Here we are, people–it’s finally time to talk about dark matter!
I’ve teased this subject in my last few posts. We’ve discussed how the idea originated–with observations of the rotation of galaxies. We’ve touched on the question of whether dark matter could explain supermassive black holes.
What we have yet to do is take a proper deep dive into what the heck this stuff actually is. But there’s an even more important question…
How do we know it’s actually real?
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Way back when we spent a number of posts surveying the stars, we covered binary systems. These are star systems that contain multiple stars. Imagine if our sun had a companion, and two stars rose and set in our sky over the cycle of day and night.
It might surprise you that the majority of stars in the universe are actually in binary systems. Our solar system seems to be an outlier in that regard. Most stars have a companion or two or six…
…and so do some neutron stars.
Remember that neutron stars are the collapsed remnants of massive stars that have gone supernova. If most stars are part of binary systems, then naturally, some of these stars will evolve into neutron stars and still be part of their birth system.
Not all neutron stars are still part of their birth system. As I covered in my last post, many neutron stars rocket through space at incredible velocities, leaving their birth system behind.
Those that stay, though, provide astronomers with fascinating insight into the nature of neutron stars.
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When you hear about “space-time,” it’s just a way to say that space is related to time. And the curvature of space-time, as Albert Einstein predicted, is the way space and time alike literally bend around a mass such as the Earth or the sun.
That’s what’s diagramed above. This is a three-dimensional concept diagram of the way space sort of “clings” to an object. Notice the way it sort of tightens up when you get close to Earth? And because time is part of this whole equation…time sort of tightens up, too.
I assume that explains the “twin paradox,” as it’s called. That’s where the space-traveling twin returns home to Earth younger than their Earth bound twin.
Why? Seems to me it’s because time was tighter and passed faster on Earth, while it spread out and passed a bit slower for the traveler. (Don’t quote me on that, I just guessed that from this diagram.)
Einstein figured all this out. But scientists need evidence. Trusting Einstein’s genius wasn’t enough for them. How did they accept relativity as fact?
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Albert Einstein may have been the genius among physicists, but like all others before his time, he stood on the shoulders of giants.
Einstein did not propose that the sun was the center of the solar system; that idea was already widely accepted when he came around. He didn’t discover elliptical orbits; that distinction belongs with Johannes Kepler.
But Kepler never could figure out why planets orbit the sun in ellipses instead of circles. Even Isaac Newton, who at last identified gravity as the reason we stick to Earth’s surface, couldn’t explain what gravity was—only how it worked.
Einstein provided that explanation with his general theory of relativity.
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Cosmos at Your Doorstep 