Bad Astronomy
The entire universe in blog form

Jan. 20 2017 8:30 AM

If You Need Strength Today, Be Like Daphnis

Today is a difficult day. And it’s just the latest in what have been very, very difficult times.

I’ll be honest with you: Over the past few months, in between bouts of fury and incredulity, like so many of you I have felt real despair. Watching the country I love, the people I care about, and the science to which I have devoted my life come under such attack has been extraordinarily difficult and painful.

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It can be hard to find any comfort in situations like these. And I have no desire to utter to you any hollow phrases, any meaningless pablum that sounds deep but is of no actual content.

Instead, please indulge me for a moment.

First, read this article I wrote yesterday about Saturn’s moon Daphnis. It may seem like a non sequitur, but as you'll see it’s quite the opposite.

Daphnis
Saturn's moon Daphnis, a tiny wordlet with a long reach.

NASA/JPL-Caltech/Space Science Institute/Ian Regan

That image of Daphnis I posted yesterday is grayscale, a single picture of the moon taken by the Cassini Saturn probe. The one you see here was crafted by Ian Regan, using two images from Cassini to create a representation of the color. I actually saw his version first, the colors sublime, adding a subtle and delicate touch to the otherworldly vista.

It was in the evening when I first saw it, and I was in bed (perhaps ill-advisedly) checking Twitter before going to sleep. I was stunned… and I mean that literally, as in my brain locked up for a moment as the wonder of this image flowed into it.

For just a moment I wasn’t sure what I was seeing, and by that I mean which of Saturn’s panoply of moons and what part of the rings this depicted. Daphnis is so small that it’s only appeared as a barely resolved dot in previous images, and the detail in the surface features threw me. When I saw Regan’s caption identifying the moon I was stunned anew, since I knew this was by far the highest-resolution photo of Daphnis we’ve ever seen, and likely ever will.

The more I gawked at this photo the deeper my awe became. The ripples, the structures, the graininess of the rings, the smooth(ish) surface of Daphnis, the ringlets that are so narrow they challenge the ability of Cassini to resolve them, and most of all that gossamer thread of ring pulled away by the feeble gravity of this diminutive moon… all of this was a fantastic delight, a gift literally sent down from the heavens.

As I struggled to tease out the details of what I was seeing, a thought struck me: Daphnis was only discovered in the year 2005. Its presence was first suspected in 2004, when Cassini returned images of waves and spikes in a gap in Saturn’s rings, obviously sculpted by a tiny moon, though its exact location was at the time unknown. Observations were quickly planned to get better images of the gap where the ripples were seen, and in May 2005 astronomers announced they had found it. It was given the name Daphnis the very next year.

And here we are, a dozen years later, with a new and extraordinary view of this odd little satellite. As I lay in bed and mulled over that, a thought struck me. We’ve known about this moon for a decade or so, but how old is it? Millions of years? Billions? How long has this tiny chunk of ice been circling Saturn, carving these marvelous creations out of still tinier chunks of ice?

As I chewed on this, an honest-to-god chill went down my back. This moon has been silently gliding through Saturn’s rings since before humanity existed as a species, and likely far, far longer. It’s done this without notice, without discovery, without supervision, without any sense of purpose or any eyes seeing it.

Daphnis did what it does because it must. It follows the rules of science, dancing to the tune of gravity, and it wasn’t until just a few years ago that we too could read those notes, hear that music, and appreciate its melody.

Daphnis is so small you could circumnavigate it by foot in a few hours, provided you could maintain your traction in its faint whisper of gravity. Yet, in the vastness of Saturn’s rings, almost completely lost among a trillion, trillion particles, it still manages to make waves, to reach out and create an effect, to stir echoes in a system far larger than itself.

And when we ponder the reverberation of those echoes, they engender in us a sense of beauty. Of awe.

All of these thoughts were still ringing in my mind when I happened to see how my friend, astrophysicist Katie Mack, was herself inspired by this image from over a billion kilometers away, and how she captioned it.

This is Daphnis. Daphnis is only 8 km wide, and orbits in a ring gap of 42 km. It uses its tiny gravity to disrupt Saturn's mighty rings and make waves. Daphnis doesn't let being a tiny insignificant speck in a vast uncaring universe stop it. Be like Daphnis.

NASA/JPL-Caltech/Space Science Institute/Katie Mack

Yes, these are trying times, and it is easy to feel overcome, to be overwhelmed by events. And yes, the Universe itself is telling you that you are small. But do you know what else it’s telling you?

You are mighty.

Go out and make a difference. It may be a small one, but its reach may be profound, and extend far beyond what you intend or might perceive.

Go. Be like Daphnis.

Jan. 19 2017 8:45 AM

Saturn’s Moon Daphnis Creates Spectacular Ripples in Saturn’s Rings

When I saw the image above, I literally gasped. It’s an amazing photo, showing the small moon Daphnis inside a gap in Saturn’s rings. The beauty of this shot is apparent, but the science behind it is even cooler.

