Physicists Used Einstein’s Relativity To Successfully Predict A Supernova Explosion
“When the lens and a background source align in a particular fashion, quadruple images will result. With slightly different light-travel paths, the brightness and arrival time of each image is unique. In November 2014, a quadruply-lensed supernova was observed, showcasing exactly this type of alignment. Although a single galaxy caused the quadruple image, that galaxy was part of a huge galaxy cluster, exhibiting its own strong lensing effects. Elsewhere in the cluster, two additional images of the same galaxy also appear.”
We normally think of light traveling in a straight line, but that’s only true if your space is flat. In the real Universe, mass and matter not only exist, but clump together into massive structures like galaxies, quasars, and galaxy clusters. When a background source of light passes through these foreground masses, the light can get bent and distorted into multiple images that are magnified and arrive at slightly different times. If an event occurs in one such image, we can predict, based on General Relativity, cluster dynamics, and dark matter, when that event will appear in the other images.
In November 2014, we discovered a multiply-lensed supernova, and predicted where and when it would appear in the other images. Einstein and dark matter both win again!
Who Really Discovered The Expanding Universe?
“Recently, what was known for generations as “Hubble’s Law” has now been renamed the Hubble-Lemaître law. But the point shouldn’t be to give credit to individuals who’ve been dead for generations, but rather for everyone to understand how we know the rules that govern the Universe, and what they are. I, for one, would be just as happy to drop all the names from all the physical laws out there, and simply to refer to them as what they are: the redshift-distance relation. It wasn’t the work of just one or two people that led to this breakthrough in discovering the expanding Universe, but of all the scientists I named here and many others as well. At the end of the day, it’s our fundamental knowledge of how the Universe works that matters, and that’s the ultimate legacy of scientific research. Everything else is just a testament to the all-too-human foible of vainly grasping at glory.”
In science, we have a tendency to name theories, laws, equations, or discoveries after the individual who made the greatest contribution towards its development. For generations, we credited Edwin Hubble for discovering the expanding Universe, as his contributions in the 1920s were absolutely tremendous. However, history has not only revealed that Georges
discovered the very law we had named after Hubble two years prior, but that many other people made essential contributions to that realization. The expanding Universe didn’t come about solely because of Hubble’s discoveries, and perhaps we can do better than crediting just a single person.
Here are a slew of advances that led to and supported the expanding Universe, showing that history and science relies on contributions far richer than that of a lone, genius scientist.
An Ultra-Short History Of The Entire Universe
“This hot, primordial soup expanded and cooled, creating a slight asymmetry between matter (slightly more) and antimatter (slightly less). The cooling continued, nuclei formed, and eventually, so did neutral atoms.
These atoms clumped together in gravitationally overdense regions, forming the first stars after tens of millions of years.”
In the beginning, before even the Big Bang, all that we had was space and time, expanding rapidly according to the rules of cosmological inflation. Today, we’ve got an observable Universe full of stars and galaxies, tens of billions of light years across, with at least one instance of intelligent life: on Earth.
The story of how we got to be here was a mystery to philosophers, theologists and poets for all of human history, but advances during the last century have brought that from the realm of the speculative to firm, scientific knowledge. We understand, at least in broad strokes, how the Universe began, evolved, and came to be the way it is today, from before the Big Bang to human intelligence here on Earth.
Want to see what that entire story looks like in a mere 200 words? Come get it today!
Ask Ethan: When Do Black Holes Become Unstable?
“Is there a critical size for black hole stability? [A] 1012 kg [black hole] is already stable for a couple of billion years. However, a [black hole] in the range of 105 kg, could explode in a second, thus, definitely not stable… I guess there is a critical mass for a [black hole] where the flow of gained matter will equal to the Hawking evaporation?”
Wherever you have a black hole in the Universe, you have two competing processes. On the one hand, anything that crosses the event horizon, whether it’s normal matter, dark matter, or even pure energy, can never escape. If you fall in, you just add to the overall mass of the black hole, and grow it in size, too. But on the other hand, all black holes radiate away energy in the form of Hawking radiation, and that subtracts mass over time, shrinking your black hole. For all realistic-mass black holes, the rate-of-growth far outstrips the rate of mass loss, meaning they’ll grow for a very long time before they start to shrink.
