Post has shared content
This red nova - brighter than an ordinary nova but not as bright as a supernova - could be the brightest thing in the north hemisphere night sky in 2022... if  it happens in a season when it's in the Earth's night sky.

As Egan said in a comment on the original post:

Given that nobody knows exactly when this will happen, the main thing that determines how many people are likely to be able to see it is the declination, 46° N. So anyone in the northern hemisphere will have a good chance ... while for someone like me, at 31° S, the odds aren't great: it will never rise higher than 13° above the northern horizon, for me.

Right ascension is the celestial equivalent of longitude, but without knowing the season in advance (and the error bars on the current prediction are much too large for that) we can't tell if the sun will be too close to the object, drowning it in daylight to the naked eye.

If that happens, I guess the only comfort is that there are still sure to be telescopes able to make observations, maybe including both Hubble and James Webb.

For more on red novae, see:

where we read:

The luminosity of the explosion occurring in luminous red novae is between that of a supernova (which is brighter) and a nova (dimmer). The visible light lasts for weeks or months, and is distinctively red in colour, becoming dimmer and redder over time. As the visible light dims, the infrared light grows and also lasts for an extended period of time, usually dimming and brightening a number of times.

Red nova

A "red nova" due to two stars merging might take place in 2022, and would likely be visible from Earth. (Alas, the linked article illustrates this with a picture of two merging bluish stars.)

The stars have been observed orbiting each other with an exponentially increasing angular velocity over the last three years, and they are believed to already be surrounded by a shared envelope of gas. If they are seen merging, this will be the first case of such an event being predicted in advance, making it possible to study the pre-collision phase.

Thanks to +Peter da Silva

The full paper is here:

Post has attachment
Mini Saturn

Chariklo orbits the Sun between Saturn and Uranus.  Just 250 kilometers across, it has two tiny rings!

Is it an asteroid?  Not quite: it's a 'centaur'.  In Greek mythology, a centaur was half-human, half-horse.  In astronomy, a centaur is halfway between an asteroid and a comet.  Centaurs live in the outer solar system between Jupiter and Neptune.   They don't stay there long - at most a million years.  They come from further out, pulled in by the gravity of Neptune, but their orbits are chaotic and they eventually move in toward Jupiter.

Over 300 centaurs have been seen, and scientists believe there are over 40,000 that are bigger than a kilometer across.  But Chariklo is the biggest. And it has two rings!

A while ago I told you about a 'super Saturn' - an object in another solar system with rings almost a thousand times bigger than Saturn.  Chariklo, on the other hand, is a 'mini Saturn'.  Its rings are just 800 kilometers across - just 0.3% the size of Saturn's F ring.

These rings are narrow and dense.  One is about 6 kilometers wide and the other - which you can barely see in this artist's picture - is just 3 kilometers wide.   They're separated by a 9-kilometer gap.

How did they get there?  Some smaller objects - probably made of ice - must have collided and broken apart.   But they must have collided not too fast, or they would have shot all over instead of forming neat rings.

The rings are probably not very stable, unless Chariklo has one or more moons to stabilize them.  Saturn has such moons, called shepherd moons.

The second largest centaur, called Chiron, may also have rings.

Puzzle 1: who was Chariklo in Greek mythology?

Puzzle 2: who was Chiron?

Chariklo's full name is 10199 Chariklo:

Its rings are tentatively named Oiapoque and Chuí, after two rivers in Brazil:

They were discovered in 2013.  How come nobody told me? 

Centaurs are lots of fun if you like celestial mechanics:

I can't resist quoting a bit:

Because the centaurs are not protected by orbital resonances, their orbits are unstable within a timescale of 10^6–10^7 years. For example, 55576 Amycus is in an unstable orbit near the 3:4 resonance of Uranus.  Dynamical studies of their orbits indicate that being a centaur is probably an intermediate orbital state of objects transitioning from the Kuiper belt to the Jupiter family of short-period comets. Objects may be perturbed from the Kuiper belt, whereupon they become Neptune-crossing and interact gravitationally with that planet. They then become classed as centaurs, but their orbits are chaotic, evolving relatively rapidly as the centaur makes repeated close approaches to one or more of the outer planets. Some centaurs will evolve into Jupiter-crossing orbits whereupon their perihelia may become reduced into the inner Solar System and they may be reclassified as active comets in the Jupiter family if they display cometary activity. Centaurs will thus ultimately collide with the Sun or a planet or else they may be ejected into interstellar space after a close approach to one of the planets, particularly Jupiter.

