Readers ask concerning the Milky Means’s newfound ‘feather’, CT scan security and extra


Effective feather

A filament of chilly, dense gasoline named the Gangotri wave might bridge two spiral arms close to the Milky Means’s middle, Lisa Grossman reported in “Scientists discover the Milky Means’s first recognized ‘feather’ ” (SN: 12/18/21 & 1/1/22, p. 4).

Reader Doug Holcomb requested how this newfound “feather” differs from a galactic spur.

The language describing the completely different limbs of the Milky Means can get fuzzy, Grossman says. Usually, our galaxy has 4 major spiral arms emanating from its middle, and an unknown variety of smaller arms. A spur tends to be an offshoot of an arm, however the line between spur and arm shouldn’t be so strict.

“The primary distinction between the Gangotri wave and different galactic tendrils is that Gangotri runs perpendicular to the bigger arms of the galaxy, and crosses two of them,” Grossman says. “That crossing of the 2 arms is exclusive, though researchers anticipate that there are in all probability extra of them all through the Milky Means which have but to be found.”

Reader Jasmine Melvin puzzled whether or not the Gangotri wave has stars.

“Many areas throughout the wave are websites of energetic star formation,” says astrophysicist Veena V.S. of the Max Planck Institute for Radio Astronomy in Germany. Future research are wanted to characterize the entire variety of stars throughout the construction, she says.

Carbon curiosity

Large stars with an orbiting accomplice star shed on common about twice as a lot carbon as loner stars do, Ken Croswell reported in “How stars flip into carbon factories” (SN: 12/18/21 & 1/1/22, p. 12).

When a large star with a accomplice explodes, its carbon is solid into house, Croswell reported. However, a single star’s core would have destroyed a lot of its carbon earlier than such an explosion. Reader Invoice Camenga wished to know what turns into of the carbon in single stars.

“The carbon doesn’t simply vanish,” Croswell says. Throughout a single star’s life, most of its carbon will get reworked into oxygen. When the star explodes, that oxygen is solid into house, serving to make oxygen the third most plentiful aspect within the universe after hydrogen and helium. The precise nuclear response, he says, is carbon-12 + helium-4 → oxygen-16 + power.

X-ray! X-ray! Learn all about it!

In 1971, the primary X-ray CT scan of a affected person supplied an unprecedented picture of the human mind. Fifty years later, CT scans are nonetheless saving lives and serving to researchers higher perceive the world round us, Emily Conover reported in “Celebrating 50 years of CT scans” (SN: 12/18/21 & 1/1/22, p. 44).

A number of readers puzzled whether or not radiation from CT scans must be a priority for these receiving them.

Scientists have regularly improved CT know-how over time, not solely making it quicker and better decision, but additionally lowering the quantity of radiation that folks obtain, Conover says. Though CT scans usually expose sufferers to extra radiation than normal X-ray imaging, the quantity of radiation from one scan remains to be comparatively small. Relying on the kind of CT scan, the radiation acquired could also be lower than the typical background radiation an individual will get from numerous sources within the atmosphere over a 12 months, she says.

There’s nonetheless debate amongst scientists concerning the potential well being results of such low doses of radiation, Conover says. When a health care provider orders a CT scan, they usually may have decided that the profit to the affected person outweighs the small danger.


In “Pointed takedown of the mammoth hunters” (SN: 1/15/22, p. 22), archaeologist Vance Holliday of the College of Arizona in Tucson, not Vance Haynes, weighed in on archaeologist Metin Eren’s speculation that historical Clovis factors weren’t used for searching the tusked beasts.


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