Do tides trigger earthquakes? Possibly another reason to respect the moon

Tsunamis - a devastating effect of an earthquake. Although there are some tsunami warning systems and seismologists can sometimes predict when earthquakes will occur, tsunamis continue to catch us off guard (see below, the Tohaku earthquake and tsunami in Japan). Scientists are continually looking for better ways to predict earthquakes around the world. Turns out they might be able to use the phases of the moon.

(Image Credit: U.S. Navy photo by Petty Officer 3rd Class Kevin B. Gray) 

(Image Credit: U.S. Navy photo by Petty Officer 3rd Class Kevin B. Gray) 

Last year, a paper in the journal Physics and Chemistry of the Earth suggested that the moon may be responsible for triggering earthquakes. As I looked through this paper, I though to myself, "now this is interesting, but do I believe it?" The answer is I don't know. So I'd like to take this opportunity to walk through this study using a critical lens.

Syzygy:
noun ASTRONOMY
a conjunction or opposition, especially of the moon with the sun

Why did I immediately jump onto the critical train? This topic of astronomical syzygy in conjunction with earthquakes was immensely popular back in the 1800s. By the way, syzygy is used here to talk about the idea that scientists thought when the Earth, Moon, and Sun were all aligned (for instance, in that order during new moon), the tidal forces should be strongest, causing earthquakes and other phenomenon to happen. Scientists were obsessed but were never able to find a definitive link between earthquakes and the phases of the moon. So what has changed?

The Hellenic subduction zone in Greece. (Image Credit: Wikimedia Commons, Mikenorton)

The Hellenic subduction zone in Greece. (Image Credit: Wikimedia Commons, Mikenorton)

The scientists studied earthquakes along the Hellenic Arc fault in Greece and found a correlation between the frequency of earthquakes and the tidal lunar monthly variations. 

On interesting argument in the paper is that while the tidal stresses are much less than stress from the earthquake itself, the tidal stresses are actually comparable to or greater than the tectonic stress accumulation in a fault that precedes an earthquake.

But what is the amount of force that a syzygy can actually exert on the Earth? And how does it exert this force? 

A tide schematic of the tidal effects of the Moon on the Earth with force vectors. (Image Credit: Wikimedia Commons)

A tide schematic of the tidal effects of the Moon on the Earth with force vectors. (Image Credit: Wikimedia Commons)

Let's say the alignment is Earth, Moon, and Sun. The Sun is much more massive than the moon, but it exerts a very small force on the Earth because it is very far away and you'll remember that Newton told us that gravitational force decreases with the square of distance. So although the moon is smaller, it has a bigger effect. However, this doesn't mean we can just ignore the Sun altogether. In fact, this study out of Greece found that one of the time periods of greatest correlation was when all three celestial bodies were lined up.

Okay, so the moon is pulling on water on the Earth's surface, which causes high tide on the side of the Earth towards the moon. But why is there high tide on the opposite side? The Earth is actually being pulled away from the water! There's a way to explain this with vectors, but a good way to think about it is that the water on the far side is experiencing slightly less pull than the crust on the far side because it's slightly farther away. Low tides happen where there is no pull from the moon or pulling away by the body of the Earth because the water is occupied elsewhere. 

So with our new understanding of tides, I'd like to return to the study at hand. Why haven't there been correlations found for all types of earthquakes that occur all over the earth? It turns out that although the force of the moon is also pulling on the crust it may have the biggest effect on the oceans. So during high tide, as water piles up, the weight of the water may stress underwater faults more so than land faults, leading to the discovery of this correlation appearing over an underwater fault zone. Also, like I said earlier, the force from tides may be similar to that of building up stresses in the fault already, so the tides may act as the final straw that broke the camel's back. Perhaps the fault stresses don't always need this extra push.

Regardless, the studies that have been finding correlations are all relatively new, so while it's an exciting idea that we might be able to use the forces of the moon to predict when certain earthquakes may occur, there's still much to be learned on this topic.

