Category: astrophysics

What Was It Like When The First Stars Died?

What Was It Like When The First Stars Died?

“It’s theorized that this is the origin of the seeds of the supermassive black holes that occupy the centers of galaxies today: the deaths of the most massive stars, which create black holes hundreds or thousands of times the mass of the Sun. Over time, mergers and gravitational growth will lead to the most massive black holes known in the Universe, black holes that are millions or even billions of times the mass of the Sun by today.

It took perhaps 100 million years to form the very first stars in the Universe, but just another million or two after that for the most massive among them to die, creating black holes and spreading heavy, processed elements into the interstellar medium. As time goes on, the Universe, at long last, will begin to resemble what we actually see today.”

Our Universe, shortly after the Big Bang, proceeded in a number of momentous steps. The first atomic nuclei formed just minutes after the Big Bang, while neutral atoms took hundreds of thousands of years. It took another 50 to 100 million years for the very first star to be created, but only, perhaps, a million or two years for the most massive among the first stars to die. They may have been short-lived, but the first stars were truly spectacular, and their deaths set up the first steps in a changing Universe that would take us from a pristine set of materials to, eventually, the Universe as we know it today.

Take a major step in the cosmic journey of how we got to today by looking at what it was like when the first stars died!

What Was It Like When The First Stars Began Il…

What Was It Like When The First Stars Began Illuminating The Universe?

“After the Big Bang, the Universe was dark for millions upon millions of years; after the glow of the Big Bang fades away, there’s nothing that human eyes could see. But when the first wave of star formation happens, growing in a cosmic crescendo across the visible Universe, starlight struggles to get out. The fog of neutral atoms permeating all of space absorbs most of it, but gets ionized in the process. Some of this reionized matter will become neutral again, emitting light when it does, including the 21-cm line over timescales of ~10 million years.

But it takes far more than the very first stars to truly turn on the lights in the Universe. For that, we need more than just the first stars; we need them to live, burn through their fuel, die, and give rise to so much more. The first stars aren’t the end; they’re the beginning of the cosmic story that gives rise to us.”

We like to think of the Universe evolving as a story that follows a particular order: first we had the Big Bang, then things expanded and cooled, then gravitation pulled things into clumps, we formed stars, they lived and died, and now here we are. But in reality, things are messier than that! The very first stars didn’t immediately spread light throughout the Universe, but instead had a cosmic ocean of neutral atoms to contend with: one that they weren’t energetic enough or numerous enough to break through. The first stars in the Universe fought a battle against the clumping, neutral, atomic-based matter that surrounded them… and lost.

Come get the valiant but ultimately unsuccessful story of the first stars in the Universe, and learn why “letting there be light” didn’t illuminate the Universe!

This Is Why Dark Energy Must Exist, Despite Re…

This Is Why Dark Energy Must Exist, Despite Recent Reports To The Contrary

“We do not do science in a vacuum, completely ignoring all the other pieces of evidence that our scientific foundation builds upon. We use the information we have and know about the Universe to draw the best, most robust conclusions we have. It is not important that your data meet a certain arbitrary standard on its own, but rather that your data can demonstrate which conclusions are inescapable given our Universe as it actually is.

Our Universe contains matter, is at least close to spatially flat, and has supernovae that allow us to determine how it’s expanding. When we put that picture together, a dark energy-dominated Universe is inescapable. Just remember to look at the whole picture, or you might miss out on how amazing it truly is.”

20 years ago, the supernova data came back with an extraordinary surprise: it looked like the Universe wasn’t just expanding, but that the expansion rate was increasing as we head further into the future. While there were many dark energy skeptics to start, the increased flow of improved data from many lines of evidence that all kept pointing to the same conclusion has led to a cosmological consensus: dark energy dominates the Universe today. Last week, a story made waves, as Subir Sarkar and collaborators published their second paper (the first was in 2016) claiming that the evidence from supernovae is not good enough to support the existence of dark energy, and our cosmological foundation for it is extraordinarily shaky.

This is not true. This is demonstrably untrue. And the claim shows a deliberate unwillingness to pay attention to the rest of the field. Find out why dark energy must exist, despite recent reports to the contrary.

