What are all of the different types of alive stars?
How do Coronal Mass Ejections affect us?
Check out this post from a while back, “What are Coronal Mass Ejections and how do they affect us”!
If that doesn’t answer your question, feel free to ask again!
When you have a binary star system with the stars close together, what happens when one of the stars starts to turn into a red giant?
Binary stars are actually pretty common (about a third of the stars in our galaxy are in some kind of binary), although the very close pairs are a little less common.
For the majority of the lifetime of the stars in a binary, both stars just spin around each other, burning their own hydrogen and orbiting tranquilly. However, unless the two stars are exactly the same size when they’re formed (not generally the case), then one star will run out of hydrogen before the other, and will transform into a red giant star.
Red giants are pretty fuzzy stars, only loosely held together by their own gravity. For some scale, our own Sun will become a red giant in its future. It will expand from its current (quite large) radius of 695,500 kilometers to something 200 times that large. But it won’t have gained any material to grow that much bigger - it just spreads out what’s already there.
If the star is on its own, this newfound wispiness doesn’t change much. But if there’s another star nearby, the other star can begin to tug on the outer layers of the red giant, pulling some of the outer layers towards itself. (This is the same thing that the moon does to our oceans.) Because the red giant is so big, the outer layers are only weakly tied to the centre of the star. If the companion star in the binary is close enough or massive enough, it can begin to tear the outer layers of the red giant away, and pull them towards itself. This will change the shape of the red giant from a diffuse sphere into a diffuse teardrop, with the point of the teardrop facing the companion star.
What the companion star does with that surface material depends on what kind of star the companion is. By the time one star has aged its way to being a red giant, its companion is in one of two states, which will be dictated by how massive the companion was when it began its life.
If the companion started out with a lower mass than its red giant partner, it will still be burning hydrogen in its core when the red giant begins to form. As it siphons gas off of the red giant, this companion star will grow in mass. Depending on how rapidly the red giant is growing, and how quickly the companion is siphoning material, the lower mass star can actually grow so large that it becomes more massive than the red giant. After having so much of its material drawn away from itself and onto its neighbor, the red giant will slow its donation of mass. This can result in a fairly stable configuration - the red giant, having lost a good amount of its atmosphere to its neighbor, will continue to slowly bleed gas into its neighbor’s gravitational well, and the neighbor will continue burning hydrogen until it has exhausted its own resources.
The other option for these binaries is if the red giant was the smaller of the two stars when they started their lives. This means that the star now turning into a red giant took much longer to reach the end of its life than its neighbor. (The bigger your mass, the shorter your life, if you’re a star.) So the companion star has already gone through its death throes, and can be one of a number of interesting stellar remnants.
The main options for your stellar companion in this case are: a white dwarf, a neutron star, or a black hole.
If your red giant is pouring gas down onto a white dwarf, you will eventually trigger some kind of explosion: either a nova or a supernova. A nova is a thermonuclear detonation on the surface of a white dwarf, and can recur multiple times, as it’s just a surface explosion. This kind of behavior makes these binaries fairly noticeable, because the brightness of the star will flare to many times its original brightness. A supernova, on the other hand, will detonate the entire white dwarf, blasting itself apart, and leaving nothing behind (also quite noticeable). This kind of supernova occurs when the white dwarf gains too much material to be stable (these stars are balancing gravity against an electron’s unwillingness to be pushed too close to another electron), and some trigger in the core sparks a runaway burning of material.
If the other object is a black hole or a neutron star, you’ll wind up with what’s called an X-ray binary, for the somewhat boring reason that it produces a lot of X-rays. For these objects, as the gas from the red giant is pulled off of the red giant star, it gets pulled into a very thin disk, surrounding the black hole or neutron star. The disk forms because it’s very hard for gas to lose a lot of momentum all at once and plunge straight down onto the black hole, but as a result, the gas winds up heating up to an incredible temperature before it makes it all the way to the neutron star or black hole. This heat causes the X-ray glow, and keeps the disk itself almost invisible in optical light.
So there you have it! A binary system of stars with one red giant will result in the companion tearing the outer layers of the red giant star away. From there, you wind up growing the object nearby, or causing a nova, a supernova, or the creation of a lot of X-rays.
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Wondering why Astroquizzical has been so quiet?
