Month: September 2024

EROs Atop A Ladder

On By rolcottIn Astronomy: Techniques, UncategorizedLeave a comment

“‘That’s where the argument started‘? That’s right up there with ‘Then the murders began.’ Cathleen Cliff‑hanger strikes again.”

<giggling> “Gotcha, Sy, just like always. Sorry, Kareem, we’ve had this thing since we were kids.”

“Don’t mind me, but do tell him what’s awry with the top of your galactic distance ladder.”

“I need to fill you in first about the ladder’s framework. We know the distances to special ‘standard candles’ scattered across the Universe, but there’s oodles of other objects that aren’t special that way. We can’t know their distances unless we can tie them to the candles somehow. Distance was Edwin Hubble’s big thing. Twenty years after Henrietta Swan Leavitt identified one kind of candle, Hubble studied the light from them. The farthest spectra were stretched more than the closest ones. Better yet, there was a strict relationship between the amount of stretch, we call it the z factor, and the candle’s distance. Turns out that everything at the intergalactic scale is getting farther from everything else. He didn’t call that expansion the Hubble Flow but we do. It comes to about 7% per billion lightyears distance. z connects candle spectrum, object spectrum and object distance. That lets us calibrate successive overlapping steps on the distance ladder, one candle type to the next one.”

“A constant growth rate — that’s exponential, by definition. Like compound interest. The higher it gets, it gets even higher faster.”

“Right, Kareem, except that in the past quarter-century we’ve realized that Hubble was an optimist. The latest data suggests the expansion he discovered is accelerating. We don’t know why but dark energy might have something to do with it. But that’s another story.”

“Cathleen, you said the distance ladder’s top rung had something to do with surface brightness. Surface of what?”

“Galaxies. Stars come at all levels of brightness. You can confirm that visually, at least if you’re in a good dark‑sky area. But a galaxy has billions of stars. When we assess brightness for a galaxy as a whole, the brightest stars make up for the dimmest ones. On the average it’ll look like a bunch of average stars. The idea is that the apparent brightness of some galaxy tells you roughly how many average stars it holds. In turn, that gives you a rough estimate of the galaxy’s mass — our final step up the mass ladder. Well, except for gravitational lensing, but that’s another story.”

“So what’s wrong with that candle?”

“We didn’t think anything was wrong until recently. Do you remember that spate of popular science news stories a year ago about giant galaxies near the beginning of time when they had no business to exist yet?”

“Yeah, there was a lot of noise about we’ll have to revise our theories about how the Universe evolved from the Big Bang, but the articles I saw didn’t have much detail. From what you’ve said so far, let me guess. These were new galaxy sightings, so probably from James Webb Space Telescope data. JWST is good at infra‑red so they must have been looking at severely stretched starlight—”

“z-factor near 8″

“— so near 13 billion lightyears old, but the ‘surface brightness’ standard candle led the researchers to claim their galaxies held some ridiculous number of stars for that era, at least according to current theory. How’d I do?”

“Good guess, Sy. That’s where things stood for almost a year until scientists did what scientists do. A different research group looking at even more data as part of a larger project came up with a simpler explanation. Using additional data from JWST and several other sources, the group concentrated on the most massive galaxies, starting with low‑z recent ones and working back to z=9. Along the way they found some EROs — Extremely Red Objects where a blast of infra‑red boosts their normal starlight brightness. The researchers attribute the blast to hot dust associated with a super‑massive black hole at each ERO’s center. The blast makes an ERO appear more massive than it really is. Guess what? The first report’s ‘ridiculously massive’ early galaxies were EROs. Can’t have them in that top rung.”

“Kareem, how about the rungs on your ladder?”

~~ Rich Olcott

One Step After Another

On By rolcottIn Astronomy: Techniques, UncategorizedLeave a comment

Mid-afternoon, time for a coffee break. As I enter Cal’s shop, I see Cathleen and Kareem chuckling together behind a jumble of Cal’s distinctive graph‑lined paper napkins. “What’s the topic of conversation, guys?”

