, enough gas and matter come together to collapse into a star. The remaining matter surrounding the new star eventually does the same, coalescing into larger and larger bits until something recognizable as a rock or chunk of ice orbits chaotically around the star. Eventually, the evolution of a solar system leads to these chunks joining together to form planets.

A young solar system is a hellish place. Newly formed planets travel in a very chaotic neighborhood and are frequently bombarded by all the coalesced “stuff” still drifting around aimlessly or plummeting inward towards the star. As more objects, dust and gas are caught up in the early planet’s gravity wells, the solar system gradually quiets down until you have an established system like our own. The large mass bodies (planets) act like vacuum cleaners, sucking up all the dirt and debris in their paths. Impacts become less frequent, orbits more stable, stray objects more rare.

Though we’ve not traveled out to see other solar systems, I’d venture a guess that each one is unique in its own right. There are plenty surprises awaiting us, I’m sure. But, using our solar system as a general model, we can expect them to include the star, planets, a Kuiper belt (a belt of material on the same general orbital plane as the planets) in which primitive, loose material still orbits in the form of comets and icy bodies, and even an Oort cloud. An Oort cloud is a very loose conglomeration of leftover “stuff” that completely envelops a world. It differs from a Kuiper belt in that the belt is on an orbital plane with the rest of the relevant matter and an Oort cloud wraps around the entire star like an eggshell around a yolk. The Oort cloud marks the edge of the solar system, a point at which the star’s gravitational and dynamic (think solar winds) influence effectively ends. We can see stars shine through Oort clouds (and can see out through our own) because the material is so loose and widely spaced as to be invisible to the naked eye.

In addition to the physical, or more accurately, visible stuff, a solar system is packed full of radiation cast off by its star. Solar winds, which are actually streams of highly charged particles streaming from the star, also influence the objects around them. Evidence of this can be seen in comet tails (which always point away from the star rather than trailing behind the comet in the opposite direction of travel) and in a phenomenon known as Aurora Borealis, a dazzling show of mysterious light in the sky caused by charged particles interacting with particles in our magnetosphere.

The few indirect observations we’ve made of other solar systems imply that ours isn’t necessarily the definitive model. Some alien planets behave in ways that are counter intuitive to the lessons we’ve learned from our own neighborhood. Future generations will make shocking and exciting discoveries for centuries to come.