It’s been a busy month for your faithful Astroquizzical writer!
So here’s what’s been going on. Remember this? I had to take a mini-break to crunch through the last of writing my thesis. Well, on April 15th, I successfully defended my PhD!
The rest of the month was dedicated to making the changes that my committee requested before my thesis could be officially accepted; all of these changes had to be completed before the end of April. So, as of April 28th, I completed all requirements for my PhD, and will shortly be handed a diploma. (It’s very exciting.) With this complete, I should be free to start answering your questions more regularly!
Astroquizzical still wants and needs your questions! If you have even the slightest curiosity about space, please send your questions my way, and I will do my best to clear things up for you.
I appreciate all your patience, and I hope to answer your questions soon!
(What is a kiloparsec, and what do we use it for?)
(Note: I am assuming this submission means “What is a kiloparsec, and what do we use it for?”. If that was not your question, please feel free to ask again!)
Kiloparsecs are another unit used to measure huge distances between objects in space, and if the ‘kilo’ part seems familiar from having seen words like kilogram and kilometer, you’d be exactly right - the prefix here just means 1000 of the part that follows. In this case, the base unit is a parsec, instead of a gram or a meter.
The parsec (regardless of what you remember from Star Wars’ infamous line re: the Kessel Run) is a unit of distance that’s equivalent to 3.26 light years. A light year, as we’ve talked about before, is quite a long distance, but once you get away from the immediate group of stars surrounding our solar system, it’s less useful as a ruler, since everything is so far away. The distance from us to the center of our galaxy is measured in tens of thousands of light years.
Unlike the light year, which is based in the physics of light, a parsec was determined geometrically using the size of the orbit of the Earth around the sun, and the apparent motion of nearby stars. The actual term “parsec” has a somewhat fun origin - it’s actually a mashup of the words “parallax” (the apparent motion of the stars) and “arcsecond” (how far they move). Arcseconds are frequently abbreviated as “arcsec”, so parallax-arcsec got shortened into parsec.
Parallax, as we just mentioned, is describing the apparent motion of a star. But more generally, parallax is the term for the relative motions of any two objects at different distances. The most common example is looking out the window of a moving vehicle - the shrubs, trees, and telephone poles near the road move very quickly past your window, but things further away - any mountains or distant buildings will appear to move at a much slower pace from your perspective. Applying this idea to the stars, stars which are quite close to us will appear to shift ever so slightly relative to other stars in the sky which are at much greater distances, which will appear fixed.
Arcseconds tell us how far these stars appear to move. They are a unit of size on the sky - sixty arcseconds go into an arcminute, sixty arcminutes go into a degree, and 360 degrees makes a full circle (no one has ever said that astronomers use sensible units). To give you some scale, the full moon is half a degree across - thirty arcminutes. Venus, the bright morning or evening star, tends to be a few tens of arcseconds in the sky.
One parsec is defined geometrically as the distance from the Sun where the motion of the earth around the Sun causes a parallax of one arcsecond. (The image at the top shows a diagram of this.) As our planet moves from one extreme in our orbit to the other extreme, it has moved by 2 astronomical units side to side - 186 million miles. And after moving 186 million miles, we are looking for a star which has moved by less than one tenth the size of Venus in the sky. If the star moved by exactly 1 arcsecond, it was defined to be at a distance of precisely one parsec from the sun. Most of the stars in the sky are too distant to make these measurements directly, but we can still use this geometric definition as a ruler.
This unit was useful back in the day when the speed of light was not so precisely known. Since the distance from the earth to the Sun was well known, and the rest of the calculation is just geometry, the parsec could be used as a distance measurement without depending on the speed of light. Nowadays, we have the speed of light measured to phenomenal precision, so we can use either unit of distance, depending on which one is more convenient.
Kiloparsecs (1000 parsecs, or 3260 light years) are the unit of choice for measuring distances when galaxies are involved. Rather than saying that the Earth is about 30,000 light years from the center of our galaxy, it’s easier to say that it’s a little over 8 kiloparsecs. The distances between galaxies can also be given in kiloparsecs, although unless something exciting is happening, or they’re in a very particular region of space, the distances between galaxies are often several hundred kiloparsecs or more. Andromeda, our galactic neighbor, is 780 kiloparsecs away. That’s about 2.5 million light years.
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What is the speed of light equivalent to?
