The fascination of origins—the very long view.
Curiosity about personal ancestry has made Ancestry DNA and 23andMe booming businesses. Marketing has grown this kind of curiosity into a lucrative appetite. Indications are that the customer base is doubling annually.
Curiosity about cosmic origins might be growing more slowly, but the explosion of new information about the early universe thrills a lot of folks, without much money changing hands. To consider where we come from on the largest time scales has a calming effect in this tempestuous, maddening, frightening, and tragic moment in human history. Launching one’s imagination into the vastness of space leaves behind much of the craziness of our political, social, and cultural (melo)dramas.
TABLE OF CONTENTS
This is a very long post, perhaps of little interest to those who don’t share my fascination with cosmic origins. I present a table of contents of the sections below as a guide to what’s in store.
- Not just another pretty face: ancient spiral galaxy.
- The unmiraculous miracle of gravitational lensing
- Implications of the age of the earliest spiral galaxy
- Galactic structure, supermassive black holes, and a question of timing
- Primordial black holes to the rescue!
- An aside on supermassive black holes at the centers of galaxies
- More on spirals
- A Family Tree of galaxies
- THE END
Not just another pretty face: ancient spiral galaxy
Don’t we just love our spiral galaxies?!? It’s not so much love, it’s more like being awestruck by ineffable beauty, combined with the knowledge that each typically contains hundreds of billions of stars spread out across distances up to hundreds of thousands of light years. (Another plus is that we actually live in one.) I’ve cheated a bit here by picking a particularly gorgeous example, the Pinwheel Galaxy—a kind of canonical form of which all spirals are variations on a starry theme. (For a spectacular collection of spiral galaxy images, follow the link: glorious spirals in abundance .)
Spiral galaxies are hotbeds of star formation. Older elliptical and irregular galaxies are more diffuse, and dimmer. Newer elliptical galaxies are also formed by collisions of galaxies, such as the impending collision of the Andromeda and Milky Way galaxies (some 4 billion years hence) simulated in this YouTube video:
The shape of the oldest spiral, recently discovered, is not so well-defined—and, because of its distance and speed of recession, its light is extremely red-shifted.* It’s a bit of a blurry snapshot (see the link four paragraphs below), but the fact that we can see it at all, at a distance upwards of 11 billion light years, is close to miraculous.
Before I give you a link to a depiction of the oldest spiral, a few words on gravitational lensing—the “miracle” that enables us to see such a distant object that is not only stupendously far away, but is also located behind a slew of stars and galaxies and cosmic dust, such that seeing it is equivalent to seeing around a corner.
The unmiraculous miracle of gravitational lensing: how the oldest spiral galaxy was viewed
You may recall that Einstein’s General Theory of Relativity was decisively confirmed in 1919 by observing the “bending” of light from stars behind our sun during a solar eclipse. ** (“Bending” is a misnomer. In General Relativity, mass shapes space such that stuff—planets, satellites, asteroids, rockets, photons, fuel dragsters, wide receivers—moves along “geodesics,” apparently curved paths, but really as straight as physics will allow.)
A massive enough object, such as our sun, can “bend” light around itself sufficiently to make an object behind it visible—thus the term gravitational lensing. To view the ancient spiral, the object used was actually an entire cluster of galaxies. (Clusters of galaxies bound together by gravity continue to resist the force of Dark Energy which is driving the expansion of the universe at an accelerating rate. It is not yet known if Dark Energy will eventually tear apart galactic clusters, galaxies, stars, solar systems, planets, Trump Tower, rocks, and even atoms themselves in a “Big Rip”—a few trillion years off, but a sobering prospect nonetheless.)
