Rage, rage (5/18/23)

Good afternoon, and happy Thursday. Let’s hop right into it.

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Do Not Go Gentle

The signs of a specific type of supernova—one in which a dying star simply refuses to die just once, and releases a signal that’s key to helping scientists understand the universe’s expansion—have been caught in radio observations for the first time.

In a study published yesterday in Nature, Stockholm University and National Astronomical Observatory of Japan researchers observed radio signals from a Type Ia (that’s “one-A”) supernova, in which a white dwarf star fed on another star trapped alongside it in a binary system, then destabilized and went supernova.

A storied history: Astronomers don’t fully understand the exact way that a Type Ia supernova forms, but they’ve pieced together certain parts of the story.

First, a white dwarf forms. This occurs when a Sun-like star uses up most of its nuclear fuel, resulting in a last-gasp explosion where the core collapses and the outer layers expand far beyond the original star boundaries: the red giant phase. Eventually, that outer stellar material sheds off, leaving behind colorful clouds of interstellar gas and a hot, dense white dwarf where the star used to be.

That’s the end of the line for most white dwarfs, but in this case, things took a turn. This dying star was locked in a binary system, orbiting another, helium-rich star. Over time, the white dwarf pulled in stellar material from that other star—about 1/1000 the mass of the Sun per year—and accrued so much material that it destabilized and exploded.

• The point at which a star is big enough to become a supernova is defined as the Chandrasekhar limit, and it’s when a star becomes about 1.4 times the mass of the Sun.

Spotting the signals: For decades, astronomers have been searching for the signs of a Type Ia supernova in radio observations. Surely, they thought, such a huge explosion would deliver a shock to the clouds of gas surrounding the binary system and produce radio waves that we could detect from Earth. Until now, though, Type Ia supernovae have only been detectable at optical wavelengths—not radio.

• This could be explained if all Type Ia supernovae consisted of two white dwarfs spiraling into one another and exploding cleanly, with no gas to shock and kickstart radio waves.

• Otherwise, there was a piece of the puzzle missing.

The supernova studied in yesterday’s paper was first observed in 2020 at the Keck observatory in Hawaii. The researchers saw helium gas readings and decided to double-check for radio waves just in case, and lo and behold, they found them.

Guiding the path: Type Ia supernovae are interesting to scientists because they tend to explode when they reach roughly the same mass, resulting in remarkably similar brightness. This uniform brightness makes them great markers for measuring distances and rate of universal expansion—a key question in cosmology.

“The question now is why we haven’t seen this radio signal before in any other Type Ia supernova,” wrote authors Erik Kool and Stuart Ryder in a piece for The Conversation. “Perhaps we tried to detect them too soon after the explosion, and gave up too easily. Or maybe not all companion stars are as helium-rich and prodigious in shedding their gaseous outer layers.”

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Other News from the Cosmos

• NASA has officially given up on resuscitating Lunar Flashlight, a CubeSat mission that failed to fire up its thrusters to get to the Moon.

• JUICE, on the other hand, has notched a success, freeing its RIME antenna as it makes its way to Jupiter.

• The UAE announced which asteroids it is planning to visit with a flagship mission no earlier than 2028.

• ISRO, the Indian space agency, completed qualification testing of the crew capsule propulsion system for its Gaganyaan mission to the Moon.

• Volcanoes were detected on an Earth-sized exoplanet called LP 791-18 d (gotta love those catchy exoplanet names).

• Faster, but less accurate, satellite data assimilation can be used to predict space weather much more effectively than current methods.

• JWST spied water vapor around a comet in the main asteroid belt.

• Astronomers spotted a radiation belt in a foreign solar system for the first time.

The View from Space

Sentinel-6 data identified early signs of El Niño, a periodic warming of the oceans along the west coast of the Americas, propagating across the equatorial Pacific.