Allow me to explain.

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On Nov. 30, the Cassini spacecraft orbiting Saturn took on a new and risky mission. It began a series of orbits that are taking it over the planet’s north pole and then down just outside the main rings.

In mid-January it dipped through the ring plane on one of these orbits, passing a mere 28,000 kilometers from the tiny moon Daphnis when it took that shot with its narrow-angle (i.e. high-magnification) camera.

That’s the highest-resolution image of Daphnis ever taken; for scale, the flying-saucer-shaped moon is about 8 x 8 x 6 km in size. Measured from sea level, Mount Everest is roughly the same size. You can see some structure to Daphnis; there’s a ridge around its equator that’s probably due to ring particles that have piled up there, and a second ridge at higher latitude. The soft appearance to the moon is probably due to the accumulation of small grains of ice from the rings that have coated it, filling in the craters and other features.

That gap in the rings is real. It’s called the Keeler Gap, and it’s about 30–40 km wide. The width of the gap appears foreshortened because Cassini was just above the ring plane when it took the shot; it’s actually several times wider than the moon is long.

But, oh, those ripples! That, my friends, is the result of gravity. It’s a complicated and intricate dance between moon and rings, but it’s worth learning the moves.

Saturn’s rings are composed of countless tiny particles of ice, each in its own separate orbit around Saturn. They’re tremendously wide—the main rings are 300,000 km across, and would stretch 3/4 of the way from the Earth to our own Moon—but are astonishingly flat. In some places they are only 10 meters high from top to bottom, the height of a three-story house. To scale, this makes them far thinner than a piece of paper.

wide angle shot of Daphnis
Cassini took this wide-angle shot around the same time as the narrow angle one. Note how far the waves go around the rings. Saturn is to the upper right. This is a raw image, so there are some blemishes that aren't real objects.

NASA/JPL-Caltech/Space Science Institute

There are several subdivisions of rings, given letter designations in order of discovery. The broad A ring has distinct two gaps in it, carved by moons orbiting Saturn embedded in the ring. The Encke gap is 325 km wide, and is from the moon Pan. The much narrower Keeler Gap is due to Daphnis.

If you plunk a small moon down in a ring, it will of course carve a gap as it plows through material. Its gravity will attract more material as well, so particles just inside and outside the moon will, over time, fall onto it. The gap grows, but the width of the gap depends on the strength of the moon’s gravity. At some distance, the gravity is too feeble to pull particles all the way out of the ring and onto the moon. Pan has nearly 100 times the mass of Daphnis, so its gravity is stronger, and the gap it carves wider.

What causes those ripples? The orbit of Daphnis is not a perfect circle, but instead is very slightly elliptical. That means it’s sometimes closer to the inner edge of the Keeler gap, and sometimes closer to the outer one. The change is small, only about nine km, but that’s enough. When it’s closer to one edge it pulls on the ring particles a bit harder, creating the wave.

But there’s more to it. The orbit of Daphnis is also tipped a bit to the ring plane, a mere 0.0036° from being exactly aligned. That means it bobs up and down out of the ring plane by about 17 km. When it does it drags the ring particles at the gap edges as well. Those waves you see in the image go in and out of the gap, but also up and down by a kilometer or so.

Perspective makes that hard to see here, but twice every time Saturn orbits the Sun, the rings are edge-on to the Sun, and any vertical excursion can cast long shadows.

Daphnis and rings
In 2009, the Sun shone straight along the rings, so any features out of the ring plane cast long shadows.

NASA/JPL-Caltech/Space Science Institute

That image was taken at Saturn’s northern hemisphere spring equinox in 2009. It’s incredible! You can see Daphnis and the long shadow it casts on the ring. You can also see the vertical waves caused by the moon’s feeble pull. Each wave corresponds to one up-and-down bob of the moon relative to the rings. Eventually, tides from Saturn pull the particles back down, but that takes a while, and the ripples extend for a long way around the ring.

How about that? But wait! There’s more!

Look again at the first picture. You can see the ripple to the left of Daphnis is fuzzier than the others. That may be due to very tiny grains being pulled out (that ripple is on the outside of Daphnis, so was created the last time Daphnis passed those particles). The particles are brighter there than on the ripple right next to Daphnis, which is interesting; that may be due to the Sun’s illumination on the wave.

Daphnis
Daphnis in higher resolution.

NASA/JPL-Caltech/Space Science Institute

That’s a closer look at the top photo. You can see a very thin ribbon of material to the left of Daphnis. That may be due to a clump of material in the ring that was pulled apart by the moon! Note the shape, too; it mimics the ripple but looks like it goes deeper into the gap. Amazing. When I saw that I had to sit back and stare in awe. I don’t think anything like that has ever been seen before.

Also in that shot you can see the rings look grainy. That may very well be a hint of the actual grainy particulate nature of the rings, where material has clumped up! Cassini is getting closer to the rings than it ever has before, so we see them in more resolution. I hope we get even better shots of them over the next few months.