 

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Peeking through the Veil: An exploration of astronomical images

They say a picture is worth 1000 words. But sometimes you need 1000 words to describe a picture. Astronomical images often beg more explanation and so today I'd like to do them justice by taking us on a journey through a famous nebula - the Veil:

(Image Credit: Ken Crawford, Wikimedia Commons)

(Image Credit: Ken Crawford, Wikimedia Commons)

Wow, this image is gorgeous.

Before I dive into the picture above I'd like to take a step back and put this image in context. This nebula is part of a much larger structure called the Cygnus Loop. The Cygnus Loop is a supernova remnant from a star that exploded probably somewhere between 5000-8000 years ago. It takes up an area on the sky equivalent to 36 full moons! If you happened to be alive at the time, this supernova would definitely have been visible from Earth.

An ultraviolet image of the Cygnus Loop taken by NASA's Galaxy Evolution Explorer. The Veil nebula is NGC 6960, which is part of the Western Veil. (Image Credit: NASA/JPL-Caltech)

An ultraviolet image of the Cygnus Loop taken by NASA's Galaxy Evolution Explorer. The Veil nebula is NGC 6960, which is part of the Western Veil. (Image Credit: NASA/JPL-Caltech)

Whoa, wait a minute. If this thing is 36 times the area of the full moon, why don't we get a lovely view of it at night? The short answer is that these images are composite images that are captured by telescopes that put the human eye to shame.

The blue image with the labels above is an ultraviolet images. Humans can only see visible light, so this telescope is capturing very faint emission with a long exposure time that humans could never hope to see because our eyeballs don't have access to this part of the electromagnetic spectrum. 

The second ionized transition of oxygen, or OIII occurs at an energy associated with the wavelength 5007 Angstroms, or 500 nanometers. (Image Credit: Academo)

The second ionized transition of oxygen, or OIII occurs at an energy associated with the wavelength 5007 Angstroms, or 500 nanometers. (Image Credit: Academo)

The first image up top with the lovely pink color is a color-composite RBG image that has been processed to highlight some very interesting features of the nebula. The pink color is representative of a very narrow filter type of exposure that tracks a specific emission feature known as H alpha, or Hydrogen alpha. The teal tracks my favorite emission feature, Oxygen III, or OIII for short. While these emission features are very interesting to astronomers because of the processes they track in nebulae, they also make for a beautiful image. 

H alpha is a red color at 656 nanometers.

H alpha is a red color at 656 nanometers.

What color are these transitions? OIII is a green color and H alpha is red (look to the left). So in astronomical images, astronomers usually attempt to keep these transitions closely related to their true colors. But while these transitions are actually visible to the human eye, we wouldn't be able to see them looking up at the sky.

 

This image is created by combining a cumulative 36 hours of exposures. This telescope also has superior light collecting ability. The amount of light a telescope can capture is related to the area of the mirror. Put this way, you can see why the human eye falls short. But this is why we build telescopes, right?

 

 

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The Earth is Changing on Human Timescales

Earth's atmosphere from the International Space Station. (Image Credit: NASA Image of the Day)

Earth's atmosphere from the International Space Station. (Image Credit: NASA Image of the Day)

We know so little about Earth.

There's an expression floating around out there that we know less about the ocean floor than we know about the moon. This is true if you're talking about high resolution maps of the ocean floor as compared to high resolution maps of the moon surface.

Something that has been bothering me a lot lately is how little we know about Earth's climate and how the oceans, land, ice, weather, and atmosphere interact. I'm not here to diss climate scientists; in fact, kudos to them for embarking on a journey to explore a complicated interconnected web of Earth systems. 

No. Instead, I'm talking about everything I've been learning about the effects climate change. Our world is changing in ways that we couldn't have predicted. In fact, climate change is making some areas warmer, some colder, some wetter, some drier, some stormier, and some calmer in a complicated web of cause and effect.

Here is a chart from the National Oceanic and Atmospheric Administration (NOAA) on some climate anomalies from August 2016:

(Image Credit: NOAA)

(Image Credit: NOAA)

I'd like to take some time to focus on some of the surprising results of climate change that we see here. It turns out that climate change doesn't always imply global warming. There's the famous example of a senator throwing a snowball to disprove 'global warming' on the floor of the senate. And you have to think, he sort of has a point.

