Old favourites, new findings and hopes for a halcyon era
Astronomers celebrate dawn of a new decade.
By Richard A. Lovett
Last week, while most of us were still trying to remember to write 2020 rather than 2019 on our documents, 3600 astronomers were greeting the new decade at a gathering often referred to as the “Super Bowl of astronomy”.
The largest-ever meeting of the American Astronomical Society (AAS), in Honolulu, Hawaii, heard some 2700 papers about new discoveries, new wrinkles on old discoveries, and the status of both ground-based and space-based research.
Much of the research involved NASA’s workhorse Hubble Space Telescope, now approaching its 30th year in orbit but still, thanks to repairs and upgrades, churning out cutting-edge data about everything from the expansion of the Universe to exoplanets and the sky’s most beautiful objects.
But there were other dramatic findings, such as the revelation of a snake-like dust feature in our own Milky Way galaxy, or the latest data from the world’s most sensitive radio telescope, the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, which Ezequiel Treister, an astrophysicist at University Católica, Santiago, used to take pictures of a galaxy 400 million light years away, caught in the process of merging with another.
This galaxy, called NGC 6240, has giant clouds of gas in its centre, with a combined massing of more than nine million times that of the Sun – about 13 times more than all the gas in our entire Milky Way galaxy.
Until ALMA came online, Treister says, it wasn’t possible to view it in detail. But thanks to ALMA, it’s possible now to look at NGC 6240 in 10-times finer detail than before.
“That allows us to go from the equivalent of being legally blind, at 20/200 vision, to having 20/20 vision,” he says. “It’s like being able to see a football field at the distance of the Moon.”
Not surprisingly, it also shows structures never before seen, including a thin filament of material connecting the back holes at the centres of the two merging galaxies.
“We think this is a transient structure generated by the merger, that will probably last for something like 10 million years,” he says, “which is short over the lifetime of a merger of two galaxies.”
Other researchers reported that NASA’s TESS space telescope (Transiting Exoplanet Survey Satellite) has discovered its first potentially habitable exoplanet, a world known as TOI-700d, orbiting a star about 40% the size of the Sun, 101.5 light years away.
This planet, says Emily Gilbert, from the University of Chicago, and Joseph Rodriquez, an astronomer at the Harvard–Smithsonian Center for Astrophysics in Cambridge, Massachusetts, is about 1.22 times the size of the Earth, and orbits its star in about 37.42 days, putting it the right distance from its star that it might be able to have surface water.
Adding to the good news, Gabrielle Engelmann-Suissa, from NASA’s Goddard Space Flight Centre modelled the planet’s climate, finding that it could indeed be earthlike.
She found that even though the world is close enough to the Sun that it is almost certainly tide-locked to it (meaning that it always keeps one face toward it, with one part of the planet at perpetual noon, and another part at perpetual midnight) it could still be temperate enough for liquid water. “We find it is a robust candidate for habitability,” she says.
That said, it is too small and far away for present telescopes – including the next-generation James Webb Space Telescope, scheduled for launch early next year – to be able to measure its atmosphere for signs of life.
Still, Engelmann-Suissa says, it’s an interesting planet that will “help motivate” the technological advances needed to someday peer at it in detail.
Meanwhile, one of the concerns voiced at the meeting was that NASA’s Spitzer Space Telescope, which played a major role in studying TOI-700d, is nearing the end of its life.
“That just shows the power of what Spitzer’s been able to do,” Rodriguez says of his own measurements. Once it goes offline, with the James Webb Space Telescope yet to be launched, he says, “the options are a bit limited”.
Happily, other instruments are coming on line, including NEID, named for the Tohono O'odham word “to see”, in honor of the Tohono O'odham people, on whose land it sits, on Arizona’s Kitt Peak.
This instrument, whose “first light” observations were reported at the AAS meeting, is a hyper-precise Doppler spectrograph designed to search for wobbles in the motions of stars, indicating the presence of exoplanets, says project scientist Jason Wright of Penn State University.
Earth’s gravity, he says, causes the Sun’s motion to wobble by 10 centimetres per second as our orbit moves from one side of the Sun to the other – something not yet detectable by the best exoplanet-hunting spectrographs. “The previous state of the art has been 1 meter per second,” Wright says.
NEID won’t cure that completely – it’s wobble-detection threshold is only 30 centimetres per second – but still, it’s closed the gap considerably, and will help astronomers find earthlike worlds circling smaller-mass stars than the Sun, where their gravity would induce correspondingly larger wobbles.
But even being able to detect these, Wright says, means being able to see spectral lines shifting by only 1/1000th of a pixel. “That’s 15 silicon atoms on a detector like you have on your phone,” he says. “This is extremely difficult.”
In fact, he adds, doing it requires stabilising the temperature of the detector to a precision of a thousandth of a degree.
The fact that this can be done at all, let alone through the confines of the Earth’s atmosphere, means that the 2020s could easily be a halcyon era for astronomy.
If so, the 2030 AAS meeting might produce discoveries like nothing we are currently able to imagine.