So, in the last issue (#829), I made an error that apparently confused folks. I fixed it in the archived web article, but since a lot of you read this newsletter via email you didn’t see the update — a built-in problem with email-based newsletters, I suppose.

I wrote about how the period of X-ray pulses from a black hole went from 18 minutes down to 7. Unfortunately, I mixed up two different concepts: the period of the pulses verses their rate (these are inverse quantities!). I said the period had “slowed”, but what I meant was the period was shorter. I was also thinking about how the rate of the pulses was itself changing, slowing over time, so this got pretty messed up. To be clear, here’s the corrected version:

What they found was something even more weird [link to journal paper]. In mid-2022 the black hole was emitting flashes of X-ray light, pulses, every 18 minutes. When they observed it again in February 2023 the pulses had quickened to one every 10 minutes. By August they were one every 7.5 minutes, and finally by March 2024 there was one every 7.1 minutes.

So something was pulsing, but the pulse rate was increasing over time. Even weirder, the rate at which it increased was slowing. In 2022 – 2023 the time between pulses dropped rapidly from 18 to 10 minutes in less than a year, but by 2024 it dropped from 7.5 to only 7.1 in roughly the same amount of time. What could do this?

I hope that clears things up. My apologies for confusing you. I do make mistakes sometimes, and it’s irritating, so if you find one don’t hesitate to let me know.

WASP-127b is a windy planet. Like, very windy; at the equator, the wind is so fast it would tear your head off, and I mean that quite literally: astronomers measured a top wind speed there of approximately 9 kilometers per second. That’s about 33,000 kilometers per hour, or 35 times faster than the cruising speed of a jet airliner, if that helps.

That’s actually faster than orbital speed around Earth. I lied before; you wouldn’t get your head torn off. You’d be vaporized like a meteor.

OK, so what’s the deal here?

WASP-127b was discovered in 2016 using the Wide-Angle Search for Planets, essentially an array of cameras with really nice lenses on them that can see a large part of the sky all at once. If a star has an exoplanet with an orbit we see edge-on, then the planet will pass directly in front of the star, blocking its light a bit, creating a mini-eclipse called a transit. This dims the light a bit with a repeatable cycle, which is what WASP looks for in thousands of star simultaneously. 

WASP-127b is about 520 light-years from Earth, orbiting a star fairly similar to the Sun. It’s in a very close orbit, though, taking a mere 4.2 days to circle it once! That means it’s only about 7 million km above the star’s surface (Earth is 150 million km from the Sun, to compare), so it gets cooked. It’s average cloud top temperature is roughly 1,000°C. Yegads.

It’s a gas giant, but a weird one. It has a diameter of 1.3 times Jupiter, so it’s big, but a mass just 1/6^th of Jupiter! So it’s what’s called a puffball planet, so hot the atmosphere has expanded hugely, like a hot air balloon.

That brings us to the new observations [link to journal paper]. Astronomers used a spectrograph on the Very Large Telescope in Chile to take spectra of the planet on the infrared — essentially breaking up the incoming light into individual colors, thin slices of wavelengths. When the planet transits the star, starlight passes through the planet’s atmosphere on its way to Earth, and that’s a treasure trove of data. Different molecules absorb different wavelengths of light, creating dips in the spectra that can be measured.

The astronomers found clear signals from water and carbon monoxide, which is pretty cool! But the spectra looked weird: the water and CO signals were split in two in the wavelength direction (as in, there was a signal for water at two different but nearby wavelengths). What does that mean? 

That means Doppler shift. Material moving away from us has its wavelength lengthened a bit (what we call redshifted) and material moving toward us is shortened in wavelength (blueshifted). The spectra from WASP127-b were split from this effect. Mind you, when we look at a planet in transit it’s in silhouette against its star, so it’s all dark. But the star’s light comes through the air, so we only get a signal from around the edge of the planet. The Doppler shift is a maximum at the equator, and that’s where they saw the maximum splitting. 

The amount of shift depends on the velocity of the material, and what they found is that on one side of the planet the air is moving toward us at 8 km/sec, and on the other it’s moving away at 8 km/sec. This is the speed most of the air is moving at, likely at lower latitudes. The astronomers found that the air at the equator, where it’s moving the fastest, is more like 9 km/sec. That’s… incredible. For comparison, wind speeds on Jupiter are more like 0.4 km/sec.

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