For example, the Antarctic sea ice extent is above average this year. I've been talking to a glaciologist who says that the ocean ice has actually built up over the last year as a result of increased precipitation in the region.

This increased precipitation is an interesting effect of climate change because it means our atmosphere is changing it's normal behavior. This can be devastating as we've seen in the floods in Louisiana, for example, which were made more extreme as a result of climate change. 

However, if you look to the north to the Arctic sea ice extent, you'll notice that it is 23.1% below the 1981-2010 average. So the northern ice is melting while the Antarctic sea ice is increasing. Slightly. The net effect is a decrease in ice and thus an increase in global sea levels. 

There is a lesson to be learned here. If we're talking about global climate change, we have to think both long-term and globally. Although there are often surprising local effects such as extreme weather and colder temperatures that occur due to previously unseen interactions between the ocean currents, atmosphere, and changing weather patterns, the August 2016 report and other studies show that the earth is warming. Globally. 

As we're learning, this global change drives smaller, sometimes devastating effects as well as the long term concern of higher sea levels (which have equally, if not more devastating effects on global economies, coastal cities and habitats, international displacement, etc, etc). 

So as our home planet changes, let's keep our eyes and ears open to the new (sometimes scary, sometimes fascinating, sometimes both) ways that our climate changes and evolves. Because now, more than ever, it's increasingly important to understand the interconnected climate web of our home planet.

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A big week for the moon

It's easy to go about your days and nights here on Earth and ignore that giant companion that orbits us. However, this week a lot is going on for the moon, so let's give it some attention.

The moon during a lunar eclipse often appears red due to refraction from light bending through Earth's atmosphere. Blue light is higher energy, so it tends to be scattered away by particles in our atmosphere. Hence, only the red light survives to reflect off the lunar surface.  (Image Credit: Alfredo Garcia, Jr., Flickr)

The moon during a lunar eclipse often appears red due to refraction from light bending through Earth's atmosphere. Blue light is higher energy, so it tends to be scattered away by particles in our atmosphere. Hence, only the red light survives to reflect off the lunar surface. 

(Image Credit: Alfredo Garcia, Jr., Flickr)

First off, it's a full moon tonight! Specifically, a Harvest moon. In some parts of the world it's also a lunar eclipse tonight, although not for North and South America. Bummer for us.

Second, this week there was a cool bit of news concerning a new theory on the formation of the Earth's moon.

Let's tackle the Harvest moon/ lunar eclipse tidbit first. A Harvest moon is the name of the full moon that occurs closest to the autumnal equinox, which is September 22 this year. The equinox is an important date because it marks the day of the year when the northern hemisphere transitions from summer to fall.

Equinox actually means "equal night" in Latin which implies that day and night should be 12 hours each. This doesn't actually end up happening due to the fact that latitude also determines the length of one's day/night. However, this is mostly true in general due to the fact that the Earth's polar axis has a tilt that is pointing neither at the sun nor away from it during the equinoxes.

As you can probably guess, the full moon nearest the fall equinox would be named after the harvest due to the fact that farmers in the northern-hemisphere-centric world are generally harvesting their crops during this time of year.

Okay, moving on to lunar eclipses. A lunar eclipse happens during a full moon because the moon is on the opposite side of Earth from the sun (so we can see it fully illuminated at night). However, recall that the Earth is rotating over the course of the night AND that the moon is orbiting Earth about every month. Let's do some quick math. Over the course of one 24 hour period, or ~1/30th of a month, the moon will orbit through ~1/30th of its full orbit or 1/30th of 360 degrees, which is 12 degrees. So the lunar eclipse is not visible for everyone, because the moon will eventually leave the shadow of the Earth. Additionally, the orbit of the moon is on a slight tilt relative to the plane of the Earth and the sun, meaning that the moon is rarely perfect aligned with the shadow of the Earth. So while most of the Earth can see the eclipse today/tonight, the moon has rotated out of the shadow of the Earth by the time night rolls around for the North and South America.

