From Sky & Telescope : “The Hubble Space Telescope As Cosmic-Ray Detector”

From Sky & Telescope

May 5, 2021
Jure Japelj

Astronomers, using Hubble Space Telescope as a particle detector, have traced cosmic rays flowing in Earth’s geomagnetic field.

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Depiction of Earth’s geomagnetic field. Credit: National Aeronautics and Space Administration(US)

The Hubble Space Telescope requires little or no introduction. For more than three decades, the telescope has stood at the forefront of astronomical research, while its visually stunning images have served as a paragon of awe and inspiration.

But all this time, Hubble has also been secretly acting as a particle detector. And a good one at that, as a team of scientists demonstrated in a pilot study to appear in The Astrophysical Journal.

Energetic charged particles, or cosmic rays, populate every corner of the solar system. A near-constant flow of galactic particles originates from supernova remnants (and the stellar cinders at their cores).

The Sun also sheds energetic particles, mostly protons, during solar flares and coronal mass ejections.

These cosmic rays wiggle and push their way through the solar system under the influence of the magnetized solar wind. Many end up at Earth, where they threaten astronauts, disrupt satellites, and affect atmospheric chemistry.

Cosmic rays are every astronomer’s nightmare. Neither ground nor space telescopes are immune to the barrage of the energetic particles, and when a particle travels through a camera, it leaves a sharp and bright trace on the resulting image. Needless to say, astronomers try to remove this pollution from their data.

But now scientists have demonstrated that one person’s garbage is another’s treasure.

Hubble’s Treasure Trove

“The idea for this project started five or six years ago at a conference about space weather,” says Susana Deustua (Ars Metrologia, formerly at NASA Space Telescope Science Institute (US)), who led the study. An international group of astronomers, particle physicists, and planetary scientists put their heads together and came up with a plan. “Cosmic rays interact with the geomagnetic field,” Deustua adds. “We know that Hubble collects charged particles on its detector, therefore we should be able to glean information about the field from Hubble.”

The team dug into Hubble’s rich data archive. They looked for calibration images that were particularly well-suited for their plan and ended up with almost 100,000 images collected over the past 25 years.

Algorithms for finding and removing cosmic-ray traces from astronomical images have been around for decades. But rather than simply getting rid of the traces, the team wanted to learn as much as possible about the cosmic rays that caused them. “For example, we wanted to know how many pixels on the camera each cosmic ray affected and how much energy the particle lost in the process,” explains graduate student Nathan Miles (University of California (US)), who is first author on the study.

Miles developed software to extract such information, using cloud computing services to carry out the time-demanding computations. His algorithm harvested more than 1 billion cosmic rays from the images.

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Map of cosmic ray traces in one of the Hubble’s images. Traces may have different shapes and affect different number of pixels on the camera. Credit: Nathan Miles.

A Cosmic-ray Image of Earth’s Magnetic Field

The results provide an important proof of concept with encouraging results. The cosmic ray properties from Hubble data match those detected by the Pamela experiment (IT), a defunct particle detector in low-Earth orbit. The team also saw in their data the South Atlantic Anomaly, the famous dip in the Earth’s geomagnetic field. And they observed the expected response of cosmic rays to the solar cycle.

Claudio Corti (University of Hawai‘i at Manoa (US)), who was not involved in the study, was pleasantly surprised by the work. “There is always interest in a better understanding of the geomagnetic field and the effect it has on the particle radiation for astronauts and electronics on the satellites,” he says. The data may prove valuable to understand cosmic ray populations in the solar system.

The analysis so far has only scratched the surface. The team is looking forward to unleashing the full power of the data to better understand the relation between galactic cosmic rays, the Sun, and Earth’s environment. “One of our interests is to look if we can find subtle secular changes in the geomagnetic field,” Deustua says. “We also want to make comparisons with geophysical observatories.”

Hubble’s uninterrupted monitoring of cosmic rays over a quarter of a century nicely complements other cosmic ray detectors. “From one single-point measurement, it is hard to get information on the global space environment,” Corti says. “The more points you have, the better it is.”

See the full article here .

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Sky & Telescope, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

“Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”