The Raging Beauty of Monsoons
You know the drill: Set it to high resolution, make it full screen, and turn your volume up.
He shot that in the summer of 2016 over the course of about 36 days, and took — get this — 85,000 frames. A lot of it was shot in 8k, and I can only imagine what this must look like in full resolution.
To create a summer monsoon, first sunlight warms the land. Then the air above it gets warmed so it rises and expands, turning into a low pressure system. Moisture-laden air from the oceans sweeps in, lifts up, condenses, and storms form.
But that hardly describes the intensity and fierce beauty seen in Olbinski’s video. I was particularly impressed with the haboobs— the walls of dust blown outward from below the storm. These form when there’s a big downdraft from the storm cloud (like a microburst, when falling rain evaporates and cools the air around it, which gets denser and falls rapidly; when it hits the ground it spreads outward like an enormous splash and can be incredibly powerful. This picks up sand and dust, blasting it outwards. The size and scale of a haboob can be enormous. I’ve never seen one in person, but then, I’d maybe rather not anyway. Yikes.
It’s also amazing to see how focused the rainfall can be sometimes even when the cloud is sprawled out over a large area. The interaction of heat, air, and water produces unusual and unexpected results… at least, unexpected to me, a novice and amateur cloud watcher.
It’s also a strong reminder that the air around us is a fluid; literally, it can flow. Watching clouds and storms like these in person, the action is distant and slow. But in time-lapse videos that motion can be seen, and the air itself looks and behaves exactly like the fluid it is.
And finally, I have to note how magnificent the music is. I love it when the video is edited to match the feel and cadence of the music, as Olbinksi did to Kerry Muzzey’s “Revenge / Revenge Epilogue”. It adds a depth that gives more than its share of power to the footage.
The Sun’s Motion Reflected in the Universe
Even after all this time—13.8 billion years, give or take—hydrogen still dominates the Universe. It’s the simplest element, and the most abundant. It fuels the stars, which convert it into heavier elements like helium, iron, calcium, and more. It’s strewn between the stars and even between the galaxies themselves.
To know hydrogen is to know the Universe.
This is no exaggeration. Hydrogen in deep space hums in the radio region of the electromagnetic spectrum, and that can be detected by radio telescopes. This is incredibly useful: For example, we discovered our own Milky Way galaxy was a spiral by tracing the hydrogen gas, which outlines the majestic, sweeping arms (for more, go watch my Crash Course Astronomy episode on the Milky Way).
The image at the top of this article is a new map of the entire sky made by tracing the radio emission of hydrogen. Two huge telescopes—a 100 meter Effelsberg telescope in Germany and the 64-meter Parkes telescope in Australia—covered both hemispheres in great detail. In this map the spherical shape of the sky is, in a sense, unpeeled and shown as an ellipse, which is a convenient way to show the whole sky in a 2-D way.
When done this way, the Milky Way stretches directly across the middle of the map. The galaxy is flat, and we’re in it, so we see it as a line across the sky. In this “galactic coordinates” map, the center of the galaxy is in the map center. You can see the hydrogen gas of our two companion satellite galaxies to the lower right, and the tiny smears to the lower left of the Andromeda and Triangulum galaxies, two nearby spiral galaxies not too dissimilar to our own.
Now I need to show you something, because this is utterly, utterly cool.
Hydrogen emits light at a very specific wavelength: 21.106114 centimeters. This far longer than the wavelength of the kind of light we see—a half-million times longer! That’s why we need special telescopes to see it.
Effelsberg and Parkes are both very sensitive telescopes, and they can also detect minute changes in the wavelength of the light. If a hydrogen atom is moving toward us, the wavelength shortens a bit, and if it moves away it lengthens. This is related to the famous Doppler effect (see Crash Course Astronomy: Light for all about that).
The map above uses colors to represent that. The colors aren’t real; they just represent the velocity of the gas. Hydrogen colored blue is headed toward us; green is where it’s moving away. When I first saw this map, I saw the broad green line on the right and the blue one on the left, and realized that what it shows is the Sun’s motion as it orbits the center of the galaxy. We’re moving at about 200 km/sec around the galaxy, so we’re approaching gas on one side of the galaxy, and moving away from the gas on the other side. Neat!
