“Holy sharks, Batman, it’s periodic!”
I exclaimed on Slack.
It was the primary lockdown of 2021 in Perth, and we had been all working from house. And when astronomers search for one thing to distract themselves from looming existential dread, there’s nothing higher than a brand new cosmic thriller.
In 2020 I gave an undergraduate pupil, Tyrone O’Doherty, a enjoyable venture: search for radio sources which are altering in a big radio survey I’m main.
By the top of the 12 months he’d discovered a very uncommon supply that was seen in knowledge from early 2018, however had disappeared inside a couple of months. The supply was named GLEAM-X J162759.5-523504, after the survey it was present in and its place.
Sources that seem and disappear are referred to as “radio transients” and are often an indication of maximum physics at play.
The thriller begins
Earlier this 12 months I began investigating the supply, anticipating it to be one thing we knew about – one thing that might change slowly over months and maybe level to an exploded star, or an enormous collision in house.
To know the physics, I needed to measure how the supply’s brightness pertains to its frequency (within the electromagnetic spectrum). So I checked out observations of the identical location, taken at totally different frequencies, earlier than and after the detection, and it wasn’t there.
I used to be dissatisfied, as spurious indicators do crop up sometimes resulting from telescope calibration errors, Earth’s ionosphere reflecting TV indicators, or plane and satellites streaking overhead.
So I checked out extra knowledge. And in an commentary taken 18 minutes later, there the supply was once more, in precisely the identical place and at precisely the identical frequency – like nothing astronomers had ever seen earlier than.
At this level I broke out in a chilly sweat. There’s a worldwide analysis effort trying to find repeating cosmic radio indicators transmitted at a single frequency. It’s referred to as the Seek for Additional-Terrestrial Intelligence. Was this the second we lastly discovered that the reality is … on the market?
One of many brightest pulses from the brand new radio transient detected with the Murchison Widefield Array.
The plot thickens
I quickly downloaded extra knowledge and posted updates on Slack. This supply was extremely brilliant. It was outshining all the things else within the commentary, which is nothing to smell at.
The brightest radio sources are supermassive black holes flaring enormous jets of matter into house at almost the pace of sunshine. What had we discovered that might presumably be brighter than that?
Learn extra:
Consultants remedy the thriller of a large X-shaped galaxy, with a monster black gap as its engine
Colleagues had been starting to take discover, posting:
It’s repeating too slowly to be a pulsar. Nevertheless it’s too brilliant for a flare star. What is that this? (alien emoji icon)???
Inside a couple of hours, I breathed a sigh of aid: I had detected the supply throughout a variety of frequencies, so the ability it could take to generate it might solely come from a pure supply; not synthetic (and never aliens)!
Identical to pulsars – extremely magnetised rotating neutron stars that beam out radio waves from their poles – the radio waves repeated like clockwork about 3 times per hour. In truth, I might predict once they would seem to an accuracy of 1 ten-thousandth of a second.
So I turned to our monumental knowledge archive: 40 petabytes of radio astronomy knowledge recorded by the Murchison Widefield Array in Western Australia, throughout its eight years of operation. Utilizing highly effective supercomputers, I searched a whole bunch of observations and picked up 70 extra detections spanning three months in 2018, however none earlier than or after.
Learn extra:
Tuning in to cosmic radio from the daybreak of time
The superb factor about radio transients is that if in case you have sufficient frequency protection, you’ll be able to work out how distant they’re. It’s because decrease radio frequencies arrive barely later than larger ones relying on how a lot house they’ve traveled via.
Our new discovery lies about 4,000 mild years away – very distant, however nonetheless in our galactic yard.
Interstellar house slows down lengthy wavelength radio waves greater than brief.
ICRAR
We additionally discovered the radio pulses had been nearly utterly polarised. In astrophysics this often means their supply is a powerful magnetic discipline. The pulses had been additionally altering form in simply half a second, so the supply needs to be lower than half a light-weight second throughout, a lot smaller than our Solar.
Sharing the end result with colleagues internationally, everybody was excited, however nobody knew for certain what it was.
The jury continues to be out
There have been two main explanations for this compact, rotating, and extremely magnetic astrophysical object: a white dwarf, or a neutron star. These stay after stars run out of gasoline and collapse, producing magnetic fields billions to quintillions occasions stronger than our Solar’s.
And whereas we’ve by no means discovered a neutron star that behaves fairly this manner, theorists have predicted such objects, referred to as an “ultra-long interval magnetars”, might exist. Even so, nobody anticipated one might be so brilliant.
We expect the supply might be both a magnetar or a white dwarf, or one thing utterly unknown.
That is the primary time we’ve ever seen a radio supply that repeats each 20 minutes. However possibly the explanation we by no means noticed one earlier than is that we weren’t wanting.
Once I first began making an attempt to grasp this supply, I used to be biased by my expectations: transient radio sources both change rapidly like pulsars, or slowly just like the fading remnants of a supernova.
I wasn’t in search of sources repeating at 18-minute intervals – an uncommon interval for any recognized class of object. Nor was I trying to find one thing that would seem for a couple of months after which disappear ceaselessly. Nobody was.
As astronomers construct new telescopes that can acquire huge portions of information, it’s very important we hold our minds, and our search strategies, open to sudden prospects. The universe is stuffed with wonders, ought to we solely select to look.