The picture here was created by Nick Risinger for ESO, the European Southern Observatory in Chile.  They reported their discovery here:


Post has attachment
Super Saturn

About 400 light years away, there's something with rings like Saturn — but much, much  bigger!  

It's called J1407b.  It could be a huge planet.  Or it could be a star so small that it never lit up: a brown dwarf.  

One of Saturn's largest visible rings, the F ring, is about 140 thousand kilometers in radius.  But J1407b's rings are almost a thousand times bigger.    It has rings 90 million kilometers in radius! 

That's 2/3 as big as the Earth's orbit around the Sun.  That's insane!   It's so huge that scientists don't know why the ring doesn’t get ripped apart by the gravity of the star it orbits. 

One theory is that the rings are spinning in a retrograde way — in other words, backwards.   If you have a planet moving clockwise around a star, and its rings are turning counterclockwise, this helps keep them from getting pulled apart.   You can see a simulation here:

However, it's not obvious why the rings would turn backwards.

There's no sharp boundary between a very large planet and a very small star.    If it produces heat using nuclear fusion, it's considered a star... but there are some funny borderline cases.

Stars about 13 times heavier than Jupiter get hot enough to fuse deuterium — but they quickly fizzle out, since that isotope of hydrogen is rare.   Stars about 65 times heavier than Jupiter can also fuse lithium... but then fizzle out.  So, these things are called brown dwarfs.   Stars over 80 times heavier than Jupiter can actually fuse hydrogen, so they light up and form very small red dwarfs.

The atmosphere of a hot brown dwarf is similar to a sunspot — a cold spot on our Sun.   It contains molecular hydrogen, carbon monoxide and water vapor. This is called a class M brown dwarf.

But after they run out of fuel, they cool down. The cooler class L brown dwarfs have clouds!

But the even more chilly class T brown dwarfs do not. Why not?

Here's a popular theory: the clouds may rain down, with material moving deeper into the star!  People seem to be seeing this in Luhman 16B, a brown dwarf 7 light years from us.  It's half covered by huge clouds. These clouds are hot — 1200 °C — so they’re probably made of sand, iron or salts.  But some of them have been seen to disappear!

Finally, as brown dwarfs cool below 300 °C, astronomers expect that ice clouds start to form: first water ice, and eventually ammonia ice. These are called class Y brown dwarfs.

Wouldn’t that be neat to see? A star with icy clouds!  And maybe it could have huge rings, too!

For more on J1407b, try Wikipedia:

The picture below is an artist's impression by Ron Miller.


Post has attachment
Solar wind

This is the solar wind, the stream of particles coming from the Sun.  It was photographed by STEREO.  That's the Solar Terrestrial Relations Observatory, a pair of satellites we put into orbit around the Sun at the same distance as the Earth, back in 2006.  One  is ahead of the Earth, one is behind.  Together, they can make stereo movies of the Sun!

One interesting thing is that there's no sharp boundary between the 'outer atmosphere' of the Sun, called the corona, and the solar wind.  It's all just hot gas, after all!   STEREO has been studying how this gas leaves the corona and forms the solar wind.  This picture is a computer-enhanced movie of that process, taken near the Sun's edge.

What's the solar wind made of?   When you take hydrogen and helium and heat them up so much that the electrons get knocked off, you get a mix of electrons, hydrogen nuclei (protons), and helium nuclei (made of two protons and two neutrons).   So that's all it is.

The Sun's corona is very hot: about a million degrees Celsius.  That's hotter than the visible surface of the Sun!  Why does it get so hot?  When I last checked, this was still a bit mysterious.   But it has something to do with the Sun's powerful magnetic fields. 