But then I saw the gas closer to the center. The colors are reversed! On the right side of the map, the gas is blue until a third of the way out then switches to green outside of that. What the what?
Then I laughed when I figured it out. We’re not the only object in the galaxy in motion! All that galactic gas is orbiting the galactic center as well. Stuff near the center is orbiting faster than we are, and stuff farther out slower. The blue gas on the right is inside our orbit, moving faster than we are, so it’s catching up to us, approaching us. But the gas colored green is outside us, moving more slowly, so we’re leaving it behind.
I know this can be hard to picture in your head, but the beauty of it is that once you do, this map sings. You can instantly see what’s what: the motion of the gas, where it’s more dense than other locations, how it’s distributed. It also shows our location in the galaxy! All those changing velocities depend on the Sun’s velocity, the velocity of the gas, but also the direction of the Sun’s motion and its position in the Milky Way’s disk. That’s a stunning amount of information.
Maps like this allow astronomers to puzzle out the structure of our galaxy, and the dynamics of the gas inside and out, and even what other galaxies are doing as well.
I really wasn’t overstating the case: To know hydrogen is to know the Universe. Sometimes it’s the simplest stuff that leads to the most profound understanding.
How Just Three Stars Light Up a Stellar Nursery
Today I’m going to toss a little bit of math your way. If you’re an arithmophobe, never fear: It’s mostly just me throwing around some gee-whiz numbers, and I’ll help you swallow this medicine with the sweet, sweet eye candy above.
That image is from Robert Gendler, Roberto Colombari, and Martin Pugh, and it shows the young star cluster called NGC 6193 embedded in a vast cloud of gas and dust called NGC 6188. Both are very roughly 4,000 light-years away in the constellation of Ara. The image combines data from the huge 8.2 meter Very Large Telescope in Chile with some from a much smaller 32 cm telescope.
The cluster is young, only a few million years old. The brightest stars in it are massive, hot, luminous, and blue. They flood out light, illuminating and ionizing the gas in the cloud, which responds by glowing red.
I could go into details, but I already have in countless posts about emission nebulae, as well as in Crash Course: Nebulae. I’ll leave it up to you, Bad Readers, to determine how deeply you want to dive into those particulars by clicking those links.
But I want to point something out. Images like this are gorgeous, and always stop me in my tracks. The details, the colors, the structure of the gas … all of these combine to make such arresting images!
Still, it’s the science behind them that touches some atavistic part of my brain, giving me a chill that is both intellectual and visceral.
In many such nebulae, there are quite a few massive stars lighting them up, sometimes dozens of them. But in others, like NGC 6188, it’s only a few. In this case I mean that literally: The vast majority of energy pumped into the gas is being done by three stars.
In the center of the nebula you can see two stars, their cores blurred into a single smear, but their distinct presence revealed by the pair of X-shaped diffraction spikes coming out from them. Moreover, one of those two is itself a binary star, two stars in close orbit, so close they appear as one. So you’re actually seeing three stars there! One is a brutal O3 star, probably 50,000 times more energetic than the Sun, and the other two are O6, smaller but still beasts. All together they probably crank out 100,000 times as much light as the Sun does.
If you replaced the Sun with any of those three stars, the Earth wouldn’t last long. It’d be fried to a crisp.
But here’s the thing: The glowing part of that nebula, the gas energized by those stars, is roughly 20 light-years across. That’s 200 trillion kilometers! All that gas, probably several times the mass of the Sun, glowing due to the light of just three stars.
That made me wonder: How many photons are those stars emitting?
The math on that isn’t so bad. I won’t start from first physics principles, because that would take a lot of words. Instead, let me skip around a bit.
First, how many photons does the Sun emit? Well, the energy of a photon is defined by its wavelength or frequency. The Sun emits most strongly in the green portion of the spectrum, and that’s a wavelength of about 0.5 microns (or 500 nanometers if you prefer). The equation of the energy in a single photon is:
Energy = h x c / wavelength
Where h is Planck’s constant (just a number that has units of energy times time), and c is the speed of light. You can look those numbers up, but in the end the answer is that a single green photon has an energy of about 4 x 10-19 Joules (a Joule is a unit of energy; the energy stored in a single calorie of food is equivalent to more than 4,000 Joules).