The speed of light in a vacuum is a constant of our universe; no matter where you are or how you’re moving, light will always travel at the same speed.
But what is that speed? It’s 299,792,458 meters per second, or 299,792.458 kilometers per second. Really fast.
Using the speed of light can be quite convenient for astronomical purposes, because we can begin to use it as an extremely long ruler. Since the speed at which light travels is always the same in the vacuum of space, the distance it will cover in a fixed amount of time is also always the same. If you’re driving 60 miles an hour exactly, then it will always take you exactly one hour to travel 60 miles. It’s the same principle with light, except on a much grander scale.
The distance between the Earth and the Sun is about 93 million miles, or 149.6 million kilometers. Light travels about three hundred thousand kilometers a second, but even at that insane speed, the distance between the Earth and the Sun is large enough that there will be lag. A little over 8 minutes of lag, in fact. 8 minutes isn’t very long, but it’s certainly noticeable. To get to Jupiter from the Sun, light takes 43 minutes - to get to Saturn, it’s about 80 minutes - almost an hour and a half. Mars gets light from the sun about 12.5 minutes later, and Neptune, the most distant major planet in our solar system, has to wait about 250 minutes - a little over four hours.
This kind of time delay is something all scientists working with spacecraft orbiting other worlds (or roving on their surfaces) must deal with. The delay will be at minimum 8 minutes less than the numbers above, but depending on where the planets are in their orbits, it can be significantly longer. It’s the root behind the “Seven Minutes of Terror” video NASA released before the Curiosity rover landed; they knew the rover should have landed, unfolded, and radioed home, but they had to wait seven minutes for light to make the trip between Earth and Mars.
Most distances in astronomy are too small to be using light minutes, seconds, or hours. The nearest star to our own is four light years away. From the Sun to the center of our galaxy is about 30,000 light years. Our galaxy is so large that it would take about 100,000 years for light to travel from edge to edge. And the distances between galaxies are even greater.
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Dear Astroquizzical: why is it called an EXOplanet? What’s the opposite of an exoplanet?
We haven’t had a naming question in a while!
An exoplanet is also called an “extrasolar planet” - both terms simply mean a planet which is in orbit around a star which is not ours.
The ‘exo’ part comes from the same root as an “exoskeleton”, “exothermic” or “exotic”. The first tells us that an animal’s skeleton is an ‘outer’ skeleton such as those of spiders and insects, not an interior skeleton like mammals have. If you’re a chemistry person, you’ll recognize “exothermic” as a sign that a chemical reaction produces more heat than it consumes. Put another way, it’s dumping heat “outside” of the reaction. “Exotic” simply means that it comes “from outside” where you’re from.
The opposite of “exo-“ is “endo-“, which means “internal” instead of “external”. While we don’t tend to use the word “endoskeleton” to mean an internal skeleton, we do use “endothermic” to mean something that must suck energy out of its environment.
An exoplanet is simply an “external” planet, in that it isn’t in our solar system. So the opposite of that would be something internal to our solar system, which also is not a planet! Any of the many moons, comets, and asteroids in our solar system (or Pluto) would qualify.
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I heard that even though the sun won’t explode for 5 billion years, we’ve only got about a billion years before it kills us. Is that true?
It’s true that we won’t have to wait for the Sun to become a red giant so large that it engulfs our planet for the Earth to be uninhabitable. The exact timing of when the Earth becomes uninhabitable depends slightly on the model used to predict these things, but generally? About a billion years, give or take, is all we have before our oceans boil as the sun grows brighter.
The Sun is currently classified as a “main sequence” star; this means that it is in the most stable part of its life, converting the hydrogen present in its core into helium. For a star the size of ours, this phase lasts a little over 8 billion years. Our solar system is just over 4.5 billion years old, so the Sun is slightly more than halfway through its stable lifetime.
After the 8 billion years of happily burning hydrogen into helium are over, the Sun’s life gets a little more interesting. Things change because the Sun will have run out of hydrogen in its core - all that’s left is the helium, but it’s not hot or dense enough in the core to burn helium. Gravity and pressure are at constant odds with each other inside a star, with the outward pressure produced as part of fusing elements together. When the star has nothing left in the core to burn, however, gravity wins the fight. Eventually, gravity will compress the center of the star to such a degree that it can start burning hydrogen in a small shell around the dead core, still full of helium. As soon as the Sun begins to burn more hydrogen, it would be considered a red giant.
