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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Weekly Space Hangout - 16 Jan 2015

Missed the latest episode of the Weekly Space Hangout? Catch it here! This week, I join Fraser Cain and the crew to talk about the SpaceX landing attempt, an alarm aboard the ISS, and much more!

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Weekly Space Hangout - 9 Jan 2015

Hello, 2015! The Weekly Space Hangout kicked off the year with a fantastic episode featuring The Martian author Andy Weir! In addition to hearing all about the (fantastic!) book's development, we covered stories stretching from an amazing picture of the Andromeda Galaxy to oceans on exoplants. Join, Fraser Cain, myself, and many more!

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The night is always darkest before the dawn

I've been spending a lot of time in the dark lately, but at least I live at 40 degrees north, not 70 degrees north in Tromso, Norway. This is a picture of a typical afternoon during the winter- although the sun isn't above the horizon, it illuminates the sky to a dark blue hue. (Image Credit: Osopolar (Own work), via Wikimedia Commons)

I've been spending a lot of time in the dark lately, but at least I live at 40 degrees north, not 70 degrees north in Tromso, Norway. This is a picture of a typical afternoon during the winter- although the sun isn't above the horizon, it illuminates the sky to a dark blue hue.

(Image Credit: Osopolar (Own work), via Wikimedia Commons)

I went to bed last night at 7 am. When I woke up this afternoon at 2 pm, I read an article that was simultaneously depressing and uplifting. And don't worry, I'm going to tell you all about it. But first, why the heck is my sleep schedule so disturbed? I was observing galaxies during the second half of the night (12-7am) and I'll be observing again tonight during the same time slot. It's great on one hand because I get the building all to myself, so, naturally, I play a lot of really loud Taylor Swift. But on the other hand, I feel like I haven't seen the sun in days.

But the Earth's rotation around the sun is also working against my internal clock. And that's where this article comes in. According to this news that I read at 2 pm right before the sun set, tonight is the longest night of the year AND the longest night ever with the exception of the winter solstice in 1912. Whoa - what's going on?

How could tonight be one of the longest nights in the 4.5 billion year history of Earth?

There's a couple of factors in this game.

First, the seasons. This is the longest night of the year for the northern hemisphere (night of December 21st, morning of December 22nd). This happens because of the tilt of the Earth as it orbits the sun. A very common misconception (that most graduating Harvard seniors believe) is that the seasons are caused by Earth being closer to the sun in summer and farther away in winter. Not only is this incorrect, but in my opinion it excludes everyone who lives south of the equator. Due to the tilt of the Earth, our friends down south are actually experiencing summer right now. Check out this infographic that demonstrates the illumination of the Earth during various seasons.

The tilt of the Earth causes more direct sunlight (hence more Energy) to fall on the northern hemisphere during the summer and vice versa. (Image Credit: Tom Ruen, Full Sky Observatory) 

The tilt of the Earth causes more direct sunlight (hence more Energy) to fall on the northern hemisphere during the summer and vice versa.

(Image Credit: Tom Ruen, Full Sky Observatory) 

The technical name for this tug-of-war is tidal braking. (Image Credit: AndrewBuck (Own work), via Wikimedia Commons)

The technical name for this tug-of-war is tidal braking.

(Image Credit: AndrewBuck (Own work), via Wikimedia Commons)

Second, gravity. Alright, blah blah blah so yeah it makes sense that this is the longest night of the year for the northern hemisphere. But why is this one of the longest nights EVER? The moon is torquing down the Earth's rotation slowly. It turns out that Newton was right - for every action, there's an equal and opposite reaction. This means that yes, the Earth is more massive than the moon, but the smaller moon exerts an equal force back on Earth. This force is evident in the Earth's tides. 

A great way to make this concept more intuitive is to imagine the massive amount of water the moon is dragging to create the tides. The earth is still rotating about it's axis, so there's this gigantic tug of war between the Earth attempting to drag it's oceans with rotation while the moon tries to hold them back. This competition works to slow down the Earth very slowly; between 15 millionths and 25 millionths of a second are added to the standard day yearly. But this is still a measurable difference.

Third, climate change. It turns out that releasing a bunch of warming agents into our atmosphere melts the ice on the poles. And when you melt ice on the poles this massive amount of water is redistributed around the equator. So the Earth has gained some love handles around the Equator. 

This explains why the longest night is not this year but instead back in 1912 before we started melting the ice at the poles. Having more mass around the equator actually makes the earth rotate slightly faster. 

So all in all, these three main factors influence why tonight is a VERY long night, but not the longest. For me, I'm excited because I get more time to observe galaxies without the sun interfering. I'll just have to go take a bunch of vitamin D supplements. But don't worry - from here on out the night will only get shorter as we march on towards summer. 

 

 

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Weekly Space Hangout - 7 Nov 2014

Did you miss the latest episode of the Weekly Space Hangout?  Then you missed the coolest image you'll see this year, updates on the VSS Enterprise, the Antares rocket, and more!

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