“Hi, Sy. Kareem and I are comparing ladders.”

I look around, don’t see anything that looks like construction equipment.

“Not that kind, Sy. What’s your definition of a ladder?”

“Getting down to definitions, eh, Kareem? Okay, it’s a framework with steps you can climb up towards something you can’t reach.”

“Well, there you go.”

“Not much help, Cathleen. What are you really bantering about?”

“Each of our fields of study has a framework with steps that let us measure something that’d be way out of reach without it.”

“You’ll appreciate this, Sy — our ladders even use different math. The steps on Cathleen’s ladder are mostly linear, mine are mostly exponential.”

“And they’re both finicky — you have to be really careful when using them.”

“And they’ve both recently had adjustments at the top end.”

“I can see the fun, I think. How about some specifics?”

They exchange a look, Kareem gestures ‘after you‘ and Cathleen opens. “Mine’s in astrometry, Sy, the precise recording of relative positions. Tycho Brahe’s numbers were good to a few dozen arcseconds—”

“Arcsecond?”

“1/60 of an arcminute which is 1/60 of a degree which is 1/360 of a full circle around the sky. Good enough in Newton’s day for him to explain planetary orbits, but we’ve come <ahem> a long way since then. The Gaia telescope mission can resolve certain objects down to a few microarcseconds but that’s only half the problem.”

“Let me guess — you have angles but you don’t have distances.”

“Bingo. Distance is astrometry’s biggest challenge.”

“Wait, Newton’s Law of Gravity includes r as the distance between objects. For that matter, Kepler’s Laws use r² and r³. Couldn’t you juggle them around to evaluate r?”

“Nope. Kepler did ratios, not absolute values. Newton’s Law has r² but you can rewrite it as F ² = GMm/r² = G(M/r)(m/r), G times the product of two mass‑to‑distance ratios. Newton’s G is our least‑accurate physical constant and we don’t have good handles on either of those numerators. Before space flight we just had mass ratios like M/m. We only discovered the Moon’s absolute mass when we orbited it with spacecraft of known mass. That’s the lowest rung on our mass ladder. Inside the Solar System we go step by step with orbit ratios. Outside the system everything’s measured relative to Solar mass.”

“I’m getting the ladder idea. So how do you distances?”

“Lowest rung is parallax, like binocular vision. You look at something from two different points a known distance apart. Measure the angle between the sight‑lines. Figure the triangles to get the something’s distance. The earliest example I know of was in the mid‑1700s when astrometers thousands of miles apart on Earth watched Venus cross the Sun’s disk. Each recorded the precise time they saw Venus touch the Sun’s disk. Given the time shift and the on‑Earth distance, some trigonometry gave them the Earth‑Venus distance. That put a scale to Newtonian orbital diagrams. Parallax across the width of Earth’s orbit yielded stellar distances out to thousands of lightyears with Hubble. We expect ten times better from Gaia.”

“That gets you maybe across the Milky Way. What about farther out?”

“Several ingenious variations on the parallax idea, but mostly standard candles.”

“Candles?”

“Suppose you measure the brightness of a candle that’s a known distance away and there’s an equally luminous candle some unknown distance away. Measured brightness falls as the square of the distance, so if the second candle appears half as bright it’s four times the distance and so on. Climbing the cosmic distance ladder is going from one kind of uniformly‑luminous candle to another kind farther away.”

“Such as?”

“We know how brightness relates to bright‑dim‑bright cycle time for several types of variable stars. That gets us out to 30 million lightyears or so. Type I‑a supernovas act as useful candles out to a billion lightyears. Beyond that we can use galaxy surface brightness. That’s where the recent argument started.”

~ Rich Olcott

  • Thanks to Ken Burke for mentioning tellurium‑128’s septillion‑year half‑life.

Mushy stuff

On By rolcottIn Uncategorized, Physics: Black Holes and Relativity, Crazy TheoriesLeave a comment

“Amanda! Amanda! Amanda!”

