Thursday, January 19, 2017

Pulsars

Pulsars are neutron stars whose EM radiation (light, radio waves, gamma rays) seem to blink or pulse. This is related to how they rotate (and their rotation can be measured to be slowing down). Because the magnetic poles don't usually line up with the axis of rotation, sometimes the pole is pointed more in our direction, sometimes less so--and it seems to pulse.

But what they radiate seems to be all over the map. Sometimes they radiate gammas but not radio, sometimes radio but not gammas, sometimes both. Why? Maybe it has to do with which way the star is pointed relative to us.

based on these observations, Geminga’s magnetic poles appear to be oriented at the top and bottom of the neutron star from our point of view, which also align with its spin poles. Because these areas are where a pulsar’s radio emission should originate, it makes sense that no radio waves are detected. The pulsar’s gamma rays, however, are created over a larger area at higher altitudes, causing them to sweep out over a larger area of the sky and making them detectable from Earth.

It makes sense. Verifying that would be kind of hard--we'd have to have a clear idea of how far from the rotational axis the magnetic poles point, and then try to correlate that with the ratio of gamma to radio. But I've no idea how to measure that angle. You could get some notion of the direction of the axis of rotation from the jets of stuff shot away from it (you'd measure the doppler shifts of each of the two lobes to try to pin down their speed and direction), but measuring the magnetic field direction sounds hard. Polarization of light would be going this way and that with the moving field, and I'm not sure you could tell that from randomness.

Tuesday, January 17, 2017

Differences

Pick one:
NASA has approved a mission to explore 16 Psyche, an iron-rich asteroid whose contents are said to be worth over 100-thousand times the value of the entire world economy.

Or
"Psyche is almost certainly an iron-nickel alloy asteroid, possibly formed after a larger body, like a dwarf planet, had its mantle stripped away from a violent collision with another asteroid. So, Psyche is probably the exposed core of a small planet," Bercovici said.

Do you want to pull your hair out when you see "gee wow" reporting like this? "Psyche is an asteroid with a diameter in excess of 125 miles, about the same size of the state of Massachusetts, and is almost entirely composed of iron and nickel. The abundance of these metals gives the asteroid's contents an estimated worth of a staggering $10 quintillion — that is a one, followed by 19 zeros. Comparatively speaking, the world economy is estimated to be worth just under $74 trillion. Psyche's contents are worth approximately 130,000 times as much as every single human industry put together." Transportation costs aside, supply and demand considerations make complete nonsense of this sort of calculation. You're supposed to get excited about big numbers, even when they don't make any sense.

If Psyche is indeed the remains of a much bigger object, that's more exciting. The problem is, I don't know if explorations would tell us much about a long-gone planetary crash. So it may just be exciting in a T-Rex skeleton sort of way. (The Field Museum's Sue exhibit has a case with some extra "belly bones" and the confession that nobody knows where they fit.)

Maybe the composition and structure can tell us about how planetary cores form--though the details of the composition will surely have been different from Earth's. Unfortunately the probe is supposed to launch in 2023 and arrive in 2030. A bit of a wait.

Paris streets

I saw a report today from the Mirror saying that French told not to fear wolves roaming Paris streets as 'they only eat four-legged animals'.

That sort of encouragement doesn't comfort. Even if Parisians were OK with wolves that only ate pets, wolves still threaten everybody.

But who else is on the streets? I don't think wolves stand a chance. People can be very thorough when dealing with threats.

Thursday, January 12, 2017

Merging black holes

We all remember the LIGO discovery: a pair of black holes merging to produce a beautiful gravity wave signal. It was followed shortly thereafter by a smaller pair producing not-so-nice a signal, but good enough.

LIGO didn't take data very long, but got 2 signals in only a few months. (They're starting up again.)

From that rate, Ioka et al estimated how many mergers there have been in our galaxy so far (mostly much smaller ones, and obviously we weren't looking at the time--weren't here for most of that time). (Basically they figure that if LIGO detected really big ones at the range they did, it would have missed the many more smaller ones in the same volume, because it wasn't sensitive enough.)

When two orbiting bodies like that merge, the result has fantastic angular momentum. If you spin a bicycle wheel and grab it, you know that it "doesn't like" being stopped. Imagine if the bicycle wheel were made of lead, and spinning that fast. You might break your hand trying to stop it. Now spin it up faster, and faster. There's a lot of energy in that thing now. There's unimaginably more in the black hole you get from merging two others.

