A strange intermittent radio signal from space has astronomers puzzled

When astronomers flip our radio telescopes out in the direction of space, we generally detect sporadic bursts of radio waves originating from throughout the huge expanse of the universe. We name them “radio transients”: some erupt solely as soon as, by no means to be seen once more, and others flicker on and off in predictable patterns.

We predict most radio transients come from rotating neutron stars often known as pulsars, which emit common flashes of radio waves, like cosmic lighthouses. Usually, these neutron stars spin at unimaginable speeds, taking mere seconds or perhaps a fraction of a second to finish every rotation.

Just lately, we found a radio transient that is not like something astronomers have seen earlier than. Not solely does it have a cycle nearly an hour lengthy (the longest ever seen), however over a number of observations we noticed it generally emitting lengthy, shiny flashes, generally quick, weak pulses—and generally nothing in any respect.

We won’t fairly clarify what is going on on right here. It is almost definitely a really uncommon neutron star, however we won’t rule out different prospects. Our research is printed in Nature Astronomy.

A fortunate discover

Meet ASKAP J1935+2148 (the numbers within the title level to its location within the sky). This periodic radio transient was found utilizing CSIRO’s ASKAP radio telescope on Wajarri Yamaji Nation in outback Western Australia.

The telescope has a really broad discipline of view, which suggests it might probably survey giant volumes of the universe in a short time. This makes it very nicely suited to detecting new and unique phenomena.

Utilizing ASKAP, we had been concurrently monitoring a supply of gamma rays and trying to find pulses from a quick radio burst, once we noticed ASKAP J1935+2148 slowly flashing within the information. The sign leapt out as a result of it was made up of “circularly polarized” radio waves, which suggests the route of the waves corkscrews round because the sign travels by way of space.

Our eyes can’t differentiate between circularly polarized mild and bizarre unpolarized mild. Nonetheless, ASKAP features like a pair of polaroid sun shades, filtering out the glare from 1000’s of bizarre sources.

After the preliminary detection, we performed additional observations over a number of months utilizing ASKAP and in addition the extra delicate MeerKAT radio telescope in South Africa.

The slowest radio transient ever discovered

ASKAP J1935+2148 belongs to the comparatively new class of long-period radio transients. Solely two others have ever been discovered, and ASKAP J1935+2148’s 53.8 minute interval is by far the longest.

Nonetheless, the exceptionally lengthy interval is just the start. We now have seen ASKAP J1935+2148 in three distinct states or modes.

Within the first state, we see shiny, linearly (somewhat than circularly) polarized pulses lasting from 10 to 50 seconds. Within the second state, there are a lot weaker, circularly polarized pulses lasting solely about 370 milliseconds. The third state is a quiet or quenched state, with no pulses in any respect.

These totally different modes, and the switching between them, may outcome from an interaction of complicated magnetic fields and plasma flows from the supply itself with strong magnetic fields within the surrounding space.

Comparable patterns have been seen in neutron stars, however our present understanding of neutron stars suggests they shouldn’t be capable of have such an extended interval.

Neutron stars and white dwarfs

The origin of a sign with such an extended interval stays a profound thriller, with a slow-spinning neutron star the prime suspect. Nonetheless, we can’t rule out the chance the item is a white dwarf—the Earth-sized cinder of a burnt-out star that has exhausted its gasoline.

White dwarfs typically have sluggish rotation durations, however we do not know of any means one may produce the radio alerts we’re seeing right here. What’s extra, there are not any different extremely magnetic white dwarfs close by, which makes the neutron star rationalization extra believable.

One rationalization may be that the item is a part of a binary system wherein a neutron star or white dwarf orbits one other unseen star.

This object may immediate us to rethink our decades-old understanding of neutron stars or white dwarfs, notably in how they emit radio waves and what their populations are like inside our galaxy. Additional analysis is required to verify what the item is, however both situation would offer priceless insights into the physics of those excessive objects.

The search continues

We do not understand how lengthy ASKAP J1935+2148 has been emitting radio alerts, as radio astronomy surveys do not normally seek for objects with durations this lengthy. Furthermore, radio emissions from this supply are solely detected for a mere 0.01% to 1.5% of its rotation interval, relying on its emission state.

So we had been fairly lucky we occurred to catch sight of ASKAP J1935+2148. It is fairly doubtless there are numerous different objects prefer it elsewhere in our galaxy, ready to be found.

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