This Is Why There Are No Alternatives To The B…

This Is Why There Are No Alternatives To The Big Bang

“For more than 50 years, no alternative has been able to deliver on all four counts. No alternative can even deliver the Cosmic Microwave Background as we see it today. It isn’t for lack of trying or a lack of good ideas; it’s because this is what the data indicates. Scientists don’t believe in the Big Bang; they conclude it based on the full suite of observations. The last adherents to the ancient, discredited alternatives are at last dying away. The Big Bang is no longer a revolutionary endpoint of the scientific enterprise; it’s the solid foundation we build upon. It’s predictive successes have been overwhelming, and no alternative has yet stepped up to the challenge of matching its scientific accuracy in describing the Universe.”

The last adherents to alternative theories to the Big Bang are at last dying away. Advocates of tired light, steady-state, or plasma cosmologies have ceased arising among the scientific ranks for one reason: these ideas cannot even explain the Cosmic Microwave Background observations, much less the full suite of the four major cornerstones of the Big Bang. When all we had were Hubble’s data and the evidence for the expanding Universe, it was a great idea to explore all the conceivable alternatives. Now that the data has come in, the alternatives have been scientifically falsified, and the Big Bang is the foundation we use as the base for our future theorizing.

This may disappoint some, but for the scientifically-minded among us, it’s a monument to the success of a fantastic theory. Here’s the scientific story of why no alternatives remain.

The Simplest Solution To The Expanding Univers…

The Simplest Solution To The Expanding Universe’s Biggest Controversy

“This is how dark energy was first discovered, and our best methods of the cosmic distance ladder give us an expansion rate of 73.2 km/s/Mpc, with an uncertainty of less than 3%. 


If there’s one error at any stage of this process, it propagates to all higher rungs. We can be pretty confident that we’ve measured the Earth-Sun distance correctly, but parallax measurements are currently being revised by the Gaia mission, with substantial uncertainties. Cepheids may have additional variables in them, skewing the results. And type Ia supernovae have recently been shown to vary by quite a bit — perhaps 5% — from what was previously thought. The possibility that there is an error is the most terrifying possibility to many scientists who work on the cosmic distance ladder.”

We live in an expanding Universe that’s 13.8 billion years old, full of two trillion galaxies, containing dark energy, dark matter, normal matter and radiation. For decades, we’ve been refining and better-understanding this cosmic picture, with one of the goals of modern astrophysics to measure the rate of expansion. Right around the year 2000, results from the Hubble key project, the scientific reason the Hubble space telescope was built, indicated that the expansion rate was 72 km/s/Mpc, with an uncertainty of around 10%. Now, we have multiple independent ways to measure that rate to even greater precision, but the problem is that two different groups no longer agree. One claims a rate of 73.2 km/s/Mpc, and the other claims a rate of 67.4 km/s/Mpc. The claimed uncertainties are small, and do not overlap.

Is this a crisis for cosmology? Or is one group simply mistaken due to an unidentified error? Is this a loose OPERA cable all over again? Here’s the big question keeping scientists up at night.

Ask Ethan: Is Spacetime Really A Fabric? “I&r…

Ask Ethan: Is Spacetime Really A Fabric?

“I’d like somebody to finally acknowledge and admit that showing balls on a bed sheet doesn’t cut it as a picture of reality.”

Okay, I admit it: visualizing General Relativity as balls on a bedsheet doesn’t make a whole lot of sense. For one, if this is what gravity is supposed to be, what pulls the balls “down” onto the bedsheet? For another, if space is three dimensional, why are we talking about a 2D “fabric” of space? And for another, why do these lines curve away from the mass, rather than towards it?

It’s true: this visualization of General Relativity is highly flawed. But, believe it or not, all visualizations of General Relativity inherently have similar flaws. The reason is that space itself is not an observable thing! In Einstein’s theory, General Relativity provides the link between the matter and energy in the Universe, which determines the geometric curvature of spacetime, and how the rest of the matter and energy in the Universe moves in response to that. In this Universe, we can only measure matter and energy, not space itself. We can visualize it how we like, but all visualizations are inherently flawed.

Come get the story of how to make as much sense as possible out of the Universe we actually have.