“All right, everyone, settle down for our final Crazy Theorist. Jim, you’re up.”

“Thanks, Cathleen. To be honest I’m a little uncomfortable because what I’ve prepared looks like a follow-on to Newt’s idea but we didn’t plan it that way. This is about something I’ve been puzzling over. Like Newt said, black holes have mass, which is what everyone pays attention to, and charge, which is mostly unimportant, and spin. Spin’s what I’ve been pondering. We’ve all got this picture of a perfect black sphere, so how do we know it’s spinning?”

Voice from the back of the room — “Maybe it’s got lumps or something on it.”

“Nope. The No-hair Theorem says the event horizon is mathematically smooth, no distinguishing marks or tattoos. Question, Jeremy?”

“Yessir. Suppose an asteroid or something falls in. Time dilation makes it look like it’s going slower and slower as it gets close to the event horizon, right? Wouldn’t the stuck asteroid be a marker to track the black hole’s rotation?”

“Excellent question.” <Several of Jeremy’s groupies go, “Oooh.”> “Two things to pay attention to here. First, if we can see the asteroid, it’s not yet inside the horizon so it wouldn’t be a direct marker. Beyond that, the hole’s rotation drags nearby spacetime around with it in the ergosphere, that pumpkin‑shaped region surrounding the event horizon except at the rotational poles. As soon as the asteroid penetrates the ergosphere it gets dragged along. From our perspective the asteroid spirals in instead of dropping straight. What with time dilation, if the hole’s spinning fast enough we could even see multiple images of the same asteroid at different levels approaching the horizon.”

Jeremy and all his groupies go, “Oooh.”

“Anyhow, astronomical observation has given us lots of evidence that black holes do spin. I’ve been pondering what’s spinning in there. Most people seem to think that once an object crosses the event horizon it becomes quantum mush. There’d be this great mass of mush spinning like a ball. In fact, that was Schwarzchild’s model for his non-rotating black hole — a simple sphere of incompressible fluid that has the same density throughout, even at the central singularity.”

VBOR — “Boring!”

“Well yeah, but it might be correct, especially if spaghettification and the Firewall act to grind everything down to subatomic particles on the way in. But I got a different idea when I started thinking about what happened to those two black holes that LIGO heard collide in 2015. It just didn’t seem reasonable that both of those objects, each dozens of solar masses in size, would get mushed in the few seconds it took to collide. Question, Vinnie?”

“Yeah, nice talk so far. Hey, Sy and me, we talked a while ago about you can’t have a black hole inside another black hole, right, Sy?”

“That’s not quite what I said, Vinnie. What I proved was that after two black holes collide they can’t both still be black holes inside the big one. That’s different and I don’t think that’s where Jim’s going with this.”

“Right, Mr Moire. I’m not claiming that our two colliders retain their black hole identities. My crazy theory is that each one persists as a high‑density nubbin in an ocean of mush and the nubbins continue to orbit in there as gravity propels them towards the singularity.”

VBOR —”Orbit? Like they just keep that dance going after the collision?”

“Sure. What we can see of their collision is an interaction between the two event horizons and all the external structures. From the outside, we’d see a large part of each object’s mass eternally inbound, locked into the time dilation just above the joined horizon. From the infalling mass perspective, though, the nubbins are still far apart. They collide farther in and farther into the future. The event horizon collision is in their past, and each nubbin still has a lot of angular momentum to stir into the mush. Spin is stirred-up mush.”

Cathleen’s back at the mic. “Well, there you have it. Amanda’s male-pattern baldness theory, Newt’s hyper‑planetary gear, Kareem’s purple snowball or Jim’s mush. Who wins the Ceremonial Broom?”

The claque responds — “Amanda! Amanda! Amanda!”

