Meet the Milky Way in its own words.

The Milky Way: An Autobiography of Our Galaxy takes a tour of our home in the cosmos from an unexpected perspective. Astrophysicist and folklorist Moiya McTier presents herself not as the author, but as the lucky human vessel through which the Milky Way has chosen to tell its story. Then she lets the galaxy take it away, with humor, heart and a huge dose of snark.

The book alternates chapters between science and mythology, reflecting McTier’s dual specialties (her bio says she was the first student in Harvard University’s history to study both). “Many of you don’t realize this, but myths were some of your species’ first attempt at scientific inquiry,” the Milky Way tells us.

The Milky Way is telling its story now because it’s sick of being ignored. Once upon a time, humans looked to the glittering smudge of stars in the sky for insight into when to plant crops or avoid floods. We told stories about the Milky Way’s importance in the origin and fate of the world.

Our galaxy ate it up: For an entity that spends most of its time ripping up smaller galaxies and watching its own stars die, “your stories made me feel loved and needed and, perhaps for the first time in my long existence, more helpful than I was ruinous.” But in the last few centuries, technology and light pollution have pulled humankind away. “At first, I thought it was just a phase,” the Milky Way says. “Then I remembered … that several hundred years is actually a long time for humans.”
So the Milky Way decided to remind us why it’s so important. Its autobiography covers big-picture scientific questions about galaxies, like where they come from (“When a gas cloud loves itself very much,” the Milky Way explains, “it hugs itself extra tight, and after a few hundred million years, a baby galaxy is born. Leave the storks out of it, please.”). It also gets into what galaxies are made of, how they interact with other galaxies, and how they live and die. The book then zooms out to cover the origins and possible ends of the universe, mysteries like dark matter and dark energy, and even humankind’s search for other intelligent life (SN: 8/4/20).

The author takes pains to explain scientific jargon and the technical tools that astronomers use to study the sky. A lot of popular astronomy writing glosses over how astronomers think about cosmic distance or exactly what a spectrum is, but not this book. If you’ve ever been curious about these insider details, The Milky Way has you covered.

McTier’s version of our home galaxy is heavily anthropomorphized. The Milky Way is brash, vain and arrogant in a way that may hide a secret insecurity. Its central black hole is characterized as the physical embodiment of the galaxy’s shame and regrets, a source of deep existential angst. And its relationship with the Andromeda galaxy is like a long-term, long-distance romance, with each galaxy sending stars back and forth as love notes until the two can eventually merge (SN: 3/05/21).

This could have felt gimmicky. But McTier’s efforts to make the metaphors work while keeping the science accurate and up-to-date made the premise endearing and entertaining.

I laughed twice on Page 1. I learned a new word on Page 2. I dog-eared the endnotes early on because it became instantly clear I would want to read every one. I read this book while traveling in rural upstate New York, where the sky is much clearer than at my home outside of Boston. The Milky Way reminded me to look up and appreciate my home in the universe, just like its narrator wanted.

Whenever paleontologist Dana Ehret gives talks about the 15-meter-long prehistoric sharks known as megalodons, he likes to make a joke: “What did megalodon eat?” asks Ehret, Assistant Curator of Natural History at the New Jersey State Museum in Trenton. “Well,” he says, “whatever it wanted.”

Now, there might be evidence that’s literally true. Some megalodons (Otodus megalodon) may have been “hyper apex predators,” higher up the food chain than any ocean animal ever known, researchers report in the June 22 Science Advances. Using chemical measurements of fossilized teeth, scientists compared the diets of marine animals — from polar bears to ancient great white sharks — and found that megalodons and their direct ancestors were often predators on a level never seen before.
The finding contradicts another recent study, which found megalodons were at a similar level in the food chain as great white sharks (SN: 5/31/22). If true, the new results might change how researchers think about what drove megalodons to extinction around 3.5 million years ago.

In the latest study, researchers examined dozens of fossilized teeth for varieties of nitrogen, called isotopes, that have different numbers of neutrons. In animals, one specific nitrogen isotope tends to be more common than another. A predator absorbs both when it eats prey, so the imbalance between the isotopes grows further up the food chain.

For years, scientists have used this trend to learn about modern creatures’ diets. But researchers were almost never able to apply it to fossils millions of years old because the nitrogen levels were too low. In the new study, scientists get around this by feeding their samples to bacteria that digest the nitrogen into a chemical the team can more easily measure.

The result: Megalodon and its direct ancestors, known collectively as megatooth sharks, showed nitrogen isotope excesses sometimes greater than any known marine animal. They were on average probably two levels higher on the food chain than today’s great white sharks, which is like saying that some megalodons would have eaten a beast that ate great whites.

“I definitely thought that I’d just messed up in the lab,” says Emma Kast, a biogeochemist at the University of Cambridge. Yet on closer inspection, the data held up.

The result is “eyebrow-raising,” says Robert Boessenecker, a paleontologist at the College of Charleston in South Carolina who was not involved in the study. “Even if megalodon was eating nothing but killer whales, it would still need to be getting some of this excess nitrogen from something else,” he says, “and there’s just nothing else in the ocean today that has nitrogen isotopes that are that concentrated.”

“I don’t know how to explain it,” he says.

There are possibilities. Megalodons may have eaten predatory sperm whales, though those went extinct before the megatooth sharks. Or megalodons could have been cannibals (SN: 10/5/20).

Another complication comes from the earlier, contradictory study. Those researchers examined the same food chain — in some cases, even the same shark teeth — using a zinc isotope instead of nitrogen. They drew the opposite conclusion, finding megalodons were on a similar level as other apex predators.

The zinc method is not as established as the nitrogen method, though nitrogen isotopes have also rarely been used this way before. “It could be that we don’t have a total understanding and grasp of this technique,” says Sora Kim, a paleoecologist at the University of California, Merced who was involved in both studies. “But if [the newer study] is right, that’s crazy.”

Confirming the results would be a step toward understanding why megalodons died off. If great whites had a similar diet, it could mean that they outcompeted megalodons for food, says Ehret, who was not involved in the study. The new findings suggest that’s unlikely, but leave room for the possibility that great whites competed with — or simply ate — juvenile megalodons (SN: 1/12/21).

Measuring more shark teeth with both techniques could solve the mystery and reconcile the studies. At the same time, Kast says, there’s plenty to explore with their method for measuring nitrogen isotopes in fossils. “There’s so many animals and so many different ecosystems and time periods,” she says.

Boessenecker agrees. When it comes to the ancient oceans, he says, “I guarantee we’re going to find out some really weird stuff.”