Here ‘Tis: I hope that helps explain the rendering you will find of the observation found at : oldest spiral
For a more thorough explanation of gravitational lensing, check out
http://www.cfhtlens.org/public/what-gravitational-lensing
Implications of the age of the earliest spiral, and an even older irregular galaxy
Aesthetics aside, the discovery of the oldest spiral galaxy is a Very Big Deal in astrophysics. At 11 billion light-years away, it represents definitive structure emerging from random smatterings of irregular proto-galaxies and elliptical galaxies when the Universe was just a tad over 2 billion years old. The appearance of this galaxy adds to accumulating evidence that star and galaxy formation occurred earlier and faster in cosmic history, than recently believed.
An even older, irregular galaxy was sighted in 2016, at a distance of more than 13 billion light years (and 13 billions years ago in time.
Finding this extremely old galaxy shattered existing models of galaxy formation. To have this much clumping of matter, star formation, and organization of stars in galaxies so early in cosmic evolution raises the riddle of a Missing Cosmic Link.
It’s not too surprising that the answer to the riddle of early galaxy formation may lie wrapped in the enigma of Black Hole formation—and not just any old garden variety black holes, but primordial black holes.
Galactic structure, supermassive black holes, and a question of timing
Recent findings indicate that galaxies—probably all galaxies—have supermassive black holes (greater than 1,000 solar masses) at their center.*** Certainly all spiral galaxies do. The age of the earliest spiral galaxy implies that supermassive black holes have a very long lineage.
If you’re like me, knowing that many black holes result from the collapse of huge stars, you may have thought that supermassive black holes grow from “ordinary” black holes gorging on matter that falls into them, pulled by their enormous gravity. Given enough time, an originally modest black hole could grow to enormous proportions: “supermassive.”
Given enough time. But the existence of supermassive Black Holes in the very early universe contradicts that supposition. There wasn’t enough time for ordinary (“stellar”) black holes of 4 to 100 solar masses—to have sucked in enough material to become supermassive.
So where—if there was insufficient time for ordinary black holes to grow into supermassive black holes—did the first supermassives come from?
Primordial black holes to the rescue! Early galactic structure, D__k M____r, and supermassive black holes
Primordial black holes may sound like the spookiest celestial creatures ever to slither across the face of the cosmos, but they may have had a positive role to play in furthering the processes that have resulted, at long last, in Us. In theory, according to the Standard Model of cosmic evolution, these little giants were spawned within the first second after the Big Bang. But one of the questions bedeviling the Standard Model has been, if primordial black holes were created, where did they get to?
Problem: since primordials are small and dark, they are really, as you can imagine, hard to see. Ordinary black holes (3.8 solar masses on up) can be perceived indirectly by their effects on things around them—gravitational effects on other stars, and bright surrounding disks (accretion disks). Not only are primordials hard to detect, but while theory dictates their existence, it does not dictate how many would have been created.
What if there were zillions† of primordial black holes, spewed throughout expanding space, right from the cosmic get-go?
Those zillions of primordials could tie up some loose ends in the puzzle, not only of galactic structure in the early universe, but also one of the most humongous mysteries of physics: what the heck makes up Dark Matter?††
At this point, you may not be amazed to hear that this slaying of two stupendous cosmic birds with one theoretical stone comes from the hypothesis that Dark Matter is all, or mostly, made of primordial black holes.
We already know that Dark Matter is key to holding together most of the galaxies we currently see, including our own Milky Way. Dark matter forms “halos” around galaxies that keep especially frisky stars from flying off into intergalactic voids. Ergo, (1) dark matter consisting of primordial black holes is the best candidate for pulling together early galaxies, and (2) primordial black holes could have formed the first supermassive black holes at the center of galaxies.
So the answer to the question of where the primordial black holes got to, is: all over the Universe.
New hypotheses concerning primordial black holes have gained instant stardom (!!) due to the observations of collisions between some unexpectedly hefty, distant black holes by the LIGO gravity wave detectors (the sensational instruments which you may recall from the Part 3 of this Most Amazing Year in Space series, in the discussion of colliding neutron stars: https://www.markheinickewrites.com/2018/01/15/the-most-amazing-year-in-space-ever-part-3-when-neutron-stars-collide/ ).