When they're this hot, some electrons are moving fast enough to break free of the Sun's gravity.   Its escape velocity is 600 kilometers per second.  The protons and helium nuclei, being heavier but having the same average energy, move slower.  So, few of these reach escape velocity.

But with the negatively charged electrons leaving while the positively charged protons and helium nuclei stay behind, this means the corona builds up a positive charge!   So the electric field starts to push the protons and helium nuclei away, and some of them - the faster-moving ones - get thrown out too.  

Indeed, enough of these positively charged particles have to leave the Sun to balance out the electrons, or the Sun's electric charge would keep getting bigger.   It would eventually shoot out huge lightning bolts!  The solar wind deals with this problem in a less dramatic way - but sometimes it gets pretty dramatic.  Check out this proton storm:

When storms like this happen, the US government sends out warnings like this:

Space Weather Message Code: WATA50
Serial Number: 48
Issue Time: 2014 Jan 08 1214 UTC
WATCH: Geomagnetic Storm Category G3 Predicted
Highest Storm Level Predicted by Day:
Jan 08: None (Below G1) Jan 09: G3 (Strong) Jan 10: G3 (Strong)
Potential Impacts: Area of impact primarily poleward of 50 degrees geomagnetic latitude.
Induced Currents – Power system voltage irregularities possible, false alarms may be triggered on some protection devices.
Spacecraft – Systems may experience surface charging; increased drag on low Earth-orbit satellites and orientation problems may occur.
Navigation – Intermittent satellite navigation (GPS) problems, including loss-of-lock and increased range error may occur.
Radio – HF (high frequency) radio may be intermittent.
Aurora – Aurora may be seen as low as Pennsylvania to Iowa to Oregon.

The solar wind is really complicated, and I've just scratched the surface.  I love learning about stuff like this, surfing the web as I lie in bed sipping coffee in the morning.  Posting about it just helps organize my thoughts - when you try to explain something, you come up with more questions about it.

For more on space weather, visit this fun site:

You can see space weather reports put out by the National Oceanic and Atmospheric Administration here:

For more on the solar wind, see:

For more on STEREO, see:

#physics   #astronomy  
Animated Photo

Post has attachment
Dark mysteries

You probably heard the news this week: astronomers found a galaxy that's 98% dark matter. 

It's called Dragonfly 44.  It's extremely faint, so it doesn't have many stars.   But we can use redshifts to see how fast those stars are moving - over 40 kilometers per second on average.  If you do some calculations, you can see this galaxy would fly apart unless there's a lot of invisible matter providing enough gravity to hold it together.   (Or unless something even weirder is happening.)

Something similar is true for most galaxies, including ours.   What makes Dragonfly 44 special is that 98 percent of the matter must be invisible.   And this is just in the part where we see stars.   If we count the outer edges of the galaxy, the halo, the percentage could rise to 99% or more! 

By comparison, the Milky Way is roughly 90% dark matter if you count the halo.  We know this pretty well, because we can see a few stars out in there and measure how fast they're moving.

There are also galaxies like NGC 3379 that may have less than the average amount of dark matter in their halo, though this is debatable.

And most excitingly, sometimes clusters of galaxies collide and stop moving, but their dark matter keeps on going! 

We can see this because light from more distant galaxies is bent, not toward the colliding clusters, but toward something else.   The most famous example is the Bullet Cluster, but there are others.

All these discoveries - and more - make dark matter seem more and more like a real thing.  So it's more and more frustrating that we don't know what it is.  As I explained a while ago, recent experiments to detect particles of dark matter have failed.  So it could be something else, like black holes about 30 solar masses in size.  And intriguingly, the first black hole collision seen by LIGO involved a 35-solar-mass and a 30-solar-mass black hole.  These are too big to have formed from the collapse of a single star.  They might be primordial black holes, left over from the early Universe.

But more on that later.