~ Rich Olcott

A Big Purple Snowball

On By rolcottIn Astronomy: Planetary Science, Crazy Theories, UncategorizedLeave a comment

Cathleen’s back at the mic. “Okay, folks, now for the third speaker in tonight’s Crazy Theory seminar. Kareem, you have the floor.”

“Thanks, Cathleen. Some of you already know I do old‑rock geology. If a rock has a bone in it, I’m not interested. Paleontology to me is like reading this morning’s newspaper. So let me take you back to Precambrian times when Earth may have been purple.”

Kareem’s a quiet guy but he’s got the story‑teller’s gift, probably honed it at field expedition campfires, so we all settle back to listen.

“Four and a half billion years ago, Earth was bright orange. That’s not the color it reflected, that’s the color it glowed. You’ve all seen glass‑blowers at work, how the material gives off a bright orange light coming out of the flame or furnace, soft and ready to be formed. That’s what the planet’s surface was like after its Moon‑birthing collision with Theia. Collisions like that release so much heat that there’s no rocks, just layers of smooth molten glassy slag floating on fluid silicates and nickel‑iron like in a blast furnace. No atmosphere, all the volatiles have been boiled off into space. Got the picture?”

General nodding, especially from maybe‑an‑Art‑major who’s good at pictures.

“Time passes. Heat radiating away cools the world from the outside inward. Now the surface is a thin glassy cap, black like obsidian and basalt, mostly smooth. The cooling contracting cap fractures from the tension while the shrinking interior pulls inward, slow but not gentle. The black glassy surface becomes low craggy mountains and razor‑rubble, sharp enough to slice hiking boots to ribbons. There’s no erosive wind or water yet to round things off. Everything stays sharp‑edged.”

Voice from the back of the room — “Where’s our water from then?”

Juno photo of Jupiter’s clouds Credits: NASA/JPL‑Caltech/SwRI/MSSS/Gerald Eichstädt /Seán Doran © CC NC SA

“Good question. Could be buried water that never got the chance to escape past the cap, could be water ferried in on icy comets or worldlets. People argue about it and I’m not taking sides. The planet gets a new color after it cools enough to hold onto water molecules however they got there — but that water doesn’t stay on the surface. Raindrops hitting still‑hot rock hiss back into steamy clouds. If you were on the moon at the time you’d see a white‑and‑grey Earth like Jupiter’s curdled cloud-tops. Visualize a series of million‑year Hurricane Debbies, all over the world.”

He pauses to let that sink in.

“When things finally cool down enough to allow surface water there’s oceans, but they’re not blue. Millions of years of wind and water erosion have ground the sharp rubble to spiky dust. Most of the thrust‑raised mountains, too. Much of the dust is suspended or dissolved in the ocean turning it black. For a while. The dust is loaded with minerals, especially sulfides, very nutritious for a group of not‑quite bacteria called Archaea that eat sulfides using a molecule that’s powered by green light but reflects red and blue. When the Archaea take over, the oceans look magenta from the reflected red and blue.”

Maybe‑an‑Art‑major giggles.

“Next major event, we think, was the Huronian Glaciation, when most or all of the Earth was a solid white because it was covered with ice. Killed off most or the Archaea. When that melted, different parts of the ocean turned black from floating dead Archaea and and then milky turquoise from sulfur particles. Next stage was purple, from a different group of sulfur‑eating purple almost‑bacteria. Then we had snowball whiteness again, which gave green‑reflecting chlorophyll‑users a chance to take over, clear our the sulfur and leave the oceans blue.”

VBOR — “That’s your Crazy Theory?”

“No, that’s mostly mainstream. Question is, what terminated the deepfreezes? Lots of ideas out there — solar dimming and brightening, different combinations of CO2 and methane from volcanoes or bacteria, even meteorites. Anyone remember Ian Malcom’s repeated line in the Jurassic Park movies?”

Everyone — “Life will find a way!”

“Right on. My crazy’s about the two almost‑bacteria. Suppose each kind managed to infiltrate their day’s Great Extinction glaciers. Suppose planet‑wide bacterial purple pigments absorbed sunlight’s energy, melting the ice. Karma, yes?”

