The scale of things

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Time lapse: stunning Australian skies over a pathfinding array
Phil Plait | Bad Astronomy | 03OCT12 9:58 AM

In the Australian Outback, hundreds of kilometers from the noise and lights of any city, stand three dozen radio telescopes, each a dozen meters across. Working as a single unit, they patrol the skies looking at cosmic objects emitting low-energy light.

Photographer Alex Cherney visited this remote observatory and created a really lovely time lapse video of the telescopes at work:



The telescopes taken together are called the Australian Square Kilometre Array Pathfinder, or ASKAP. The Square Kilometer Array is a project currently underway in Australia and South Africa to create the largest radio telescope in the world. ASKAP is a testbed for SKA, used to check out various technology and techniques that SKA will employ. But ASKAP is a full-fledged observatory in its own right, and will add to our arsenal of instruments peering into deep space.

The video is beautiful, and as always when I watch these from Australia, I’m overwhelmed by the southern skies. The stars are different than the ones we see up here, but it’s not just that. What always gets me is how, from my own experience, the motion is backwards! When I want to see Orion from my home I face south; it rises on my left, moving to the upper right. But in Oz, it rises on the right and moves to the left! Things are flipped when you’re upside-down relative to what you’re used to… and that’s driven home by seeing Orion standing on his head!

And the Milky Way. Wow. The center of our spiral galaxy never gets very high from Boulder, but in Australia it passes well overhead, freed from the haze and murk of the horizon. Blazing gloriously, in it you can pick out nebulae, dust clouds, and more as you gaze over tens of thousands of light years of interstellar space. Alpha and Beta Centauri, the Coal Sack, the Large Magellanic Cloud… all of these are easy to spot to the trained eye.

Every time I’m at a dark site and I look out into the sky, I soak up its beauty and am awed by it. But more than that, I know what I’m looking at. Knowledge adds another dimension to what you see, a profound sense of connection and understanding that warms the brain and the heart.

Learn everything you can. Not just about astronomy, but everything. Don’t be afraid of knowledge; revel in it. Far from taking away any beauty or art from the world, it makes life richer, and far, far more wonderful.

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Amateur planet hunters find a world with a four star rating
Phil Plait | Bad Astronomy | 15OCT12 9:30 AM

A new exoplanet – a planet outside our own solar system – has been found, and it’s pretty cool for two reasons: it was found by amateur planet hunters, and it’s in a four-star system!

OK, first, the planet: called PH-1, it’s bigger than Earth, about six times our radius, or about half the diameter of Jupiter. The mass isn’t well known, but may be as high as 170 times our own mass, though far more likely it’s closer to 20 – 50 times our mass. That makes it closer physically to Uranus and Saturn than Earth, so it’s likely a gas giant. It’s also hot, with a probable cloud-top temperature of 400+ Celsius (800+° F). Even if it has Earth-sized moons they’re likely to be too hot to be hospitable. And since it’s 5000 light years away, we’re not headed there any time soon, anyway.

But the more interesting thing about this planet is its host stars: PJK-1 orbits a binary star, two stars that orbit each other (like Tatooine, if you like). Six other planets are known to orbit binary stars, but PH-1 is even cooler: the binary star is itself orbited by another binary pair much farther out, making it the first planet found in a four-star system.

So we have two stars orbiting each other, orbited by a planet, and also orbited by two other stars which orbit each other. Yegads.

But it gets better yet. This planet was not found by professional astronomers! It was discovered by two amateurs who participate in the Planet Hunters program. This project was started by astronomers using the orbiting Kepler Observatory, designed to stare at 100,000 stars and look for dips in light from them as any potential planets orbiting them block their light. These transits show up in graphs of the stars’ brightnesses, and actually our human eyes and brain are pretty good at picking them out. Planet Hunters puts Kepler data online for anyone to go in and poke around.

The two citizen scientists, Kian Jek and Robert Gagliano, are listed as authors on the scientific paper recently published. I love this: the digital nature of these data make it far, far easier to analyze the science than it was in the past, and also easier to get the data out to people. Because of this, we have an explosive growth in these kinds of projects. Planet Hunters is great, but then so is Galaxy Zoo, Moon Mappers, Ice Hunters, and so many others. You can find several of these collected at the CosmoQuest website.