For more on Dragonfly 44, see:

• Pieter van Dokkum, Roberto Abraham, Jean Brodie, Charlie Conroy, Shany Danieli, Allison Merritt, Lamiya Mowla, Aaron Romanowsky and Jielai Zhang, A high stellar velocity dispersion and ~100 globular clusters for the ultra diffuse galaxy Dragonfly 44,

For our failure to find dark matter particles, see this post of mine:

For more on dark matter on the outer edges of galaxies, see:

For the Milky Way's dark matter halo, see:

• G. Battaglia et al, The radial velocity dispersion profile of the Galactic halo: constraining the density profile of the dark halo of the Milky Way,


Post has attachment
Not like Earth

At the end of August, the European Southern Observatory will announce a planet orbiting Proxima Centauri - the star closest to our Sun, 4.24 light years away.   They're trying to make this planet sound like Earth... and that's cool.   But I'll tell you some ways it's not.

Mainly, Proxima Centauri is really different from our Sun! 

It's a red dwarf.   It puts out just only 0.17% as much energy as our Sun.  So any planet with liquid water must be very close to this star.

And because it's cooler than the Sun, Proxima Centauri mainly puts out infrared light - in other words, heat radiation.   Its visible luminosity is only 0.005% that of our Sun!

So if you were on a planet as warm as our Earth orbiting Proxima Centauri, it would look very dim - about 3% as bright as our Sun.

Of course, if there's life on this planet, it would probably evolve to see infrared. 

But there's a more serious problem.  Proxima Centauri sometimes puts out big flares, with lots of X-rays!  That's not very nice.

Why does a wimpy little red dwarf have bigger flares than the Sun?

The Sun has a core where fusion happens, and helium produced down in the core mainly stays there.   A red dwarf doesn't have a core: it's fully convective.  In other words, heat moves through the star not by radiation, but by hot gas actually moving up to the surface. 

All this ionized gas moving around makes big magnetic fields.  The magnetic field lines get twisted up and sometimes explode out in flares!  These flares get so hot that they emit X-rays.  That's very  hot.

Our Sun has flares too, but on a smaller scale.  Even on a calm day, Proxima Centauri puts out as much X-ray energy as our Sun.  But when a big flare occurs, it can put out 10 times more.   This happens pretty often. 

So: any "Earth-like" planet orbiting this star will be a lot closer than the Earth is to our Sun, and get a lot more X-rays. 

Puzzle 1.  Use what I've told you to estimate how much closer a planet must be, to be at the same temperature as the Earth.

Puzzle 2.  Estimate how much more X-rays it will get.

On top of this, Proxima Centauri could be part of a triple star system!

The closest neighboring stars, Alpha Centauri A and B, orbit each other every 80 years. One is a bit bigger than the Sun, the other a bit smaller. They orbit in a fairly eccentric ellipse. At their closest, their distance is like the distance from Saturn to the Sun. At their farthest, it’s more like the distance from Pluto to the Sun.

Proxima Centauri is fairly far from both: a quarter of a light year away. That’s about 350 times the distance from Pluto to the Sun! We’re not even sure Proxima Centauri is gravitationally bound to the other stars. If it is, its orbital period could easily exceed 500,000 years.

On the bright side, Proxima Centauri will last a lot longer than our Sun. As it ages, it will get smaller and hotter, gradually changing from red to blue.  After about four trillion years it will grow to 2.5% of the Sun's luminosity.   When its hydrogen is exhausted, it will then become a white dwarf, without ever puffing out into a red giant like our Sun.

So, any planet orbiting this star will be a weirdly different world.  But if we ever get there, we could stay for trillions of years, long after our Sun has become a red giant, roasting life on Earth.

For rumors of ESO's announcement, see this:

For more on Proxima Centauri, try this:


Post has attachment
Watch Juno meet Jupiter on NASA TV!   Go here:

Here's the timeline - all these times are Eastern Daylight Time (GMT-4):

July 4th, 9:13 p.m. Start of transmission of single frequency “tones” that will provide updates on the spacecraft’s condition.

9:16 p.m. Juno begins turning away from the sun to position the engine in the right direction to slow the spacecraft for its arrival at Jupiter.

10:41 p.m. With the main antenna pointing away from the sun, Juno switches to a smaller antenna for sending the tones.

10:45 p.m. Juno adjusts itself to eliminate any wobbling.