The moons of the solar system. (Image Credit: NASA)

The moons of the solar system. (Image Credit: NASA)

Let's talk about the big moon news from this week. Astronomers have known that the moon is weird for quite some time. It's highly unusual for a planet as puny as the Earth to have such a large companion. It's hard for Earth to gravitationally capture an object this large. Just look at the other planets and moons in our solar system. Saturn and Jupiter have a plethora of large moons that compare in size to the moon, but planets similar to the Earth in size have tiny moons (such as Mars' Phobos and Deimos).

So what gives?

The most widely accepted scientific theory for the formation of moon is the giant impact hypothesis. It is exactly what it sounds like. A giant impactor, named Theia, smashed into the Earth in a relatively low energy collision. The debris from this collision coalesced into the moon. However, computer simulations of this low energy giant impact predicted that most of the moon should consist of material from Theia. 

The problem is that the composition of the Earth and moon match almost exactly. This seems unlikely if the moon were built mostly from another unknown composition. Statistically, Theia's composition should not exactly match that of Earth. Scientists thought more precise measurements of composition might resolve this problem but a study in 2016 only confirmed the existing problem.

So what are the new theories? How can the moon's composition so closely match that of Earth? The leading theory so far is a higher energy collision that vaporized Theia and the early Earth down to the entire mantle! This would explain how the surface compositions of the moon is slightly richer in potassium-41, which a heavier isotope of potassium. This heavier isotope would have a chance to condense in a high pressure cloud that the moon formed from in the higher energy impact event. 

So as you take the time tonight to gaze up at the Harvest moon, spend a second to think about the fact that we're still in the process of learning about our closest companion.

 

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Why is the Milky Way Milky?

This week I ran away from my life as a graduate student and went backpacking in Mt. Rainier National Park. The last night was clear and we spent some time staring at Mt. Rainier with a backdrop of the Milky Way galaxy. It looked like this:

Did you know that an estimated 80% of North Americans cannot see the Milky Way at night? This tidbit made me reflect on the fact that I'm incredibly lucky to have both the time and the funds to escape the city lights. (Image Credit: Michael Matti)

Did you know that an estimated 80% of North Americans cannot see the Milky Way at night? This tidbit made me reflect on the fact that I'm incredibly lucky to have both the time and the funds to escape the city lights. (Image Credit: Michael Matti)

While we were staring at the galaxy my friends were asking me why it looks, well, Milky. 

There are several reasons:

  1. Our location in the galaxy
  2. Low Surface Brightness
  3. Dust

Location is always everything. We live in the galactic suburbs, in a spiral arm. The human eye can only see so far into the galaxy, so we're only seeing a fraction of the visible light of the galaxy. This is part of the reason the Milky Way looks so faint.

Our galaxy is known to astronomers as a Low Surface Brightness galaxy, meaning that it is often fainter than the ambient light in the sky. This means it is inherently faint. Even when you're in a very dark location it can still be difficult to discern the galaxy from the background sky, which makes it appear very diffuse and cloudy to our eye.

Lastly, our galaxy may have billions of stars but it also has a lot of dust and gas. Visible light cannot go through dust. Part of the spilled milk appearance comes from the fact that we're seeing the effect of dust obscuring our line of sight towards the rest of the galaxy. If you want to look through dust, you have to use infrared light. I will leave you with this Spitzer (infrared) image looking towards the center of our galaxy:

The Spitzer space telescope is able to peek through the dust in our galaxy. This is a false color composite from Spitzer - red is hot dust, blue is cooler stars. The stars around the central black hole are shown by the white blob at the center. Astronomers rely upon a variety of different types of light to avoid some of the problems of visible light that I mentioned above. (Image Credit: NASA/JPL-Caltech/S. Stolovy (SSC/Caltech))

The Spitzer space telescope is able to peek through the dust in our galaxy. This is a false color composite from Spitzer - red is hot dust, blue is cooler stars. The stars around the central black hole are shown by the white blob at the center. Astronomers rely upon a variety of different types of light to avoid some of the problems of visible light that I mentioned above. (Image Credit: NASA/JPL-Caltech/S. Stolovy (SSC/Caltech))

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How does lightning work?