The process of compression in the center allows the outer regions of the star to expand outwards, and the burning of hydrogen in the shell around the core produces a lot more light than the Sun did earlier in life. Because the size of the star has expanded, the surface cools down, and goes from white-hot to “only” red-hot. Because the star is brighter, redder and physically larger than before, we dubbed these stars “red giants”.
It’s widely understood that the Earth as a planet will not survive the Sun’s expansion into a full-blown red giant star. The surface of the sun will probably reach the current orbit of Mars, and while the Earth’s orbit may also have expanded outwards slightly, it won’t be enough to save it from being dragged into the surface of the sun, whereupon our planet will rapidly disintegrate.
However, life on the planet will run into trouble well before the planet itself disintegrates. Even before the Sun finishes burning hydrogen, the Sun is evolving. The sun has been increasing its brightness by about 10% for every billion years it’s spent burning hydrogen on the main sequence. Increased brightness means an increase in the amount of heat our planet receives. As the planet heats up, the water on the surface of our planet will begin to evaporate.
An increase of the Sun’s luminosity by 10% over the current level doesn’t sound like a whole lot, but this small change in our star’s brightness will be pretty catastrophic for our planet. This change is a sufficient increase in energy to change the location of the habitable zone around our star. The habitable zone is defined as the range of distances away from any given star where liquid water can be stable on the surface of a planet. With a 10% increase of brightness from our star, the Earth will no longer be within that zone. This will mark the beginning of the evaporation of our oceans. By the time the sun stops burning hydrogen in its core, Mars will be in the habitable zone, and the earth will be much too hot to maintain water on its surface.
This 10% increase in the Sun’s brightness, triggering the evaporation of our oceans, will occur over the next billion years or so. Predictions of exactly how rapidly this process will unfold depend on who you talk to. Most models suggest that as the oceans evaporate, more and more water will be present in the atmosphere instead of on the surface. This will act as a greenhouse gas, trapping even more heat, and causing more and more of the oceans to evaporate, until the ground is mostly dry and the atmosphere holds the water, but at an extremely high temperature. As the atmosphere saturates with water, the water held in the highest parts of our atmosphere will be bombarded by high energy light from the Sun, which will split apart the molecules, and allowing water to escape as hydrogen and oxygen, eventually bleeding the Earth dry of water.
Where the models differ is on the speed with which the earth reaches this point of no return. Some suggest that the Earth will become inhospitable before the 1 billion year mark, since the interactions between the heating planet and the rocks, oceans, and plate tectonics will dry out the planet even faster. Others suggest that life may be able to hold on a little longer than 1 billion years, due to the different requirements of different life forms, and periodic releases of critical chemicals by plate tectonics. The Earth is a complex system, and quite hard to model, but it seems that as a rough guide, 1 billion years is a reasonably robust guess of how long life has left on our planet.
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Can you transport life on meteorites?
The short answer to this question is that we don’t know - although there is a whole field of study dedicated to trying to figure it out. What I’m about to describe are not truly theories - they’re suggestions. If you could transport life around a solar system, how could you do it? We don’t have any evidence to show that these are the ways in which it happens, or even if nature needs the help.
The hypothesis that suggests that either bacterial life or the building blocks for it could be transported via comets or meteorites is called panspermia. It proposes that once life were to arise somewhere in the universe, a large impact upon that planet could create such an explosion that pieces of rock carrying bacteria were flung into space, where they cruise about until crash-landing on another life-friendly planet.
We know that meteorites blasted off other planets can make it to our own planet, since we’ve collected a few meteorites that originated on Mars (as discussed in a previous post), so the real question is whether or not bacterial life is hardy enough to survive this whole process, including the blasting off the original planet and the landing on the new planet. If it can, then this might be one way to get bacterial life from Planet A to Planet B within a solar system, however unlikely it might be for those pieces of rock to be flung in exactly the right directions. We have been testing how resilient some bacteria can be to exposure to outer space, which is a pretty unforgiving environment. Some microbes from the English town of Beer managed to partially survive a 533 day stint on the outside of the ISS, which is pretty impressive, but there’s no guarantee that a rock blasted off the surface of another planet will be covered with a particularly space-hardy breed of microbe, nor is there a guarantee that the meteoroids will arrive at another planet in a short period of time.