We’d better, because time is running out. Cassini’s end-of-mission is in September of this year, and when it’s done engineers will command it to plunge into Saturn’s atmosphere, where it will burn up and be crushed. This is done to prevent any possible contamination of the moons in case Cassini might impact them in the future after fuel has run out. Instead, the remaining wisps of fuel will be used to send the probe into the planet itself.

I’ll hate to see Cassini go. But images like the ones of Daphnis make me glad we had Cassini for as long as we did. It’s a truly historic mission, and its legacy will live on for a long, long time.

Tip o’ the RTG to Ian Regan.

Jan. 18 2017 10:41 AM

2016 Was the Hottest Year on Record

Well, it’s official: 2016 was the hottest year globally on record.

The National Oceanic and Atmospheric Administration released its numbers for the year, and there’s no way to sugarcoat this: It’s bad.

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We've had three consecutive years of record-breaking heat all over the planet.

Looking at land and ocean temperatures, the NOAA finds that the planet in 2016 was the hottest since records began in 1880, with a global average temperature 0.94°C (1.69°F) above the 20th-century average of 13.9°C (57.0°F). That may not sound like much, but it’s actually huge.

Think of it this way: The surface of the Earth is about 200 million square kilometers. All of that, everywhere, is now nearly a degree hotter than it was in the previous century. That’s a vast, staggering amount of extra energy.

Update, Jan. 18, 2017 at 16:20 UTC: NASA's Goddard Institute for Space Science and Berkeley Earth also released their results, which agree with NOAA: 2016 is the hottest year ever recorded.

As the planet warms, you’d expect the land to heat up faster than the ocean; water responds more slowly to changing temperature. And that’s just what we see: The land only temperature was 1.43°C above the 20th-century average, and the ocean-only temperature was 0.75°C warmer. Both are records; the land temperature easily surpassed 2015, though the ocean temperature was only a bit more than the previous record.

Normally, I’m not too concerned with breaking records; sometimes you get fluctuations due to statistics that can edge out a previous high mark. But in this case it’s different, because we’re talking about a hugely sampled number of temperature measurements taken over a substantial amount of the Earth’s surface.

But what makes this far more worrisome is the trend. If it’s getting hotter, you’d expect the hottest years to be the more recent ones, of course. Well, from the NOAA rankings, 15 of the 16 record hottest years were from 2001–2016, with 2016 being the hottest. Before that, 2015 was the record holder, and before that it was 2014.

The world is heating up.

There’s more. To wit:

  • Sea ice in the Arctic has been declining precipitously for some time, but this past year took a huge dip. The average extent for 2016 was about 10 million square kilometers, the lowest on record.
  • Record high temperatures were seen all over the planet. Tellingly, no land areas were cooler than average. It was hotter everywhere over Earth's solid surface.
  • 2016 was the second hottest year on record for the contiguous United States, with every single state getting above average temperatures.
  • The lower and middle troposphere (the atmosphere from the Earth’s surface up to about 10 km, though it varies by latitude) also saw record high temperatures.
  • The stratosphere (the atmospheric layer above the troposphere) saw record cold temperatures, but ironically this is exactly what you expect from global warming (you can get more details of why that is at Real Climate and Yale Climate Connections).
global map
Annually averaged deviations of temperature. Note that over land, not a single bin was cooler than average (no blue spots anywhere).

NOAA

Global warming is real, and it’s happening now, and it’s our fault. The overwhelming majority of climate scientists agree with this. Peter Gleick, a scientist who studies the impact of global warming, puts it this way: “Not a single national science academy disputes or denies the scientific consensus around human-caused climate change.” And not just in America, but all over the globe.

Of course, some politicians disagree. And to the detriment of all humanity, many of them are currently in power in the United States, and are about to consolidate that power more. Nearly every single Cabinet nominee Donald Trump has chosen denies the reality of global warming. As my friend and science advocate Sheril Kirshenbaum noted, just getting one of Trump’s appointees to admit that climate change isn’t a hoax is surreally encouraging.

In a world heating up, that’s a tepid victory.

There is some good news, or at least less bad news. President Obama just sent $500 million to the United Nation’s Green Climate Fund, a program to help developing countries—which tend to be the hardest hit by climate change—adapt to this new world. That’s great, but he did it on his way out, and what’s coming in is an administration hellbent on tearing down any legislation to help mitigate global warming that’s been enacted the past eight years.

For example, the House Committee on Science, Space, and Technology still has a GOP majority, and they just added several new reality-denying members. I have little doubt that Rep. Lamar Smith, R-Texas, the committee chairman, will continue his baseless attacks on climate scientists, and I’m sure he will issue a challenge to this newest NOAA hottest year finding, just as I’m sure it will distort the facts. That’s been his modus operandi for years.