There Was No Big Bang Singularity “Every time…

There Was No Big Bang Singularity

“Every time you see a diagram, an article, or a story talking about the “big bang singularity” or any sort of big bang/singularity existing before inflation, know that you’re dealing with an outdated method of thinking. The idea of a Big Bang singularity went out the window as soon as we realized we had a different state — that of cosmic inflation — preceding and setting up the early, hot-and-dense state of the Big Bang. There may have been a singularity at the very beginning of space and time, with inflation arising after that, but there’s no guarantee. In science, there are the things we can test, measure, predict, and confirm or refute, like an inflationary state giving rise to a hot Big Bang. Everything else? It’s nothing more than speculation.”

The Universe, as we observe it today, is expanding and cooling, with the overall density dropping as the volume of space increases. If we ran the clock backwards, however, instead of forwards, things would appear to contract, become denser, and grow hotter. If you go back farther and farther in time, you’d come to an epoch before there were stars and galaxies; before neutral atoms could stably form; before atomic nuclei could remain; etc. You’d go all the way back to hotter and denser states, eventually compressing all the matter and energy in the Universe into a single point: a singularity. This was the ultimate beginning of everything according to the original Big Bang: the birth of time and space.

But this picture is almost 40 years out of date, and known to be wrong. Why’s that? Come learn how we know that there was no Big Bang singularity.

Ask Ethan: How Large Is The Entire, Unobservab…

Ask Ethan: How Large Is The Entire, Unobservable Universe?

“We know the size of the Observable Universe since we know the age of the Universe (at least since the phase change) and we know that light radiates. […] My question is, I guess, why doesn’t the math involved in making the CMB and other predictions, in effect, tell us the size of the Universe? We know how hot it was and how cool it is now. Does scale not affect these calculations?”

Our Universe today, to the best of our knowledge, has endured for 13.8 billion years since the Big Bang. But we can see farther than 13.8 billion light years, all because the Universe is expanding. Based the matter and energy present within it, we can determine that the observable Universe is 46.1 billion light years in radius from our perspective, a phenomenal accomplishment of modern science. But what about the unobservable part? What about the parts of the Universe that go beyond where we can see? Can we say anything sensible about how large that is?

We can, but only if we make certain assumptions. Come find out what we know (and think) past the limits of what we can see on this week’s Ask Ethan!

What Was It Like When The Big Bang First Began…

What Was It Like When The Big Bang First Began?

“Once inflation comes to an end, and all the energy that was inherent to space itself gets converted into particles, antiparticles, photons, etc., all the Universe can do is expand and cool. Everything smashes into one another, sometimes creating new particle/antiparticle pairs, sometimes annihilating pairs back into photons or other particles, but always dropping in energy as the Universe expands.

The Universe never reaches infinitely high temperatures or densities, but still attains energies that are perhaps a trillion times greater than anything the LHC can ever produce. The tiny seed overdensities and underdensities will eventually grow into the cosmic web of stars and galaxies that exist today. 13.8 billion years ago, the Universe as-we-know-it had its beginning. The rest is our cosmic history.”

The Big Bang is normally treated as the very beginning of the Universe, but in reality there’s a phase that came before the hot Big Bang to set it up. During cosmic inflation, the Universe was filled with an extremely large amount of energy inherent to space itself, causing the Universe to inflate, stretch flat, and achieve almost exactly the same properties everywhere. The Universe we have today, however, is full of matter and radiation, and originated in a hot Big Bang 13.8 billion years ago. How did we go from this inflating state to our hot, dense, uniform and expanding-and-cooling Universe?

This tells you the best scientific story of how we got there, along with an in-depth description of what it was like at those first moments where our Universe gave us something to look at.

The 7 Most Powerful Fireworks Shows In The U…

The 7 Most Powerful Fireworks Shows In The Universe

“Forget mere chemical reactions; in space, matter-energy conversion creates unprecedentedly powerful explosive events.

Here are the 7 most powerful natural displays of cosmic fireworks.

7.) Type Ia supernova: when two white dwarf stars collide, they initiate a runaway fusion reaction, destroying both stellar remnants.”

Throughout the Universe, there are many beautiful displays of cosmic fireworks. Stars are born; galaxies collide; gas gets heated and expelled; stars and stellar remnants explode and die. We typically think of supernova events as the culmination of the brightest, most energetic things that can happen in the cosmos. But supernovae only fill up the bottom rungs on the list of the most powerful, natural fireworks shows that the Universe provides us with.

Which ones are the most energetic? Find out on this incredible start to your pre-4th-of-July Monday!