The Sun emits about 4 x 1026 Joules of energy every second. That’s spread out over many different colors, each with their own energy, but I’m being really rough here, so assume they’re all green for math purposes. Dividing that total energy by the energy per photon gives us the number of photons the Sun emits:
4 x 1026 / 4 x 10-19 = 1045
Holy. WOW. That’s a lot of photons. Written out it’s:
And that’s every second. The Sun has been doing this for 4.6 billion years, so I’ll leave it to you to figure out how many photons total the Sun’s given off since it was born (but it’s roughly 1062, and yikes).
Mind you, those stars lighting up NGC 6188 are 100,000 times brighter than the Sun, so they emit 1050 photons per second! They also tend to emit higher energy light, like ultraviolet. That kind of light is preferentially absorbed by the hydrogen in the gas cloud. That ionizes the gas, blasting the electrons off the atoms. When the electron recombines, it re-emits that energy as light, usually that characteristic red you see in the image.
That’s how (well, in part that’s how) just a few stars can light up gas for trillions of kilometers around.
Funny, too: As bright as those stars are, distance is more important. At 4,000 light-years away, they’re 250 million times farther away from the Sun*. So even though they blast out 100,000 as much energy, they’re just barely visible to the naked eye at that distance. I’m not sure what’s more unnerving: The energies involved, or the vast distances. Both are mind-numbing.
So in case you were wondering, when I see astronomical images, that’s the sort of stuff that goes through my mind. I’ve said it many times, but it bears repeating: There is great beauty in astronomy, but that’s dwarfed by what these cosmic artworks teach us about the Universe.
* Correction (Oct. 26, 2016): I originally wrote 250 billion here. Oops. Still, they're a long ways off.
Astronomers X-Ray Colliding Galaxies to Find a Pair of Monster Black Holes
When whole galaxies collide, it’s a train wreck on a cosmic scale.
Usually there’s a near miss first, with each galaxy flying past the other. Both galaxies get distorted, their mutual gravity stretching them like taffy. They pull apart, but then their mutual gravity draws them together again, and the collision begins for real. What may have started as two lovely spiral or elliptical galaxies becomes chaos, the stars and gas clouds flung this way and that, and the resulting coalescing object a lumpy mess.
Eventually the two galaxies merge. We know that all big galaxies have supermassive black holes in their cores, millions and even billions of times the mass of the Sun. After two galaxies collide, eventually their central black holes collide and merge as well, forming a bigger black hole (and blasting out gravitational waves). But that doesn’t happen for quite some time; during the actual galaxy collision each black hole is its own entity.
Not only that, but gas clouds tossed about by the collision can drop into the center of each galaxy, doomed to fall into the black hole there. When they do, the material piles up into a disk just at the edge of forever, swirling madly, heating up, and blasting out X-rays.
Which brings us to Arp 299, a pair of gorgeously colliding galaxies about 140 million light-years from Earth. We know that the collision has been going on a while; the system glows brilliantly in infrared, putting out almost a trillion times the Sun’s energy output just in that one wavelength! That’s due to huge amounts of dust around their black holes, which absorbs a lot of the energy, gets warm, and re-emits it in the infrared.
The cores of the two galaxies are separated by less than 15,000 light-years, which is pretty close on a galactic scale. That’s interesting, but it’s also irritating to astronomers: They’re so close together it’s been difficult to separate them using X-ray telescopes. And we know they’re emitting copious X-rays; the problem is knowing which black hole is emitting what.
Now, though, they’ve been teased apart. Using both NuSTAR and Chandra—two orbiting X-ray observatories—astronomers have figured out what each black hole is doing. In the image above, it’s the one on the right (Arp 299B) that’s pouring out X-rays, and is what we call an Active Galactic Nucleus, or AGN. The galaxy on the left (Arp 299A) is also emitting X-rays, and might be an AGN as well, but it’s only contributing about 10 percent of the total X-ray emission of the system.