In order to transport entire bacteria, a lot has to go exactly right. But it might be a little easier to transport not the live bacteria, but the the organic molecules that are required to build them. Amino acids are one such set of complex organic molecules, and are often called the building blocks of life. If a comet or meteorite can bring amino acids to a planet, it might help to jump-start the development of life on that planet by skipping the steps required to build those molecules from scratch. These molecules don’t need to have formed on the surface of another life-bearing planet - surprisingly complex molecules can form in the gas between stars in our galaxy. Because these simpler building blocks may be more widely available than planets with life that are also being bombarded with impacts, it may be easier to distribute these molecules than it is to distribute entire bacteria.
Until we have more concrete proof of either of these processes happening out there, they will remain suggestions, but we’re working towards testing each of the steps individually to get a sense of how plausible all of the steps together might be.
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Astroquizzical is one year old today!
Thanks to everyone who has read along, both old and new, and my particular thanks to all of you who have submitted your questions!
Here’s to many more questions and answers to come!
What kinds of meteorites are there?
Unlike the shooting stars we see in meteor showers, which burn up entirely in our atmosphere, meteorites are the fragments we find that have made it all the way down to the ground. Like anything that enters our atmosphere, meteorites have also been burned by the friction of our air, which means that the pieces that we find are only a fraction of the original object; the rest of it was burnt up as a colourful vapor in our sky, like the pieces of grit that make up a meteor shower.
Meteorites are usually made of a combination of one of two substances: rock, or iron. With the infinite inventiveness of astronomers, we duly called them stony, iron, or stony-iron, if they’re a relatively even blend of the two. Stony meteorites can (and often do) contain some small fraction of iron, but only those meteorites which are almost entirely metal are classified as iron meteorites. The vast majority - over 90% - of meteorites that fall to earth are stony, leaving less than 10% of all meteorites as primarily iron. However, the iron ones are a little more well known, and that’s because for a long time, the iron ones were much easier to identify as meteorites.
Stony meteorites look like stones (see the picture just below), so unless you know exactly what you’re looking for, they can be hard to spot. In certain parts of the world, they can be a little easier to pick out - the deserts of Africa or the high deserts of Chile will let unusual-looking rocks stand out a little more. The best place to look for stony meteorites, however, is the glaciers of Antarctica. The ice there is so old and so slow-moving that meteorites that fall there will stay put for a long time. Meteorites are also quite easy to spot there, since anything dark will stand out for miles against the white ice.
That said, even though they look like one of many other stones on our planet, they are still fantastically interesting to scientists. Some of these stony meteorites are some of the oldest untouched rocks in the solar system, and they give us a sense of what the early solar system was made of and how it built itself up.
We also have some stony meteorites which have been blasted off of other worlds. In particular, we have a little collection of about 30 different meteorites which were originally part of Mars, one of which is shown just below. These are chunks of the surface of Mars which were flung so far away from the surface after another impact that they never fell back to the surface, and wandered the solar system until they encountered the Earth. These martian meteorites tend to be much younger than the rest, and are composed of a different set of elements and minerals, so we can pick them out without too much trouble.
Iron meteorites are much easier to spot than the stony ones. This is partially because it’s relatively unusual to find weathered chunks of iron sitting on the ground, so they are more easily recognized as out of place. As with the stony meteorites, they are most easily found in deserts and in the glaciers of Antarctica, where they are likely to stand out more starkly from their background, but they can also be relatively easily picked out in other places. Iron meteorites don’t wear down as much by erosion as the stony ones do, so they’re also more likely to stay around for a longer period of time. The iron meteorites are not actually completely made of iron, but contain a significant fraction of nickel, and this blend of metals is part of what makes them unique.
This one has been sliced in half and polished to show off the metal crystals inside it - but without this extra treatment, they look much less dramatic.
Opportunity, one of our Mars rovers, discovered a basketball-sized iron meteorite on Mars in 2005, which people got very excited about. The discovery of that meteorite was the first time we’d found a meteorite on a planet other than our own. This is much more what iron meteorites tend to look like before being sliced in half.