Still, there’s hope. I’ve said it before: We need a public that’s excited about science. Most people in America know climate change is real, and want the government to take action about it. The next two years will be very difficult, but then there’s the midterm congressional election. Two years after that is the next presidential election. These elections have consequences, and right now those consequences are more than 700 days of climate inaction, if not outright hostility. We need to be ready to fight legislation taking aim at making our planet hotter, and be ready to throw out our representatives if they deny the science.

Never forget that word: our. They represent us. And if we chose it, then we can put science-friendly legislators back in power. It will literally save humanity.

Jan. 17 2017 8:45 AM

Apollo Astronaut Gene Cernan Has Died at 82

Apollo 17 Cmdr. Gene Cernan has died.

Besides being a Naval aviator, a fighter pilot, and an engineer, he is best known as the last human to have stood on the surface of the Moon.

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Like every other astronaut of the time, Cernan was quite the character, with a storied life. He had been an aviator for five years when, in 1963, NASA tapped him to be an astronaut. In 1966 he piloted Gemini 9A, the pre-Apollo mission for which he was part of the backup crew before the prime crew died in an airplane crash*. Gemini was a precursor to Apollo, a way for NASA to learn the skills needed for the mission to the Moon.

9A had a series of mishaps itself. Its primary mission was to rendezvous and dock with an uncrewed vehicle that was to be launched hours earlier, but that rocket failed during flight. A second uncrewed vehicle was launched successfully two weeks later, but on its first attempt, the rocket with Cernan and Thomas Stafford suffered a malfunction and didn’t launch. It finally went up two days later.

Things still went poorly. Once in orbit they found the rendezvous vehicle slowly spinning (and a shroud had failed to jettison, making docking impossible). Cernan’s extravehicular activity (EVA) was postponed until the mission’s third day. Even then he had serious problems with his suit, and the two-hour EVA exhausted him. They had to cut it short, but he was so overheated and tired there was real concern he wouldn’t be able to get back into the capsule. He did, of course, and NASA eased up the workload of future missions to prevent overtaxing the astronauts.

I cannot stress enough how difficult that Gemini 9A EVA situation was, and how hard Cernan pushed himself to get done what had to be done. I suggest reading the Wikipedia entry for the mission to get a flavor of it, and to let the word hero be fixed in your mind as you do.

Six years later, on Dec. 7, 1972, he commanded Apollo 17, and despite everything else he did to earn his mark in history, this will be forever why we remember him. You can read about its exploits in many places; I suggest you pick up a copy of my friend Andy Chaikin’s book A Man on the Moon, which, in my opinion, is the single best written history of the Apollo program. Cernan (along with co-author Don Davis) wrote about this as well in his book The Last Man on the Moon.

About that mission …

At 05:40 GMT on Dec. 14, 1972, a week after he left Earth and after completing three successful lunar EVAs with his fellow crew member Jack Schmitt, Cernan stood on the surface of the Moon, preparing to go back up the ladder and get back inside the Lunar Module. Just before he did, he said:

I'm on the surface; and, as I take man's last step from the surface, back home for some time to come—but we believe not too long into the future—I'd like to just (say) what I believe history will record: that America's challenge of today has forged man's destiny of tomorrow. And, as we leave the Moon at Taurus–Littrow, we leave as we came and, God willing, as we shall return, with peace and hope for all mankind. Godspeed the crew of Apollo 17.

He then climbed aboard the LM, and in that moment became the last human to stand on the Moon.

For now.

Cernan’s family released this statement upon his death:

Even at the age of 82, Gene was passionate about sharing his desire to see the continued human exploration of space and encouraged our nation's leaders and young people to not let him remain the last man to walk on the Moon.

Cernan himself did not wish himself to hold this place in history and pushed for NASA to go back to the Moon. All these years later we still haven’t, but that will not stand. China and India have both said they want to send people to the Moon, and Russia has made similar claims.

NASA has set its sights on Mars, but I still hope we go back to the Moon first, doing something similar to Gemini before Apollo: Use our more advanced technology to learn about how we can achieve human deep-space flight better, and most importantly, more sustainably. Apollo, as heroic and historic as it may have been, was, after all, a “flag and footprints” mission, designed to get there before the Soviets did. A race to the finish cannot be a long-term plan. We must commit to going back, and doing it to stay.

I remember the Apollo missions, barely. I was a child at the time. But I hope that within my lifetime I will see a wonderful thing: Another human stepping out of a lander and dropping down onto the surface, a puff of regolith dust arcing out ballistically from their boots in the airless environment.

And when this happens, we will update our references to Cmdr. Cernan, adding the words “… of the Apollo era” to his descriptor, “the last human to walk on the Moon.” At that moment he will become the last of the first, and, with our eyes open and our dedication firmly in place, there will never be another last.

Gene Cernan
Gene Cernan, 1934–2017.

NASA

*Correction, Jan. 17, 2017: I originally wrote that Cernan was the commander of Gemini 9A, but he was the pilot; Stafford was the commander.

Jan. 16 2017 8:45 AM

SpaceX Returns to Flight

Over the weekend—on Saturday—SpaceX launched a Falcon 9 into space, successfully completing its primary mission of deploying 10 Iridium communication satellites.