The energy of the X-rays Arp 299A is emitting is also consistent with it having lots of what are called high-mass X-ray binaries (or HMXB), which consist of a high-mass star orbiting a black hole. In this case, the black hole in a HMXB is far smaller than the ones in the centers of the galaxies; it may have a few times the Sun’s mass, not millions of times. But it’s enough to draw material off its companion star, which then (like its supermassive counterpart) creates a disk of material that heats up and emits X-rays. But the way these emit rays is different then the cores of AGN, making it possible to distinguish between them (in general HMXB emit much higher energy X-rays than AGN).
Well, sometimes. In the case of Arp 299 it’s hard to be sure; the observations aren’t distinct enough to be certain Arp 299A is not an AGN. The astronomers who observed the system mention they plan on observing lots of other galaxies in this same way, specifically galaxies that are known to be rapidly forming stars. These tend to have more HMXBs in them, and that will act as a benchmark, helping astronomers distinguish between AGN and HMXB. The more “starburst” galaxies observed, the easier it will be to understand colliding ones as well.
All of this underscores a very important aspect of astronomy, science, and really just life in general: You have to observe things in more than one way to understand them. Using telescopes like Hubble or other big optical-light observatories is great, but they only give you part of the picture (literally), only tell part of the story.
Changing your viewpoint gives insight and perspective. That sounds like pretty good advice to me, whether you’re thinking about something scientifically or exercising a little bit of human compassion. In my opinion, we could use a lot more of both.
A Year of Record Heat
Every month since March 2016, I’ve posted an article that is almost exactly the same every time. For the nth month in a row, I’ve written, we’ve had a month that broke the temperature record historically. And even when I wrote the first one in March, we’d already seen record months since October of 2015.
And it’s happened again. September 2016 was the hottest September on record. That makes it the 12th month in a row this has happened*.
After repeating the same article nearly word for word every month since March, I just can’t do it again. It seems too glib this time.
We’ve had a year of record heat. A year.
To be fair, this September just barely beat the previous record holder, by 0.004 degrees Celsius, putting it essentially in a statistical tie. But the previous record was in 2014, which again shows you that the world is heating up; all the record high temperatures are recent. The only way to even be a record high these days is to beat out some record from a year or two before.
The world is too damn hot. It’s a foregone conclusion that 2016 will be the hottest year ever recorded.
This latest record—all the recent records—are not individually critical. But we see so many of them that they should trigger warning bells in your head. And when you see the trend—a paper recently published by climate scientists claims that the Earth is hotter than it’s been in more than a hundred thousand years—those bells should be clanging louder than anything else. Global warming is an existential threat to our species.
So why is it we had three presidential debates with only barely a mention of this? And why do we have flat-out deniers still sitting in Congress?
Here’s a bit of good news: A total of 469 seats in the U.S. Senate and House are up for re-election on Nov. 8. Better yet, many vulnerable seats in the Senate are held by Republicans, the party that is far and away the most responsible for climate change denial in Congress. It’s literally in the party platform for the GOP.
That makes the Senate up for grabs for the Democratic Party, and a lot of the House as well. Even such stalwarts of GOP denial as Rep. Lamar Smith (R-Texas) are not looking as solid as they once were; for the very first time, in Smith’s home town the San Antonio Express-News refused to endorse him because he’s using his power as a congressman to bully scientists about climate change. His rabid denial has led him to abuse his position, and as the newspaper has shown, whether you agree with him or not, this alone is enough that he should be kicked to the curb. I’ll note that his opponent this election is Tom Wakely, a Democrat.
While Smith is probably safe, perhaps in two years a more moderate Republican who understands science will see his or her opportunity to unseat him. I dearly hope so.
I need not go into detail on the horrendous threat Donald Trump poses to our nation and our planet. But have no doubt that down-ballot candidates are every bit as dangerous. Denying global warming is as fundamentally wrong as saying the Earth is flat. It’s long, long past time to vote those flat-Earthers out of power.
Go out and vote. It’s not too late.
*Correction, Oct. 26, 2016: Several people brought to my attention that GISS reanalyzed the data and found that June 2016's temperature was lower than first thought by 0.05° C, making it the third hottest June recorded by a small margin. I missed this when I read the webpage. However, as I say in this very article, the actual records aren't as important as the trend. And that trend is heading up. My overall point remains true.