The first direct detections of gravitational waves (GWs) from black hole (BH) mergers, GW150914, GW151226 and LVT151012, give a robust lower limit ∼70000 on the number of merged, highly-spinning BHs in our Galaxy. The total spin energy is comparable to all the kinetic energy of supernovae that ever happened in our Galaxy.

They go on to estimate what kind of activity you can get from interstellar gas falling into these things, which is of interest to people trying to study cosmic rays (like IceCube).

Let me emphasize that most of these black holes aren't very big--only a few solar masses. Still, 70,000 merged black holes in our galaxy--wow.

Of course there are some assumptions that go into that--like assuming that the rate of black hole merger is essentially constant in time. I'm not sure that's realistic. And they may have the distribution of the rate of production of different size black holes wrong. But nobody found any showstopper problems with it at the meeting today.

Tuesday, January 10, 2017

Appendix

I've never been confident in the claim that the appendix is a useless vestigial organ. Everything else is doing something, sometimes many somethings at once. Why waste energy growing something useless? Maybe it is a bacteria reservoir?
They discovered that the appendix has evolved independently in several mammal lineages, over 30 separate times, and almost never disappears from a lineage once it has appeared. This suggests that the appendix likely serves an adaptive purpose.

Saturday, January 07, 2017

Dust never sleeps

Or, when it does, the ultraviolet wakes it up.

On the Moon, and presumably any airless body, UV-stimulated emission and re-capture of electrons in the cavities left between dust grains can charge the dust, and the negatively charged particles can be levitated by electrostatic repulsion.

We have recorded micron-sized insulating dust particles jumping to several centimeters high with an initial speed of ~0.6 m/s under ultraviolet illumination or exposure to plasmas, resulting in an equivalent height of ~0.11 m on the lunar surface that is comparable to the height of the so-called lunar horizon glow.

Since there's no reason it should jump straight up, a particle will fall down again some distance from its original location. So dust will spread.

This is only significant in airless regions, so don't blame the state of the bookcase on UV light.

Friday, January 06, 2017

Mark your calendars

Molnar et al are predicting that a binary star system will merge and explode in 2022. If true, Cygnus will look a little funny for a couple of years.

The eclipses of one star by the other are coming faster and faster, and if V1309 is anything to go by the pair should spiral in and merge in a moderately dramatic way in about 5 years.

If this event is anything like the 2008 explosion, it’ll take about six months to rise to its full brightness — 10,000 times greater than the brightness of the original. When it comes to space phenomena, it can sometimes be hard to tell what big numbers are actually as impressive as they sound and which are not actually big at all relative to, you know, the scale of the universe. This is the former. It will mean a noticeable change in the brightness of the night sky.

And if it takes 6 months to grow, the weather shouldn't get in the way, as it tends to with things like solar eclipses and comets and auroras.

Tuesday, January 03, 2017

Pithy wisdom and slogans

Back in 2013 I wrote about proverbs that "I don't hear these much, though perhaps I don't travel in the right circles, and I suspect we suffer for it." Since then I've been looking for places where old proverbs, or what used-to-be familiar scripture would fit in.

I'm surprised that I didn't hear anyone cite "Better the devil you know than the devil you don't" about the last presidential election. It was certainly one of the major themes.

You hear plenty of slogans and phrases encapsulating some political or social ideas, but that's not quite the same thing. The slogans anticipate, while the proverbs react to, classes of situations. For example "The people united will never be defeated" is an aspirational slogan (and piano composition): history is chock-a-block with counterexamples and compromises that only vaguely resemble victory. "He who slaughters a beast does not hesitate about skinning it," on the other hand, warns the wishful thinkers in every age. We hear "Liberty, Equality, Fraternity," or "no justice, no peace"--both aspirational (since the latter implies that there will be peace once there is justice). But "A camel never sees its own hump." You know people like that.


I like this one. Albanian: "Fire, water and government know nothing of mercy." And this "A benevolent man should allow a few faults in himself to keep his friends in countenance."

Saturday, December 31, 2016

New Year

In honor of the day and the celebrations of the evening, a little Peter Sinclair (who should please publish a new collection one of these days):

Yes, we're planning a low key evening. How did you guess?

