Mysterious radio signal from the center of the Milky Way intrigues scientists

In 2020, astronomers in Australia detected several mysterious radio waves coming from somewhere near the center of the galaxy. But when the team pointed a more sensitive instrument to the source, they saw the signals just one more time before disappearing, behaving differently than they had previously. The new behavior of waves was described in a scientific article published at the Astrophysical Journal.

“The strangest property of this new signal is that it has a very high polarization. This means that its light oscillates in only one direction, but that direction changes over time,” said Ziteng Wang, an astrophysicist at the University of Sydney, Australia, who led the new study, in a press release. In other words, radio waves were intermittently spiraling down to Earth for no reason. And since they were detected, the ‘trail’ has cooled down.

The signal was discovered using the Australian Square Kilometer Array Pathfinder Variables and Slow Transients Survey (ASKAP VAST), a radio telescope from Western Australia. The mysterious object that produced the signal was named ASKAP J173608.2-321635. The name refers to the device that found it and its coordinates in the sky.

“This object was the only one that started out invisible, turned bright, faded and then reappeared. This behavior was extraordinary,” said Tara Murphy, also an astrophysicist at the University of Sydney and co-author of the article, in the same statement.

The Milky Way seen from Uruguay. The radio source was near the galactic center. Photo: MARIANA SUAREZ / AFP (Getty Images)

When the radio source went out, the team checked the visible light spectrum—but found nothing. They also resorted to a different radio telescope, who also did not acknowledge his presence. Using the MeerKAT radio telescope in South Africa, the researchers finally spotted the object again — only it disappeared within a day. Scientists haven’t seen him since.

“As for why a source stops emitting light, it could be something related to instabilities in the magnetic field. They can get tangled up and release energy in bursts,” said David Kaplan, co-author of the paper and astrophysicist at the University of Wisconsin-Milwaukee, in an email to Gizmodo US. “This happens with our Sun, with magnetars — neutron stars with high magnetic field value — and with other types of objects. So it’s not at all that this object has stopped emitting, as it only casts light sporadically — most of the time it’s really ‘off’.”

Researchers have some ideas about what this radio source might have been, but they’re not sure about any of them. The wave pattern of this type has similarities to a class of objects called Galactic Center Radio Transients (TRCC), although it also has some differences. TRCC does not represent a specific object, but a group of radio-emitting objects around the center of the Milky Way, which do not have an identity.

Because of the characteristics of its explosion, the team at first thought that ASKAP J173608.2-321635 might be a spinning dead star whose brightness varies regularly for observers on Earth. But this object’s fluctuations in brightness were not regular, and its lack of other electromagnetic waves meant that it didn’t look like a small brown dwarf star or some kind of magnetar. It may have been a “strange” body, Kaplan said, but the team can’t define this using only current data.

Even though ASKAP J173608.2-321635 is not seen again, they expect future observations to determine whether the object was the rule or the exception. That is, whether this mysterious source is the first of a hitherto unobserved class of objects.

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Rather than switching from a radio telescope in the future, the team hopes to use the Square Kilometer Array, the world’s largest radio telescope, with 130,000 antennas, to make your future observations of distant radio sources. The matrix should start periodic scientific observations by the end of this decade.