Last night I was running as an increasingly alarming thunderstorm descended upon Boulder. As I clocked one of my fastest ever runs in a desperate attempt to rush home, I couldn't stop thinking about the ~300 or so reindeer who were casualties of a lightning strike in Norway last Friday. Needless to say, I've been thinking about lightning a lot lately.

Before you get too worried, check out this beautiful picture of a lightning storm from space. This strike was bright enough to light up the solar panels of the space station! (Image Credit: NASA)

Before you get too worried, check out this beautiful picture of a lightning storm from space. This strike was bright enough to light up the solar panels of the space station! (Image Credit: NASA)

So how does it work?

The thing is, scientists aren't actually sure. They know that you need powerful wind circulation in a cloud and ice particles. The goal is to drive positive charges towards the top of the cloud and negative charges will then gather along the base. Although the details of this process are largely unknown, the result is understood. The negative charges along the base of the cloud attract their opposites along the ground, causing the ground to have an excess of positive charge.

What about the actual lightning strike?

Watch this video. Lightning appears to first travel downwards. This is the negative charges forming a step ladder. Then, what our eye interprets as "lightning" shoots upwards into the cloud. Upwards?!?!? This is the more powerful return stroke; once the conductive path has been created by the downward step ladder, this return stroke follows it upwards.

However, the lightning strike itself is not the most dangerous part; the 300 reindeer in Norway learned that the ground current is far more deadly. Once the return stroke has occurred, the negative charge will dissipate along the ground.

But what about the intra-cloud lightning?

When I was running last night, I heard very little thunder. Thunder is a direct result of lighting; the lightning heats the surrounding air and causes air molecules to experience immense pressure. Immense pressure = shock wave = audible sound. 

Intra-cloud lightning strikes occur between the top and bottom of the thunderheads. Last night, this was happening at a great enough distance that I heard none of the thunder that is usually associated with lightning. 

In conclusion, clouds form a charge separation, lightning travels from the ground up, the ground current is the most dangerous part, and intra-cloud lightning can be quiet because it is so far away. So here's to enjoying the tail end of the summer thunderstorms!

 

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Proxima Centauri b: A new galactic neighbor

Exoplanet

noun

A planet that orbits a star outside our own solar system.

An artist's impression of Proxima Centauri b, which orbits the red dwarf Proxima Centauri. Here, Proxima b is depicted as a rocky exoplanet. Proxima Centauri is the white star to the left. (Image Credit: ESO/M. Kornmesser)

An artist's impression of Proxima Centauri b, which orbits the red dwarf Proxima Centauri. Here, Proxima b is depicted as a rocky exoplanet. Proxima Centauri is the white star to the left. (Image Credit: ESO/M. Kornmesser)

The universe is a huge, mostly empty, and lonely place. This week it became a little bit less lonely. On August 25th, a team of astronomers from the ESO (European Organization for Astronomical Research in the Southern Hemisphere) published evidence of an Earth-like planet orbiting the closest star to Earth. Our new neighbor, Proxima Centauri b (Proxima b for short), orbits the star Proxima Centauri, so named due to its proximity to our own solar system. It is only four light years away from Earth. This exoplanet has a minimum mass of 1.3 times the mass of Earth and races around its star, orbiting once every 11.2 days. This orbital radius puts Proxima b solidly in the ‘habitable zone’ around Proxima Centauri; the habitable zone is the region around a star where liquid water may exist on the surface of a planet.

The announcement of this exoplanet follows the confirmation of thousands of other exoplanets, many of which have been described as 'Earth-like' in the news. What’s so special about this one after we’ve been inundated with news of Earth-like exoplanets for years? It's all about the location. Most of the confirmed exoplanets are tens of light years away. These distances are unattainably far for any sort of light-speed communication. Proxima b is close enough to send and receive a radio signal in eight years! In the greater metropolitan area of the Milky Way galaxy, we live in the galactic suburbs, which makes Proxima b the neighbor we pop in on to borrow a cup of sugar. So as astronomers continue to learn more about our new neighbor, perhaps it's time to start considering how we might drop by and introduce ourselves.