The secondary mission? To land the first stage booster on a drone ship in the Pacific. And that happened perfectly:

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How cool is that? What happened is that after boosting the second stage toward orbit, the first stage flipped around, performed an engine burn to slow down, flipped again, deployed the steerable grid fins, then (after much shorter burns of the main engine and some help with cold jets for attitude control) landed smack dab in the center of the drone ship Just Read the Instructions (the barges are named after sentient ships in the science-fiction novels of Iain M. Banks).* This was the first successful landing of a booster in the Pacific Ocean; an earlier attempt in January 2016 came close, but one of the landing legs failed to lock, the booster fell over after the soft landing, and then exploded (and you want to click that link; the video is really something).

This mission was important, marking the return-to-flight status for SpaceX after an explosion during fueling of a Falcon 9 in September. SpaceX traced the cause of that to a liquid helium tank in the second stage.

As my colleague Eric Berger at Ars Technica writes, the helium tanks are mounted inside the liquid oxygen tanks; as the oxygen is used up during launch, helium is released to maintain pressure in the tank. However, the liner wrapping of the helium tanks under a carbon fiber coating appears to have buckled in the extreme cold environment, letting oxygen in between the coating and the tank itself. Liquid oxygen isn’t flammable, but when it contacted the much colder liquid helium tank, it froze and combusted, causing the explosion. To prevent this from happening again, they’re returning to their “flight proven configuration” of the tanks for now (an older setup with warmer helium), and in the future will change the fiber wrapping to prevent it from buckling.

Berger also has an interesting article about SpaceX’s finances; it lost quite a bit of money ($250+ million) in the 2015 accident where a rocket was lost on its way to the space station but still has ambitious plans for more than two dozen launches this year alone. That includes tests for the first crewed flight, and the first flight of the Falcon Heavy, its next-generation rocket that will be the most powerful rocket in the world … though Blue Origin has its goals of building some pretty big boosters as well.

This should be a pretty exciting year for space exploration. Let’s hope it all goes well. In the meantime, congratulations to SpaceX for getting the planet underneath them once again.

*Correction, Jan. 16, 2017: I originally had embedded the wrong video, it was from an earlier launch. Also, I said the carbon fiber wrapping had buckled, when it was the aluminum liner under the carbon fiber that buckled.

Jan. 13 2017 8:45 AM

Give Me Your Tired, Your Poor, Your Huddled High-Mass Stars …

Let me tell you something funny about that picture above.

Somewhere between 7,000 and 10,000 light-years away—estimates vary—lies the huge nebula NGC 3576. It’s very roughly 75 light-years across, making it one of the bigger star forming regions in the galaxy.

And that’s just the visible part of it. It appears to be part of a larger complex of dark, dense gas as well, which is pretty typical of such objects. But the part we do see is impressive enough: It has 10,000 times the mass of the Sun just in hot gas, and glows at a fierce 10 million times the brightness of the Sun as well. Many hundreds of stars are in the process of being born there, making it a fairly fecund stellar nursery.

Jan. 12 2017 8:45 AM

The Clouds of Andromeda

The image above is as baffling as it is gorgeous.

First, kudos go to my pal Rogelio Bernal Andreo, who took this magnificent shot. It shows the Andromeda galaxy, the closest big spiral galaxy to our own, and in fact the other big member of our neighborhood galaxy minicluster called the Local Group. At 2.5 million light-years away, it’s bright enough to see with the naked eye from moderately dark sites and shows quite a bit of detail even through small telescopes.

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Rogelio’s image is unusual. First of all, it shows a huge area of the sky; Andromeda is several times the apparent size of the full Moon in the sky (see here for a comparison). Hold up your hand, and fold in your pinky and thumb; the width and length of your three middle fingers extended at arm’s length would be about the same area of sky as the photo.

The image is a composite of “natural” color imaging using red, green, and blue filters to mimic what we’d see with our eyes, together with a “luminance” or white-light image, taken with no filter. That adds detail and depth to the image; together astrophotographers call it an LRGB image.

But there’s more. He also took many hours worth of observations using a filter that lets through a very specific wavelength, or color, of light. This red light, called Hα (literally, “H alpha”) is emitted by warm hydrogen gas. Since hydrogen is so common throughout the Universe, an Hα filter is very useful; you can use it to accentuate nebulae and galaxies.

The red clouds in the image are hydrogen nebulae. They’re extremely faint; Rogelio had to work very hard to make them visible above the background light of the sky. In the photo their brightness has been magnified by a substantial amount, so the image isn’t “natural” in that sense; if Andromeda had been scaled on the same brightness range as the clouds, the galaxy would be vastly overexposed, a huge white blob blotting out everything around it.

So the image isn’t really what your eyes would see through a telescope but has been adjusted to show these two very different views simultaneously. Still, it’s beautiful for sure … and very odd.

The big question is, what are those clouds?

