Magnetic (8/17/23)

Good afternoon, and happy Thursday. If you captured any good photos of the Perseid meteor shower this weekend, send ’em my way—I’m feeling some major FOMO from here in NYC.

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How a Giant Space Magnet Forms

The strongest magnets in the universe are dead stars.

They’re not just any dead stars, though. These powerfully magnetic celestial objects are called magnetars, and they’re fairly rare in our galaxy, consisting of an ultradense core surrounded by a very strong magnetic field. How magnetars behave is pretty well documented. How they form, on the other hand, is still unknown.

In a paper published today in Science, a team led by University of Amsterdam and NSF researchers say they’ve found an excellent candidate for what could precede a magnetar: a highly magnetic, unstable star that looks as though it could collapse into a magnetar at any moment.

Starting with a Wolf-Rayet: The star the researchers turned their attention to for this study has been somewhat of a mystery since it was first identified more than 100 years ago. Named HD 45166, the star is rich in helium, bigger than our Sun, and is part of a binary star system, caught in orbit around another star. What caught researchers’ attention, though, was its unique spectral signature.

Most starlight, when broken down into its component wavelengths, shows a fairly narrow spectrum of emissions. The spectra picked up from stars of a particular type called a Wolf-Rayet are distinctly different.

• Wolf-Rayet stars are massive—often more than 25x the size of the Sun—and they shed stellar material very quickly.

• Because of this, they have remarkably short lifetimes and are rarely spotted. In the Milky Way, astronomers have only found ~220.

Because of the strange, broad spectra HD 45166 showed, astronomers assumed it was some kind of Wolf-Rayet star. Some behavior, though, was still unaccounted for.

Magnetic attraction: “I remember having a Eureka moment while reading the literature: ‘What if the star is magnetic?’” Tomer Shenar, an astronomer at the University of Amsterdam and lead author of the study, said in a release.

Sure enough, follow-up observations using the Canada-France-Hawaii Telescope revealed that the star in question had a remarkably strong magnetic field, clocking in at 43,000 gauss (a measurement of magnetism)—more than any other star of this one’s size. The researchers believe that at the end of this star’s life in a few million years, it will explode as a supernova and the core will contract, trapping the existing magnetic field and forming a brand-new magnetar.

“We thought that the most likely magnetar candidates would come from the most massive of stars,” said André-Nicolas Chené from NSF. “What this research shows us is that stars that are much less massive can still become a magnetar, if the conditions are just right.”

Guessing games: Though the research team believes all signs point to HD 45166 as the stage before a magnetar forms, we haven’t actually witnessed this happening. At the end of this star’s life, signs point to the formation of a magnetar with a magnetic field around 100T gauss—but right now, all we’ve got are signposts.

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Other News from the Cosmos

• Europa Clipper received its high-gain antenna, which will allow it to transmit and receive data during its journey to the eponymous Jovian moon.

• Lunar Trailblazer was also equipped with an important instrument: its Lunar Thermal Mapper camera.

• Ingenuity, the little Mars chopper that could, has completed its 54th flight (and systems are still looking good).

• Maisie’s Galaxy ranks as the fourth oldest galaxy we’ve observed yet, dating to ~390M after the Big Bang.

• Andromeda, our galactic neighbor, could be used to study dark energy.

• STEREO-A, a 17-year-old mission to observe the Sun, made the first Earth flyby in its history.

• The Parker Solar Probe made a small correction to its orbit in preparation for its next Venus flyby.

• Satellites have been collecting ocean fluorescence data via optical imagery for decades, and now researchers are using it to measure phytoplankton nutrition.

The View from Space

One of Planet’s Earth-imaging SkySats captured this photo of the Five-hundred meter Aperture Spherical Telescope in China. (cue spiderman meme)