10:56 p.m. Juno speeds up its spin rate from two rotations a minute to five rotations a minute, a process that takes about five minutes.

11:18 p.m.  The main engine begins firing!

11:38 p.m. The spacecraft has slowed down enough to be captured into orbit around Jupiter.

11:53 p.m. The main engine shuts off, leaving Juno in the desired orbit.

11:55 p.m. The spacecraft starts slowing its spin rate back down to two revolutions per minute.

July 5th, 12:07 a.m. Juno changes direction to point its antenna back at Earth.

12:11 a.m. Juno ends the transmission of status tones and switches to its medium-gain antenna.

12:16 a.m. Juno begins transmitting detailed telemetry, although it may take 20 minutes or longer to lock into the signal.

So, the real excitement starts at 11:18 pm on July 4th if you live on the East Coast of the US.  In California this is 8:18 pm, in London it's 4:18 am on July 5th, here in Singapore it's 11:18 am on July 5th, etc.

From the New York Times:

What could possibly go wrong?

Juno blows up.  In August 1993, NASA’s instrument-packed Mars Observer spacecraft vanished. An inquiry concluded that a fuel leak caused the spacecraft to spin quickly and fall out of communication. While Juno’s setup is different, there is always a chance of an explosion with rocket fuel.

The engine doesn’t fire at all. The Japanese probe Akatsuki was all set to arrive at Venus in December 2010, but its engine didn’t fire, and Akatsuki sailed right past Venus. Last year, Akatsuki crossed paths with Venus again, and this time, using smaller thrusters, it was able to enter orbit.

It crashes into something. Jupiter does not possess the majestic rings of Saturn, but it does have a thin of ring of debris orbiting it. Juno will pass through a region that appears clear, but that does not mean it actually is. Even a dust particle could cause significant damage, as Juno will be moving at a speed of 132,000 miles per hour relative to Jupiter.

It flies too close to Jupiter and is ripped to pieces. In one of NASA’s most embarrassing failures, the Mars Climate Orbiter spacecraft, was lost in 1999 because of a mix-up between English and metric units. Climate Orbiter went far deeper into Mars’ atmosphere than planned. On its first orbit, Juno is to pass within 2,900 miles of Jupiter’s cloud tops, so a miscalculation could be catastrophic.

The computer crashes. On July 4 last year, the mission controllers of the New Horizons spacecraft that was about to fly by Pluto experienced some nervous moments when the spacecraft stopped talking to them. The computer on New Horizons crashed while trying to interpret some new commands and compressing some images it had taken, the electronic equivalent of walking while chewing gum.

The controllers put New Horizons back in working order within a few days, and the flyby occurred without a hitch. For Juno, the scientific instruments have been turned off for its arrival at Jupiter. “We turn off everything that is not necessary for making the event work,” said Dr. Levin, the project scientist. “This is very important to get right, so you don’t do anything extra.”

The intense barrage of radiation at Jupiter could knock out Juno’s computer, even though it is shielded in a titanium vault. Usually, when there is a glitch, a spacecraft goes into “safe mode” to await new instructions from Earth, but in this case, that would be too late to save Juno. The spacecraft has been programmed to automatically restart the engine to allow it to enter orbit.

“If that doesn’t go just right, we fly past Jupiter, and of course, that’s not desirable,” Dr. Bolton said.


Post has attachment
Jupiter orbit insertion

On the 4th of July, a NASA spacecraft named Juno will try to start orbiting Jupiter.  It has traveled for 5 years and 2.8 billion kilometers to get there.  This is going to be exciting!

Juno will try to aim its main engine towards the Sun, turn it on for 35 minutes, and slow down to 58 kilometers per second, so it can be captured by Jupiter's gravitational field.   Says the lead scientist:

“There’s a mixture of tension and anxiety because this is such a critical maneuver and everything is riding on it. We have to get into orbit. The rocket motor has to burn at the right time, in the right direction, for just the right amount of time.”