On his website (and in a follow-up on his Facebook page), Rogelio describes his observations, their history, and his research into the glowing clouds. He points out he loves chasing faint, diffuse clouds. Called galactic cirrus (or the fancier Integrated Flux Nebulae), these are generally very thin streamers of dust—grains of silicates or long carbon molecules—strewn throughout space inside our galaxy. They’re exceedingly faint, and difficult to image. But if the dust is warm, it can glow in infrared. So Rogelio checked professional observatory infrared images of that area in the sky, but the clouds seen in them don’t fit well to what he observed. That seems to rule out galactic cirrus.

However, he did see them, barely, in a pair of surveys that mapped the sky in Hα. He shows this on his page, and looking at them I’m confident these clouds are real, and consist of glowing hydrogen.

Rogelio also argues, and I agree, that the clouds aren’t physically associated with the Andromeda galaxy. At that distance those clouds would have to be huge, tens of thousands of light-years across, far too large to make any sense. We do see clouds of gas this big in the Universe, but generally speaking they don’t display the structure in the image. For example, that one above the galaxy near the top center shows a long, flat, bright edge. Features like that are common in smaller gas clouds a few light-years in size. You get them when an expanding (or rapidly moving) gas cloud hits material outside it. The gas piles up, forms a sharp edge, and gets denser and brighter. But something like that would be highly unusual, to say the very least, in a cloud of galactic size.

So clearly these are gas clouds inside our own Milky Way, and we’re looking through and past them to the much more distant Andromeda galaxy. But that’s still odd. Nebulae like that are usually heated up and lit by nearby massive stars. The stars emit ultraviolet light, which pumps energy into the gas, and it responds by glowing like a neon sign (literally). But I don’t see any stars close by that could do that.

So why are they glowing?

Given the lack of nearby luminous stars, my first guess was that they are colliding with lower density gas around them. That would explain the one cloud with the sharp edge, but the others are even more diffuse, so I’m not sure that explanation works for them.

I have another idea. Perhaps there’s enough ambient ultraviolet light from massive stars spread out in space that, combined, they can cause these clouds to softly glow. This would be a sort of background UV light, very faint, but enough to trigger the nebulae into emitting Hα light. While that’s a guess, it seems plausible … and I don’t see anything else that makes much sense.

Let me say here that I love this. Andromeda is one of the best studied objects in the entire sky, yet here are objects in the same field of view that have essentially escaped notice all this time. That’s understandable; Andromeda is so bright that faint clouds are ridiculously hard to see, but our technology and techniques are getting so good that the previously hidden is becoming revealed. And on top of that, it also took the dedication of someone like Rogelio to pursue this.

The next step, I should think, is to find a research astronomer who can take an interest in this and get even deeper images and take spectra of these clouds (to determine their chemical composition as well as motion, which can help nail down their distance). There are lots of fascinating questions to answer here. How common are these clouds? How old are they—are they recently cast off by dying stars, or primordial, dating back to when the galaxy was young? Are they everywhere in the sky, or do they tend to be clumped near the galactic plane? And to me, the most interesting question of all: What’s lighting them up?

They’re certainly lighting me up. I hope we can find out more about these elusive beasts soon.

Jan. 11 2017 10:53 AM

Talk Nerdy: Anti-Science, Trump, and Why I Hope Science Will Help Save the World

Funny how things work out.

I had already drafted an article about an interview I did over the weekend with my friend Cara Santa Maria for her Talk Nerdy podcast. We spent a lot of time talking about critical thinking, science, and Donald Trump.

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And then, as I was editing that article, a whole passel of revelations came out about Trump. By now you’ve probably heard about the intelligence reports reporting ties between Russia and Trump's campaign to manipulate the presidential election.

Almost lost in all the noise over that was that Trump had a meeting with Robert F. Kennedy Jr., purportedly asking him to be on a panel on the safety of vaccines. I have written about RFK Jr.’s crackpot anti-vaccine stance many times (see, in order, this article, then the follow-up, and then a third one). His views are wrong, anti-scientific, and downright dangerous.

All of which makes this interview all that much more timely and, if I may say so, important. Please give it a listen.

Cara had me on her podcast back in 2015, and asked me to be on again because she happened to see my name in the credits of the movie Arrival, and wanted to know what my involvement was (spoiler: I made some minor comments on the script before it was finalized). The first half of the podcast is about that as well as the influence of science in movies and TV.

But then we spent quite a bit of time talking about Trump and his predilection for anti-science. As an easy example, his incoming Vice President Mike Pence and Cabinet picks Rick Perry and Ben Carson are all young-Earth creationists. Trump’s nominees are all basically the worst people a rational person would pick for those positions.

And while you might argue that someone being a creationist doesn’t disqualify them from being secretary of energy, for example, it does show Trump’s egregious propensity to actively seek out people who deny science for positions of power. The meeting with RFK Jr. just confirms that.

So. The big question is, is there hope?

Yes, I think there is. And it may come from an unlikely direction.