And a word about this new planet; this isn’t the first planet found by Planet Hunters, but it’s the first ever found in a quaternary star system. In the image here, the central binary is the big blob in the middle, and the second pair the elongated double-blob to the lower left. The planet is far too close to the middle stars to be seen here – its orbit is smaller than Earth’s around the Sun, far smaller than a pixel in this image at that distance.

The central binary is made up of a bluish star hotter and brighter than the Sun, and one that’s cooler, fainter, and redder. The second binary is made of one star much like the Sun, and another dinky red one. Their distance from the planet – about 150 billion kilometers – means they’d both still be very bright, with the brighter of the two almost as bright as the full Moon as seen from Earth. What a sight that would be! The second star would be hard to pick out in the glare of the other, but with binoculars you could spot it.

Not that anyone could, since the planet is hot enough to melt tin and assuming it had a solid surface to start with. Still though, it’s not hard to imagine a smaller planet orbiting that binary farther out, in a cooler, more life-friendly position. And we know such a planet exists; Kepler recently revealed a planet orbiting a binary star at the right spot to have liquid water as well. Like PH-1, that planet is probably a gas giant, but it might have big moons…

And this shows us once again that nature just loves to make planets, even ones in really weird places that at first may seem inhospitable for planet formation. But there it is.

Every time we find a strange planet like this, it fills me with hope that the ultimate goal of this work is close: finding an Earth-sized planet in the habitable zone of another star. We’re getting closer every day to that announcement, I think. In fact, I strongly suspect that planet is already sitting in the Kepler data, faint and hard to tease out, but just waiting to be found.

Go sign up for Planet Hunters. Maybe you’ll be the one to find it.

Image credits: Haven Giguere/Yale; Keck Observatory/Megan E. Schwamb et al.

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ALPHA CENTAURI HAS A PLANET! | Phil Plait
Bad Astronomy | 16OCT12 4:45 PM

Huge news! Astronomers have announced they have found a planet orbiting one of the stars making up the most famous star in the sky: Alpha Centauri, the closest star system to our own! At 4.3 light years distant, this is far and away the closest exoplanet known… and of course, it has to be.



Alpha Centauri is triple-star system, composed of a binary star, two stars much like the Sun – one slightly larger and hotter, called Alpha Centauri A, and the other slightly smaller and cooler, called Alpha Centauri B – orbited themselves by a red dwarf (called Proxima Centauri) much farther out.

The planet orbits close in to Alpha Cen B, and is technically called Alpha Centauri Bb – planets have lower case letters assigned to them, starting at b. Its mass is only 1.13 times the Earth’s mass, making this one of the lower mass planets yet found! But don’t get your hopes up of visiting it – its period is only 3.24 days, meaning it must be only about 6 million kilometers (less than 4 million miles) from its star. Even though Alpha Cen B is a bit cooler than the Sun, this still means the planet is baking hot, far too hot to sustain any kind of life as we know it, or even liquid water.

Still. Holy crap! A planet for Alpha Cen. Wow.

The reason this is a big deal is twofold. For one, Alpha Cen is the closest star system in the sky. Because of that it’s very bright, and well studied. Planets searches have looked there for decades, and in fact for a while it was thought the dinky red dwarf Proxima might have a planet. Those earlier findings have been shown to be wrong, though. If it has a planet, it’s too small or too far out from the star (or both) to detect it easily.

The other reason this is important is that the signal from the planet is incredibly weak. It was found through its gravity. As it orbits Alpha Cen B, the planet tugs on the star, like two children holding hands and swinging each other around. This sets up a very small but detectable Doppler shift in the starlight. The more massive the planet is, the harder it tugs on the star, and the bigger the signal (making it easier to detect). Also, the closer in a planet is, the larger the signal is… and you get the added benefit of a short orbital period, so you don’t have to observe as long to see the cycle of the Doppler shift.

In this case, the planet is low mass but very close in. The Doppler shift in the starlight amounts to a mere half meter per second – slower than walking speed! When I read that I was stunned; that low of a signal is incredibly hard to detect. Heck, the star’s rotation is three times that big. But looking at the paper, it’s pretty convincing. They did a fantastic job teasing that out of the noise.

The graph displayed shows the effect of the planet on the star. RV means “radial velocity”, the speed toward and away from us as the star gets tugged by the planet. The x-axis is time, measured in units of the period of the planet (in other words, where it reads as 1 that means 3.24 days). The dots look like they’re just scattered around, but when you average them together – say, taking all the dots in a one hour time period – you get the red dots shown (the vertical lines are the error bars). The signal then pops right out, and you can see the tell-tale sine wave of a planet pulling its star.

