LIGO: The Next Generation

As everyone knows, I’m a total surfer dude.  So after all my recent blog posts about the LIGO project (click here, here, or here), I’ve been wondering: could I “hang ten” on a gravitational wave?

There’s still a lot we don’t know about gravitational waves.  LIGO—the Laser Interferometer Gravitational-wave Observatory—is one of the most delicately sensitive scientific instruments ever built.  But as sensitive as LIGO is, it’s still not sensitive enough.  The next generation of gravitational wave detectors promises to do better.

  • Cosmic Explorer: The United States wants to build a bigger LIGO.  Cosmic Explorer will use the same L-shaped interferometer design as LIGO, only ten times bigger.  This will increase the signal amplitude without adding to the amount of background noise the detector picks up, according to the Cosmic Explorer website.  Click here to learn more.
  • Einstein Telescope: Meanwhile the Europeans are planning to build a gravitational wave detector underground.  The Einstein Telescope, as the project is named, will incorporate not one but two laser interferometers, arranged in a triangular pattern.  One of these interferometers will pick up low frequency gravitational waves; the other will pick up waves of higher frequencies.  Click here to learn more.
  • LISA: And lastly, NASA wants to put a gravitational wave detector in space.  The project is called LISA, which stands for Laser Interferometer Space Antenna.  LISA will consist of three small spacecraft beaming lasers at each other, forming a giant equilateral triangle.  Size really does matter when it comes to gravitational wave detectors, and this space laser triangle will be far, far larger than anything we could have built here on the ground.  Click here to learn more.

Some of the questions these next generation gravitational wave detectors could help us answer: How many black holes are there in the universe?  What’s going on inside neutron stars?  What about pulsars or magnetars?  Are there gravitational waves associated with the cosmic microwave background?  Are there gravitational waves associated with dark matter?  Are any gravitational waves coming from unexpected or unknown sources?

So much science will be gained from these projects!  However, I’m not sure if Cosmic Explorer, the Einstein Telescope, or LISA will be able to answer the question I asked at the beginning of this post.  Total bummer!

Disclaimer: I’m not really a surfer dude.  Actually, I’m terrified of the ocean and I’ve never even learned how to swim.

Sciency Words: Kilonova

Sciency Words: (proper noun) a special series here on Planet Pailly focusing on the definitions and etymologies of science or science-related terms.  Today’s Sciency Word is:


In a recent presentation at Princeton University, Dr. Beverly Berger—an astrophysicist from LIGO—used a very interesting term.  Imagine a pair of neutron stars orbiting each other, spiraling closer and closer together, until suddenly “they go splat!” as Dr. Berger enthusiastically described it.

The more official-sounding term for this is kilonova, Dr. Berger then explained.  The term kilonova originates from this 2010 paper, which predicted that the merger of either two neutron stars or a neutron star and a black hole would produce a very bright flash of light.

The authors of that paper calculated that, at peek luminosity, this flash of light would be approximately a thousand times brighter than a nova explosion—hence “kilonova.”  (In case you’re wondering, a kilonova is still not as bright as a supernova—a supernova is “as much as 100 times brighter than a kilonova” according to this article from NASA.)

Of course the LIGO project is designed to detect gravitational waves, not bright flashes of light.  But as you can see in the highly technical diagram below, a kilonova is accompanied by subtle ripples in the fabric of space-time—gravitational waves, in other words.

In August of 2017, the LIGO project detected exactly the kinds of ripples that would indicate two neutron stars had “gone splat.”  As this article from the LIGO website explains, alerts were “sent out to the astronomical community, sparking a follow-up campaign that resulted in many detections of the fading light from the event, located near the galaxy NGC 4993.”

One thing I’m still not clear about: what happens after a kilonova?  It seems the scientists at LIGO are wondering about that too.  According to that same article from the LIGO website, the 2017 kilonova produced either the largest neutron star that we’ve ever observed OR the smallest black hole.  “Both possibilities are tantalizing and fascinating,” the article says, “but our data simply isn’t good enough to tell us one way or the other.”

Fortunately there are a few projects in development that might help us understand kilonovae—and similar cosmic cataclysms—a little bit better.  We’ll take a look at some of those upcoming projects in Monday’s post.

That Time the Galaxy Ripped Itself Apart

Do you remember that time back in 1969 when the entire galaxy ripped itself apart?  No?  Me neither.