Cara ends every podcast asking her guest two questions: What is your biggest fear for the future, and what is your biggest hope?

My answer this time was similar to the last time I was on her show: climate change and science, respectively. But I generalized it a bit this time.

Certainly climate change on its own is terrifying; I’ve written many times how it’s the single greatest threat we as a species face right now, and how denying it is a threat to our national security. But it’s more than that. The denial of human-induced climate change is just one symptom of the much larger suppression and active antagonism toward science, especially with the incoming Trump administration.

Yet I still have hope. Why? Because there are tens of millions, hundreds of millions, of Americans who are still reality-based. The majority of us understand that climate change is human-caused and a real threat. That means science can still prevail over politics and personal ideology.

In his farewell speech Tuesday night, President Obama said this:

Politics is a battle of ideas; in the course of a healthy debate, we’ll prioritize different goals, and the different means of reaching them. But without some common baseline of facts; without a willingness to admit new information, and concede that your opponent is making a fair point, and that science and reason matter, we’ll keep talking past each other, making common ground and compromise impossible.

Science is a critical piece of that common ground. We need people to be more comfortable with science, which means exposing more of them to it. Even more importantly they need to understand scientific thinking: being critical of sources, data, and conclusions; questioning the process all along the way; and looking for personal biases that might lead to incorrect conclusions.

And that’s why I answered Cara’s last question the way I did. One way to get people to see science is to get it into all aspects of modern culture. Two of the biggest influences on society are TV and movies, and that’s why I’m so happy to see science and scientists being portrayed better in those media. It may seem fatuous, but I contend that it’s an excellent place to start. Like it or not, people, especially younger ones, consume a lot of entertainment. If we show them stories where scientists are just like them, where science is important, where it’s fun, where it can help, where it can save us all, then we still have a chance here.

We have a long, long way to go, and the next two to four years will be trying indeed. But we can do this. Make your voice heard, and make it a voice for science. As long as there are people who would tear down the fabric of reality, there will be those of us who will give their all to defend it.

Jan. 10 2017 8:45 AM

My God. It’s Full of Black Holes.

The image above doesn’t look like much at a glance, does it?

Look again. What you’re seeing are thousands of black holes. Thousands.

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That image is a part of the Chandra Deep Field South, the result of a series of very long exposures of one small section of the sky using the space-based Chandra X-Ray Observatory. Astronomers combined images taken over the 18-year period from 1999 to 2016, creating a stacked image that’s the equivalent of a single 7,016,500 second exposure. That’s more than 81 days.

So yeah, it’s a deep image. The entire Deep Field image covers roughly the area of the full Moon on the sky using multiple pointings of the telescope. The center of the field has the most observations and is therefore the most sensitive; the image above shows that inner portion of it.

Everything you see in that image is a source of high-energy X-rays—a form of light like the kind we see but with far, far higher energy. Each dot represents the X-rays from an entire galaxy, some more than 12 billion light-years away! The light we see from those most distant galaxies left them when the Universe itself was only a little more than 1 billion years old.

Only very powerful astronomical objects can generate strong X-ray emission, and the X-rays from the galaxies in the Deep Field are coming from one or both of two very luminous sources: high-mass X-ray binary stars and supermassive black holes.

high mass X-ray binary art
Artist depiction of a high-mass star losing material to a companion black hole.

ESA

The binaries are pretty cool. Many very massive stars are born in pairs, which orbit each other. After a short time, one of them can explode as a supernova, and its core collapses to become an ultra-compact neutron star or a black hole. This compact object can feed off material from the “normal” star; as that stuff falls down into the tiny companion’s ferocious gravity, it can heat up to millions of degrees and emit X-rays.

One important part is that these binary systems are young. These stars are so massive they use up their nuclear fuel in the blink of a cosmic eye, perhaps a few million years. That’s critical, because these stars are born in gigantic gas clouds that form lots of stars. By adding up all the X-ray emission we see from high-mass binaries, we can calculate how many there are in a galaxy, and from that extrapolate how many stars are being born in total. That tells us a lot about the conditions in galaxies, and in really distant galaxies we can then see what they were like when they were very young.

Our galaxy was very young once, but we only see it now, after it’s more than 10 billion years old. By looking at distant galaxies we can better understand how our own was formed.

But that’s only half the story. In the center of every big galaxy today we think there lurks a supermassive black hole, a beast with millions or even billions of times the mass of the Sun. That’s still small compared with the host galaxy (the Milky Way has a mass of hundreds of billions of times the Sun), but that supermassive black hole is important. We’ve found that the mass of the central supermassive black hole in the galaxy is correlated with galactic characteristics like the total mass, luminosity (how much energy it emits), and rotation. These are hard to measure directly in distant galaxies, so by looking at their central black holes we can learn more about the galaxies themselves.

