I am retiring — for the third time.

I was an academic physicist, then a high-tech entrepreneur, and then a physics teacher.

Now I will enjoy my favorite roles: husband, father, and grandfather.

However, recent discoveries by the James Webb Space Telescope (JWST) inspire a final newsletter.

Cosmology is a developing science. Driven by observations and lab experiments, we have learned a great deal about most entities of nature — particles, atoms, molecules, planets, and stars — their formation and evolution over cosmic time. We know much less about the formation and evolution of galaxies and the immense black holes at their centers.

To address these mysteries, NASA made JWST, humankind’s most powerful telescope, which can see our universe as it was 13.6 billion years ago (200 million years after the Big Bang).

With a 6.5-meter (21.3 feet) mirror, JWST can detect objects 7 times fainter than can Hubble. It can analyze infrared light at wavelengths 50 times longer than visible light. See footnote 1 for more about lookback time, distance, and redshift.

Cosmologists had ideas about the formation and evolution of the first galaxies and their supermassive black boles. JWST is now testing these ideas.

What JWST sees is very surprising — as surprising as finding a day-care full of one-year-olds, each weighing 200 pounds.

The EIGER / FRESCO teams took these images of “little red dots” that JWST is finding “by the dozen”.

These “little red dots” are our universe’s first galaxies, born in our universe’s first few 100 million years. Despite the great difficulty of seeing them at all, they appear much brighter than expected.

To be this bright, astronomers first thought these galaxies must be very massive, with an immense number of stars. Growing that big so quickly would be in stark conflict with our calculations, which as always, are laden with assumptions.

After much longer exposures, JWST collected enough light to analyze the galaxies’ spectra (how their light intensity varies with wavelength). The spectra proved the “little red dots” are actually small galaxies harboring voracious black holes.

A star like our sun converts about a tenth of a trillionth of its mass into energy per year. Voracious black holes can convert mass into energy a trillion times faster; before entering the event horizon, in-falling matter emits intense radiation. As they grow, black holes deplete their environs, lessening that radiation.

Mature galaxies, such as the ones we see nearby, are typically over 100 times more massive than their central black holes, even though these black holes are often billions of times more massive than our Sun. But in the first galaxies, it seems the central black holes contain nearly half their galaxy’s mass. This mass-ratio and the voracity of their growing black holes mean the galaxies’ brightness comes in great part from its central black hole rather than its stars. So these “little red dots” require far fewer stars and much less time to develop than first thought. For more on black holes see footnote 2.

Spectral analysis shifts the mystery from “how did galaxies grow so fast” to “how did massive black holes grow so fast”.

We believe we understand stellar mass black holes, which are 5 to a few dozen times more massive than our Sun, and that form in the cataclysmic explosions of massive stars. We know far less about supermassive black holes, which can be many billions of times our Sun’s mass and that we find in the centers of all major modern galaxies.

Black holes grow via mergers and acquisitions. Like all massive bodies, black holes attract other bodies gravitationally. But black holes are much smaller than other bodies of the same mass, which means objects can get much closer to their centers and be exposed to much stronger gravity. A black hole with our Sun’s mass is a million times smaller and has a trillion times stronger gravity at its event horizon than the Sun does at its surface.

Any gas cloud, planet or star that gets too close to a black hole will be torn apart and swallowed piecemeal. The black hole’s mass then increases by the mass of the acquired morsel.

Black holes also grow by mergers. LIGO, the gravitational wave observatory, has detected 90 mergers of stellar mass black holes. The post-merger black hole’s mass is nearly equal to the sum of the mass of the pre-merger bodies, with a modest fraction being converted into gravitational wave energy.

When major galaxies collide and coalesce, we believe the supermassive black holes in the original galaxies will eventually merge. NANOGRAV and other pulsar timing observatories may have detected gravitational waves from these mergers as well.

Our estimates of acquisition and merger rates fall far short of explaining the staggering number of early galaxies with voracious black holes that JWST observes. There are 10 to 100 times more “little red dots” than anyone expected.

One possible explanation is these black holes were born huge, by direct collapse. Due to its own self-gravity, an immense primordial gas cloud might collapse into a single black hole ten thousand times or more as massive as our Sun. Theorists have long dismissed direct collapse, saying such immense clouds would fragment, with each fragment collapsing into a single star. Only when those stars die, would black holes form.

JWST observations are resurrecting direct collapse. Bypassing an intermediate star stage and directly forming massive black holes, accelerates development by several 100 million years. Black holes born with kilo-Sun masses can then grow voraciously by merger and acquisition, attaining mega-Sun masses and powering the myriad “little red dots” JWST sees.

I wish all of you the very best.

Best Wishes,

Robert

September 2023

Footnote 1. Lookback time, distance, and redshift.

For very remote objects, astronomers rely on redshift to determine distance and lookback time. As our universe expands, the wavelengths of every photon (particle of light) stretch. This is called redshift, since visible light shifts to the red (long wavelength) end of our visible spectrum. Each type of atom emits and absorbs light at only certain wavelengths, a spectrum unique to that atom type. When we observe the spectrum of hydrogen, but with all its wavelengths 4 times longer, we know that light was emitted when the universe was 4 times smaller.

From Einstein’s General Theory of Relativity and measurements of the universe’s energy density, we can calculate lookback time — how long ago the universe was 4 times smaller. Looking farther back requires a telescope that can analyze longer wavelengths.

Since light’s speed never changes, lookback time yields distance (how much space) this light has traversed to reach us. Since space is continually expanding, this distance is not the distance to the light source now, nor the distance to where it was when it emitted that light.

Footnote 2: Black holes.

No one has ever directly observed a black hole, and no one ever will — they are totally black, neither emitting nor reflecting light. Our understanding of black holes comes from General Relativity and indirect observations. Black holes are the ultimate triumph of gravity over all other forces of nature.

A black hole consists of a singularity surrounded by an event horizon. The self-gravity of a black hole — each of its particles pulling on all its other particles — overwhelms all other forces and squeezes its entire mass into a singularity, an infinitesimal ball, 300-trillion-trillion times smaller than a hydrogen atom. The event horizon is not a material object, but rather the collection of all points in space where nothing inside can ever escape to the outside — where the escape velocity from the black hole’s gravity equals the speed of light. Inside the event horizon, the escape velocity is greater than the speed of light, so nothing can escape.