Last week, I had the opportunity to attend a physics seminar at Princeton University.  The presenter was Dr. Beverly Berger of LIGO.  She was there to tell us all about the discovery of gravitational waves.

Part of Dr. Berger’s presentation was historical.  There were attempts to detect gravitational waves before the LIGO experiment.  The first such attempt was conducted by Joseph Weber of the University of Maryland.  Weber’s idea was that gravitational waves would cause solid objects to expand and contract ever so slightly.  This expansion and contraction would produce friction and thus heat.

In principle, this change in temperature could be measured.  So Weber constructed a giant metal cylinder to serve as a gravitational wave detector (click here to see a picture of it).  And in 1969, Weber detected his first gravitational wave!  Or at least he thought he did. There was a tiny pulse in his data which, as Dr. Berger described it in her presentation, indicated that gravitational waves were emanating from the center of our galaxy!

Except no one was able to confirm Weber’s findings, and the discovery was widely discredited as a result.  But of course we now know, thanks to LIGO, that gravitational waves do exist.  We also know (or at least we strongly suspect) that there is a supermassive black hole in the center of our galaxy, right where Weber’s gravitational waves supposedly came from.

Given all that we now know, I think it’s fair to ask if Joseph Weber might have detected gravitational waves after all.  Someone in the auditorium did, in fact, ask that question.  But no, it’s absolutely impossible.  Weber’s instruments simply weren’t sensitive enough.

According to Dr. Berger, the only way Weber’s gravitational wave detector would have detected gravitational waves is if the entire galaxy had suddenly ripped itself apart.  Obviously that didn’t happen. The galaxy is still here. [citation needed]

P.S.: I’ve had the pleasure of meeting Dr. Beverly Berger several times now.  It’s sort of a friend of a friend situation.  Anyway, Dr. Berger has very kindly introduced me to a new scientific term.  I’ll have that for you in Friday’s episode of Sciency Words!

Sciency Words: Gravity Waves vs. Gravitational Waves

A few years back, I made a bit of a fool of myself in front of a professional physicist from LIGO.  You see, I kind of have a reputation, both online and in real life.  I’m the Sciency Words guy.  I’m the guy who knows stuff about scientific terminology.

So it’s pretty embarrassing when I get my scientific terms mixed up!  For today’s episode of Sciency Words, I’d like to share with you the two terms I got confused about so that the next time you meet a physicist from LIGO, you won’t make my mistake.


Gravity waves have to do with fluid dynamics: the movement of liquids and gases.  As an example, imagine an air mass being blown up and over a mountain range. Once over the mountains, that air mass will start to fall downwards again due to the force of gravity.

But of course air masses don’t sink straight down like lead weights.  Air has a lot of buoyancy, so that air mass will bob up and down for a while until it settles into a stable equilibrium.  This bobbing up and down motion will produce ripples in the atmosphere, and those ripples are called gravity waves.

Gravity waves have been observed both in Earth’s atmosphere and Earth’s oceans.  They’ve been observed on other planets as well.  Basically any time part of a liquid or gaseous medium is forced upwards, you can expect gravity to pull it back down again, producing gravity waves.


Gravitational waves have to do with Einstein’s theory of general relativity.  As an example, imagine two black holes spinning rapidly around each other. Even if you’re watching this from a safe distance, you might notice the combined gravitational attraction of those black holes grows stronger and weaker in a regular, oscillating pattern.

Well, actually you probably won’t notice that.  Even in the most extreme circumstances, those oscillations in gravity are barely detectable.  But they do happen.  The LIGO Project confirmed that in 2015 (the news wasn’t announced until 2016).

French theoretical physicist Henri Poincaré gets credit for coining the term gravitational waves (ondes gravifiques in French).  He first wrote about them in 1905, around the same time Einstein was formulating his theory of special relativity.  I’m not sure who coined the term gravity wave, but English mathematician George Biddle Airy was the first to mathematically describe gravity waves in 1841.

My mistake was asking a physicist who studies gravitational waves for LIGO a question about gravity waves in the atmosphere of Titan.  I mean, it’s an understandable mistake, getting these two terms confused—unless you’ve been introduced as an expert on scientific terminology!!!  Then it’s super embarrassing!!!

P.S.: As it so happens, I got the chance to meet up with that same LIGO physicist once again this week.  She was giving a presentation at Princeton University.  Don’t worry.  I didn’t embarrass myself too much this time.  I’ll tell you more in Monday’s post!