 

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A Storm in Space and Time: Gravitational Waves Detected

This is an artist's conception of two black holes doing the gravity tango. (Image Credit: NASA, Wikipedia Creative Commons)

In September, there was a storm in space and time. The scientists at the Laser Interferometric Gravitational wave Observatory (LIGO) announced today that on September 14th, 2015, they detected the unmistakable signal of two black holes merging together. 

I cannot stress enough that this is a tremendous scientific breakthrough made by an instrument with unprecedented sensitivity. Many many scientists from diverse backgrounds invested years and years of time and effort into laying the groundwork of theory and technology for this detection to be made possible. They built an instrument that can detect distortions in space that are comparable to 1/1000th the size of the nucleus of an atom for crying out loud!

Scientific Theory:

noun
1. a coherent group of propositions formulated to explain a group of facts or phenomena in the natural world and repeatedly confirmed through experiment or observation
— Dictionary.com

However, I'd like to allow myself to geek out a tiny bit. So today I'll pay homage to Einstein and explain his theory of General Relativity and what this discovery means for the past and future of our understanding of the universe.

Note that I'll be talking a lot about scientific theories and I'd like to make one thing exceptionally clear. Although colloquially we often use the word theory to describe something that is unfounded or not well proven, when I'm talking about scientific theories, this type of theory is an idea that is well understood, characterized, and repeatedly tested. The scientific community accepts it as what we would colloquially refer to as a fact.

The Theory of General Relativity

(Image Credit: E. O. Hoppe, Wikipedia Creative Commons)

Meet Dr. Albert Einstein, technical assistant at the patent office, social activist, violinist, hater of socks, oh yeah, and famous theoretical astrophysicist. 

Meet Newtonian physics, also known as classical mechanics, which is a theory about how objects with mass interact. Recall Newton's F=MxA (force = mass x acceleration). In classical mechanics, a force acting on an object with mass can completely describe its acceleration. You should feel comfortable with classical mechanics, since it uses common-sense approaches to describe how matter and forces work together in the universe; in classical mechanics we know that objects have a definite place in space and a knowable speed.

The setting: At the end of the 19th century, many scientists believed that all the important laws of physics had been discovered and that research should be concerned mainly with fixing tiny inconsistencies they saw in measurement errors of the universe.

But here's something unsettling. Around that time, astronomers made careful observations of the orbit of Mercury around the Sun and observed that its orbit precesses around the sun rather quicker than Newton's laws of gravity predict. (Precession means that Mercury's closest point to the sun shifts forward with each pass.) Something weird was going on with gravity.

In an artist's impression, the Cassini spacecraft orbits Saturn and tests the warping of spacetime (blue lines) around the sun's mass as it sends a radio signal back to Earth in green. (Image Credit: NASA/JPL-Caltech, Wikipedia Creative Commons)

In an artist's impression, the Cassini spacecraft orbits Saturn and tests the warping of spacetime (blue lines) around the sun's mass as it sends a radio signal back to Earth in green. (Image Credit: NASA/JPL-Caltech, Wikipedia Creative Commons)

Enter Einstein. After finishing his theory of Special Relativity,—a fascinating topic for another time—Einstein spent a decade mulling over gravity itself. He eventually developed a complicated mathematical formula to describe the curvature of spacetime itself (If you're curious, see Wikipedia for the math). He published his theory of General Relativity in 1915, explaining that spacetime itself can be warped by massive objects like the sun.

But what is spacetime? We're used to thinking of the universe as a three dimensional space. Spacetime incorporates time as an additional dimension of space, which is important because massive objects can slow down time itself (see Special Relativity). 

Note that without General Relativity your cell phone's GPS would be off by as much as 10 km accumulated error per day! A satellite's clock runs faster by 38 microseconds a day due to the warping of spacetime around Earth. Lucky for us, scientists can make this GR correction for us behind the scenes.

Einstein published his theory along with some testable predictions. General relativity has predicted the observed precession rate of Mercury, something called gravitational lensing (light itself can be warped around massive objects like the sun), and frame dragging (the Earth's gravity actually causes the axes of gyroscopes aboard satellites to drift over time).

