Astrophysics | The American Sentinel Newsletter

A Southwest Research Institute-led team discovered never-before-detected, fine-grained structures in the Sun’s outer atmosphere, or corona. The team imaged this critical region in detail using sophisticated software techniques and longer exposures from the COR-2 camera onboard NASA’s Solar and Terrestrial Relations Observatory-A (STEREO-A).

The Sun’s outer corona is the source of the solar wind, the stream of charged particles that flow outward from the Sun in all directions. Measured near Earth, the magnetic fields embedded within the solar wind are intertwined and complex.

“Previous images showed the outer corona as a smooth structure, but in deep space, the solar wind is turbulent and gusty,” said SwRI’s Dr. Craig DeForest, a solar physicist and lead author of “The Highly Structured Outer Corona,” an article published by Astrophysical Journal July 18, 2018.

“Using new techniques to improve image fidelity, we realized that the corona is not smooth, but structured and dynamic. Every structure that we thought we understood turns out to be made of smaller ones and to be more dynamic than we thought.”

To understand the corona, DeForest and his colleagues started with extended exposures of STEREO-A’s coronagraph images – pictures of the Sun’s atmosphere produced by a special telescope that blocks out light from the bright solar disk.

The coronagraph is sensitive enough to image the corona in great detail, but in practice its measurements are polluted by noise both from the space environment and the instrument itself. The team’s key innovation was identifying and separating out that noise, boosting the signal-to-noise ratio and revealing the outer corona in unprecedented detail.

“We couldn’t tinker with the instrument itself, so we took a software approach, squeezing out the highest quality data possible by improving the data’s signal-to-noise ratio,” DeForest said. “We developed new filtering algorithms, designed and tested to delineate the true corona from the noisy measurements.”

The algorithms filtered out light and adjusted brightness. But the most challenging obstacle is inherent: blur due to the motion of the solar wind. “This technique adjusted images not just in space, not just in time, but in a moving coordinate system,” DeForest said.

“That allowed us to correct motion blur not just by the speed of the wind, but by how rapidly features changed in the wind.”

With the resulting unprecedented view of the corona, the team made several groundbreaking discoveries. For example, coronal streamers – magnetic loops that can erupt into coronal mass ejections that send blobs of solar material into space – are far more structured than previously thought.

“What we found is that there is no such thing as a single streamer,” DeForest said. “The streamers themselves are composed of myriad fine strands that, together, average to produce a brighter feature.”

Then there’s the theoretical Alfven surface – a proposed surface, or sheet-like layer where the gradually accelerating solar wind reaches a critical speed. But that’s not what DeForest’s team observed.

“What we found is that there isn’t a clean Alfven surface,” DeForest said. “There’s a wide ‘no-man’s land’ or `Alfven zone’ where the solar wind gradually disconnects from the Sun, rather than a single clear boundary.”

And the close look at the coronal structure also raised new questions. Techniques used to estimate the speed of the solar wind revealed that the wind suddenly changes its character at a distance of around 10 solar radii, well within the conventional boundary of the corona itself.

“Some interesting physics is happening around there,” DeForest said. “We don’t know what it is yet, but we do know that it is going to be interesting.”

These first observations will provide key insight for NASA’s upcoming Parker Solar Probe, the first-ever mission to gather measurements from within the outer solar corona.

A telescope in outback Western Australia has been used to listen to a mysterious cigar-shaped object that entered our solar system late last year.

The unusual object – known as ‘Oumuamua – came from another solar system, prompting speculation it could be an alien spacecraft. So astronomers went back through observations from the Murchison Widefield Array (MWA) telescope to check for radio transmissions coming from the object between the frequencies of 72 and 102 MHz – similar to the frequency range in which FM radio is broadcast.

While they did not find any signs of intelligent life, the research helped expand the search for extraterrestrial intelligence (SETI) from distant stars to objects closer to home.

When ‘Oumuamua was first discovered, astronomers thought it was a comet or an asteroid from within the solar system. But after studying its orbit and discovering its long, cylindrical shape, they realised ‘Oumuamua was neither and had come from interstellar space.

Telescopes around the world trained their gaze on the mysterious visitor in an effort to learn as much as possible before it headed back out of the solar system, becoming too faint to observe in detail.

John Curtin Distinguished Professor Steven Tingay, from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), said the MWA team did not initially set out to find ‘Oumuamua.

“We didn’t set out to observe this object with the MWA but because we can see such a large fraction of the sky at once, when something like this happens, we’re able to go back through the data and analyse it after the fact,” Professor Tingay said.

“If advanced civilizations do exist elsewhere in our galaxy, we can speculate that they might develop the capability to launch spacecraft over interstellar distances and that these spacecraft may use radio waves to communicate. Whilst the possibility of this is extremely low, possibly even zero, as scientists it’s important that we avoid complacency and examine observations and evidence without bias.”

The MWA is located in Western Australia’s remote Murchison region, one of the most radio-quiet areas on the planet and far from human activity and radio interference caused by technology. It is made up of thousands of antennas attached to hundreds of “tiles” that dot the ancient landscape, relentlessly observing the heavens day after day, night after night.

Professor Tingay said the research team was able to look back through all of the MWA’s observations from November, December and early January, when ‘Oumuamua was between 95 million and 590 million kilometres from Earth.

“We found nothing, but as the first object of its class to be discovered, `Oumuamua has given us an interesting opportunity to expand the search for extra-terrestrial intelligence from traditional targets such as stars and galaxies to objects that are much closer to Earth. This also allows for searches for transmitters that are many orders of magnitude less powerful than those that would be detectable from a planet orbiting even the most nearby stars.”

‘Oumuamua was first discovered by the Pan-STARRS project at the University of Hawaii in October. Its name loosely means “a messenger that reaches out from the distant past” in Hawaiian, and is the first known interstellar object to pass through our solar system.

Combining observations from a host of telescopes, scientists have determined that ‘Oumuamua is most likely a cometary fragment that has lost much of its surface water because it was bombarded by cosmic rays on its long journey through interstellar space.

Researchers have now suggested there could be more than 46 million similar interstellar objects crossing the solar system every year. While most of these objects are too far away to study with current technologies, future telescopes such as the Square Kilometre Array (SKA) will enable scientists to understand more about these interstellar interlopers.

“So once the SKA is online,” said Professor Tingay, “we’ll be able to look at large numbers of objects and partially balance out the low probability of a positive detection.”