Iron meteorites and stony meteorites also tend to behave a little differently as they come through the atmosphere. Stony ones tend to be a little more fragile against the force of the atmosphere, and as a result, they can shatter more easily before they hit the ground. Iron meteorites are a little more resilient; heating up the outer layers of a metal lump doesn’t create enough stress to fracture them the way the stony ones would.
The Chelyabinsk meteor that exploded over Russia a little over a year ago also left behind some pieces for us to examine; the largest of the pieces were extracted out of a lake. One of the confirmed pieces is shown at the top. The meteorite pieces confirmed that the object that came through our atmosphere was a stony type meteor. It had already been suspected of being stony since it had exploded so brilliantly in the air.
Both iron and stony meteorites give us a fascinating look at the early solar system, and help us to understand how the planets formed and when, so finding more and more meteorites helps us to understand the variety that was present when the planets were first being formed.
Thanks for your patience while my thesis was being completed, everyone!
This is a quick announcement to say that your Astroquizzical astronomer is currently in the final stages of writing a Ph.D thesis and as a result, posts may be a little more sporadic than usual.
Please continue to send in your questions! I will get to them all as promptly as I can. As always, questions can be submitted anonymously through the sidebar, the ask page, or less anonymously through Facebook or twitter!
Thank you for continuing to make Astroquizzical a success!
If we were trying to reach out to somewhere outside of our universe, what would our overall universal address be? The closest I’ve come is this: (personal address), state. USA North America, Earth, Solar System, Global Cluster, Milky Way, Local Group, Virgo Cluster.
This is a surprisingly tricky thing to work out, but the difficulty lies in being able to locate ourselves in three dimensions on large scales more than anything else.
Your addressing scheme (as far as you’ve written it) is pretty accurate up to the Virgo supercluster, which itself is really a conglomeration of other clusters, both small and large, shown above. (This is distinct from the Virgo Cluster, which is about 65 million light years away from our local group.) But that address would really only help people if they know where to look for the Virgo supercluster. The next step up from the supercluster is a loose affiliation of other superclusters, so if you could get everyone in that supercluster affiliation to look at the right supercluster, they might be able to zoom in from there and find us using your address.
We have dealt with this problem on a much smaller scale before. Both the Pioneer and Voyager spacecrafts tried to relay our position in the unlikely event that they were ever encountered and picked up by another intelligent race of beings. The Pioneer plaque showed the location of our planet within our solar system, but it (and the Voyager Golden record) also gave a map that would be useful to someone else within our galaxy. The set of lines radiating out from a single point on the left hand side of the Pioneer plaque and the Voyager record is this map. This gives the positions and frequencies of a set of pulsars - incredibly rapidly spinning objects that beam light out into the cosmos like a lighthouse. Each pulsar has its own unique frequency - the number of times per second it flashes in our direction. Pointing out the distances and frequencies of 14 pulsars, as we’ve done here, should allow someone else, observing the same set of pulsars, to triangulate our position.
However, this can only be scaled up so far. If you’re trying to tell someone outside our universe where we are - or really, anyone sufficiently far away in our own universe - you swiftly become tangled in a different problem, which is that the more distant from our planet you would like to map out for our faraway friends, the more you travel back in time. At some “distance” from our planet, our exploration becomes one much more of time than of space. Even just the Virgo supercluster (a tiny corner of the universe) is some 110 million light years across. Undoubtably, between light leaving that side of the cluster and our receiving it, things have changed over there in the intervening 100 million years. If our visitor happened to be at a 90 degree angle to the line that connects us to the other side of the cluster we observe, they would receive light from both of us at the same time. This means that particular observer wouldn’t have the same time delay that we observe between our current time and the time that light left the other side of the cluster. They would have a different, but equal, delay on their observation of both of us. They might see a structure that looks a little different from the way we understand it, as a result.
This becomes an increasingly disruptive problem the further back in time we go. At some point, we are looking at structures and objects that no longer exist. Many things can happen in a couple billion years, and they usually do, so using those objects on our map isn’t very useful for an inter-universe traveller.
So what can we use as a universal reference frame? Unfortunately, one of the fundamentals tenets of cosmology tells us that there are no “preferred” or “special” perspectives on the universe. This means that there’s no overall zero point everyone can agree on, which makes it difficult to give directions. I’ve talked about this total lack of a universe-wise reference frame once before, and there’s no easy solution at hand.