Mars Lander Impact Site Seen From Orbit
So, half of the European Space Agency’s ExoMars mission went well the other day. The Trace Gas Orbiter is now circling the planet, and appears to be healthy and happy.
Unfortunately, the Schiaparelli lander didn’t do so well. Instead of gently touching down on the surface, an as-yet undetermined problem shut the landing rockets off while it was still two to four kilometers above the ground. It impacted at an estimated speed of 300 km/hr. That’s 180 mph. Oof.
The image above is from NASA’s Mars Reconnaissance Orbiter, and shows the impact site. The lander’s planned descent was very similar to that of NASA’s Curiosity rover. Its heat shield took the brunt of first slamming through the atmosphere and then was ejected. After that a parachute slowed it further, then it and the back shell attaching it to the lander were ejected. Finally, the lander itself would slow using rockets and drop down to the surface.
In the image near the bottom you can see a bright spot below the cluster of pits to the lower right; that’s likely to be the parachute and back shell. And near the top is the, um, rather large black spot. That smudge is 15 x 40 meters in size, or about half the size of an American football field. The lander’s rockets would disturb the surface as it came down, but not nearly that much. It’s far more likely it’s an impact site.
This animation shows it better:
From telemetry, it seems that the thrusters switched off far too early. That means the fuel tanks were nearly full of propellant, so it’s likely they exploded upon impact. That would explain the size of the impact disturbance. It’s not clear why it happened, but engineers are poring over the data and hopefully will figure it out soon.
This is pretty disappointing, but it’s important to note that that lander was a technology testbed, literally designed and built to test the tech needed to land a future rover or other equipment on Mars. For the most part, the lander was a success! Most of the hardware and software worked, but obviously a very important piece did not.
And more importantly, the Trace Gas Orbiter is doing well. This is an extremely sensitive observatory that will look for methane in the atmosphere of Mars. Methane is a simple carbon-based compound that breaks down easily in the atmosphere. It’s been detected in the air of Mars before, but it’s very diffuse and difficult to nail down. Methane can be created both by geological activity (outgassing from the interior) and by biological action. Obviously, the question of life on Mars looms large, and if it exists and is anything like life here, it might make methane. Detecting the gas is a big clue.
TGO will not only map methane, it will also look for different isotopes of it. A carbon atom usually has six protons and six neutrons. An isotope of an atom has a different number of neutrons; for example carbon-13 has seven neutrons, not six. Biologically made methane usually has more C12 in it than C13, so mapping the various isotopes can give us clues about the origin of the gas as well.
So let me stress again that TGO is ticking along. And hopefully engineers at ESA will learn enough about what went wrong with Schiaparelli to make sure the next attempt will go a little bit more gently.
We humans have sent a lot of probes to Mars, and nearly half have failed in one way or another. Space exploration is hard. But it’s so very worth it. I hope the folks at ESA working on this remember this as they continue to strive to better understand the Universe around us.
Twinkle Twinkle, Little Star, Who Wrote You? ’Twas Not Mozart.
“I never made a mistake in my life. I thought I did once, but I was wrong.” –Charles Schulz
Despite being a beloved internet personality, I have my flaws. Sometimes—rarely, of course—I make mistakes. I know. You’re shocked. Take a moment to recover, if you need one.
But it happens. If it’s small and doesn’t impact the writing in an article I fix it and move on, or (because TPTB at Slate are quite strict about such things) I issue a correction in the article itself. Sometimes the mistake is extensive, or worth diving into more fully, or as happens often is illustrative of an interesting issue, and in those instances I’ll write a separate follow-up article.
Sometimes it’s more of the “Oh. Huh!” variety. Such is the case here.
In my first book, Bad Astronomy, I offhandedly mention that the tune for “Twinkle, Twinkle, Little Star” was written by one Wolfgang Amadeus Mozart. Perhaps you’ve heard of him, and perhaps you’ve heard this claim as well.