But I can't resist one last dig at 2016:

Year in Review

I generally enjoy Dave Barry's Year in Review columns. This year,
NOVEMBER

… the Chicago Cubs win the World Series. Finally! Yay! What a fun month! OK, that’s our summary of November. Now it’s time to move along to the events of …

DECEMBER

Sometimes it pays to wait

Remember that story about the bags of plastic rice in Nigeria? It sounded pretty wild, just the sort of story you'd like to comment on, and maybe speculate about. Except--how did they know? The original story said it smelled chemical-ly, and when cooked was extremely sticky. That's not very solid evidence.

Nigeria rice 'contaminated, not plastic' - NAFDAC

Customs officials' claims that the rice seized in Lagos last week was "plastic" sparked confusion and official denials. ...

Tests on samples of the rice showed that it was "unwholesome for human consumption", exceeding the maximum limit for bacteria including "Coli form", Nafdac said in a statement.

The Nigerian customs service, speaking at the same press conference, said that it had acted on "credible intelligence" that "large consignments of plasticized rice were.... to be shipped from the Far East to Africa".

Probably somebody washed the rice in waste water. That would account for the smell and the bacteria.

Saturday, December 24, 2016

Nativity set

I remember looking at a ceramic nativity set when I was quite small. I didn’t think I’d seen anything prettier than those smooth white clean figures. I got to touch one, and it was as lovely to touch as to look at. I wanted them, of course—and our little plaster figures didn’t seem to quite measure up. I didn't have the words to say so then, but could painted plaster possibly represent purity as well as unstained ceramic? I don’t know if we had the plaster set at the time, or got it later—it doesn’t matter, I’d seen them at church already.

My Youngest Daughter has such a set now, handed down to her by her sister from her grandfather, who had a ceramics business for a while. They are set up around the Advent wreath and candles. I can still see what I admired in them. True, the features are not crisp, and the postures represent a fleeting moment of greeting, and I’ve an adult’s painful awareness of how fragile they are. But I appreciate others now, and don’t covet ceramic anymore.

A large wooden set from Liberia, standing wobbly(*) under the tree, is the family traditional set. I remember each of the children doing their part with them. That matters a lot more than silky feel.

Nativity still life scenes aren’t meant to be realistic. Mary wouldn’t be kneeling, she’d be sitting to rest, or lying down. The animals would be outside, and of course the magi didn’t show up for a while—and they didn’t stick around long enough to give Mary an undergraduate course in astronomy. It doesn’t matter. Do I take a moment and remember? That matters. When Youngest Daughter sets up hers again next year, she'll remember her grandfather and her sister, and baby Jesus--and that matters.

And I remember what babies are like. The smooth ceramic is like a baby’s smooth skin—but cold.


(*) Every year I promise myself I'll flatten out the bases to stop the wobble, but it is cold in the winter, and the set is packed away by spring.

Extreme nutcracker

Crack walnuts with a grenade. Yes, I agree, it was probably a practice grenade. Still, it will be a good story to tell his grandkid. I like the comment: "It's more stable than a Samsung phone."

Wednesday, December 21, 2016

Jets of iron

Did you ever, when washing dishes, shove a funnel wide-side-down into the water to see how high the water would jet up from the narrow end? Or, in the tub, put your palms together underwater and quickly squeeze them tightly together, to see how far the water would shoot? When you're dealing the continent-sized chunks of molten and solid iron moving around, it seems you can get fast-moving jets of iron under the mantle. Of course "fast" is a relative term: O(40)km/year isn't going to rival the jet stream, but it represents quite rapid progress through rock.

The image at the site is a little misleading--it's just a toy model of what things might be like. Nobody really thinks there are cylinders like that in the core.

The discovery of the jet involved tracking two massive but unusually strong lobes of magnetic flux originating from the core-mantle boundary, situated beneath Canada and Siberia respectively, but moving with the flow of the molten iron. Because their motion could originate only from the physical movement of molten iron, the lobes served as markers, allowing the researchers to track the flow of iron.

Livermore likens it to being able to track the course of a river at night by watching candles floating on the surface. “As the iron moves, it drags the magnetic field with it,” he says. “We can’t see the flow of iron itself, only the motion of the flux lobes.”

