Category: astrophysics

This Is How Astronomers Know The Age Of The Universe (And You Can, Too)

“The reason that we can claim the Universe is 13.8 billion years old to such enormous precision is driven by the full suite of data that we have. A Universe that expands more quickly needs to have less matter and more dark energy, and its Hubble constant multiplied by the age of the Universe will have a larger value. A slower-expanding Universe requires more matter and less dark energy, and its Hubble constant multiplied by the age of the Universe gets a smaller value.

However, in order to be consistent with what we observe, the Universe can be no younger than 13.6 billion years and no older than 14.0 billion years, to more than 95% confidence. There are many properties of the Universe that are indeed in doubt, but its age isn’t one of them. Just make sure you take the Universe’s composition into account, or you’ll wind up with a naive — and incorrect — answer.”

Earlier this year, there was a report that the Universe could have been a billion years younger than we currently think. Many people still think that you can calculate the age of the Universe directly from the Hubble constant. And even though the concept of the age of the Universe is a simple one to understand, the pitfalls are so numerous that even Nobel Laureates can fall into them.

We know the age of the Universe to a remarkable and unambiguous precision: 13.8 billion years. Here’s how we get there and how you can get there yourself, too.

Ask Ethan: Do Ancient Galaxies Get Magnified By The Expanding Universe?

“Do ancient galaxies appear larger to us than they really were, due to the expansion of the Universe? If so, then by how much?”

It seems like the simplest, most straightforward idea in the world: the farther away an object is, the smaller it appears. View the same object when it’s twice as far away, and it will only appear to be half as large in terms of angular size. Place it ten times as far away, and you’ll see it appear just one-tenth the size. 

But this is only true in flat, static space. In the expanding Universe, this relationship falls apart, particularly when you factor in dark energy. More distant objects appear smaller the farther away you look, but only to a point. Galaxies that are about 14-to-15 billion light-years away will appear the smallest, and then the same-sized galaxy will actually appear larger the farther away you look! This may be counterintuitive, but there’s real, solid science to back it up. 

Come learn how the expanding Universe really does magnify the most distant galaxies of all, and what the fascinating implications are for the next generation of ultra-powerful telescopes!

Advanced LIGO Just Got More Advanced Thanks To An All-New Quantum Enhancement

“The current observing run of LIGO has been going on since April of this year, and there are already more than double the number of candidate signals than the total number of signals from all previous runs combined. This isn’t due to using the same instruments for longer periods of time, but owes this newfound success to some very exciting upgrades, including this clever new technique of squeezed quantum states.

For decades, scientists have had the idea to leverage squeezed quantum states to reduce the quantum uncertainty in the most important quantities for gravitational wave detections. Thanks to hard work and remarkable advances made by the LIGO Scientific Collaboration, this new, third observing run is already seeing more success than any gravitational wave detector in history. By reducing the phase uncertainty in the quantum vacuum that LIGO’s photons experience, we’re in exactly the right position to make the next great breakthrough in astrophysics.”

Did you know that LIGO and Virgo have been engaged in a new observing run since April of this year? Have you heard that the new run is up to 50% more sensitive than prior runs? That’s true, and it’s due to a number of improvements in noise reduction, including one fascinating way to leverage and control how quantum uncertainty plays out. These squeezed quantum states enable you to put the uncertainty where you most want it, and measure the corresponding quantity even more precisely as a result.

Come find out how we’re bending the quantum rules of the Universe to our will for the benefit of science; it’s a remarkable story!

This Is Why Scientists Will Never Exactly Solve General Relativity

“One of the most valuable lessons I ever got in my life came during the first day of my first college math class on differential equations. The professor told us, “Most of the differential equations that exist cannot be solved. And most of the differential equations that can be solved cannot be solved by you.” This is exactly what General Relativity is — a series of coupled differential equations — and the difficulty that it presents to all those who study it.

We cannot even write down the Einstein field equations that describe most spacetimes or most Universes we can imagine. Most of the ones we can write down cannot be solved. And most of the ones that can be solved cannot be solved by me, you, or anyone. But still, we can make approximations that allow us to extract some meaningful predictions and descriptions. In the grand scheme of the cosmos, that’s as close as anyone’s ever gotten to figuring it all out, but there’s still much farther to go. May we never give up until we get there.”

In our best theory of gravity, General Relativity, we can compute to arbitrary accuracy the effects on matter of any spacetime that we can write down. Unfortunately, most of the spacetimes that we can dream up in our head aren’t ones that we can write down, and most of the ones that we can write down can only be solved approximately, not exactly.