But eventually, they will shrink. And although we think they don’t exist, a low-enough mass black hole would start shrinking today. Find out when black holes become unstable today!
This Is How We Will Discover The Most Distant Galaxy Ever
“Sometime in the distant past, likely when the Universe was less than 2% its current age, the very first galaxy of all formed when massive star clusters merged together, resulting in an unprecedented burst of star formation. The high-energy light from these stars struggles to escape, but the longer-wavelength light can penetrate farther through neutral atoms. The expansion of the Universe redshifts all the light, stretching it far beyond anything Hubble could potentially observe, but next-generation infrared telescopes should be able to catch it. And if we observe the right part of the sky, with the right instruments, for a sufficiently long time to reveal the right details about these objects, we’ll push back the cosmic frontier of the first galaxies even farther.
Somewhere, the most distant, first galaxy of all is out there, waiting to be discovered. As the 2020s approach, we can feel confident that we’ll not only shatter the current cosmic record-holder, but we know exactly how we’ll do it.”
13.8 billion years ago, our Universe as-we-know-it began with the hot Big Bang. There were no stars or galaxies back then; there weren’t even bound structures of any type. Everything was too energetic, and would immediately be destroyed by the unfathomably high temperatures and energies that every particle possessed. Yet, with time, the Universe expanded and cooled. Protons, nuclei, and neutral atoms formed; overdense regions gravitationally pulled-in mass and matter; stars were born, lived, died, and new stars were born in their aftermath. At some point, the first large star clusters merged together, passing a critical threshold and forming the first galaxy in the Universe.
That’s what we want to find. We’ve gone back to when the Universe was just 3% its present age, but that’s not enough. We must go father. We must find the first one. Here’s how we’ll do it.
Ask Ethan: How Do Black Holes Actually Evaporate?
“[J]ust what is Hawking radiation? The science press articles keep referring to the electron-positron virtual pair production at the event horizon, which makes a lay person think that the Hawking radiation consists of electrons and positrons moving away from the black hole.”
Halloween may be over now, so you are free to return to your regularly scheduled existential crises instead of being scared by ghouls and goblins. To help you with that, let’s think about the fact that everything in the Universe, given enough time, will eventually die and decay away. The longest-lived entities, as far as we know, are the supermassive black holes at the centers of galaxies. While stars will burn out after billions or trillions of years, and white dwarfs will cool down after quadrillions, and galaxies will gravitationally dissociate after perhaps 10^24 years, black holes will stick around for far longer: up to 10^100 years. But even they don’t live forever. Hawking radiation ensures that they will decay away, eventually, too.
But if you learned about Hawking radiation from Hawking’s explanation itself, you were lied to. Come find out how black holes actually evaporate today!
Why Don’t We Put A Space Telescope On The Moon?
“For almost every conceivable application to astronomy, going to the Moon is a vastly inferior location than simply being above the Earth’s atmosphere. The temperature extremes experienced everywhere on the Moon are an extraordinary challenge over and above any benefit you get from being on the Moon’s surface. Only in radio frequencies do the benefits of being on the lunar far side offer an opportunity for observing that we cannot get from either terrestrial or space-based observing.
Until the cost is either brought down or something we demonstrate we’re willing to pay, though, it is unlikely we’ll ever see a lunar telescope that’s superior to the other options. The Universe is out there, waiting for us to discover its secrets. When we decide a lunar radio array is worth it, we’ll advance tremendously in uncovering our cosmic origins.”
Practically everyone knows that our opportunities to view the Universe and learn about it, astronomically, are limited here on Earth. The atmosphere interferes with our ability to observe what’s out there, as do weather, human-created signals, and many other issues. We could go to space, of course, but many problems persist there as well. Perhaps putting a telescope on the far side of the Moon would hold the answer? As it turns out, the Moon is an even harsher environment, in many ways, than the depths of interplanetary space. There’s only one specific application that we know of, for radio astronomy, that offers a tremendous advantage. When we’re ready to invest and build a lunar array of radio telescopes, though, we’ll learn more about the early Universe than we ever have before.
Come learn why we haven’t yet built a telescope on the far side of the Moon, and what we’ll gain when we finally get there.
What Was It Like When The First Supermassive Black Holes Formed?