The best thing we may be able to do right now is to create a really good map of our little local set of superclusters, and tell our visitors to stop by if they happen to see something that matches it in their travels.
Is it possible that maybe dark matter may be the reason why there is gravity? That is, the more mass takes its place, the more it tends to squeeze mass therefore creating gravity? If so, can we invent something that contracts this dark matter by making it think that there is something very heavy then release it so that we skip a portion of space and keep repeating the process to reach a consistent speed?
With regards to fast travel, you’re actually not that far off from something that was proposed in 2011 by NASA employee Harold White!
It seems there’s a bit of confusion about dark matter and gravity, though. The phenomenon we call gravity is really just a distortion of space and time. Both dark matter and regular matter interact in the same way with space; the more of it there is, the more space bends. Dark matter is five times as plentiful but impossible to observe directly, so we have less of an intuitive grasp on it. But both dark and regular matter warp space, and the more heavily distorted space is, the ‘stronger’ the gravitational pull is. It’s true that in places with a lot of dark matter, you also tend to collect normal matter (this is how we think galaxies begin to form). And while collecting a little bit of normal matter will increase the overall amount of mass in a given region, thereby deepening the pucker in space we’re looking at, neither the dark matter nor the regular matter are responsible for ‘causing’ gravity. The combination of both forms of matter are responsible for causing the distortion in space and time that causes things to feel a gravitational pull.
As far as we know, we can’t make dark matter do much of anything, since it seems to only interact with other things in the universe through its disturbing affect on space (i.e., via gravity). However, what you’re after with your proposed method of travel is, fundamentally, a way to distort space, compressing the part in front of you, and releasing it once you’re past. This is precisely what every proposed (mathematically plausible) warp drive is trying to achieve. Since you create an expansion of space behind you, as the image above shows, you can almost surf space-time on an artificial distortion.
The main distinction is that instead of proposing to bend space by moving heavy objects around, it’s more efficient to bend space using the energy equivalent of that mass. Space does not like to bend, and the math used to predict how much energy this would require had always indicated that you would need to convert a mass the size of Jupiter entirely into energy in order to make it work. (Jupiter, for the record, is 317 times the mass of the earth, which weighs it in at 1.9 x 10^27 kilograms.) Hauling Jupiter masses around with your spacecraft is hugely unfeasible, so this idea had been mostly discarded. This is why people got very excited about Dr. White’s modification to the math in 2011. He found that changing the geometry of the bubble of surfable space would drop the energy required to force the distortion by factors of many thousands and into the range of plausibility. He’s currently trying to design a miniature version in the lab to make sure that his idea can work at small scales.
For the moment, even Dr. White’s model is still science fiction. Even if it does work, there may be other tangles to work out - a few theoretical physicists have worked out that this kind of travel might trap high energy particles inside the warp bubble, releasing them outwards in a potential death ray when you arrive at your destination - not quite ideal.
Does the sun cast shadows on itself?
You can try this one at home. Get an incandescent light bulb, switch it on, and try to use the light from the bulb to cast a shadow on the bulb.
The problem you’ll run into is that every point on the surface of the light bulb is actively producing light, and in order to form a shadow, you need the surface to be dark, blocked from the light. It’s easy for a bulb or a star to cast shadows outwards; simply place a solid object at some distance from the light. A piece of paper or your hand will suffice for a light bulb; something on the opposite side of your hand will be deprived of the light from the bulb.
The shadow casters around stars tend to be planets and moons. Solar eclipses are the most dramatic proof of this. If you stick the Moon in the way of the Sun, some parts of our planet will be placed in the shadow of the moon. Lunar eclipses, show us the colour of the Moon when it travels through the shadow of the Earth. Like shading your eyes from the sun with your hand (yet another way of forming a shadow around our star), the Earth blocks the light travelling towards the Moon, plunging it into darkness.
Because every point on the Sun’s surface is glowing with light, there’s no way to deprive it of light by casting a shadow. Even if you put another source of light near the surface of the sun (for instance, a glowing filament as shown above), it doesn’t change the fact that the main surface of the sun is still glowing. Any attempt to put an object between the filament and the surface of the sun in order to cast a shadow would simply result in both sides of the object being illuminated! And very likely, said object would subsequent vaporize, given the 5500 degree Celsius temperatures near the surface of the sun.