However, it appears I and everyone else who repeats this little factoid are wrong. In an article at Woot, professional smart person Ken Jennings corrects this common misconception. It turns out the tune did not come from Mozart, but instead is actually a French folk song that dates from before him. I urge you to read Jennings’ article for details, as he mentions how Mozart got saddled with the credit.
Jennings also calls me out specifically for making the claim, especially and ironically in a book I wrote trying to correct misconceptions. Mea culpa. I remember writing that claim back in 2000 when I was drafting the book, and I even vaguely remember both thinking to myself that I should check its veracity, and actually doing so. However, I must have found some article that confirmed my own bias about the song’s authorship and went with it. Unfortunately, no one else in the editorial process caught it either, most likely simply assuming the old claim was correct.
Ah well. If you buy my book and are saddled with existential conflict due to this error, I suggest you take a pen, cross out the offending portion, and smile knowingly as you have gained more knowledge, a noble goal.
And if you’re the kind of person who delights when someone in my position makes an error, I suggest you buy somewhere between 10 to 20 copies of the book and distribute them among your friends, so that you may all gather and bask in my factual wrong turn.
Of course, none of this affects another book, Astronomically Correct Twinkle Twinkle, written by my friends Henry Reich and Zach Weinersmith, which is quite delightful. Ironically, I suppose, I fact checked their book, and came up empty of errors. But then, they’re both smarter than I am, and combined they possess fierce intellect.
Now, for penance, I’m going to go listen to “The 1812 Overture,” which I hear was written by Francis Bacon.
The Lone Icy Volcano of Ceres
It’s hard to pick the one weirdest thing about Ceres. It’s the largest object in the asteroid belt between Mars and Jupiter. Most of the billions of chunks of debris in the belt really are leftover rubble from the early solar system, but some grew larger by the power of their own gravity, drawing more material in.
As it happened, Ceres was well on its way to becoming a planet before it ran out of material to feed on. Bigger than an asteroid, but smaller than a planet, scientists call it a protoplanet.
Out past Mars, the early solar system had lots of ice, and Ceres trapped this material as well. Its surface is dotted with white spots, what are now thought to be salt deposits left over as briny water leaked to the protoplanet’s surface and sublimated away.
The surface is heavily cratered, of course, and hilly. But one features stands out … and I do mean literally.
Ahuna Mons is the lone true mountain on Ceres, and it’s far and away the tallest: It towers an amazing 4 kilometers over the surface, and is 18 km across at its base. Nothing else on Ceres even comes close to it.
But Ceres doesn’t have tectonics like Earth does. So what could possibly create such a huge feature?
Ice. And lots of it.
We know salty water is oozing up to the surface because we see those shiny spots. Most of the spots are small, indicating low flow. But apparently that’s not the case for Ahuna Mons. New research just released analyzed data from the Dawn spacecraft, which has been orbiting Ceres since March 2015.
There must have been a lot of salty water under the surface at the location of Ahuna Mons, and it kept pushing its way up and out. Mixing with the rock and dust of Ceres, it piled up over time, forming the mountain out of muddy brine.
On Earth, when material flows out of the interior and forms a mountain, we call that mountain a volcano. But on Ceres, the material isn’t lava, it’s ice. So, Ahuna Mons isn’t just a volcano. It’s a cryovolcano. We know of several objects in the solar system with cryovolcanism, including moons of the outer planets, and even Pluto.
And this gives us another piece of the puzzle that is Ceres. Clearly, ice plays a role locally in the surface of Ceres. However, another bit of research shows that its role is less important over long stretches of terrain.
While the surface of Ceres is loaded with craters, it seems to have a deficit of truly big craters; several are expected to have formed from impacts, but only a couple exist (and even those are faint and hard to trace). It looks like the crust of Ceres is weak on the large scale, so that material in big craters can flow around and erase them, but still relatively stiff on local scales, allowing smaller craters to exist.
All of these data are clues to how Ceres formed, how it changed over time, and why it came to look and behave the way it does now. Astronomers and planetary scientists are like sleuths, mulling over the evidence to figure out whodunit. And how.
We’ve only been studying Ceres up close for a year and a half, and look how amazing it is! I wonder what else we’ll find there as we hold our magnifying glass to it.
How Big Is Proxima Centauri’s Planet?