“The earliest galaxies and quasars we’ve ever found are among the brightest, most massive ones we expect to exist. They are the great winners in the gravitational wars of the early Universe: the ultimate cosmic overdogs. By time our telescopes reveal them, 400-to-700 million years after the Big Bang (the earliest quasar comes from 690 million years), they already have billions of stars and supermassive black holes of many hundreds of millions of solar masses.
But this is not a cosmic catastrophe; this is a piece of evidence that showcases the runaway power of gravitation in our Universe. Seeded by the first generation of stars and the relatively large black holes they produce, these objects merge and grow within a cluster, and then grow even larger as clusters merge to form galaxies and galaxies merge to form larger galaxies. By today, we have black holes tens of billions as massive as the Sun. But even in the earliest stages we can observe, billion-solar-mass black holes are well within reach. As we peel back the cosmic veil, we hope to learn exactly how they grow up.”
One of the great challenges for modern astrophysics and cosmology is to explain where these behemoths at the centers of galaxies, the supermassive black holes found throughout the Universe, came from. How did they get so big? And how did they get so big so fast? It might seem reasonable to get a few billion solar mass black holes by today, 13.8 billion years after the Big Bang. But how could you get something nearly that large when the Universe was just 5% of its current age? Through the physics of the first stars, first galaxies, and gravitational attraction and collapse, of course!
Come get the cosmic story of where these ultimate objects come from, and learn how it really is possible without any new physics!
This Is How We Know There Are Two Trillion Galaxies In The Universe
“Over time, galaxies merged together and grew, but small, faint galaxies still remain today. Even in our own Local Group, we’re still discovering galaxies that contain mere thousands of stars, and the number of galaxies we know of have increased to more than 70. The faintest, smallest, most distant galaxies of all are continuing to go undiscovered, but we know they must be there. For the first time, we can scientifically estimate how many galaxies are out there in the Universe.
The next step in the great cosmic puzzle is to find and characterize as many of them as possible, and understand how the Universe grew up. Led by the James Webb Space Telescope and the next generation of ground-based observatories, including LSST, GMT, and the ELT, we’re poised to reveal the hitherto unseen Universe as never before.”
How many galaxies are there in the Universe? If you had asked Carl Sagan a generation ago, the answer might have been something vague, like billions and billions. Just a decade or two ago, people would have guesstimated around 100 billion, as deep surveys from Hubble could give us a count of galaxies both near-and-far in a small region of the sky. But those estimates aren’t necessarily any good, except to serve as lower limits. In order to understand how many galaxies must truly be out there, it requires us to understand both what the Universe is made of and what constitutes a galaxy. Only in the last few years have we reached that level of sophistication, and come up with what we believe, for the first time, is an accurate number.
That number? Two trillion. There are two trillion galaxies in the Universe. This is the story of how we know.
What Was It Like When Starlight First Broke Through The Universe’s Neutral Atoms?
“The light created in the earliest era of stars and galaxies all plays a role. The ultraviolet light works to ionize the matter around it, enabling visible light to progressively farther and farther as the ionization fraction increases. The visible light gets scattered in all directions until reionization has gotten far enough to enable our best telescopes today to see it. But the infrared light, also created by the stars, passes through even the neutral matter, giving our 2020s-era telescopes a chance to find them.
When starlight breaks through the sea of neutral atoms, even before reionization completes, it gives us a chance to detect the earliest objects we’ll ever have seen. When the James Webb Space Telescope launches, that will be the first thing we look for. The most distant reaches of the Universe are within our view. We just have to look and find out what’s truly out there.”
Something existing in our Universe is not quite the same as something being detectable in our Universe. We know that, at some point in our past, we created the first generation of stars, the second generation of stars, and the very first galaxies to exist in our Universe. But in order to detect them, there has to be some way for that light to travel through the Universe to our observatories and telescopes monitoring the skies today. There’s an obstacle standing in the way of that, though: the neutral atoms formed just hundreds of thousands of years after the Big Bang. When the first hints of starlight begin permeating through space, they encounter these neutral atoms, which largely thwarts them. It takes hundreds of millions of years for starlight to win.
But with enough persistence and star-formation, the light will eventually break through. Come get the cosmic story of how this all actually happens!