Three satellites sensing the magnetic fields as they orbit the Earth found some variations with time, and it looks like these variations come from the mantle-core boundary.

I don't know if seismography would have the resolution to confirm this.

Wild notions department

The woman with the hemorrhage who touched Jesus' clothes was unclean. So was the coffin of the dead boy which Jesus touched. She became clean. The dead boy, restored to life, was now clean. When John baptized Jesus, did Jesus' touch make the waters clean--baptize the waters?

Sunday, December 18, 2016

Word of the day

"Wouldling"
"The kind of religion that God requires, and will accept, does not consist in weak, dull, and lifeless "wouldlings"--those weak inclinations that lack convictions--that raise us but a little above indifference." Jonathon Edwards

Obviously useful in many contexts...

Instrument question

The rising of the sun

And the running of the deer,

The playing of the merry organ,

Sweet singing in the choir.

"Merry" is not usually the word I'd associate with a pipe organ. One site claimed that the word meant "great," which would certainly fit, but volume 1 of the OED and a jeweler's loupe found nothing resembling that, so the usual "happy" meanings apply. ("Merry-bout" meant what you probably think it did.)

So was the organ a merry accordion, perhaps? Or a jazz organist on the church organ? The song is older than 1700, but there were plenty of church organs then. Were church songs upbeat, as a rule?

Along the way, I stumbled on this from Wikipedia: "Henry VIII wrote a love song Green groweth the holly which alludes to holly and ivy resisting winter blasts and not changing their green hue So I am and ever hath been Unto my lady true."

Friday, December 16, 2016

Good manners

From Galateo: or, A treatise on politeness and delicacy of manners: some unexpected advice.
For the same reason, it is by no means a decent custom for any one, upon meeting with any thing offensive in the way, (as it often happens) to turn immediately to his companion, and point it out to his notice: much less ought he to hold up any thing foetid to another, that he may smell to it; which some people are apt to do; and are even so impertinent as to thrust what is nasty up to their very noses, and smear them with it: "Pray smell it, I beseech you, how it sticks."

On the other hand, some things don't change much:

It is also very impolite to appear melancholy and thoughtful; and, as it were, absent from the company where you are, and wrapt up in your own reflections. And, though this perhaps this may be allowable in those, who, for many years, have been entirely immersed in the study and contemplation of the liberal arts and sciences(*): yet in other people, this is by no means to be tolerated. Nay, such persons would act but prudently, if, at those seasons when they are disposed to indulge their own private meditations, they would sequester themselves entirely from the company of other people.

(*) Thomas Aquinas, dining with the king of France, after a short pause, with his eyes fixed, struck his hand upon the table, crying out; "I have confuted the Manichaeans."

Or

But, however this may be, we ought not to bring a gloom over the minds of those with whom we converse, especially in places where people meet together to enjoy themselves, and not to lament the miseries of human life: although, perhaps, we may sometimes meet with a gloomy mortal of weak nerves, who is fond of squeezing out a tear upon all occasions; whose longing one might easily satisfy by the acrimony of a little mustard, or by entertaining him in a smoaky room. ... To introduce a narration, therefore, of such dismal and melancholy events, on such an occasion, is so very absurd that it were much better entirely to hold one's tongue.

This one struck a little chord:

When, therefore, you address a single person of any rank, who represents a number of people as a society, you do not pay him that civility on his own account: and, if you should speak to him in the singular number, (and call him thou instead of you) you would deprive him of what was really his due, and certainly affront him, by giving him an appellation which belongs only to mere rustics, and men of no importance.

In A Secular Age Taylor notes that there was a change in the meaning of etiquette and good manners some centuries past, in which one was to treat peers, and even inferiors, with courtesies due superiors. I suppose that's the reason we use you universally, with family and rulers alike. (And y'all if we need a plural.) I often run into people who think Thou is a sacred word used only for God. The font of knowledge cites Webster saying that thou had vanished in southern England by about 1650. (Similarly in Dutch?)

I was told to be quite careful about vous and tu usage, but I'm told that tu/toi is getting to be fairly universal. I wonder if there is, or once was before the meaning was forgotten, a difference in attitude between addressing men equally ("When Adam delved") by being formal/respectful, or by being familiar.