~ Rich Olcott

A Great Big Mesh

On By rolcottIn Uncategorized, Physics: Black Holes and Relativity, Crazy TheoriesLeave a comment

Cal has my coffee mug filled as soon as I step into his shop. “Get to the back room quick, Sy. Cathleen’s got another Crazy Theories seminar going back there.”

So I do. First thing I hear is Amanda finishing her turn at the mic. “And that’s why humans evolved male pattern baldness.”

A furor of “Amanda! Amanda! Amanda!” then Cathleen regains control. “Thank you, Amanda. Next up — Newt Barnes. What’s your Crazy Theory, Newt?”

“Crazy idea, not a theory, but I like it. Everybody’s heard of black holes, right?”

<general nodding>

“And we’ve all heard that nothing can leave a black hole, not even light.”

<more nodding>

“Well in fact that’s mostly not true. There’s so much confusion about black holes. We’ve known about a black hole’s event horizon and its internal mass since the 1920s. It took years for us to realize that the central mass could wrap a shiny accretion disk around itself, and an ergosphere, and maybe spit out jets. So, close outside the Event Horizon there’s a lot of light‑emitting structure, right?”

<A bit less nodding, but still.>

“Right. So I’ll skip in past a few controversial layers and get down to the famously black event horizon. Why’s it black?”

Voice from the back of the room — “Because photons can’t get out because escape velocity’s faster than lightspeed.”

“That’s the answer I expected, but it’s also one of the confusing parts. You’re right, the horizon marks the level where outward‑bound massy particles can’t escape. The escape velocity equation depends on trading off kinetic and gravitational potential energy. Any particle with mass would have to convert an impossible amount of kinetic energy into gravitational potential energy to get through the barrier. But zero‑mass particles, photons and such, are pure kinetic energy. They aren’t bound by a gravitational potential so escape velocity trade‑offs simply don’t apply. There’s a deeper reason photons also can’t get out.”

VBOR — “So what’s trapping them?”

“Time. It traps photons and any kind of information. The other thing about the Event Horizon is, it’s the level where spacetime is so bent around that the time‑coordinate is just on the verge of pointing inward. Once you’re inside that boundary the cause‑and‑effect arrow of time is against you. Whatever direction you point your flashlight, its beam will emerge in your future and that’s away from the horizon. Trying to send a signal outside would be like sending it into your past, which you can’t do. Nothing gets away from a black hole except…”

“Except?”

“Roger Penrose found a loophole and I may have found another one. There’s something that Wheeler called the No-Hair Theorem. It says that the Event Horizon hides everything inside it except for its mass, electric charge and angular momentum.”

“How do those get out?”

“They don’t get out so much as serve as backdrop for all the drama in the rest of the structure. If you know the mass, for instance, you can calculate its temperature and the Horizon’s diameter and a collection of other properties.”

Cathleen senses a teachable moment and breaks in. “Talk about charge and spin, Newt.”

“I was going there, Cathleen. Kerr and company’s equations take account of both of those. Turns out the attractive forces between opposite charges are so much stronger than gravity that it’s hard for an object in space to build up a significant amount of either kind of charge without getting neutralized almost immediately. Kind of ironic that the Coulomb force, far stronger than gravity, generates net energy contributions that are much smaller than the gravity‑based ones. Spin, though, that’s where the loopholes are. Penrose figured out how particles from the accretion disk could dip into the black hole’s spinning ergosphere, steal some of its energy, and stream up to power the jets.”

VBOR — “What’s your loophole then?”

“Speed contrast between layers. The black hole mass is spinning at a great rate, dragging nearby spacetime and the ergosphere and the accretion disk around with it. But the layers go slower as you move outward. Station a turbine generator like an idler gear between any two layers and you’re pulling power from the black hole’s spin.”

Silence … then, “Amanda! Amanda! Amanda!”

~ Rich Olcott