MILKY WAY BACKSTORY
I thoroughly enjoyed “Our Turbulent Galaxy,” Ann Finkbeiner’s article on how recent star maps have revealed more about the events that led to the Milky Way’s current state. But some questions remain. When in the timeline did our galaxy acquire its central supermassive black hole, Sagittarius A* (Sgr A*)? And how did Sgr A* come to be? Did the other galaxies that merged with the Milky Way also have black holes?
JOHN SOLTESZ LOGANDALE, NEV.
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How can random collisions of galaxies result in an orderly spiral like the Milky Way? I had thought the common result was an elliptical galaxy. For example, that is expected to be the case when Andromeda and the Milky Way eventually collide to form Milkomeda.
K. CYRUS ROBINSON TAMPA BAY, FLA.
FINKBEINER REPLIES: Soltesz asks lovely questions. The answers are hard to find, but in theory, Sgr A* would have formed during the gravitational collapse of the primordial gas cloud that created our galaxy around 13 billion years ago. Regarding the mergers in the Milky Way’s history: If galaxies that merged with ours were dwarf galaxies, the formation of supermassive central black holes like Sgr A* would have been unlikely but not impossible. If the mergers involved globular clusters, any black holes were probably star-sized.
Robinson asks another lovely question. I think the idea of two large spiral galaxies merging to form an elliptical one comes mainly from theories and simulations of galaxy evolution. But the dwarf galaxies or globular clusters that collided with the Milky Way were a fraction of its size and eventually just merged into the spiral. When I asked astronomers this question, they said that even the bean-shaped batch of stars called the Gaia-Enceladus Sausage was not massive enough to perturb the Milky Way for long.
COGNITION AND TRAUMA
I read “Minds Everywhere,” Rowan Jacobsen’s article on how simple cells show basic cognitive abilities, with a mix of astonishment and confirmation bias. The information about how bioelectric cellular activity in plants allows them to sense and respond to their environment was truly astounding. And although the information about cellular intelligence in the animal kingdom was just as enlightening, I received it with the joy that comes from seeing new discoveries that shed light on old mysteries.
As anyone who’s been paying attention to the field of psychotherapy and to treatment for post-traumatic stress disorder knows, many recent developments in counseling have focused on the growing awareness that trauma is stored not just in our minds but in our bodies as well. My wife and I have experienced this dynamic firsthand. We are well acquainted with traditional approaches to mental health. But the healing modalities we’ve found most beneficial all include some mechanism for releasing trauma stored in the physical body.
The reported findings about the behavior of planaria and slime molds provide the first hard scientific underpinning I’ve seen for these approaches to trauma therapy. I hope someone thinks to start an interdisciplinary dialogue with the psychiatric profession so this understanding of cellular memory can remove some of the stigma and inform more advances in treating trauma and mental illness.
JERRY BARRAX SHERMAN, TEX.
“We must not console ourselves by imagining a future where things are humming along much as they do now.”
—Tobias D. Robison Princeton, N.J.
Jacobsen’s article suggests that human intelligence and cognition might be exceptional in degree but not in kind. As the article notes, “People are just another animal species. But real cognition—that was supposed to set us apart.” This topic was by far the most significant in the February issue.
TOM WELCHEL CHARLOTTE, N.C.
PREDICTIVE PRIORITIES
“Quantum-Proof Secrets,” by Kelsey Houston-Edwards, has a problem that occurs in a number of other articles in Scientific American and other outlets. Houston-Edwards asks us to imagine the future as a technological race: When people manage to develop a powerful quantum computer, it will crack codes that are routinely used for encryption. Meanwhile other people seek to develop effective encryption methods that will be secure even from quantum computers. We must remember that while this race is going on, we are also dealing with the effects of global warming, overpopulation, and all the results of poisoning and tinkering with Earth’s ecology. We must not forget the much greater risks we face, and we must not console ourselves by imagining a future where things are humming along much as they do now except for the effects of quantum computers on decryption.
TOBIAS D. ROBISON PRINCETON, N.J.
ROOT OF RUST
In “Rusting Rivers” [January], Alec Luhn describes how streams in Alaska are turning orange with iron and sulfuric acid. I grew up in south-central Alaska. As a child, when I lived in the state’s city of Kenai during the early 1990s, I often played in a small creek that ran from a large patch of muskeg riddled with kettle ponds across a flat of magnetite sand. The stream was bright orange, its water almost gelatinous at the edges. My friends and I always assumed that this effect was caused by the acidic muskeg water interacting with the magnetite sand. Your article was a fascinating treatment of a phenomenon I had always thought isolated and fairly straightforward.
MARCUS GOTTSCHE VIA E-MAIL
VITAMIN SUPERPOWER?
Kudos to Christie Aschwanden for “The Rise and Fall of Vitamin D” [January], her article on vitamin D deficiency and the vitamin’s purported health benefits. I appreciated the excellent history that highlighted how claims of vitamin D’s superhealing powers have been overstated. I especially appreciated her explanation of co-occurrence versus a cause-and-effect relation: as she notes in her apt analogy, rich people are likely to purchase expensive cars, but buying an expensive car does not make you rich.
JAN COTE-MEROW VIA E-MAIL
ERRATA
“The Great Eclipse,” by Rebecca Boyle [March], should have described magnetic fields as rising from the sun’s core, not from iron in its core.
“Touching the Stars,” by Nia Imara [March], should have said that molecular clouds contain a significant amount of helium, not a trace amount. Additionally, the box “The Birth of a Star” should have said that collapsing cores become dense and hot enough to ignite the fusion of hydrogen into helium, not the merging of two hydrogen atoms to create helium.
“Total Eclipse of the Heartland,” by Katie Peek [Graphic Science, March], should have said that the moon’s shadow will run up to Newfoundland, Canada, not Labrador.
“A Truly Intelligent Machine,” by George Musser [April], should have said that Nancy Kanwisher is at the Massachusetts Institute of Technology and that Anna Ivanova is at the Georgia Institute of Technology.