The Milky Way’s black hole isn’t currently feeding, so it’s relatively quiet. But in other galaxies the black holes are eating, and when they do that, matter piles up in a disk and can reach temperatures of millions of degrees due to friction and other forces. That’s hot enough to blast out X-rays, which is why we can see them in the Chandra image.

black hole
Artwork: A disk of material around a black hole heats up and emits X-rays, as well as a beam of energy due to twisted magnetic fields.

NASA/JPL-Caltech

That’s why this deep observation is so important! By examining the X-rays from each source we learn a lot about the galaxy that emits them, far more than simply how much X-ray light they’re blasting out.

Remarkably, astronomers were able to see X-rays from galaxies more than 12.5 billion light-years away, the farthest ever reliably detected. Also, they did not see X-rays from galaxies even a bit farther than that (about 12.6 billion light-years), suggesting either those sources are too faint, or that it was around that time (1.2 billion years after the birth of the Universe) that these sources started turning on, or that they are so obscured by dust in the host galaxy we can’t see them.

The scientists estimate that roughly 70 percent of the objects in that image are supermassive black holes, and in the whole image there are about 5,000 sources. Imagine: Thousands of black holes in just that one tiny part of the sky! Extrapolating to the whole sky, astronomers estimate there must be more than 1 billion supermassive black holes out in the deep Universe that Chandra could see. A billion.

That’s a lot of black holes. And it’s actually only a tiny percentage of what’s out there; there are hundreds of billions or even trillions of galaxies in the Universe. Each may have its own central black hole, but we just don’t see them (because they’re quiet, or feeding but still too faint to see at large distances).

And that’s just the supermassive black holes. Ones with lower mass, formed when stars explode, probably number in the many millions per galaxy. Extrapolating that means there are quadrillions of black holes in the visible Universe. More.

Holy cow. The good news is they’re far away, and don’t pose any sort of threat to us. And in reality, instead of being scared, you should be thankful: Galaxies and black holes form together, so the Milky Way being here the way it is today is due to its central supermassive black hole. And massive stars exploding seed the Universe with heavy elements like iron, calcium, and other ingredients necessary for life to form. They may leave behind a black hole after the supernova, but they also made it possible for us to be here at all.

It’s a weird Universe indeed where we owe our existence to these cosmic devourers. But, literally, that’s where we are. And that’s why I love this Chandra image and research so much. It tells us so much about ourselves and how we came to be.

Jan. 9 2017 8:45 AM

A Distant View of Home

When I saw the image above, the hair on the back of my neck stood up. Recognize them? Those are the Earth and Moon, as seen from Mars.

That image was taken by the phenomenal HiRISE camera on board the Mars Reconnaissance Orbiter, which was more than 200 million kilometers from Earth at the time. It’s actually a composite of a few separate images, processed to show the relative size and position of our planet and its moon.

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HiRISE normally points down to take amazing images of the surface of Mars; it can resolve objects less than a meter across! But it sometimes is pointed at Earth to take calibration images; Earth has known characteristics like color and reflectance that make it a nice test subject for the camera. The image above is composed of ones taken in near-infrared, red, and blue/green, and that’s displayed as red, green, and blue here. Vegetation is highly reflective in near IR, so continents look red; Australia is in the center and Southeast Asia to the upper left. Antarctica is the bright white patch to the lower left.

Also, the contrast has been changed; the Earth is on average more than three times as reflective as the Moon. At the contrast scale Earth is displayed at, the Moon would be almost black, so the brightness of the Moon image has been increased. In this image, you can clearly see features on the Moon, the darker basaltic scars from ancient giant impacts.

Mars and Earth posiitons
The physical locations of Mars, Earth, and the Sun when the image was taken: From Mars, Earth appeared half-lit.

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This image was taken on Nov. 20, 2016. At the time, the Earth, Sun, and Mars made an isosceles triangle, with Mars at the narrow angle. From Mars, Earth appeared half-lit, at “first quarter,” if you will. From Earth, the Moon was at third quarter, half lit by the Sun and approaching its new phase. That puts the Moon on the far side of Earth as seen from Mars, about 300,000 kilometers farther away. But that’s a drop in the 200 million kilometer bucket, so for all intents and purposes they’re at the same distance. This means the scale of this is right; the Moon is ¼ the size of Earth.

It’s amazing to think that’s home, that we can see our planet and its attendant satellite from so far away. We’ve seen it from farther, of course, including the famous Voyager 1 Pale Blue Dot image (the Moon is invisible in that one), and others taken by the Cassini spacecraft orbiting Saturn and MESSENGER at Mercury (though that last one, I think, was from closer). But in this case, it’s the tantalizing detail that makes it so eerie; there’s just enough there to remind us of home, but not quite enough to make it easy.

Would you have known that was Australia without it having been pointed out? I’m not sure I would have.

It makes me think that there will come a day, perhaps not too long in the future, when we will have an image like this, but it won’t be of the Earth and Moon, or any planet in our solar system. It’ll be an exoplanet, an alien world orbiting an alien star. When that happens, will we see fuzzy continents, pixelated oceans, or a blobby moon?

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