American Scientist

In this roundup, managing editor Stacey Lutkoski summarizes notable recent developments in scientific research, selected from reports compiled in the free electronic newsletter Sigma Xi SmartBrief.

Competing “Cow” Theories

Astronomers are puzzling over an unusual flash in the sky on June 16, 2018. The blast of light—officially named AT2018cow and nicknamed “the Cow” after the randomly assigned last three letters—occurred in a galaxy 200 million light-years from Earth in the constellation Hercules. The flash was at least 10 times brighter than a typical supernova. It grew over the course of three days and then faded over the next few months. Researchers have developed two competing theories to explain the Cow, which they presented at the American Astronomical Society meeting on January 10 in Seattle, Washington. One group contends that the blast was from a black hole ripping apart a white dwarf star, a phenomenon known as a tidal disruption event (illustrated below). The other group argues that it was caused by a massive star dying in a supernova and transforming into either a black hole or a neutron star. In any case, astronomers have witnessed a never-before-seen event in real time, which will provide a wealth of data for future studies.

Margutti, R., et al. 2018. An embedded x-ray source shines through the aspherical AT2018cow: Revealing the inner workings of the most luminous fast-evolving optical transients. arXiv. https://arxiv.org/abs /1810.10720 (October 25)

Kuin, N. P. M., et al. 2019. Swift spectra of AT2018cow: A white dwarf disruption event? arXiv. https://arxiv.org/abs /1808.08492 (January 10)

Transcortical Vessels in Bones

Human anatomy is one of the oldest branches of science, but developments in microscopy allow researchers to make new discoveries even in this well-trodden field. A team of immunologists used advanced imaging techniques to examine long bones (such as the tibia) in mice and found that they were covered in capillaries. Previous studies had suggested that long bones primarily had blood vessels at the ends with a small number in the middle, so the revelation that the bones are covered in capillaries, which they named transcortical vessels, provides new information about how bones interface with the body’s vascular system. These capillaries provide a passage for immune cells to exit the bone marrow—where they are made—and enter the bloodstream to circulate throughout the body. Subsequent tests on a human femur bone fragment suggest that human long bones also have transcortical capillaries. This information may provide new insights on the causes and possible treatments for bone diseases such as osteoporosis.

Grüneboom, A., et al. 2019. A network of trans-cortical capillaries as mainstay for blood circulation in long bones. Nature Metabolism. doi:10.1038/s42255-018-0016-5 (January 21)

Glacial Origins of Geologic Gaps

When trekking to the bottom of the Grand Canyon, hikers can glimpse geologic evidence of the Earth’s past. Each striation of the rock wall represents a distinct period in Earth’s history. But there are also gaps in that record, where Proterozoic crystalline rocks that formed a billion years ago abut Cambrian rocks half their age (below). Geoscientists have theorized since the 18th century about what caused these missing pieces in the geologic record, a phenomenon called the Great Unconformity. A new theory is that glaciers rapidly eroded large swaths of the Earth’s crust during a period known as snowball Earth. Snowball Earth is the hypothesis that approximately 750 million years ago, the entire planet was encased in snow. A team of geoscientists compared radioactive isotopes contained in zircons—tiny crystals in grains of sand that hold evidence of Earth’s early development (see Zircons: More Precious than Diamonds)—that they collected at different depths throughout the Great Unconformity. Their analysis uncovered a geochemical shift that coincides with the proposed beginning of snowball Earth, supporting the theory that parts of the Earth’s crust were scraped off by massive glaciers. As the planet warmed and the snowball melted, new sediment settled on top of areas where the older rocks were exposed, creating these anomalous gaps in the geologic record.

Keller, C. B., et al. 2019. Neoproterozoic glacial origin of the Great Unconformity. Proceedings of the National Academy of Sciences of the U.S.A. doi: 10.1073/pnas.1804350116 (January 22)

Termites Combat Drought

As droughts caused by global climate change become more frequent, termites may play an important role in helping rainforests weather the dry conditions. A team of biologists studied termite communities in a Malaysian tropical rainforest during the 2015–2016 “super El Niño” by creating several plots where they suppressed termite activity. In control plots, where activity was not suppressed, the termite population doubled during the drought, and the increased insect activity helped with leaf decomposition, soil nutrient balance, and soil moisture retention. Furthermore, there was a 51-percent increase in seedling survival on control plots compared to the termite-suppressed plots, suggesting that termites might help protect new growth against drought by increasing the availability of moisture and nutrients in the soil.

Ashton, L. A., et al. 2019. Termites mitigate the effects of drought in tropical rainforest. Science. doi:10.1126/science.aau9565 (January 11)