Amazing.

This is incredibly exciting to me! A few years ago, when I worked on Hubble, I looked into using it to search for planets around Alpha Cen. I worked out some simulations to see if we could detect anything, and at best we could see a Jupiter-sized planet orbiting far enough out that its faint light wouldn’t be blasted out by the star itself. It was deemed too risky an observation (too low a chance of payoff) so we didn’t get time on the telescope to make it. We’d never have seen this planet anyway; looking for a planet reflecting its star’s light is very different than looking for the Doppler shift. Obviously!

Also, c’mon. This is Alpha Centauri! Famed and fabled in a thousand science fiction stories. It’s where the Robinson family was supposed to go in “Lost in Space”. It’s where Zefram Cochrane lived in “Star Trek”. It’s where the Fithp came from in Footfall. Because the system is bright and close, and the stars so close to being like our own Sun, they’re an obvious place to put aliens. Plus, you get the exotic locale of a binary star plus the red dwarf thrown in on top. It’s perfect!

So I, and a lot of people like me, grew up hoping against hope we’d find a planet around one of these stars someday.

And here we are.

My very, very sincere and gracious thanks to the team that made these observations. Even if this planet is cooked to within an inch of its life, this is still literally a fantasy come true.

And it reinforces my own thinking that we are very close to finding a planet with the same mass as Earth at just the right distance from its star to have liquid water, and therefore, potentially life. We are finding planets the right mass but at the wrong place, and at the right place but with the wrong mass.

But we’re zeroing in on Terra Nova, folks, and statistically speaking there should be millions of them in the galaxy. It’s only a matter of time before we find the first one.

Image credits: ESO/L. Calçada; ESO/Digitized Sky Survey 2 (Davide De Martin)

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The raw power of the Sun | Phil Plait
Bad Astronomy | 19OCT12

Early this morning, while you were sleeping, or working, or reading Twitter, the Sun had different plans: it erupted, blasting an immense tower of plasma upward off its surface:



This image was taken by NASA’s Solar Dynamic Observatory at 08:15 UTC this morning. The scale of it is staggering. The Sun is 1.4 million kilometers across – 860,000 miles – so this plume was at least 400,000 km long. Going back through the images, it had been brewing for hours, but really got its start around 05:00, meaning it erupted upwards at well over 100,000 km per hour. That’s fast enough to cross the face of our planet in less than 8 minutes.

By the way, did I mention the total mass of such a prominence is billions of tons? And the Sun does this kind of thing all the time.

We’re in no real danger from an eruption like this, especially this one: it’s on the Sun’s limb, so it was heading away from us. But these events can trigger storms like coronal mass ejections, where billions of tons of material is sent hurtling across the solar system at mind-crushing speeds. Those can interact with our magnetic field, creating havoc with our satellites and causing power outages.

But that’s why we keep an eye – many eyes, in fact – on our Sun. Never forget: our Sun is a star, with all the power and fury that implies. The better we understand it, the better we can protect ourselves from it when it gets angry.

Image credit: NASA/SDO. Tip o’ the welder’s glasses to Camilla SDO.

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The image below shows why
I’ve come to love astronomy.

Some highlights are mine.
Links in original.

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From Here To Infinity | Phil Plait
Bad Astronomy | 22OCT12

Looking up into the night sky, it seems like you can see forever. If you use binoculars or a telescope that feeling is, literally, magnified – you can see thousands, millions of stars.

But what you’re seeing is barely scratching the depths of the Universe. You’re looking out a few thousand light years into a galaxy a hundred thousand light years across, in a Universe where we can see distant galaxies over 10 billion light years away.

We build bigger telescopes so we can see those far-flung objects, and we even put them in space so our bothersome atmosphere doesn’t interfere with the view. The most famous is of course the Hubble Space Telescope. It’s hard to describe just how much of an impact this Grande Dame of astronomy has had on our perception of the Universe… though looking into the Hubble Deep Fields, you get a glimmer of it. In 1995, Hubble stared at one spot in space for over 140 hours, creating the first Deep Field. It revealed thousands of galaxies at tremendous distance, showing us that the sky is filled with galaxies.