With luck, Juno will enter a highly eccentric polar orbit, and make 37 orbits lasting 14 days each.   Each time it will dive down to just 4000 kilometers above Jupiter's cloud tops, closer than we've ever come!  Each time it will shoot back up to a height of 2.7 million kilometers.   It will map Jupiter using many instruments.  The first dive is scheduled for August.

Juno will gradually be damaged by Jupiter's intense radiation, even though the main computer is encased in a 200-kilogram titanium box.   After its last orbit, it will deliberately plunge to its death - so that it has no chance of contaminating the oceans of Europa.

Juno has already entered Jupiter's magnetosphere - the region of space dominated by Jupiter's powerful magnetic field.  You can hear it here:

For details of Juno's trajectory, go here:

And watch the NASA "preview" here.  It's like the preview of a science fiction movie, emphasizing the dangers rather than the potential rewards - but it's fun.

The Jupiter orbit insertion should begin at 03:18 July 5th UTC, which is 20:18 on the 4th of July in California.


Post has attachment
Does dark matter have dark hair?

By now there's a lot of evidence that dark matter exists, but not so much about what it is.  The most popular theories say it's some kind of particles that don't interact much with ordinary matter, except through gravity.  These particles would need to be fairly massive - as elementary particles go - so that despite having been hot and energetic shortly after the Big  Bang, they'd move slow enough to bunch up thanks to gravity.  Indeed, the bunching up of dark matter seems necessary to explain the formation of the visible galaxies!  

Searches for dark matter particles have not found much.  The DAMA experiment, a kilometer underground in Italy, seemed to detect them.  Even better, it saw more of them in the summer, when the Earth is moving faster relative to the Milky Way, than in the winter.  That's just what you'd expect!  But other similar experiments haven't seen anything.  So most physicists doubt the DAMA results.  

Maybe dark matter is not made of massive weakly interacting particles.  Maybe it's a superfluid made of light but strongly interacting particles.  Maybe there are lot more 25-solar-mass black holes than most people think!  There are lots of theories, and I don't have time to talk about them all.  

I just want to tell you about a cool idea which assumes that dark matter is made of massive weakly interacting particles.  It's still the most popular theory, so we should take it seriously and ask: if they exist, what would these particles do?

In the early Universe they'd attract each other by gravity.  They'd bunch up, helping seed the formation of galaxies.  But after stars and planets formed, they'd pull at the dark matter, making it thicker in some places, thinner in others.  

And this is something we can simulate using computers!  After all, the relevant physics is well-understood: just Newton's law of gravity, applied to stars, planets and zillions of tiny dark matter particles.  

Gary Prezeau of NASA's Jet Propulsion Laboratory did these simulations and discovered something amazing. 

When dark matter flows past the Earth, it gets deflected and focused by the Earth's gravity.  Like light passing through a lens, it gets intensely concentrated at certain locations!

This creates long thin 'hairs' where the density of dark matter is enhanced by a factor of 10 million.   Each hair is densest at its 'root'.   At the root, the density of dark matter is about a billion times greater than average!

The hairs in this picture are not to scale: the Earth is drawn too big.   The roots of the hairs would be about a million kilometers from Earth, while the Earth's radius is only 6,400 kilometers.  

Of course we don't know dark matter particles exist.  What's cool is that if they exist, it forms such beautiful structures!  And if we could do a dark matter search in space, near one of these possible roots, we might have a better chance of finding something.   

Let me paraphrase Prezeau, because the real beauty is in the details.  From his abstract:

It is shown that compact bodies form strands of concentrated dark matter filaments henceforth simply called 'hairs'. These hairs are a consequence of the fine-grained stream structure of dark matter halos surrounding galaxies, and as such they constitute a new physical prediction of the standard model of cosmology. Using both an analytical model of planetary density and numerical simulations (a fast way of computing geodesics) with realistic planetary density inputs, dark matter streams moving through a compact body are shown to produce hugely magnified dark matter densities along the stream velocity axis going through the center of the body. Typical hair density enhancements are 10^7 for Earth and 10^8 for Jupiter. The largest enhancements occur for particles streaming through the core of the body that mostly focus at a single point called the root of the hair. For the Earth, the root is located at about 10^6 kilometers from the planetary center with a density enhancement of around 10^9 while for a gas giant like Jupiter, the root is located at around 10^5 kilometes with a enhancement of around 10^11. Beyond the root, the hair density precisely reflects the density layers of the body providing a direct probe of planetary interiors.

