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AAS #237: five things we learned

Each January, the American Astronomical Society (AAS) conducts a meeting widely hailed as the “Superbowl of astronomy”, in which astronomers gather from around the world to share their latest results.

Last year it was in Honolulu. But this year, thanks to COVID-19, it was online—something that AAS had already practised for smaller meetings as far back as June 2020. Not surprisingly, given the rehearsal, they did a smash-bang job of it. But they also had a remarkable amount to present… plus a lot of fun. 

Part of the fun is simply that astronomy is the realm of gorgeous pictures. Who can help but be enchanted by things with names like the Butterfly Nebula or the Jewel Bug?

But gorgeous images weren’t the only thing to come out of the meeting. Here are five other highlights.

1. Astronomers love acronyms

Gone are the days when things were generally named for people or places: Mt Palomar, Lowell Observatory, Kitt Peak, Arecibo. Now, they’re cuter… and virtually everything is an acronym.

Some are simply designed to be short, pronounceable, and reasonably related to their purpose. ALMA is the Atacama Large Millimeter-submillimeter Array (ie, a radio telescope) in Chile’s Atacama Desert. Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) is a telescope that pans the heavens for anything that moves or quickly changes.

But there’s also a trend toward increasingly cool names, like CHIME (Canadian Hydrogen Intensity Mapping Experiment), and DECaLS (Dark Energy Camera Legacy Survey).

How cool is COOL? Or, more precisely, COOL-LAMPS: ChicagO Optically-Selected Lenses at the Margins of Public Surveys (don’t ask; it’s about using human eyes to scan enormous amounts of data for gravitationally lensed galaxies that escape AI algorithms, which is a bit too much of a mouthful to explain in detail.)

But wildest by far? The Burst Alert Telescope (for gamma ray bursts), and a companion project called Gamma-Ray Urgent Achiever for Novel Opportunities. The acronyms: BAT and BAT-GUANO.

So, ahem: WAHOO (What in All Hell are these Organisations Originating?

2. Astronomers are persistent

If they encounter a mystery or a difficult problem, astronomers may set it aside for years, but eventually they’ll come back to it. 

Such was the case for a star called KOI-5, which hosted the second possible exoplanet identified by NASA’s Kepler space telescope only 10 days into its mission.

The problem, says David Ciardi, of California Institute of Technology, was that KOI-5 turned out to be in a triple star system – ie, Tatooine, plus one. When Kepler first spotted it, Ciardi says, “it was promising”, but astronomers quickly gave up on trying to confirm that it had a planet, “mostly because it got complicated”.

Now, he says, thanks to additional observations by the Kepler’s successor, TESS (Transiting Exoplanet Survey Satellite), it’s become possible to unscramble the orbits of the three stars and determine that there really is a fourth body in the system: a planet about 60% the size of Saturn, orbiting one of them every five days. Persistence finally paid off.

3. The Milky Way is a Pringle doing “the wave” 

Most of us know that the Milky Way is a spiral galaxy. But that produces a rather simplistic mental image. “Our usual picture is as a flat disk, thinner than a pancake, peacefully rotating around its centre,” says Xinlun Cheng of the University of Virginia. “The reality is more complicated.”

Astronomers have long known that other spiral galaxies are actually slightly warped, like a potato chip or an old-fashioned vinyl record left out in the sun. Now, Cheng says, we know that the same also applies to ours.

By studying high-precision images of billions of stars collected by APOGEE and the European Space Agency’s Gaia space telescope, Cheng’s team was able to not only detect our galaxy’s own warp, but describe it in detail.

What’s happening, he says, is that a long-ago perturbation, probably from another galaxy, pulled some of the Milky Way’s stars up, out of the plane of the disk. These then pulled neighbouring stars out of the plane, before themselves being drawn back into it, producing a warp that circles the galaxy about once every 440 million years.

Cheng compares it to football fans doing the wave. “All you do is stand up and sit down, but the effect is that the wave goes all the way around the stadium.”

4. There’s such a thing as a magnitude 27.8 starquake

The strongest earthquake ever known to have hit Earth was a magnitude 9.5 temblor that struck offshore from Chile in 1960. But now, astronomers have found evidence for one that was 1,000,000,000,000,000,000,000,000,000 times more powerful, which cracked the crust of an object known as a magnetar and produced a giant flare that astronomers spotted as a burst of gamma rays. 

The burst was so intense that, for a fraction of a second, it carried more gamma-ray energy than the entire rest of the universe, combined.

Magnetars are neutron stars with magnetic fields 100 trillion times stronger than the Earth’s, says Kevin Hurley, a space scientist at the University of California, Berkeley. 

The cause of the burst, he says, appears to have been a sudden shift in the star’s magnetic field, which ripped open its surface in a magnitude 27.8 starquake. 

That, says Hurley’s co-investigator Oliver Roberts, of Universities Space Research Institute, Alabama, US, allowed a jet of hot plasma to escape from the magnetar’s interior, “much like a photon torpedo from Star Trek”. And thus we boldly learn. 

5. The Milky Way has a “defensive halo”

Galaxies like our own remain young and vibrant by capturing gas clouds from intergalactic space. These clouds contain the materials that can produce the next generation of stars and planets… and, maybe, creatures like us.

But they also have halos of million-degree ionised gas that act as barricades to keep these clouds at bay – shredding and dispersing them before they reach us. 

“Our galaxy is in a gas crisis,” says Kat Barger, of Texas Christian University, US. “[Eventually] it will run out of gas.”

To study how this works, she used radio-telescope data to examine an incoming gas cloud called Complex A, mapping its density and motion at 123,000 locations. Based on this, she calculated that the cloud, which contains the mass of 2 million Suns and is currently 21,000 light years away, is getting severely “beaten up” as it moves through the halo. 

Only a fraction of it will eventually make its way through, she says – somewhere between half and 25%. “It’s getting elongated and fractured,” she says. “It’s dissolving.” 

Meanwhile, other astronomers are finding other unexpected structures in the galaxy. One of these, says Jeffrey Andrews, of Northwestern University, Illinois, US, is a streamer of 468 stars called Theia 456.

Prior generations of astronomers, he says, thought the Milky Way had only two types of star clusters: tight balls of hundreds of thousands to millions of stars, known as globular clusters; and smaller, less-dense groups known as “open clusters”, of which the Pleiades is the most famous.

But now, he says, the latest generation of star surveys are showing that the Milky Way has large numbers of previously unknown structures. “This is just the beginning,” Andrews says. “Theia 456 is just the tip of the iceberg.”

AAS #238 is scheduled for June this year: set your atomic clock.