The region of the sky for the first Deep Field was chosen because it was nearly devoid of stars and known galaxies, objects that would interfere with their more distant brethren. But what does that field look like from the ground? Astronomer Detlef Hartmann decided to tackle this question, and has done us all a favor by showing us. Using a 44 cm (17”) telescope he built himself, he took an incredible 247 five-minute images to create this extraordinary picture with a total of 20 hours of exposure… and then lets it morph into the actual Hubble Deep Field to compare them:


^ [The image is an animated GIF that weighs in at nearly 6 Mb, so it may take a while to load. I urge patience; it’s worth it. Click to edwinenate.]

Holy. Wow.

Let me be clear: Detlef’s image is amazing. It’s a tremendous effort by an “amateur”*, and shows dozens of the galaxies (and the same scattered handful of stars) in the Hubble image. It’s an amazing achievement. A bigger telescope would show more galaxies, of course, and resolve them more clearly, but even the biggest telescope located on the surface of our planet needs to peer through the soup of air above it, which dims the faintest galaxies into obscurity. You need to get above our atmosphere to see the cosmos as clearly as possible.

And when you do, look at what Hubble shows us. That tiny region of the sky – easily blocked by a grain of sand held at arm’s length – contains thousands of galaxies, each a sprawling city of billions of stars. It represents a relatively random part of the sky, so you can expect to see something like it no matter where you point a telescope… and that picture shows just one 24-millionth of the entire sky.

The implication is clear: there are hundreds of billions of galaxies in our Universe. That in turn means there are sextillions of stars, each a Sun, and many, if not most, circled by a retinue of planets.

It’s the most ironic aspect of any science I know: it crushes my sense of scale and ego into dust, but also fills me with wonder and amazement that we can know such things, and be a part of it.

As is so often the case in science, you don’t know what you’ll get when you build a new instrument. You build it for one reason or for many, but later on new applications arise, new ways to use it. And sometimes, years down the road, it’s utilized in a just such a new way which profoundly changes how you see the Universe, how you see yourself and your place in it, and in a way you had may have only had an inkling of when you started out. The Hubble Deep Fields are perfect examples of this.

We knew intellectually the Universe was deep, and our place in it infinitesimal yet rare and beautiful. But Hubble showed that to us.

Image credits: R. Williams (STScI), the Hubble Deep Field Team and NASA; Detlef Hartmann. My deep thanks to Salvatore Iovene (who hosts AstroBin where Detlef’s image is displayed) for letting me know about this amazing work.

* Oh, that word. Detlef built his own ‘scope, took hundreds of these images, then combined them in a painstaking and difficult process that probably took him many, many hours. The word “amateur” has many connotations, but as usual here when I use it, I simply mean someone who is not a career astronomer. Detlef clearly has it going on.

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Looking up to Saturn | Phil Plait
Bad Astronomy | 30OCT12, 7:00 AM

Just in case you’ve forgotten how brain-destroyingly big Saturn is:

This shot of the ringed wonder was taken by the Cassini spacecraft when it was well over 2 million kilometers from the planet. The spacecraft was south of the rings, looking “up” toward the north. The Sun is shining down on the rings from this perspective, so they look darker than you might expect, and the use of a near-infrared filter accentuates storms in the southern hemisphere cloudtops.

So why does this picture grind my mind to dust? Look at the the very top, near the center. Can you see that dot of light? You might need to click the picture to get the hi-res version to see it better; that’s how small it is.

Except it isn’t. That dot of light is Mimas, a moon of Saturn, and it’s 400 km – 250 miles – across! That’s roughly the size of the state of Missouri, and compared to Saturn it’s reduced to a mere pixel of light. And even then, Saturn’s rings are still too big to fit in this picture!

The scale of the solar system crushes me. And yet there we are, poking around and sticking our noses into it. We humans are pretty awesome.

Image credit: NASA/JPL-Caltech/Space Science Institute

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Fermi Measures Light from All the Stars That Have Ever Existed
Universe Today | Nancy Atkinson, 01NOV12


^ This plot shows the locations of 150 blazars (green dots) used in the a new by the Fermi Gamma-Ray Telescope. Credit: NASA/DOE/Fermi LAT Collaboration

All the light that has been produced by every star that has ever existed is still out there, but “seeing” it and measuring it precisely is extremely difficult. Now, astronomers using data from NASA’s Fermi Gamma-ray Space Telescope were able to look at distant blazars to help measure the background light from all the stars that are shining now and ever were. This enabled the most accurate measurement of starlight throughout the universe, which in turn helps establish limits on the total number of stars that have ever shone.