This is not a flaw nor a benefit: it is simply a property of the theory that we have. Is it the final answer? Perhaps not. But it’s the best one we’ve got so far. Here’s what it means.

Sorry Science Fans, Discovering A 70-Solar-Mass Black Hole Is Routine, Not Impossible

“Astronomers aren’t perplexed by this object (or similar ones to it) at all, but rather are fascinated with uncovering the details of how they formed and how common they truly are. The mystery isn’t why these objects exist at all, but rather how the Universe makes them in the abundances we observe. We don’t falsely generate excitement by spreading misinformation that diminishes our knowledge and ideas prior to this discovery.

In science, the ultimate rush comes from discovering something that furthers our understanding of the Universe within the context of everything else we know. May we never be tempted to pretend anything else is the case.”

Did you hear about this “impossible” black hole that “perplexes” astronomers and “defies” theory? If you followed the news cycle last week, that’s probably what you’ve heard. But the truth is far more interesting, and includes facts like:

-this is the fourth black hole we’ve found like it, not the first,
-there are two other ways to make black holes that would explain this object in addition to the one way that can’t,
-and that we’ve seen each and every one of the steps necessary to make a black hole like this,
-but that finding this black hole with this particular method really is revolutionary?

As always, the real science is far more interesting than the mangled hype you’ve seen before. This black hole doesn’t defy theory, but sure does teach us a lot. Come get the real story today.

This Is Why ‘Multi-Messenger Astronomy’ Is The Future Of Astrophysics

“The three types of signals we know how to collect from the Universe — light, particles, and gravitational waves — all deliver fundamentally different types of information right to our front door. By combining the most precise observations we can take with each of these, we can learn more about our cosmic history than any one of these signal types, or “messengers,” can provide in isolation.

We’ve already learned how neutrinos are produced in supernova, and how their travel path is less impeded by matter than light’s is. We’ve already linked merging neutron stars with kilonovae and the production of the heaviest elements in the Universe. With multi-messenger astronomy still in its infancy, we can expect a deluge of new events and new discoveries as this science progresses throughout the 21st century.

Just as you can learn more about a tiger by hearing its growl, smelling its scent, and watching it hunt than you can from a still image alone, you can learn more about the Universe by detecting these fundamentally different types of messengers all at once. Our bodies might be limited in terms of the senses we can use in any given scenario, but our knowledge of the Universe is limited only by the fundamental physics governing it. In the quest to learn it all, we owe it to humanity to use every resource we can muster.”

In 2017, three different gravitational wave observatories from across the world, LIGO Livingston, LIGO Hanford, and the Virgo detector all witnessed the arrival of gravitational waves from a neutron star collision some 130,000,000 light-years away. Two seconds after the wave signal ceased, the first light from the merger arrived. A new term that was previously reserved for professional astronomers, “multi-messenger astronomy,” suddenly entered the public arena.

But what is multi-messenger astronomy? What makes something a “messenger” and why is it important? As it turns out, it’s going to revolutionize how we understand our Universe in the 21st century. Come find out how today.

This Is Why Three Of The Lightest Elements Are So Cosmically Rare

“When you smash a high-energy particle into a massive nucleus, the large nucleus splits apart into a variety of component particles. This process, known as spallation, is how the majority of lithium, beryllium, and boron was formed in our Universe. These are the only elements in the Universe that are primarily formed by this process, rather than by stars, stellar remnants, or the Big Bang itself.

When you look at how abundant all of the elements we know of are, there’s a superficially surprising dearth of the 3rd, 4th, and 5th lightest elements of all. There’s an enormous gulf between helium and carbon, and at last we know why. The only way to produce these cosmic rarities is by a chance collision of particles streaking across the Universe, and that’s why there’s only a few billionths the amount of any of these elements compared to carbon, oxygen and helium. Cosmic ray spallation is the only way to make them once we’ve entered the age of stars, and billions of years later, even these trace elements are essential to the book of life.”

If you were to measure the abundance of each of the elements on the periodic table, you’d find that hydrogen was the most abundant element in the Universe, followed by helium, oxygen, and then carbon. Many other elements show up hot on their heels, including nitrogen, neon, iron, magnesium and silicon. But way, way down, at only around a billionth of these elements, can you find elements like lithium, beryllium and boron. This is surprising, because these are elements number 3, 4 and 5 on the periodic table!

If helium (2) and carbon (6) are so abundant, why are lithium (3), beryllium (4) and boron (5) so scarce? Science holds the answer, and you can find out why today.

