Did Astronomers See a Distant, Dying Star? Or an Earth-bound Satellite?

Apollo 11 photo of Earth with glare from Sun
Apollo 11’s view of low-Earth orbit

Last year, astronomers caught a surprising flash of light from probably the most distant galaxy recognized — GN-z11, which existed simply 400 million years after the Big Bang. The workforce proposed, after ruling out different potentialities, that what they’d seen was the fading afterglow of a dying star. The occasion would have heralded the earliest instance of star loss of life within the recognized universe.

That is, if the sunshine got here from a star in any respect. Two research showing October 4th in Nature Astronomy make the case that what the unique workforce noticed was not a pure phenomenon however the likelihood passing of a artifical object in Earth orbit.

The Flash

Linhua Jiang (Peking University, China) led a workforce in observing GN-z11 in near-infrared mild utilizing the Multi-Object Spectrometer for Infrared Exploration (MOSFIRE) on the Keck I telescope in Hawai‘i.

The galaxy is so faint that the team was planning to combine more than 100 images before measuring the spectrum. But during one of these individual exposures, which lasted 179 seconds, something happened. A bright source of light crossed the slit, apparently right at the center of the galaxy.

Jiang’s workforce checked whether or not different close by objects might have photobombed their observations and got here up clean. They concluded they’d seen the ultraviolet afterglow of a lengthy gamma-ray burst (GRB), the violent destruction of one of many universe’s earliest stars.

Gamma-ray burst
This illustration exhibits the commonest kind of gamma-ray burst, thought to happen when a huge star collapses, kinds a black hole, and blasts particle jets outward at practically the speed of sunshine. Credit: NASA/GSFC

But there have been curiosities on this discovery. For one, the spectrum wasn’t fairly what one would anticipate for a GRB, although it was nonetheless inside the realm of risk. Curiouser nonetheless was how extremely fortunate the workforce needed to be: Based on the galaxy’s star formation fee, it should host between 1 and 200 GRBs each million years. The likelihood of Jiang’s workforce really catching one in every of them throughout one in every of their exposures was 1 in 10 billion.

What Are the Chances?

Immediately after the research’s publication in Nature, different astronomers started placing concept papers on the astronomy preprint archive that examined the conclusion of seeing such an unlikely occasion.

Scientists don’t like flukes — they like repeatable, testable issues. That’s to not say unlikely issues don’t occur. But when one thing with a near-zero likelihood of occurring really involves move, it makes one suppose: Maybe that sort of factor isn’t so uncommon in spite of everything.

“You shouldn’t believe you got a 1 in 10 billion lucky break,” says Charles Steinhardt (Cosmic Dawn Center, Denmark). “You should instead believe that you’ve misunderstood the physics of an area where we know we need to learn a lot about the physics.”

Indeed, many astronomers had been placing their heads collectively to contemplate what it was we’ve misunderstood. But as Steinhardt talked the invention over with colleagues down the corridor, he realized that in actual fact the likelihood of getting discovered a GRB was so low that that different actually unlikely issues may in actual fact be extra possible.

Together along with his colleagues, Steinhardt posted on the arXiv in January that maybe the flash had been a artifical object in Earth orbit. However unlikely, he argued, it was nonetheless value contemplating. (That paper seems at present in Nature Astronomy‘s Matter Arising.)

Then, simply a month later, Michał Michałowski (Adam Mickiewicz University, Poland) and colleagues posted on the arXiv that they’d discovered the article: the Breeze-M higher stage of a Russian Proton rocket. (Their paper additionally seems at present in Nature Astronomy‘s Matter Arising.)

A Russian Proton-M rocket arrives for launch. Once such a rocket reaches low-Earth orbit, the Breeze M higher stage under the nosecone offers the extra oomph wanted to loft a satellite tv for pc into distant geostationary orbit. Once used, the booster stays for awhile in a extremely elliptical orbit round Earth.
Alex Lane / Flickr / CC BY-SA 2.0

“Our calculations showed that the [rocket booster] crossed through the slit that covered the distant galaxy GN-z11,” Michałowski explains.