“The optical and ultraviolet light from stars continues to travel throughout the universe even after the stars cease to shine, and this creates a fossil radiation field we can explore using gamma rays from distant sources,” said lead scientist Marco Ajello from the Kavli Institute for Particle Astrophysics and Cosmology at Stanford University in California and the Space Sciences Laboratory at the University of California at Berkeley.

Their results also provide a stellar density in the cosmos of about 1.4 stars per 100 billion cubic light-years, which means the average distance between stars in the universe is about 4,150 light-years.

The total sum of starlight in the cosmos is called the extragalactic background light (EBL), and Ajello and his team investigated the EBL by studying gamma rays from 150 blazars, which are among the most energetic phenomena in the universe. They are galaxies powered by extremely energetic black holes: they have energies greater than 3 billion electron volts (GeV), or more than a billion times the energy of visible light.

The astronomers used four years of Fermi data on gamma rays with energies above 10 billion electron volts (GeV), and the Fermi Large Area Telescope (LAT) instrument is the first to detect more than 500 sources in this energy range.

To gamma rays, the EBL functions as a kind of cosmic fog, but Fermi measured the amount of gamma-ray absorption in blazar spectra produced by ultraviolet and visible starlight at three different epochs in the history of the universe.


^ Fermi measured the amount of gamma-ray absorption in blazar spectra produced by ultraviolet and visible starlight at three different epochs in the history of the universe. (Credit: NASA’s Goddard Space Flight Center)

“With more than a thousand detected so far, blazars are the most common sources detected by Fermi, but gamma rays at these energies are few and far between, which is why it took four years of data to make this analysis,” said team member Justin Finke, an astrophysicist at the Naval Research Laboratory in Washington.

Gamma rays produced in blazar jets travel across billions of light-years to Earth. During their journey, the gamma rays pass through an increasing fog of visible and ultraviolet light emitted by stars that formed throughout the history of the universe.

Occasionally, a gamma ray collides with starlight and transforms into a pair of particles — an electron and its antimatter counterpart, a positron. Once this occurs, the gamma ray light is lost. In effect, the process dampens the gamma ray signal in much the same way as fog dims a distant lighthouse.

From studies of nearby blazars, scientists have determined how many gamma rays should be emitted at different energies. More distant blazars show fewer gamma rays at higher energies — especially above 25 GeV — thanks to absorption by the cosmic fog.

The researchers then determined the average gamma-ray attenuation across three distance ranges: The closest group was from when the universe was 11.2 years old, a middle group of when the Universe was 8.6 billion years old, and the farthest group from when the Universe was 4.1 billion years old.


^ This animation tracks several gamma rays through space and time, from their emission in the jet of a distant blazar to their arrival in Fermi’s Large Area Telescope (LAT). During their journey, the number of randomly moving ultraviolet and optical photons (blue) increases as more and more stars are born in the universe. Eventually, one of the gamma rays encounters a photon of starlight and the gamma ray transforms into an electron and a positron. The remaining gamma-ray photons arrive at Fermi, interact with tungsten plates in the LAT, and produce the electrons and positrons whose paths through the detector allows astronomers to backtrack the gamma rays to their source.

From this measurement, the scientists were able to estimate the fog’s thickness.

“These results give you both an upper and lower limit on the amount of light in the Universe and the amount of stars that have formed,” said Finke during a press briefing today. “Previous estimates have only been an upper limit.”

And the upper and lower limits are very close to each other, said Volker Bromm, an astronomer at the University of Texas, Austin, who commented on the findings. “The Fermi result opens up the exciting possibility of constraining the earliest period of cosmic star formation, thus setting the stage for NASA’s James Webb Space Telescope,” he said. “In simple terms, Fermi is providing us with a shadow image of the first stars, whereas Webb will directly detect them.”

Measuring the extragalactic background light was one of the primary mission goals for Fermi, and Ajello said the findings are crucial for helping to answer a number of big questions in cosmology.

A paper describing the findings was published Thursday on Science Express.

Source: NASA

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A new old view of an old friend | Phil Plait
Bad Astronomy | 19JAN11

[Yes, that title is correct. Bear with me.]