Earlier this year, astronomers announced amazing news: The closest star to the Sun, called Proxima Centauri, has a planet! Not only that, but the planet’s size is roughly the same as Earth’s, and at its distance from Proxima it gets about the same amount of heat as the Earth does from the Sun.
In other words, we’re looking at a potentially Earth-like planet.
Potentially. The problem is that we don’t really know how big the planet is; and I mean that literally. Its diameter is unknown, and we need that to get any kind of understanding of what the planet may be like.
Why? Because if the planet (called Proxima Centauri b, or just Proxima b) is small and massive that means it’s dense, and so is will probably be composed of mostly metals and rock. If it’s large and massive it’ll be far less dense, and could be rocky with lots of water. Somewhere in between means it could have the same overall composition as Earth. These are three very different outcomes, and they all depend on the planet’s size. My friend Ian O’Neill has a good article outlining this.
The only way we know to measure the physical size of a planet is if it transits its parent star; that is, the orbit of the star is edge-on as seen from Earth, so we see the planet pass in front of the star once per orbit. When it does that the star’s light drops a bit, and the amount it drops depends on the size of the planet: A big planet blocks more light than a small one. If we know the size of the star (and we generally can determine that) then the amount the light dips tells you the size of the planet.
Knowing this, some astronomers observed Proxima using the Microwave and Oscillations of Stars Telescope (or MOST), a ‘scope with a 15 centimeter mirror that orbits the Earth. MOST is tiny; it only has a mass of 53 kg (that’s less than the mass of a typical adult human) and has a relatively small mirror, but being in space means it’s very stable. It doesn’t have to worry about peering through Earth’s atmosphere, which is wiggly and wavy. That means even a small ‘scope can make very precise measurements of a star’s brightness.
They observed Proxima for more than 40 days, looking for any tell-tale dip in its brightness. And they found one! Better yet, it was about what you’d expect from a planet the size implied by Proxima b’s mass. But the problem is the data are a bit noisy, and the transit inconclusive. It’s possible, even likely, it’s just a statistical fluctuation in the data, and so in the paper they say the odds are actually against the transit being real.
That’s disappointing. But not really unexpected; if the planet is roughly the size of Earth, the orbit has to be almost exactly edge-on for us to see a transit. Even a small tilt means it would appear to pass above or below the star from our viewpoint. The chance of a transit was only expected to be about 1.5 percent anyway.
Helpfully, David Kipping from the Cool Worlds group—and also the lead author on the Proxima transit paper—has made a video explaining this, too:
By the way, that tilt affects the mass we find for the planet, too. The planet’s existence was found because as it orbits Proxima, it pulls on the star with its gravity. While the planet makes a big circle around the star, the star also makes a smaller circle. We call that reflexive motion. The more massive the planet, the bigger the reflexive motion of the star.
In the research that found Proxima b, they found the likely mass of the planet is about 1.27 times Earth’s. But that depends on the tilt of the orbit! If the orbit is edge-on we see the reflexive motion maximized; if we see the orbit face-on we won’t see any reflexive motion at all. So the mass we find is the minimum for the planet; it could be larger if the orbit is tilted.
The thing is, at around twice the mass of the Earth, a planet starts to look more like Neptune than our fair world. It has enough gravity to accumulate a thick atmosphere, and would not be Earth-like as we think of it. So knowing the exact mass is important. And we don’t know it.
But there’s hope. As the paper authors point out, observations in the infrared, light outside the range our eyes can see, would help. Proxima is several hundred times brighter in the infrared, making the observations easier. Also, like many red dwarfs, Proxima is a flare star, blasting out huge stellar storms due to its magnetic activity. That makes observing it very difficult; it keeps changing its brightness, and that interferes with planet transit hunting. But in the infrared flares are much dimmer, again making it easier to observe there.
Mind you, the odds of Proxima b actually having an orbit that allows it to transit are long. But not zero! I think it’s worth a big infrared telescope’s time to look for a transit. This is, after all, the closest known planet in the Universe outside our solar system.
I think it’s a good idea to get to know our neighbors.