Another prediction of general relativity that until now has been untested observationally is gravitational waves. Which leads us to our second discussion point...

Gravitational Waves

A binary white dwarf system, which are predicted to produce a gravitational wave signature as they merge to produce a supernova. (Image Credit: NASA, Wikipedia Creative Commons)

A binary white dwarf system, which are predicted to produce a gravitational wave signature as they merge to produce a supernova. (Image Credit: NASA, Wikipedia Creative Commons)

Gravitational waves are different from gravity waves, which you can think of as waves in the ocean. Gravitational waves are disruptions in the very fabric of spacetime caused by massive objects undergoing very energetic gravitational interactions. 

Scientists have run theoretical simulations and have been able to predict the frequency and type of gravitational waves that would theoretically arise from some of the most powerful and exotic gravitational interactions in the universe. For instance, gravitational waves could be produced from the interactions of neutron stars, which are the extremely dense remnants of massive stars. They could also result from a supernova, which is the result of a star much larger than the sun collapsing in on itself. They could also occur when black holes merging together.

The theoretical signal in gravitational waves of two black holes merging matches the signal detected back on September 14th of last year at LIGO.

The detection itself is exciting because it validates one of the main predictions of General Relativity exactly a century after the theoretical groundwork was laid by Einstein in his 1915 paper. However, this detection also lays the groundwork for some really exciting work. Scientists can now begin to learn about the energy released in this erstwhile undocumented event.

The galaxy Hercules A hosts a powerful supermassive black hole (4 billion times more massive than the sun) that ejects jets of material that astronomers observe at radio frequencies in pink. (Image Credit: NASA, Wikipedia Creative Commons)

The galaxy Hercules A hosts a powerful supermassive black hole (4 billion times more massive than the sun) that ejects jets of material that astronomers observe at radio frequencies in pink. (Image Credit: NASA, Wikipedia Creative Commons)

I'm an astrophysicist who studies the supermassive black holes at the centers of galaxies and how they interact with one another and their host galaxy. We have been able to predict that smaller black holes should merge together (such as the LIGO discovery) and this is how they grow to their morbidly-obese supermassive states that we observe today. HOWEVER, extragalactic astronomers have entirely relied upon either theoretical simulations, experiments on Earth, or looking at light itself to understand the universe outside our galaxy. Now we can learn about the tremendous energy released from events in our universe through the very warping of space and time itself. 

In fact, based upon the gravitational wave signal, the LIGO scientists have announced that the signature was produced from the merging of black holes 1.3 billion light years away, one 36 times the mass of the Sun, and one 29 times the mass of the Sun. They merged to form a single black hole 62 times the mass of the Sun. Wait, 29+36 does not equal 62. This merging event was so powerful, three times the mass energy of the Sun was released into the universe. For comparison, when we talk about mass energy released in the largest nuclear bombs, we talk about masses of a couple of kg at the most. So even with this one detection, we have made huge advances in our understanding of merging black holes.

And so I leave you with this thought: Today, nearly a century after the theoretical groundwork of GR was laid in 1915, we are able to verify and observe one of the major predictions of general relativity. While my excitement cannot be contained about this exciting new discovery, I look forward to how our understanding of spacetime and the universe itself is about to change!

A simulated black hole within the Milky Way and the distortion of spacetime around it. (Image Credit: Ute Kraus, Physics education group Kraus, Universität Hildesheim, background image: Axel Mellinger)

A simulated black hole within the Milky Way and the distortion of spacetime around it. (Image Credit: Ute Kraus, Physics education group Kraus, Universität Hildesheim, background image: Axel Mellinger)

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Mailbag - 5 April 2015

Got a question you want to ask me? Submit it using the button below and it could feature in the next edition of the mailbag!


If the funding for the International Space Station gets repurposed, could the ISS itself also get repurposed? I’m sure the answer must be no but I still have to ask. If the ISS was fit with ion thrusters, could it be used like Hermes?
— Jesse

Sadly, you're intuition is correct, or at least NASA is posturing in that regard. In response to news that Russia plans to pull out of the ISS, INASA Administrator Charles Bolden said astronauts aboard the American section of the station would make an "orderly evacuation" if that were to occur. The trouble is that many of the safety and backup systems used to keep astronauts aboard the orbiting laboratory safe are spread throughout the entire station. Removing half of it could put our men and women at risk.