I’ve seen the Orion Nebula approximately… well, how many times? Let’s see… um, carry the two… yeah, a gazillion times. You have too, probably, since to the unaided eye it appears as a star in the dagger hanging below Orion’s famous belt*. I’ve also seen it with binoculars and through telescopes ranging in size from dimestore junkers to a one-meter on a mountaintop. And yet, every new picture of it reveals something interesting… like this spectacular shot does:

First, some stats: this picture is a combination of five separate images from the red to the ultraviolet (that last colored violet, actually), including a filter that sees just the glow from warm hydrogen (colored red in this image). The telescope used was a 2.2 meter in Chile. The nebula is pretty big — the full Moon would just fit inside this image — so the detail on this is truly stunning.

The nebula is a vast cloud of gas, both atomic and molecular, and dust located about 1350 light years away. It’s one of the largest star forming factories in the Milky Way, and what you see here is well over 20 light years across.

For years I figured it was just a diffuse glowing thing in space, but it turns out to be more complicated than that. In reality, a lot of the nebula is actually a dark, dense molecular cloud — literally, composed of molecules like H2 (molecular hydrogen) and CO (carbon monoxide). This cloud is actually far, far larger than what you see in this image, perhaps 20 times the width! But it’s dark, so we don’t see it in visible light… and what we’re seeing in this picture is not really a free-floating gas cloud, but a cavity in the wall of the denser dark cloud.

Stars are being born inside that cloud. Some of them are very massive, hot, and bright. They blast out a fierce stellar wind, like the solar wind but far more powerful. They also emit a fierce flood of ultraviolet photons. Together, these two forces erode away at the material of the cloud, breaking apart the molecules into their constituent atoms, ionizing them, and causing them to glow. It so happens that some of these stars were born near the side of this cloud, so when they ate away the insides of the cloud it caused a blister in the side which burst open.

You can actually see that in this image! The bulk of the colorful nebula, from the upper left on down, is actually gas inside this cavity set aglow. The far wall is opaque and dark, so you don’t see it here. But you can get a sense of the bubble-like nature of the nebula.

I always get a bit of thrill when I see a picture that makes the concave nature of the nebula apparent. It’s not clear from some photographs, depending on the filters used, but I can see it in this one. And an interesting thing; these weren’t new observations! Igor Chekalin found several images of the nebula in the European Southern Observatory archives as part of their Hidden Treasures contest, and put them together to create this new image.

See? My title really was correct.

And oh, about that contest; amazingly, this image didn’t win. What did? An image of another nebula in Orion called M78… put together by Igor Chekalin!

Image credit: ESO and Igor Chekalin

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* My roommate in grad school questioned the taxonomy of it being a “dagger”, ifyouknowwhatImean winkwinknudgenudge saynomore.

POST 2888

[Luther Blissett]

...

a bit of perspective

...

For anyone who suffered from Alice in Wonderland Syndrome as a kid, this hits the nail right on the head.

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Luther, this image might not
depict what you’ve had in mind,
although it’s one of my favorites
with regard to perspective.

POST 2893

[Luther Blissett]

Auditory hallucinations do accompany the syndrome, and did so in my case. That is, again, a fair visual representation. As long as what that mouth is screaming is utterly gobbledygook.

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Auditory hallucinations do accompany the syndrome, and did so in my case. That is, again, a fair visual representation. As long as what that mouth is screaming is utterly gobbledygook.

I was thinking two ideas when I remembered that image, Luther. The first was the mention by you of the Alice syndrome, which just today I read it as some things appearing smaller or larger than normal relative to others, and there we are hanging with the scale of things.

The other idea was using the image with Music as torture/Music as weapon against defenseless ears, and in that context, I imagined screaming. That image could be used for different contexts, like when I’ve experienced surreal moments three or four times in my life during which my thinking and tasks were slowed or stopped until that veil faded. Then, I guess, afterward, the silent screen scream would have been appropriate .

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Getting closer: Super-Earth found in a star’s habitable zone | Phil Plait
Bad Astronomy | 08NOV12

Well now, this is an interesting discovery: astronomers have found what looks like a “super-Earth” – a planet more massive than Earth but still smaller than a gas giant – orbiting a nearby star at the right distance to have liquid water on it! Given that, it might – might – be Earthlike.



This is pretty cool news. We’ve found planets like this before, but not very many! And it gets niftier: the planet has at least five siblings, all of which orbit its star closer than it does.

Now let me be clear: this is a planet candidate; it has not yet been confirmed. Reading the journal paper (PDF), though, the data look pretty good. It may yet turn out not to be real, but for the purpose of this blog post I’ll just put this caveat here, call it a planet from here on out, and fairly warned be ye, says I.