Jiang’s workforce was really conscious of this precise booster; they’d used a web site common with novice astronomers, Calsky.com, to calculate its trajectory and located that it handed outdoors the telescope’s area of view.

“CalSky.com was a really useful website for determining when things in the sky (moonrise, Jupiter set, satellite passes, ISS crossing in front of the Moon) would occur from an observer’s location,” says S&T’s Kelly Beatty. “It shut down in October 2020 due to lack of funding.”

Both Jiang’s and Michałowski’s teams tried to contact the previous house owners of Calsky, however to no avail. It stays unclear why the teams’ calculated trajectories for the booster had been completely different by a number of arcminutes.

But Michałowski is definite the booster is accountable for the flash, including that his workforce has double-checked the calculations: “In addition to our own software, we used three publicly available satellite orbit software packages: JPL Horizons, OREKIT, and SkyField. The resulting orbits agree with our calculations within 0.1 km (1.5 arcsec).”

While Jiang’s team replied to the newly printed research sustaining the validity of their outcomes, additionally they clarify that they by no means conclusively claimed the flash was a GRB. “We just reported this event and provided our most probable interpretation,” Jiang says.

“I do think the original paper by Jiang and colleagues was a reasonable thing,” Steinhardt says. “Ultimately, when you see something weird as an observer, what do you do? You put it out there for the community to give their best guesses as to what it is.”

Satellite Interference

This wasn’t the primary incident of a artifical object posing as an astronomical phenomenon. In the mid-Nineteen Eighties, Sky & Telescope reported on a number of observers who’d seen mysterious, repeated flashes within the constellation Perseus. Ultimately, astronomers decided that the sadly named “Perseus Flasher” was in actual fact merely the glints of daylight off satellites.

Nor will this be the final of artifical interference with the skies — removed from it. The stuff in Earth orbit is growing exponentially. Most notable has been the Starlink community, which can finally be made up of greater than 12,000 satellites in low-Earth orbit.

At the identical time, technological developments in astronomy are enabling telescopes to take quick, repeated exposures of the sky, turning single snapshots into movies. Astronomers can watch supernovae as they occur, catch Near-Earth objects shifting between frames. But they’ll additionally more and more discover their observations hindered, even blocked as satellites and space particles streak throughout pictures.

Early morning on Monday, November 18th, Cliff Johnson (Northwestern University) and colleagues took this picture utilizing the Dark Energy Camera on the 4-meter Blanco Telescope on the Cerro Tololo Inter-American Observatory. Trails from 19 not too long ago launched Starlink satellites crossed the picture through the six-minute publicity.

Jonathan McDowell (Center for Astrophysics, Harvard & Smithsonian) has led a workforce in creating software program and databases, together with a “more robust” model of Calsky, that may assist astronomers cope with this downside.

“We’re focusing on mainly a couple applications,” he explains. “One is to figure out at what time tonight can I observe this object and not get ‘Starlinked.’ And another is, ok, I got streaked, what can I retrieve from my data.” He provides that astronomers will even be capable to use this software program in instances just like the GN-z11 flash, to find out if/when a satellite tv for pc or different particles has interfered with a previous commentary.

But software program isn’t a cure-all. If low-Earth orbit fills to capability, it might grow to be troublesome for telescopes to keep away from satellites. And whereas it’s attainable normally to take away a path, it’s practically unattainable to look “underneath” it to see the stars and galaxies.

More troubling, it’s attainable a satellite tv for pc might intrude with an commentary with out astronomers ever figuring out it. Satellite and true astronomical supply grow to be significantly troublesome to tease aside for transient occasions and for spectroscopy — each exemplified by the GN-z11 flash.

“We’re in this world now where every paper you write on observational astronomy is going to have to ask the question, ‘Is this real or is this a satellite?’” McDowell says. “It’s not always going to be possible to tell.”


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