200718 corona

SpaceWatch: Black holes, comets and key dates

The release of the closest-ever images of the Sun understandably grabbed the headlines this week (you can read Richard A Lovett’s report for Cosmos here) but there was other news of note. Here are some announcements that took our fancy.

A black hole goes, then returns

Astronomers reported watching as a supermassive black hole’s own corona, the ultrabright, billion-degree ring of high-energy particles that encircles a black hole’s event horizon, was abruptly destroyed.

The cause is unclear, though they guess it was a star caught in the black hole’s gravitational pull. Like a pebble tossed into a gearbox, it may have ricocheted through the disc of swirling material, causing everything in the vicinity, including the corona’s high-energy particles, to suddenly plummet into the black hole.

The result was a precipitous and surprising drop in the black hole’s brightness, by a factor of 10,000, in under just one year.

“We expect that luminosity changes this big should vary on timescales of many thousands to millions of years,” says Erin Kara, from Massachussetts Institute of Technlogy, “but in this object, we saw it change by 10,000 over a year, and it even changed by a factor of 100 in eight hours, which is just totally unheard of and really mind-boggling.”

Following the corona’s disappearance, Kara and colleagues watched as the black hole began to slowly pull together material from its outer edges to reform its swirling accretion disc. In just a few months it was able to generate a new corona, with close to its original luminosity.

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How old did you say the Universe was?

Another group of astronomers at the Atacama Cosmology Telescope (ACT) in Chile took a fresh look at the oldest light in the Universe and, combining these observations with a bit of “cosmic geometry” suggest the Universe is 13.77 billion years old, give or take 40 million years.

A portion of a new picture of the oldest light in the Universe taken by the Atacama Cosmology Telescope. Emitted 380,000 years after the Big Bang, the light varies in polarisation (represented here by redder or bluer colours). Credit: ACT Collaboration

The new estimate matches one provided by the Standard Model of the Universe and measurements of the same light made by the Planck satellite. This adds a fresh twist to an ongoing debate in the astrophysics community, says Simone Aiola, from the Centre for Computational Astrophysics in New York.

In 2019, a research team measuring the movements of galaxies calculated that the universe is hundreds of millions of years younger than the Planck team predicted. That discrepancy suggested that a new model for the Universe might be needed and sparked concerns that one of the sets of measurements might be incorrect.

“Now we’ve come up with an answer where Planck and ACT agree,” says Aiola. “It speaks to the fact that these difficult measurements are reliable.”

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What carbon can tell us about comets

Astrophysicists from Russia, South Korea and the US are suggesting that carbon is an indication of how long a comet has been in our Solar System; the less carbon, the longer it’s been in the proximity of the Sun.

Comet C/2019 Y4 (ATLAS). Credit: Martin Gembec

The proof, they say, is the comet ATLAS (C/2019 Y4), which approached the Earth in May but disintegrated, displaying a major outbreak of the carbonaceous particles.

“ATLAS was expected to be the brightest comet of 2020, visible from the Earth with a naked eye. However, instead of observing the comet itself, we witnessed its disintegration,” says Ekaterina Chornaya, from Russia’s Far Eastern Federal University.

“Luckily, we had begun photometric and polarimetric studies before the process started, and because of that, we are able to compare the composition of the coma before and after the disintegration”.

The researchers say the polarimetric response of the particles from Comet ATLAS matches that of one of the brightest comets in the history of Earth – Comet Hale-Bopp, or C/1995 O1.

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For the diary

To finish, a couple of important dates were revealed this week.

The Japan Aerospace Exploration Agency (JAXA) and the Australian Space Agency jointly announced that the Hayabusa2 spacecraft containing samples from the asteroid Ryugu will arrive back on Earth in Woomera, South Australia, on 6 December this year. (You can read our most recent coverage of the mission here).

And NASA announced a new target date of 31 October 2021 for the launch of the James Webb Space Telescope from French Guiana. The ongoing coronavirus COVID-19 pandemic and technical challenges have required a move from the original planned launch in March.

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