The notion of using the ISS in a manner similar to the Hermes from Andy Weir's The Martian is an intriguing idea, but technology simply isn't ready yet. For those who haven't read Weir's (gripping!) story, the Hermes is a reusable spacecraft designed to shuttle astronauts back and forth to Mars numerous times over the course of years. In order to accomplish this with the minimum amount of fuel, it employs a technology known as the ion engine. Instead of basically starting an explosion in the back of the spacecraft as chemical rockets do, ion thrusters basically just throw charged particles out the back and rely on conservation of momentum to push the ship forward. They've been used on a number of missions, including Dawn and Hayabusa.

The problem is, the ISS is enormous. It has a mass about 350 times larger than Dawn, and that would certainly need to be even heavier for a trip to interplanetary space. Ion thrusters simply can't provide even close to enough power yet...


You mentioned the risk to the project to capture an asteroid in last week’s Weekly Space Hangout, due in large part to the long time prior to its execution. There are at least two presidential administration turnovers before that time, increasing the opportunity for changes or cancellation.

I agree with that, but I think there may be a mitigating perspective here. Maybe think of capturing an asteroid as a mining mission, mining technology development. I think that may actually increase the probability of a successful mission. It’s about the economy, a harder project to cut.
— James

Mining an asteroid is certainly a popular idea these days. Private companies like Planetary Resources hope to turn this into a viable business model, but haven't demonstrated that capability yet. I don't think that it's the pivot that the Asteroid Retrieval Mission (ARM) needs, though.

ARM is trying to spur human spaceflight beyond Low Earth Orbit once again, but asteroid mining is definitely going to be a task better carried out by robots. It's going to be slow, arduous, and extremely dangerous work - exactly what we use robots for even here on Earth. And robots will most likely be cheaper, increasing any potential return on investment.

I'm also not sure that turning it into a mining effort would save it from either Congress or a future president. Material and monetary returns in the foreseeable future, while possibly significant for a company like Planetary Resources, will be vanishingly small in the overall production of the United States. Worse yet, mining asteroids might seem like an even more pie-in-the-sky idea than just exploring them and thus draw the ire of some lawmakers even more rapidly.

Finally, there's the ongoing legal question of who owns the stuff in space. The Outer Space Treaty of 1967 states explicitly: "outer space is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means." How that applies to space mining is untested legal territory.


The part about Ceres’ white spots on a recent episode of the Weekly Space Hangout was especially riveting. I was resigned to just exposed ice. But if there is some out gassing or plume effect, what the heck would cause it? There is no gravitational tidal effect. A mystery, lets see what the mission brings us. I hope they are taking pictures on the dark side approach to see if something shows up on the edge using the back-lighting technique.
— Valentin

The white spots on Ceres are indeed fascinating! To be clear, other than the existence of two white spots in images captured by the Dawn navigational camera, nothing is known about this area for sure. But recent indications that the features might extend vertically above the rim of the crater and change in brightness over the course of the day is certainly exciting.

This actually isn't even the first indication of possible plumes at Ceres. Last year, scientists using NASA's Herschel Space Telescope reported a clear detection of water vapor above the surface of the dwarf planet. Their explanation is the most probable one: that heat from the Sun causes ice deposited on the surface to sublimate during times of the (Ceres) year when the dwarf planet is closer to it. This could also account for the daily variation, as temperatures on the surface would vary based on the local time of day, just like they do here on Earth!

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1,000,000,000,000

What does a trillion look like? It looks like the number of stars in our nearest neighbor, the Andromeda galaxy. Check this out, it's a video compilation released by the Hubble folks that I keep watching again and again. They took a series of very deep exposures of Andromeda, to fabulous results.

I don't really have much to say, other than it's freakishly breathtaking how far astronomy has come in the last hundreds of years.

And if everyone could just spend a moment witnessing the result of science and tech tax dollars, the world could be a little bit better.

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