The star is called HD 40307, and it’s a bit over 40 light years away (pretty close in galactic standards, but I wouldn’t want to walk there). It’s a K2.5 dwarf, which means it’s cooler, dimmer, and smaller than the Sun, but not by much. In other words, it’s reasonably Sun-like. By coincidence, it appears to be about the age as the Sun, too: 4.5 billion years. It was observed using HARPS, the High Accuracy Radial Velocity Planet Searcher (I know, it should be HARVPS, but that’s hard to pronounce). This is an extremely sensitive instrument that looks for changes in the starlight as a planet (or planets) orbits a star. The gravity of the star causes the planet to orbit it, but the planet has gravity too. As it circles the star, the star makes a littler circle too (I like to think of it as two kids, one bigger than the other, clasping hands and swinging each other around; the lighter kid makes a big circle and the bigger kid makes a smaller circle). As the star makes its circle, half the time it’s approaching us and half the time it’s receding. This means its light is Doppler shifted, the same effect that makes a motorcycle engine drop in pitch as it passes you.

Massive planets tug on their star harder, so they’re easier to find this way. Also, a planet closer in has a shorter orbit, so you don’t have to look as long to find it. But in the end, by measuring just how the star is Doppler shifted, you can get the mass and orbital period of the planet. Or planets.

In this case, HD 40307 was originally observed a little while back by HARPS, and three planets were found. But the data are public, so a team of astronomers grabbed it and used a more sensitive method to extract any planetary signatures from the data. They found the three previously-seen planets easily enough, but also found three more! One of them is from a planet that has (at least) seven times the mass of the Earth, and orbits with a 198 day period. Called HD 40307g (planets are named after their host star, with a lower case letter after starting with b), it’s in the “super-Earth” range: more massive than Earth, but less than, say Neptune (which is 17 times our mass).

We don’t know how big the planet is, unfortunately. It might be dense and only a little bigger than Earth, or it could be big and puffy. But if its density and size are just so, it could easily have about the same surface gravity as Earth – that is, if you stood on it, you’d weight the same as you do now!

But the very interesting thing is that it orbits the star at a distance of about 90 million kilometers (55 million miles) – closer to its star than it is to the Sun… but that’s good! The star is fainter and cooler than the Sun, remember. In fact, at this distance, the planet is right in the star’s “habitable zone”, where the temperature is about right for liquid water to exist!

That’s exciting because of the prospect for life. Now, whenever I mention this I hear from people who get all huffy and say that we don’t know you need water for life. That’s true, but look around. Water is common on Earth, and here we are. We don’t know that you need water for life, but we do know that water is abundant and we need it. We don’t know for sure of any other ways for life to form, so it makes sense to look where we understand things best. And that means liquid water.

Here’s a diagram of the system as compared to our own:



Note the scales are a bit different, so that the habitable zones of the Sun and of HD 40307 line up better (remember, HD 40307g is actually closer to its star than Earth is to the Sun – an AU is the distance of the Earth to the Sun, so HD 40307 is about 0.6 AU from its star). What makes me smile is that the new planet is actually better situated in its “Goldilocks Zone” than Earth is! That’s good news, actually: the orbit may be elliptical (the shape can’t be determined from the types of observations made) but still stay entirely in the star’s habitable zone.

And take a look at the system: the other planets all orbit closer to the star! We only have two inside Earth’s orbit in our solar system… but all five of HD 40307’s planets would fit comfortably inside Mercury’s orbit. Amazing.

So this planet – if it checks out as being real – is one of only a few we’ve found in the right location for life as we know it. And some of those we’ve found already are gas giants (though they could have big moons where life could arise). So what this shows us is that the Earth isn’t as out of the ordinary as we may have once thought: nature has lots of ways of putting planets the right distances from their stars for life.

We’re edging closer all the time to finding that big goal: an Earth-sized, Earth-like planet orbiting a Sun-like star at the right distance for life. This planet is actually a pretty good fit, but we just don’t know enough about it (primarily its size). So I’m still waiting. And given the numbers of stars we’ve observed, and the number of planets we found, as always I have to ask: has Earth II already been observed, and the data just waiting to be uncovered?

Image credits: ESO/M. Kornmesser; Tuomi et al.

