Glimpse into galaxies: Eclipse arrives 100 years after discovery our Milky Way isn't alone in universe
Mar. 10—Our status as milk-producing mammals would not be lost on intelligent aliens studying the history of our astronomy.
The ancient Greeks, they would learn, described a milkiness in the night sky. And when the road-building Romans followed, they saw in that milkiness the shape of, well, a road or a "way," now a highway.
So, it would seem to our visitors as natural as mother's milk that we came to call our home galaxy the Milky Way — and that our adjective for galaxies, galactic, can't be spelled without lactic.
In addition to being a year of total solar eclipse in Ohio, this is the 100th anniversary of Edwin Hubble's discovery the Milky Way is not the only galaxy in the universe.
An exclamation point was added 14 years ago when a telescope named for Hubble was pointed to a dark part of space the size of a grain of sand held at arm's length.
The device detected 10,000 galaxies in that tiny patch of the sky, making those who took under in the over-under bet regarding the number of galaxies losers on a galactic scale.
Dan Fleisch, professor emeritus of physics at Wittenberg University, said there are an estimated trillion — that's 1,000 billion — galaxies out there. With his help, we today focus on the Milky Way.
From above, our galaxy looks like something that goes well with milk, a Cinnabon. There's a bulge in the center like a yolk in the center of a fried egg, and that area may contain evidence of that our galaxy collided with another galaxy at a time before insurers could raise its rates.
In the central section of the galaxy is a bar of white icing shaped like Zero candy bar, produced by Hollywood candies, not Milky Way.
From there, the galaxy's icing-white arms spiral out and are divided by dark regions that in the Cinnabon are filled with sugar and its namesake spice.
Fleisch said barred spiral galaxies are about twice as numerous as those without bars and, together, they make up about half of all galaxies. The other half includes lens-shape, egg-shaped and the catch-all category of irregular galaxies. Antenna galaxies have tiny arms compared to spirals and individual galaxies called The Sombrero, The Tarantula and The Whirlpool resembled those objects. Alas, there is no Maytag galaxy.
At the dead center of the Milky Way — and many large galaxies — is a supermassive black hole around which the stars in the galaxy orbit just like the planets of our solar system orbit the sun. (As film-goers know, black holes were an interest of Robert Oppenheimer.)
The Milky Way's black hole, called Sag A-, is estimated to have a mass 4.3 million times greater than our sun, which is 330,000 times more massive than Earth.
TON 618, the most massive black hole yet discovered, is thought to be more than 66 billion times as massive as our sun, a mass that slightly edges the combined masses of all the stars in the Milky Way. Black holes are massive enough that their gravitational pull prevents even light from escaping them.
By contrast, the brightest objects of the Milky Way go by an unfortunate name that makes them sound like globs coughed out of lungs. But the root of the first word in Globular Clusters is globe, not glob, bringing to mind luminescent objects lighting up the darkness of space like Victorian street lamps.
Most stars in globular clusters are far larger and brighter than the sun and are metal-rich, evidence that they both burn at a higher temperature and formed from the heavy elements produced by previous generations of stars. Their brilliance across 50,000 lightyears of the galaxy makes them excellent reference points for locating and mapping the galaxy's other notable objects. Most significant to us is our sun, found about 26,000 lightyears from the galactic center.
Although the Milky Way is estimated to be 13.6 billion years old — just younger than the universe itself — various sections have been around for different amounts of time.
The sun and earth are about 4.5 billion years old, about the same as other stars born in the Orion spur of our galaxy.
In the star-birth process, clumps of dust in a large, cold gas cloud called a nebula are attracted by one another's gravity and combine to produce larger and larger aggregations of particles. Some of these eventually gain enough mass to condense into new stars that fuse hydrogen into helium in their cores. These new stars are orbited by free-floating matter that eventually forms planets, moons and other objects such as asteroids and comets.
Astronomers have spotted this star-formation process elsewhere in our galaxy and in other galaxies, but much mystery still remains about many processes. Perhaps the darkest mysteries involves matter and energy.
Fleisch said it's called dark matter because "it doesn't give off light or radio waves or infrared radiation. And since it doesn't radiate anything, it can only be detected indirectly."
But it's suspected to be there because, without it, the visible parts of the universe can't account for all the energy and mass required to explain movements of stars and galaxies. The math just doesn't add up.
The amount of mass needed to make it add up is what we now call dark matter, which is commonly said to be the glue that holds things together.
Then there's dark energy, the amount of energy that cannot be accounted for from observable sources but is necessary to explain the rapid rate at which the universe is expanding.
Edwin Hubble, by the way, was involved in the early thinking on that as well.
About a dozen years ago, when the scientists concluded that dark matter and dark energy constitute 80 to 90 percent of the universe, Fleisch offered a positive spin on what might seem evidence of a massive black hole of human ignorance despite our long history of studying the universe.
"You should never be depressed by what we don't know," Fleisch said, "because the amazing thing is that our brains, our curiosity and our hard work to understand the universe have allowed us to know anything at all."
Even knowing that it would take the fastest spaceship we've ever built 173 million years to cross the Milky Way, is "a stunning achievement," he said.
And anyone who has enjoyed the visually stunning images from the Hubble and the James Webb Space Telescopes can't help but be excited about what they will teach us.
Of all creatures, we mammals should know by now not to cry over spilled milk.
Next Sunday: Stars.
The first in a series by Tom Stafford.
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WittClipse talks
Wittenberg University Professor Dan Fleisch will present the first of a series of free companion talks to this series at 1 p.m. today at Wittenberg University's Weaver Observatory. Today's talk on galaxies will be followed Stars on March 16; Planets on March 23; and Cathedrals as Solar Observatories, March 31. The presentations are a part of WittClipse.