A Spiral Galaxy Defying the Cosmic Flow
I’d like to introduce you to an interesting galaxy today. The reason it’s interesting is because it’s surprising, and in a way that caught me off guard.
It’s called M98 (or NGC 4192; every object in the sky is in multiple catalogs and has multiple handles), and it’s a spiral galaxy much like the Milky Way. It’s located about 50 million light-years away, which isn’t exactly close on a cosmic scale but isn’t all that far away either. If I had to make an analogy, it’s like it’s in the next town over.
We see M98 at a pretty low angle, so it appears nearly edge-on to us; spiral galaxies are pretty flat, and can have wildly different appearances depending on our viewing angle. Still, the spiral pattern is obvious enough, and you can see bright blue regions where stars are being born; those trace the arms. There is also lots of patchy dust along the arms; molecules of silica and aluminum as well as complex carbon-based molecules that are more like soot than anything else.
I like the central region of the galaxy; it’s bright but from this angle is cut in half by a dust lane, distorting the apparent shape of the usually elliptical hub.
All in all, it’s quite lovely, and that shot by the New Technology Telescope really shows it off.
But in that way it’s like a zillion other spirals. So what makes this one special?
Unlike nearly every single other galaxy in the Universe, this one isn’t moving away from us. It’s moving toward us.
There’s no danger of a collision! At its speed of 150 km/sec, it would take a hundred billion years to get here, so don’t wait up. Also, it’s probably not heading directly at us, because it’s part of the Virgo Cluster, a grouping of about thousand galaxies bound by their own gravity. It’s the closest true cluster to us, and our own small Local Group of a couple dozen galaxies is like a small town near a bigger one. M98 is part of the Virgo Cluster, so it’s in orbit around the cluster center. We’re way outside the cluster, so it can’t hit us.
Here’s the fun bit. The Universe, as you may know, is expanding. One way to think of it is that space itself is getting bigger, and as it does galaxies are swept along with it. Galaxies aren’t really moving away from each other, they’re just floating along with the local flow.
But in many ways it’s like they really are moving away. One way is that their light is redshifted; the wavelength of the light they emit is stretched (it’s very similar to the Doppler effect that makes a motorcycle go EEEEEEeoowwwwwww as it passes you, changing the pitch of the noise). Practically every galaxy in the Universe shows this redshift, and in fact that’s how all this was discovered in the first place. The farther away a galaxy is, the more it’s light is shifted.
But not every galaxy shows it. Close by galaxies have much lower redshifts, and if the galaxy itself is moving rapidly through space (and not just with it), that local velocity will get added to or subtracted from the recession velocity.
One example of this is the monstrous Andromeda galaxy, which is headed toward us at high speed. We actually will collide with it, though not for quite some time (like, 4 billion years). But it shows a distinct blueshift in its light; it’s moving around faster than space is expanding.
M98 is doing the same thing. That surprised me when I saw it in a catalog; it’s far enough away that the Universal expansion should make it recede from us at about 1,000 km/sec.
But then I saw it was in the Virgo Cluster, and I understood. The massive gravity of all those galaxies means they orbit the center at a decent clip, so some galaxies are redshifted more than average as they head away from us, in the part of their orbit taking them to the other side of the cluster. Some have lower velocities because they’re headed toward us in their orbits.
But M98 is still unusual because it can completely overcome the recession of the cluster, and actually be physically headed toward us. That’s almost certainly because it’s recently interacted with another galaxy in the cluster; when galaxies pass each other one can be flung away at high speed, something like a slingshot effect. M98 may very well have done this, and that’s why it’s blueshifted, not redshifted.
As you look to more distant clusters this gets rare or nonexistent, because at that distance the cosmic expansion dominates, and it doesn’t matter how fast the galaxy is moving: It can’t overcome that recession. All galaxies past a certain distance are redshifted, which is yet another reason (among many, many others) that we know the Universe actually is expanding.
That’s pretty cool. I like surprises when I’m reading up on lovely astronomical objects; that means I’ve learned something. M98 is headed toward us, a rare blueshifted galaxy. Huh. That just adds to its beauty and intrigue to me.
It’s a really beautiful Universe, and it’s also a really interesting one. I’d say that’s its best quality.