This Is How Astronomers Will Finally Measure The Universe’s Expansion Directly

“This is why, by measuring the redshifts and distances to a slew of objects ⁠— objects at a variety of different distances and redshifts ⁠— we can reconstruct the expansion of the Universe over its history. The fact that a whole slew of disparate data sets are all consistent with not only one another but with an expanding, evenly filled Universe in the context of relativity, that gives us the confidence we have in our model of the Universe.

But, just as we didn’t necessarily accept gravitational waves before they were directly measured by LIGO, there’s still the possibility that we’ve made a mistake somewhere in inferring the properties of the Universe. If we could take a distant object, measure its redshift and distance, and then come back at a later time to see how its redshift and distance had changed, we’d be able to directly (instead of indirectly) measure the expanding Universe for the first time.”

We’ve measured the distance to literally billions of objects all over the Universe, from within our galaxy to more than 30 billion light-years away. By observing how the light from these distant objects is shifted, we’re able to infer that the Universe is expanding. We’re able to infer how that expansion rate has changed over time. And we’re able to infer what the Universe is made of: a monumental accomplishment.

But what we’ve never been able to do, as of 2019, is to watch an individual, distant galaxy physically expand away from us in real-time. With the new generation of 30-meter class telescopes we have coming online, though, all of that is poised to change. When the ELT arrives, the largest of the next generation telescopes at 39 meters, it will have the capability to make this measurement directly by observing the same sets of quasars 10 years apart.

You’re going to get to learn a new term today: redshift drift. When we measure it, we’ll have our first direct observation of the Universe as it physically expands on human timescales.

Ask Ethan: Did We Just Find The Universe’s Missing Black Holes?

“As interesting as this new black hole is, and it really is most likely a black hole, it cannot tell us whether there’s a mass gap, a mass dip, or a straightforward distribution of masses arising from supernova events. About 50% of all the stars ever discovered exist as part of a multi-star system, with approximately 15% in bound systems containing 3-to-6 stars. Since the multi-star systems we see often have stellar masses similar to one another, there’s nothing ruling out that this newfound black hole didn’t have its origin from a long-ago kilonova event of its own.

So the object itself? It’s almost certainly a black hole, and it very likely has a mass that puts it squarely in a range where at most one other black hole is known to exist. But is the mass gap a real gap, or just a range where our data is deficient? That will take more data, more systems, and more black holes (and neutron stars) of all masses before we can give a meaningful answer.”

Last week, an incredible new story came out: scientists discovered a massive object some 10,000 light-years away that emits no light of its own. From the giant star in orbit around it, we were able to infer its mass to a well-constrained range, with the mean value hovering right at 3.3 solar masses.The lack of X-rays from it, based on the field strength associated with neutron stars and the orbit of the giant star itself, very strongly indicates that this object is not a neutron star, but a black hole.

Does this mean we’ve discovered a black hole in the so-called “mass gap” range? Yes! But does it disprove the existence of a mass gap overall? Not so much. Come get the full story on this edition of Ask Ethan!

This Is Why The Speed Of Gravity Must Equal The Speed Of Light

“In order to get different observers to agree on how gravitation works, there can be no such thing as absolute space, absolute time, or a signal that propagates at infinite speed. Instead, space and time must both be relative for different observers, and signals can only propagate at speeds that exactly equal the speed of light (if the propagating particle is massless) or at speeds that are blow the speed of light (if the particle has mass).

In order for this to work out, though, there has to be an additional effect to cancel out the problem of a non-zero tangential acceleration, which is induced by a finite speed of gravity. This phenomenon, known as gravitational aberration, is almost exactly cancelled by the fact that General Relativity also has velocity-dependent interactions. As the Earth moves through space, for example, it feels the force from the Sun change as it changes its position, the same way a boat traveling through the ocean will come down in a different position as it gets lifted up and lowered again by a passing wave.”

According to Newtonian gravity, space and time are absolute, and the gravitational force between any two objects is defined by the distance between them. In relativity, though, different observers don’t agree on distances, which means they won’t agree on forces, accelerations, or other properties of motion from a relativistic perspective. And yet, if you use Newton’s law of gravitation to compute the orbits of Solar System objects, it gets the right answer. If you instead tried to use Newton’s laws but allowed planets to be attracted to where the Sun was in the past, you’d get the wrong answer! Does this mean that the speed of gravity is infinite?

Hardly, but you have to dive deep into relativity to understand what else is up. Thankfully, we’ve done this, and you can enjoy the answer for yourself! Here’s why the speed of gravity must equal the speed of light.