The mathematicians and physicists among you may enjoy even more detail.  Again, I'll paraphrase:

According to the standard model of cosmology, the velocity dispersion of cold dark matter (CDM) is expected to be greatly suppressed as the universe expands and the CDM collisionless gas cools.  In particular, for a weakly interacting mass particle with mass of 100 GeV that decoupled from normal matter when the Universe cooled to an energy of 10 MeV per particle, the velocity dispersion is only about 0.0003 meters per second.

As the Universe cools and the nonlinear effects of gravity become more prominent and galactic halos grow, the dispersion of velocities will increase somewhat, but 10 kilometers per second is an upper limit on the velocity dispersion of the resulting dark matter streams.

Dark matter starts out having a very low spread in velocities, but its location can be anywhere.  So, it forms a 3-dimensional sheet in the 6-dimensional space of position-velocity pairs, called phase space

As time passes this sheets gets bent, but it can never be broken.   When this sheet gets folded enough, we get a 'caustic where lots of different dark matter particles have almost the same position, though different velocities.  You can see a caustic by shining light into a reflective coffee cup, or shining light through a magnifying glass.  The same math applies here:

A phase-space perspective sheds additional light on the processes affecting the CDM under the influence of gravity.  When the CDM decouples from normal matter, the CDM occupies a 3-dimensional sheet in the 6-dimensional phase space since it has a tiny velocity dispersions. The process of galactic halo formation cannot tear this hypersurface, thanks to generalization of Liouville’s theorem.  Under the influence of gravity, a particular phase space volume of the hypersurface is stretched and folded with each orbit of the CDM creating layers of fine-grained dark matter streams, each with a vanishingly small velocity dispersion. These stretches and folds also produce caustics: regions with very high CDM densities that are inversely proportional to the square root of the velocity dispersion.

Here are some more pictures:

and here's the paper:

• Gary Prezeau, Dense dark matter hairs spreading out from Earth, Jupiter and other compact bodies,

#spnetwork arXiv:1507.07009 #astronomy  

Post has attachment
The Tagish Lake meteorite

On January 18, 2000, at 8:43 in the morning, a meteor hit the Earth's atmosphere over Canada and exploded with the energy of a 1.7 kiloton bomb.  Luckily this happened over a sparsely populated part of British Columbia. 

It was over 50 tons in mass when it hit the air, but 97% of it vaporized.  Just about a ton reached the Earth.  It landed on Tagish Lake, which was frozen at the time.  Local inhabitants said the air smelled like sulfur.

Only about 10 kilograms was found and collected.   Except for a gray crust, the pieces look like charcoal briquettes. 

And here is where things get interesting.

Analysis of the Tagish Lake fragments show they're very primitive.   They contain dust granules that may be from the original cloud of material that created our Solar System and Sun!  They also have a lot of of organic chemicals, including amino acids.

It seems this rock was formed about 4.55 billion years ago.

Scientists tried to figure out where it came from.  They reconstructed its direction of motion and compared its properties with the spectra of various asteroids.  In the end, they guessed that it most likely came from 773 Irmintraud.

773 Irmintraud is a dark, reddish asteroid from the outer region of the asteroid belt.  It's about 92 kilometers in diameter.   It's just 0.034 AU away from a chaotic zone associated with one of the gaps in the asteroid belt created by a resonance with Jupiter.  So, if a chunk got knocked off, it could wind up moving chaotically and make it to Earth!

And here's what really intrigues me.  773 Irmintraud is a D-type asteroid - a very dark and rather rare sort.  One model of Solar System formation says these asteroids got dragged in from very far out in the Solar System - the Kuiper Belt, out beyond Pluto.   (Some scientists think Mars' moon Phobos is also a D-type asteroid.) 

So, this chunk of rock here may have been made out in the Kuiper Belt, over 4.5 billion years ago!

For more, see:

Wait while more posts are being loaded