Those observations of colliding black holes have led to new proposals in astrophysics on these topics, three of which I link to as follows:
Primordial and supermassive black holes
Primordial black holes and Dark Matter
NASA scientist proposes link between primordial black holes and Dark Matter
An aside on supermassive black holes at the centers of galaxies
You may be wondering, if supermassive black holes are at the centers of galaxies, why we don’t see a sinister void in the center of a spiral galaxy such as the Pinwheel pictured above. Two reasons: (1) the bulge in the center of a spiral consists of billions of closely packed stars which serve to block the view; (2) like many black holes, the supermassive is surrounded by an accretion disk of gas revolving around the central mass and falling toward the event horizon en route to ineluctable doom in the center of the black hole (the “Singularity”). Friction from gases circling at close to the speed of light generates huge gobs of electromagnetic energy. In the case of a supermassive black hole, the radiation takes the form of visible and ultraviolet light—a lot of it. For a more thorough explanation of accretion disks, see http://stronggravity.eu/public-outreach-tmp/accretion-disks/
More on spirals
The image to the right was lifted from a highly readable, popular treatment of the unique features of spirals, explaining structure, particularly the behavior of density waves that create the arms. (Just what causes the density waves is still unexplained.) See:
https://www.thoughtco.com/spiral-galaxies-4137643
A family tree of galaxies
A belief in the hierarchical formation of galaxies has led to a classification in the shape of a “Family Tree.” On the right is a totally cool, if somewhat 
simplistic, depiction of a “tree” with simpler forms at the bottom (small irregular forms, and small ellipticals) evolving into more complex forms at the top. At the top are our beloved spirals, along with the large ellipticals resulting from merged galaxies, such as spirals having merged in the way Andromeda and the Milky Way are expected to do. For the full discussion of the family tree, including a “family album” of the Milky Way itself, link to the following:
Galactic Family Tree
=============== footnotes follow ================
* “red shift” refers to the stretching of light waves toward longer wavelengths by movement away from us, similar to the lowering of pitch of sound waves from a receding vehicle—the Doppler Effect. The red shift of celestial objects serves as a proxy for distance, because the expansion of the universe means the farther away the object is, the faster it is going away from us, and thus the redder it appears. The redder, the farther.
At the utmost limits of distance and speed away from us is the Cosmic Microwave Background (CMB), the afterglow of the Big Bang, showing photons stretched all the way out of the visible electromagnetic spectrum into microwave lengths (longer than infrared and shorter than radio waves).
The CMB, predicted by theory as far back as 1948, was first observed by accident in 1964, by two radio astronomers mapping the sky who were puzzled by a uniform hiss coming from all directions. See Big Bang electromagnetic echo
For a NASA presentation on the electromagnetic spectrum, see: https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html
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** Forbes magazine published an especially good explanation of the “proof” of General Relativity here.
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*** If you missed it in THE MOST AMAZING YEAR IN SPACE, EVER: Part 3, check out at your leisure the long video on Black Holes and galaxy formation, making the case for supermassive black holes at the centers of all galaxies: Black Hole Apocalypse!
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† technical term for lots and lots
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†† Dark Matter is not a sinister form of tracking device dreamed up by the NSA. It does not emit or reflect electromagnetic radiation, and is thus invisible to our senses and ordinary instruments. Its existence is inferred from gravitational effects; the only property we can be sure about is that it has mass, and is ubiquitous wherever there is a galaxy. There is a dwindling number of speculations as to what it actually is, in terms of known physics. I sheepishly confess to having bought an entire book by a prominent physicist full of hypotheses as to what dark matter is. I not only failed understand most of it, but eventually came to realize that the basic answer to the riddle was: we don’t know. But, thanks to the discoveries discussed in this post, maybe we do know! But don’t yet know we know.