[Allegro]

Spectacular Chaos From Two Galaxies (Literally) in Flagrante Delicto | Phil Plait
Bad Astronomy at Slate dot dom | 12NOV12

The universe is a fairly amazing place, if you know where to look. The good news is, you can look pretty much anywhere and be amazed by what you see. The even better news is that some of the things you’ll come upon will raise the hair on the back of your neck and grind your sense of scale to dust.

For proof, I present to you a Hubble Space Telescope image of the cosmic train wreck that is NGC 2623, a massive collision of galaxies taking place over a stretch of a million trillion kilometers of space:


Hubble picture of the colliding galaxies NGC 2623.
Image credit: NASA/ESA/Hubble/Martin Pugh

NGC 2623 is about 250 million light years away, a soul-crushing distance, but Hubble’s eye is keen indeed and can tease out fantastic details. This image is actually composed of several different observations by the orbiting observatory, lovingly assembled by amateur astronomer Martin Pugh as part of the Hubble Legacy Archive.

There’s so much to see here! What you’re looking at is not really one galaxy, but not really two, either. It used to be two fully mature and fairly large galaxies, but we’ve caught them in flagrante delicto (literally, since this means “in blazing offense”), right in the middle of their ridiculously photogenic collision.


R. Hurt (SSC), JPL-Caltech,
NASAA galaxy is typically composed of billions of stars, many also festooned with huge clouds of gas and dust. Our own Milky Way is a familiar spiral galaxy, and the two original galaxies making up NGC 2623 probably started out as spirals as well. By happenstance, they were traveling on paths that brought them very close together ... too close. The gravity of one galaxy started tugging on the other, the force growing inexorably as the two neared. Orbits distorted, shapes changed, and the end result is the creation of those two, long streamers of material called “tidal tails,” drawn out of each galaxy by the gravity of the other—and each more than 50,000 light years long. They loop around due to the collision being a glancing blow; the galaxies didn’t slam into each other head-on, but instead passed close and then looped around, slowly spiraling into each other like lovers embracing.

But this is hardly a tender interaction. Huge clouds of gas collided, smacking into one another at high velocity, compressing them. Collapsing clouds form stars, and that is evident as the blue color toward the tails. Young, massive stars are hot and shine blue. They also don’t live long, just a few million years, so we know this collision happened in the not-so-distant past. In fact, using various techniques to date the stars in the collision, it looks like this whole catastrophe started less than 100 million years ago. Fairly recently, if your calendar keeps galactic time.


Zoom of the core of NGC 2623.
NASA/ESA/Hubble/Martin PughThe core of the collision is just a complete mess. Huge arcs of gravitationally-stripped gas wrap around it, and it’s studded with the bright blue sites of furious star formation. The reddish and darker regions are due to dust—complex molecules that are very good at absorbing light are blocking the view behind them. Dust is created by stars, both when they form and when they die. This huge splurging swath of it cutting across to the upper left of the core is another sure sign that baby stars are popping out at a tremendous rate.

Amazingly, even with all this violence occurring, it’s highly unlikely that even two stars will physically collide! The scale here is immense, with stars separated by distances of trillions of kilometers. On that scale, stars are specks, so tiny that the odds of two smacking into each other are essentially zero. Gas clouds are millions of times bigger, which is why they can collide to form more stars.

It’s chaos on an epic scale. But it’ll settle down. In another few hundred million years, the two galaxies will actually merge, becoming one, somewhat bigger galaxy, probably a puffy, cotton-ball shaped elliptical-class galaxy. In a way that’ll be too bad; all the drama and beauty of this vast event will fade. But such is life in our Universe.

And one more thing. Sure, this galaxy is a long way off, and you may be thinking, “There but for the grace of gravity go I.” But don’t get too smug: In 4 billion years, our fate is the same. The Milky Way will collide with the equally ginormous Andromeda Galaxy—we’re barreling toward each other at a rate of hundreds of kilometers per second. And when we do eventually collide all those eons from now, we’ll wind up looking a whole lot like NGC 2623. If it makes you feel any better, perhaps some alien civilization millions of light years away will see us and gasp in awe (or whatever they do in awe) as they soak in the beauty of our two galaxies becoming one.

OK, fine, that doesn’t make me feel any better, either. Still, it’s fascinating that these collisions happen at all. When we observe them we learn a lot about how galaxies behave, and the eventual fate of our own … as well as get an eyeful of some of the most gorgeous astronomical artwork in the Universe.

Tip o’ the eyepiece to Astronomy Picture of the Day. Image credit: NASA/ESA/Hubble/Martin Pugh, used by permission.