Ask Ethan: How Big Will The Universe Get?
“The current estimate for the diameter of the universe is 93 billion light years. With the current acceleration of the universe measured by redshift, and the future exponential acceleration, how long until “we” hit a diameter of 100 billion light years?”
Our Universe is made up of a number of different types of energy, including dark energy, dark matter, normal matter, neutrinos, and radiation. When you combine those different forms of energy with our observed expansion rate, you arrive at a Universe prediction for how the Universe expanded in the past and how it will continue to expand into the future. As distant galaxies accelerate away from us, we can make predictions for how large our observable Universe will get as time goes on. At present, our visible Universe is 92 billion light years in diameter, with an age of 13.8 billion years. When will we hit 100 billion light years? Or a trillion? Or a quadrillion?
The answer is straightforward, fun, and profound. Come find out how big the Universe will get, and how fast it will get there, on this week’s Ask Ethan!
The Milky Way Is Still Growing, Surprising Scientists
“It’s no big secret that galaxies grow over time. The force of gravity is powerful enough to pull smaller galaxies, gas clouds, and star clusters into larger ones, even over distances of millions of light years. Our own Milky Way has likely devoured hundreds of smaller galaxies over its lifetime, and continues to absorb the dwarf satellites which surround us. But there’s a steadier, more subtle way that galaxies grow: by continuing to form stars from the gas already inside. While most of the stars that form will do so in the plane or central bulge of a spiral galaxy like our own, a new study has shown that galaxies also grow outward over time, meaning that their physical extent increases in space. The implication is that our own galaxy is increasing in size by 500 meters per second: growing by a light year every 600,000 years.”
Imagine a galaxy all by its lonesome out there in the Universe. It’s full of stars, with gas, dust, plasma, and dark matter permeating all throughout it. What’s going to happen to the galaxy over time? You might think that it will continue to form new stars in its spiral arms, while older stars burn out and eventually die. All of that is true, but there’s a subtle but important effect that really adds up over cosmic time: the physical extent of where stars can be found grows as even isolated galaxies age. The Milky Way itself is growing at a rate of 500 m/s, typical of spiral galaxies around this size. It means that by time the Universe is three times as old as it presently is, Milky Way-like galaxies will have grown to be twice as large as they presently are.
While our galaxy itself won’t ever make it to that stage, due to our upcoming merger with Andromeda, many will. Come get the full story here.
Why understanding scale is vital, not just for science, but for everyone
“But we need to understand what is happening and the scale of the event to the best of our abilities. This applies not only to storms like Harvey, which could be growing in frequency and power due to climate change, but to many, many challenging topics in our world that are tossed about in the daily deluge of news. We live in a society where big numbers and large concepts are thrown around on many critical topics. From the economy to the environment, from medicine to manufacturing, and from politics to polymers, we are bombarded with facts and figures that can feel meaningless without context.”
How good is your sense of scale? Humans are notoriously bad at this, and yet understanding the magnitude of an event like Hurricane Harvey is much more difficult (and important) than simply using a slew of superlatives. If someone tells you how large the flood in Houston is, and tells you it’s “100,000 times the area of the Capitol Mall in Washington, D.C.,” or “enough water to fill a cube two miles on a side,” does that help you visualize it? Scientists need to use tools and tricks like this much more frequently than they do, as these scale-based analogies are often some of the most helpful offerings they can give to help the public understand what’s going on in a quantitative way. Visualizations in relatable terms like this are what we need more of, and analogies to more tangible scales can truly help communicate science to all.
Come read this outstanding and interesting contribution by Kimberly Arcand and Megan Watzke to Starts With A Bang!
Ask Ethan: Why Do Stars Come In Different Sizes?
“Why can suns grow to… many different sizes? That is, ranging from somewhat larger [than] Jupiter up to suns exceeding Jupiter’s orbit?”
“Bigger mass makes a bigger star,” you might be inclined to say. The smallest stars in size should be small because they have the least amount of material in them, while the largest ones of all are the largest because they’ve got the most material to make stars out of. And that’s a tempting explanation, but it doesn’t account for either the smallest stars or the largest ones in the Universe. As it turns out, neutron stars and white dwarfs are almost all larger in mass than our own Sun is, and yet the Sun is hundreds or even many thousands of times larger than they are. The most massive star known is only 30 times the physical size of our Sun, while the largest star of all is nearly 2,000 times our Sun’s size. As it turns out, there’s much, much more at play than mass alone.
Why do stars really come in different sizes, and how do we even know how big a star is at all? Find out on this week’s Ask Ethan!
Ask Ethan: What Should A Black Hole’s Event Horizon Look Like?
“Shouldn’t the event horizon completely surround the black hole like an egg shell? All the artist renderings of a black hole are like slicing a hard boiled egg in half and showing that image. How is it that the event horizon does not completely surround the black hole?”
Black holes were one of the first consequences of general relativity that were predicted to exist, and the more we’ve studied the Universe, the more interesting they’ve become. We’ve calculated their physical sizes, their effects on the curvature of spacetime, their apparent angular sizes, and the properties of matter that gets caught in an accretion disk around them. But we’re about to take another giant leap forward: we’ve about to directly observe one for the first time. Sure, it will be in radio frequencies rather than visible light, but we should be able to directly image the event horizon, and contrast those observations with our best predictions. What should that event horizon look like, though, and why – if it’s completely black – should we be able to see it at all? The answers are both fascinating and informative, and when the results are released later this year, you’ll want to know.
Come learn all about it on this week’s Ask Ethan!